350LC main jets

[iainw]

I've recently acquired a rather nice '81 LC350 with a set of Allspeeds on it. When warm it's ticking over a bit high and also tends to splutter a bit until it gets past 5k then it does what it's supposed to do ;D

I've pulled the plugs and they're black and wet (I am thrashing it to within an inch of it's life)... so, I want to get hold of a set of jets to have handy before I start having a good look at the carbs.

The carbs look like the standard ones pictured in the Haynes manual and in the parts listing diagrams.

Can anyone recommend which selection of jets to buy and a good place to get them from.

Any other advice is very welcome.

Cheers,
Iain

[1260dave]

Jun 30, 2011 23:50:03 GMT 1 iainw said:

I've recently acquired a rather nice '81 LC350 with a set of Allspeeds on it. When warm it's ticking over a bit high and also tends to splutter a bit until it gets past 5k then it does what it's supposed to do ;D

I've pulled the plugs and they're black and wet (I am thrashing it to within an inch of it's life)... so, I want to get hold of a set of jets to have handy before I start having a good look at the carbs.

The carbs look like the standard ones pictured in the Haynes manual and in the parts listing diagrams.

Can anyone recommend which selection of jets to buy and a good place to get them from.

Any other advice is very welcome.

Cheers,
Iain

first thing i would do is take the carbs off and make sure the pilot jets are clear, then drop the jet needle to the last clip position then do a plug chop, if its still black try dropping the main jet one size then check the plugs again

[iainw]

Thanks chaps!
As both plugs are equally as wet and black it's probably not a blockage. I'll try dropping the needle as it's a quick and simple check. It'll be into next week when I get time to have a go but I'll report back.

[1260dave]

your pilot jets control your fuel on lowish revs so blocked pilots could be causing the bogging

[iainw]

Jul 1, 2011 21:36:54 GMT 1 1260dave said:

your pilot jets control your fuel on lowish revs so blocked pilots could be causing the bogging

Thanks,
Plugs are wet and black though, would that be the case with blocked pilots?
Cheers

[dave32]

Try putting the choke on when its warmed up,it should load up/revs drop abd cut out.
If it just brings the revs down a touch, say to 1000/1500rpm then stays there idling nicely it needs richening up,wind the airscrew all the way in and back out 1 turn and lower the needle clip a notch(be careful you dont lose it!),find a bit of steel plate or something thats flat and wont give and with the clip facing down against it push the needle while keeping ya thumb over the clip,reverse to fit(dont use plliers!and use a plasic bag to work in incase it pings off).
make sure the float height is set correctly and the pilots arent blocked and you have no airleaks on the intake side before changing the mixture.
The Mainjet wont have any bearing until at least quarter throttle so leave that for the moment.
If its just a set of Allspeeds i would get a selection of mains from 240 to 220 genuine mikuni not RD aftermarket as they flow less.
The other thing is without stripping the top end you wont know if the head or porting have been modded so ya in the dark a bit.
I doubt you will ever get rid of a slight flatspot before the band as that's what elsie's do(and why Yam invented YPVS).
If the pilots too small or blocked it will be a pig to start when hot with no choke,usually the stock pilots fine even when the motors highly tuned though.
I wouldnt worry about the plug chop yet,just get it starting and idling nicely then worry about sorting the mid and top end.
Whats the engine spec?ignition timing,reeds,pipes,plugs,2 stroke oil etc?
HTH
Let us know how it goes
Cheers
Dave

[iainw]

Thanks for the replies, all very helpful.

I've taken the carbs to bits to see what we've got, here's the dirty plugs...


Both carb slides rise to the sync windows at the same time.
The carbs are very clean on the inside.
Air screws are set at 1 3/4 turns out.
The needles are in the middle slots.
Float height on both is 21mm as best as I can measure it.
Main jets are 230
Both pilot jets are clean.

I've had a look at the oil pump too and I think that's set wrong, please can someone confirm this. It is marked with 4L1, the haynes book states that the peg should line up with the round mark nearest to the cable nipple.


