Weather effecting ypvs

[Bozzy]

Guys is you bike running different in this weather? Mine is crap nearly turned back from a ride out tonight as it was missing and spluttering really badly between 4.5 to 6 k thought motor had gone at one point! Anyway I road thought it and thrashed it chasing mates on diesels red lined it a few times. It ran great after 6 upto red really strong but just really crap in the flat bit

Still not sure if its running rich or lean.....I am sure after thrashing it 7 to 8 k for about 5 mins etc and keeping above 6 k for a good 30 min it would have gone bang on me if anything serious. Got to be jetting.....it's starting to really p###s me of this bike....

One thing putting new needles and emulsion tubes has changed it

[paulo]

Hi m8, trying dropping your needle one and see if its better or worst - I know standard position for LC2 is fourth from top so is running rich from Mr Yamaha.
Your new needles and tubes aren't from a kit!, as this may have upset the apple cart - if you can't sort and still have the old bits then try refitting back to how things were and seen how she runs. Nothing worse when the bikes not running right.
Also haven't recently had your pump done by arrow ?, as more oil than normal can lean out the mixture, I had to up on my pilots to sort my running issues. Not saying there's something wrong with arrow's work, he does a first class job.
Good luck m8, don't give up as it's worth it in the end!.

[arrow]

Hi, it will need more air on the air screws in hot weather as hot air is less dense so therefor there is less of it than at cooler conditions. In fact all the settings will change but its simply not worth re-jetting for different days, however this is done on race bikes. More oil only affects the mixture (weaker) when using premix. More oil from the pump does not reduce the petrol content. More oil from a pump actually makes the mixture richer, (but by virtually nothing). The oil burns so therefore it must have some energy value, so it becomes extra fuel, but its negligible.

[Bozzy]

Thanks for replys.

Needles and tubes were from Norbo due to issues I had read about kits off the web....after fitting them I had to turn the pilot in 1/2 turn (might have got way 1/4 turn so perhaps a bit rich its now 3/4 turns out) to get the bike to start. Looking at the orginal tubes wear could be seen. Upon fitting it had the same effect before by dropping needle being would not start very well.

I had this running issue with the Nikon pipes and now have Kenny pipes which made it 100% better but still have this low rev running issue. Standard pipes & jetting it ran straight through but has always gone bad around 4.5 to 6k range. Below 4 it pops and bangs & has the tommy gun sound a bit but runs ok, above 6 it runs great at pulls well. In this hot weather its taking some effort in the higher gears to ride through this flat spot range but if I keep the motor above 6k at all time like last night it does ride well and rapid.

Another point to add is unless it's me, I went down on the front sproket at the same time as doing the carbs above and was expecting a more wheeling violent bike than before. To me it actualy feels less power and not dramatic at the top end. Prior to this is made the front end light throught the gears but now it appears to have lost some 'excitement' to it.

I am sure top end is running ok done a plug chop and that was ok and after the thrashing round its now had I am sure it would have gone by now. Its got to be needle and pilots I expect.

One thing I do keep thinking about is if I have gone to far up on the mains ie 240 to 260's I wonder if this is making it too rich and reason I cannot dial it in. Its standard motor with airbox etc. Never tried 250's or perhaps I should try standard jetting but a bit worried about going too lean.

[arrow]

Try the air screws 1 1/4 turns out.

[Bozzy]

1 1/2 out and the bike would not start had to give it some throttle turning it back in to about 3/4 out. Something not right keeps giving weak indication when on Ederle rich

But will try it again may raise needle and richen for a start

[phil38]

Is the issue between 4-6k full or part throttle. The needle position shouldn't make any different at full throttle, but obvious will below about 3/4.

I agree with arrow, you really shouldn't be rejetting for different weather, but the warm air will make it run a bit richer, so I was marginal in the cold, it could just be going past a threshold.

My CCM (4 stroke) won't rev our with the standard (MOT) end can fitted as it goes far too rich. It's jetted at 140 standard and 160 to match the can.

The popping is probably fuel burning in the exhaust.

[Bozzy]

Phil it is part throttle top end is fine or when I give it a handful. Def amount 1/4 to 1//2. It must be running too iChat in the middle but lean lower end....going to remove air filter and see the effect....

[dusty350]

Hi
Here is "Spankeys" jetting guide, it may help you.


Spanky's Jetting Guide:

A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's powerband.

A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

It's very important that you start with the pilot circuit. The reason is simple. The pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to rejet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idleing. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet.

Once you have determined (and installed it if it's neccessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between "rich" and "lean", you'll begine to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that here.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, ansd screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer.

Dusty

[copper99]

That was a good read, thanks to both you and Spanky....so, this air screw, is it the chunky one with a slot for a flat bladed screwdriver in it, exposed on the side of the carbs?

[Bozzy]

Thanks for that guide really helpful.

Copper yes the flat slotted screw on the side of the carbs is the air screw and should be about 1 1/4 out mine is 3/4 at the moment so saying its lean on the pilots....i am considering waiting till this real unusual weather we are having ( called hot sunny day I tjhink!!) goes...seriously think if I jet the bike in now it may be to lean when we get back to normal temps....

What I am trying to find is hot days like this = too lean or too ric

Found this link as well - justkdx.dirtrider.net/printcarbtuning.html