So, I believe either I need to drop the needles or get a smaller main jet, is the result of doing this the same or different?
and adjust the cable pull on the pump.

[lckid]

Jul 1, 2011 17:26:26 GMT 1 butchers said:

hi iain and welcome on your first post
i have the same set up. i've upped the main from 220 to 230 as recommended.

done a plug chop and my plugs are Black but dry

i've then started to move the needle clip each notch up and then done a plug chop again the plug is still black even with the needle move to 4th clip and a thin washer under it. then i've found that it don't run as well lower end and bogs down pulling off.

i've rechecked my float hight, and rechecked balancing the carbs with the lollypop method (just in case). i've also fitted a boost bottle whilst there is no power gains i feel it has reduced the splutter greatly although not solved it.

so atm my best setting is the clip on the third ring and the bottle fitted not 100% but for the time being it'll do

perhaps not the answer to your concern but hope it helps in some way

for jets try here www.motoduro.co.uk

[lckid]

Jul 3, 2011 23:21:13 GMT 1 dave32 said:

Try putting the choke on when its warmed up,it should load up/revs drop abd cut out.
If it just brings the revs down a touch, say to 1000/1500rpm then stays there idling nicely it needs richening up,wind the airscrew all the way in and back out 1 turn and lower the needle clip a notch(be careful you dont lose it!),find a bit of steel plate or something thats flat and wont give and with the clip facing down against it push the needle while keeping ya thumb over the clip,reverse to fit(dont use plliers!and use a plasic bag to work in incase it pings off).
make sure the float height is set correctly and the pilots arent blocked and you have no airleaks on the intake side before changing the mixture.
The Mainjet wont have any bearing until at least quarter throttle so leave that for the moment.
If its just a set of Allspeeds i would get a selection of mains from 240 to 220 genuine mikuni not RD aftermarket as they flow less.
The other thing is without stripping the top end you wont know if the head or porting have been modded so ya in the dark a bit.
I doubt you will ever get rid of a slight flatspot before the band as that's what elsie's do(and why Yam invented YPVS).
If the pilots too small or blocked it will be a pig to start when hot with no choke,usually the stock pilots fine even when the motors highly tuned though.
I wouldnt worry about the plug chop yet,just get it starting and idling nicely then worry about sorting the mid and top end.
Whats the engine spec?ignition timing,reeds,pipes,plugs,2 stroke oil etc?
HTH
Let us know how it goes
Cheers
Dave

I agree with above but ive had x2 350LC's and both of these have never had a flat spot before the power band this i think normaly occurs with the 250LC at least it did with my 250

[iainw]

Jul 5, 2011 22:51:19 GMT 1 lckid said:

Jul 3, 2011 23:21:13 GMT 1 dave32 said:

Try putting the choke on when its warmed up,it should load up/revs drop abd cut out.
If it just brings the revs down a touch, say to 1000/1500rpm then stays there idling nicely it needs richening up,wind the airscrew all the way in and back out 1 turn and lower the needle clip a notch(be careful you dont lose it!),find a bit of steel plate or something thats flat and wont give and with the clip facing down against it push the needle while keeping ya thumb over the clip,reverse to fit(dont use plliers!and use a plasic bag to work in incase it pings off).
make sure the float height is set correctly and the pilots arent blocked and you have no airleaks on the intake side before changing the mixture.
The Mainjet wont have any bearing until at least quarter throttle so leave that for the moment.
If its just a set of Allspeeds i would get a selection of mains from 240 to 220 genuine mikuni not RD aftermarket as they flow less.
The other thing is without stripping the top end you wont know if the head or porting have been modded so ya in the dark a bit.
I doubt you will ever get rid of a slight flatspot before the band as that's what elsie's do(and why Yam invented YPVS).
If the pilots too small or blocked it will be a pig to start when hot with no choke,usually the stock pilots fine even when the motors highly tuned though.
I wouldnt worry about the plug chop yet,just get it starting and idling nicely then worry about sorting the mid and top end.
Whats the engine spec?ignition timing,reeds,pipes,plugs,2 stroke oil etc?
HTH
Let us know how it goes
Cheers
Dave

I agree with above but ive had x2 350LC's and both of these have never had a flat spot before the power band this i think normaly occurs with the 250LC at least it did with my 250

I've dropped the needle 1 notch, it's second from the top now, I've also set the air screws out 1 turn and set it up as per the lolly sticks.

All back together and tried to adjust the cable setting on the oil pump but there isn't enough slack in the cable adjustment. The pump end is right at the shortest outer cable setting and so is the twist grip end. I need a shorter outer or longer inner cable, how's that?

I might get to run it at the week end, all being well.

[dave32]

I havent run a pump for years on an lc(or any stroker come to that) after my cable end come off on my Rd125 flat out down the local bypass,quite a scary moment.
Anyway,i have the feeling the marks on the pump are supposed to line up when the carb slide marks line up with the windows which is about a 3rd of the way up,so that may explain why the cable seems too short.
I would be careful leaning the needle that far as it already sounds too lean with the high idle when warmed up.
When you say flatspot are you talking about a slight hesitance before the band or like hitting a brick wall and hard to get through without dropping gears?
A slight pause where the power drops off a bit is normal even on a completely stock bike,yamaha had the prob from day one and tried(with only some success) to fix it with recalls,araldite over airways in the carbs,holes in the top of exhaust ports etc.
Its just the nature of the port timing and one of the reasons they invented YPVS.
If it is a flatspot caused by the pipes then you should be able to dial it out with the jetting.
Go richer initially as it wont cause any damage,if its worse then work down til it improves then do some plug chops to confirm its not too lean.
altering the needle and the main will have different effects,the needle gets used most,1/4 to 3/4 mainly is where its most noticeable,the main will effect the lower rpm but only by a small amount, mainly it effects 3/4 to full hence the reason to plug chop at full throttle.
The only way to set an engine up is to ride it,what works on one doesnt always work on all even if there running the same parts.
Also try the choke while riding method as it gives a good indication there's not enough fuel if it improves.
Dave

[tobster]

hi Ian
Not sure I agree with what Dave is saying. All the carb tuning articles I've read have said to start with the main jet (and this is what I do). Here is an excellent article that clearly explains what you should do when setting up a carb and the sequence to do the changes.
justkdx.dirtrider.net/printcarbtuning.html
Rest assurred, a wet black plug is not optimal. Sure you may not break your engine running it like that , but it certainly (as you know) won't run anything like it should/could. BTW, i get my jets and carb bits from Allens
allensperformance.com/index.html

[iainw]

Thanks all, this is becoming a bit of an education.

I'm confused as many of the posts refer to it being lean, but if that's the case why are my plugs black and wet? This is the first issue I'm trying to reslove.

The high tickover is something I can adjust with the slide stops and air screw, which I think was set too far out at 1 3/4 turns and needs to go in a bit as you've suggested.

I've also noticed the oil pump isn't set as the Haynes manual describes, it's sending too much oil, but how much extra I don't know but this could also be contributing to the plug fouling.

The bike actually runs very well above 5-6K but at slow speeds it feels like it's a bit, and I mean only a bit, bogged down.

I may not get chance to run it until Saturday afternoon but I'll post back on how it is with the settings I've listed above.

Many thanks

[dave32]

If the idles ok when cold and is higher after its been warmed up then it cant be the idle screw's as it will be too high ALL the time.
Another sign of a weak mixture is when the revs dont drop quickly,they stay up and gradually creep down.
Yep most tuning books etc recommend doing the main first,but if its an idling problem the main has no effect on this.
Plug chops will show if the main is right or not,but first you wanna get it idling as it should,you can still seize an engine if the mains big enough but the needles too lean.
I would say the main isnt far out as it would either have seized or it wouldnt rev out if too rich.
The plugs dont look over rich in your pic(its a bit blurry so hard to read them exactly though) and if the pump is set too high then it will show up as similar to a rich fuel mix even though more oil is making the fuel/air mix Leaner.
If the bikes been ridden slowly for any length of time then the plug colour is meaningless anyway,your know if airscrew and lower part of needle are too rich if it starts fouling plugs,if it doesnt dont worry about it.
Let us know how it goes.
Cheers
Dave
One thing i didnt ask was at what throttle position the flatspot occurs or is it at certain revs regardless of throttle?

[bertiemollie]

Jul 6, 2011 22:18:35 GMT 1 iainw said:

Jul 5, 2011 22:51:19 GMT 1 lckid said:

All back together and tried to adjust the cable setting on the oil pump but there isn't enough slack in the cable adjustment. The pump end is right at the shortest outer cable setting and so is the twist grip end. I need a shorter outer or longer inner cable, how's that?

Hi Ian,

It may be you have a pattern throttle cable. I had this recently on my RD125lc where the oil pump adjustment was a problem. I bought a new one the problem went away.

Have a look to see if it is genuine. If not and you want to stick with the pump it might be best to buy a genuine one.

Cheers

Andrew

[uncleelsie]

hello , and welcome there are many many threads on this and other forums about jetting, it is very easy once you understand the following:- the basic rule of thumb is, as far as my bike was concerned, throw away all the info you have on stock jetting, ( "to jet" meaning "tune" all four circuits, as only two circuits have actual jets, pilot and main, a big misunderstanding is to bugger around with the main jet, which actually only controls the power from 3/4 to full throttle, if you have a problem pulling away or mid range, sodding around with the main jet is going to do jack shit,except f**k up your top end) and jet your bike until it runs right! i absolutely do not want to teach my granny how to suck eggs here, but i have found the following incredibly useful, once i understood how the carbs work it was easy to resolve the problem, hope this is of help to you. there is diagrams in this articles, but i cannot cut and paste for some reason. you will find the original article at " ian williams tuning australia". basically your carburretors are four seperate cercuits, pilot, throttle slide, needle, main, that overlap each other to run the engine... smoothly, the trick is to get all four of these circuits to run at the correct fuel/ratio for your engine. If you have had a rebore, head and/or barrel skim or upgraded the carbs ( as i did ) air filter mod, after market pipes or you may have differing barrels/pistons , (three different mods here i believe) (remember we are dealing with old machines here that have been buggered about with alot) then you may as well chuck the stock jet settings in the bin. hence the reason to jet your bike accordingly to run properly and ignore stock settings.

good luck, but honestly if i could fiqure it out then my cat could, please feel free to ask questions.

dave



Motorcycle carburetors look very complex, but with a little theory, you can tune your bike for maximum performance. All carburetors work under the basic principle of atmospheric pressure. Atmospheric pressure is a powerful force which exerts pressure on everything. It varies slightly but is generally considered to be 15 pounds per square inch (PSI). This means that atmospheric pressure is pressing on everything at 15 PSI. By varying the atmospheric pressure inside the engine and carburetor, we can change the pressure and make fuel and air flow.
Atmospheric pressure will force high pressure to low pressure. As the piston on a two stroke engine goes up (or goes down on a four stroke engine), a low pressure is formed inside the crankcase (above the piston on a four stroke). This low pressure also causes a low pressure inside the carburetor. Since the pressure is higher outside the engine and carburetor, air will rush inside the carburetor and engine until the pressure is equalized. The moving air going through the carburetor will pick up fuel and mix with the air.
Inside a carburetor is a venturi, fig 1. The venturi is a restriction inside the carburetor that forces air to speed up to get through. A river that suddenly narrows can be used to illustrate what happens inside a carb. The water in the river speeds up as it gets near the narrowed shores and will get faster if the river narrows even more. The same thing happens inside the carburetor. The air that is speeding up will cause atmospheric pressure to drop inside the carburetor. The faster the air moves, the lower the pressure inside the carburetor.

FIG 1
Most motorcycle carburetor circuits are governed by throttle position and not by engine speed.There are five main metering systems inside most motorcycle carburetors. These metering circuits overlap each other and they are:
* pilot circuit
* throttle valve
* needle jet and jet needle
* main jet
* choke circuit
The pilot circuit has two adjustable parts, fig 2. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed.

FIG 2
The pilot jet is the part which supplies most of the fuel at low throttle openings. It has a small hole in it which restricts fuel flow though it. Both the pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.
The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it, fig 3. The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway (which will be richer than a 3).

FIG 3
The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet needle is a long tapered rod that controls how much fuel can be drawn into the carburetor venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the mixture since the thicker taper will not allow as much fuel into the venturi as a leaner one. The tapers are designed very precisely to give different mixtures at different throttle openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves and holds it from falling or moving from the slide. The clip position can be changed to make an engine run richer or leaner, fig 4. If the engine needs to run leaner, the clip would be moved higher. This will drop the needle farther down into the needle jet and cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and the mixture will be richer.
The needle jet is where the jet needle slides into. Depending on the inside diameter of the needle jet, it will affect the jet needle. The needle jet and jet needle work together to control the fuel flow between the 1/8 thru 3/4 range. Most of the tuning for this range is done to the jet needle, and not the needle jet.

FIG 4

The main jet controls fuel flow from 3/4 thru full throttle, fig 5. Once the throttle is opened far enough, the jet needle is pulled high enough out of the needle jet and the size of the hole in the main jet begins to regulate fuel flow. Main jets have different size holes in them and the bigger the hole, the more fuel that will flow (and the richer the mixture). The higher the number on the main jet, the more fuel that can flow through it and the richer the mixture.

FIG 5
The choke system is used to start cold engines. Since the fuel in a cold engine is sticking to the cylinder walls due to condensation, the mixture is too lean for the engine to start. The choke system will add fuel to the engine to compensate for the fuel that is stuck to the cylinder walls. Once the engine is warmed up, condensation is not a problem, and the choke is not needed.
The air/fuel mixture must be changes to meet the demands of the needs of the engine. The ideal air/fuel ratio is 14.7 grams of air to 1 gram of fuel. This ideal ratio is only achieved for a very short period while the engine is running. Due to the incomplete vaporization of fuel at slow speeds or the additional fuel required at high speeds, the actual operational air/fuel ratio is usually richer. Figure 6 shows the actual air/fuel ratio for any given throttle opening.

FIG 6
Carburetor Jetting Troubleshooting
Carburetor troubleshooting is simple once the basic principles are known. The first step is to find where the engine is running poorly, fig 7. It must be remembered that carburetor jetting is determined by the throttle position, not engine speed. If the engine is having troubles at low rpm (idle to 1/4 throttle), the pilot system or slide valve is the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the jet needle and needle jet (most likely the jet needle) is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.

FIG 7
While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting.
Clean the air filter and warm the bike up. Accelerate through the gears until the throttle is at full throttle (a slight uphill is the best place for this). After a few seconds of full throttle running, quickly pull in the clutch and stop the engine (Do not allow the engine to idle or coast to a stop). Remove the spark plug and look at its color. It should be a light tan color (for more info on reading spark plugs click here). If it's white, the air/fuel mixture is too lean and a bigger main jet will have to be installed. If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed. While changing jets, change them one size at a time, test run after each change, and look at the plug color after each run.
After the main jet has been set, run the bike at half throttle and check the plug color. If it's white, lower the clip on the jet needle to richen the air/fuel mixture. If it's dark brown or black, raise the clip to lean the air/fuel mixture.
The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.

Altitude, Humidy, and Air Temperature
Once the jetting is set and the bike is running good, there are many factors that will change the performane of the engine. Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner and more fuel will have to be added to compensate. When the air temperature gets warmer, the engine will run richer and less fuel will be needed. An engine that is jetted at 32deg Fahrenheit may run poorly when the temperature reaches 90deg Fahrenheit.
Altitude affects jetting since there are less air molecules as altitude increases. A bike that runs good at sea level will run rich at 10,000 ft due to the thinner air.
Humidity is how much moister is in the air. As humidity increases, jetting will be richer. A bike that runs fins in the mornings dry air may run rich as the day goes on and the humidity increases.
Correction factors are sometimes used to find the correct carburetor settings for changing temperatures and altitudes. The chart in fig 8, shows a typical correction factor chart. To use this chart, jet the carburetor and write down the pilot and main jet sizes. Determine the correct air temperature and follow the chart over to the right until the correct elevation is found. Move straight down from this point until the correct correction factor is found. Using fig 8 as an example, the air temperature is 95deg Fahrenheit and the altitude is 3200 ft. The correction factor will be 0.92. To find out the correction main and pilot jets, multiple the correction factor and each jet size. A main jet size of 350 would be multiplied by 0.92 and the new main jet size would be a 322. A pilot jet size of 40 would be multiplied by 0.92 and the pilot jet size would be 36.8.

FIG 8
Correction factors can also be used to find the correct settings for the needle jet, jet needle, and air screw. Use the chart from fig 9 and determine the correction factor. Then use the table below to determine what to do with the needle jet, jet needle, and air screw.
Needle Jet/Jet Needle/Air Screw Correction Chart
Correction factor 1.04 or above 1.04-1.00 1.00-0.96 0.96-0.92 0.92 or below
Needle jet Two sizes larger One size larger Same size One size smaller Two sizes smaller
Jet needle setting Lower clip position Same Same Same Raise clip one position
Air screw opening One turn in 1/2 turn in Same 1/2 turn out One turn out
FIG 9

This article was written by, and has been reprinted with the permission of Doug Jenks. All rights reserved.
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[mellow]

interesting stuff

[dave32]

Good article!
As i see it,its pretty much impossible to jet someone's bike over the internet/phone whatever,you can only give a guideline based on whats been told to you.
There's no substitute for actually getting ya hands dirty and trying different settings for yourself,then you will get a feel for what each part of the carb does what.
The golden rules though is write any changes down you make/dont change more than 1 thing at a time and always start too rich and work down,then use the plug to confirm if its right.
As the weather has a large bearing on how the fuelling works and seeing as its a roadbike dont expect it to run the same in all conditions.
If you jet the engine on th limit in hot weather then its apt to be to lean when the temp drops,for this reason i would never jet a roadgoing motor for optimum performance in the summer months.
Also i would get the oilpump set as should before changing the jetting as it will give misleading plug readings,the manual should explain it sufficiently.
Cheers
Dave

[iainw]

I've re-read all these post and it's now clear that what I've been thinking is the cause of the wet and black plugs is not the case and my suspicions moved to the oil pump. I've set the carbs up to the recommendations posted on here, the needle is back to the middle slot and the pilot screws are at 1 ½ turns out. The carb slides are set by the lolly stick method and the tick over is smooth at 1100-1200 rpm. Pulling the choke out on a warm engine kills it.

The bogging down I've experienced has been when I've had it at partial throttle for a while then opened it up. The oil pump being set incorrectly has been delivering the correct amounts at tick over and at full throttle but at partial throttle it has been pumping too much, that’s probably why it's cleared at fully open.

I've fixed the cable by moving the ferrule out of the way and carefully cutting about 8mm from the outer and then sliding the ferrule back on. This gives me the adjustment to set it correctly.

I took it for a run yesterday afternoon and it’s improved to the extent that I'm happy with it. I didn't do a plug chop but just pulled them out when I got back after a 15 minute run and they're looking pretty much as I want them to.

So my black wet plugs weren't caused by fuel but by too much oil. Many thanks for all the advice from every one; as I said in my earlier post, it's been an education.

Iain.