holed piston

[holty]

hi folks,
had a nightmare on saturday and holed a piston in my 4lo, not stripped the engine yet, i might have it out by tonight, but by looking up the exhaust ports lh piston is holed and was a very white colour, i guess too lean, rh is a very light brown looks a bit too lean as well, it was a very windy day and i had the throttle wide open for a long time,i had done a plug chop about 300 miles ago and it looked light brown, maybe i hadnt loaded the engine enough to get a true colour, im thinking my main jets may be too small, ive got 240 s in at the moment,standard carbs running foam pods, and microns, would i be wise to put 260 mains in after ive rebuilt it, i am going to do i leakdown test as well, am also going to install a egt gauge has anyone on here done the same ?

holty 

[Tobyjugs]

Thats bad luck Holty
Correct jetting it is something we all worry about after an overhaul or modification. I think your mains jets were way too small. Someone will come along with a similar set up to you and give you a good starting point.

In my limited experiance of jetting plugs chops are only good for a rough estimate. I set my bike up once and it was running good and i was well chuffed with the rich brown colour of the plug at half and full throttle settings. When i took it to the dyno bank it was still running too weak. You should be looking for dark brown/black colour and check it out on a dyno it will be money well spent.

My 4LO is running standard pipes, standard carbs, air box with holes in lid, dry filter and a Bob Farnhan road tune the main jets are currently 290's

[arrow]

With the pods and microns 240 mains seem way too small.

[looey]

One of ours has Allspeeds, Pod filters, standard tune and has been running 290's for a long time (including a few track days)

[muttsnuts]

I would agree with 290's as a starting point and having it checked on a dyno is a must, or be sure you know what your looking for in plug colour, are you premix or pump as that has an affect as well

I have a F2 track day bike running tuned barrels, spannies (TSA's), pod filters and premix and that is 330's and next size pilots

[holty]

thanks for the advise, i will get some new jets ordered, i think a dyno run is a good idea as well once ive got it all up and running again.

[stevep]

Definatly put it on a dyno , best way of getting the fuelling right ,it will save you money in he long run .
If your in the Midlands Projex are very good

[bngt]

With foam pods you change the jetting requirement immensely. Think of the airbox as a choke. When you take away that restriction you have to compensate with much bigger main jets. 400 is not uncommon. Start from there and reduce.

At part throttle, the throttle is the big restriction and change of airbox/pods has very little impact. Therefore change of needle jet/needle is seem to seldom be needed.

Different exhausts I would assume has little effect. Changed porting though would totally change the inlet pulsing and jet requirements.

It would be interesting to hear others experiences.

[robj]

Hi, I'm running my 4lo on 250s with standard air box ,I fitted a set of ypvs microns and now it won't pull above 5k do I put bigger jets in or smaller I'm a bit stumped

[arrow]

How did it run on the 250's before you put the microns on? Or did you do the two changes together?

[robj]

To be honest it was fine but 7k is my limit still running in

[arrow]

Sounds like you need to go quite a bit bigger then.

[robj]

Would you say 300s is a good starting point

[robj]

I've ordered a set of 300s see how that goes also someone recommended removing the air box snorkel is this wise ?

[arrow]

Apr 4, 2016 8:03:12 GMT 1 robj said:

I've ordered a set of 300s see how that goes also someone recommended removing the air box snorkel is this wise ?

Mine ran like a bag of crap with the snorkel removed, but I didn't alter the jetting.

[robj]

What notch did you have the needle on and how many turns of the screw out ,just to give me a fair starting point thanks arrow

[holty]

ive got some 300 jets for mine, cant fit them yet, my engine is still in bits, crank was damaged as well, so having it rebuit.

[hudtm60]

This is interesting stuff- would anyone suggest running larger than 220's on completely bog standard 4L0 at sea level?

[robj]

I ran mine standard on 230s and it was great till I put expantions on, I will post when the 300s are fitted

[robj]

Took the snorkel out needles on mid notch screw 1 1/2 turns and 300 jets ,it ran like a spluttering dog ,put 250s in ran better ,put 230s in going like a good UN but I think I will still do a dyno

[hooligan]

Mar 29, 2016 11:45:21 GMT 1 holty said:

hi folks,
had a nightmare on saturday and holed a piston in my 4lo, not stripped the engine yet, i might have it out by tonight, but by looking up the exhaust ports lh piston is holed and was a very white colour, i guess too lean, rh is a very light brown looks a bit too lean as well, it was a very windy day and i had the throttle wide open for a long time,i had done a plug chop about 300 miles ago and it looked light brown, maybe i hadnt loaded the engine enough to get a true colour, im thinking my main jets may be too small, ive got 240 s in at the moment,standard carbs running foam pods, and microns, would i be wise to put 260 mains in after ive rebuilt it, i am going to do i leakdown test as well, am also going to install a egt gauge has anyone on here done the same ?

The white you see in the exhaust port and the pipe is vaporized aluminum deposited on everything.

While there are other reasons a piston could melt down, I think you were lean on your main jet. I took a bog stock 4LO and added a set of Uni pod filters. I am currently running 260 main jet but think that 250 would be about right. If you had pods plus expansion chambers, you should have been a fair bit bigger on the mains.

Be careful about going too big on the mains. Excess fuel can wash the cylinder walls and result in ring seizure.

I run an EGT gauge. The best advice I can give you on setting up the EGT is to go back to all standard if possible so you can understand what readings the EGT produces. For some reason my EGT shows a fair bit higher than most people recommend and so I tried to jet the thing rich to bring the temps down but no matter how rich I made it, the gauge would read high. So I just got a range I was comfortable with, using all stock settings. Now I can mod the engine, airbox and pipes as long as I stay within the acceptable range that I know works.

[hooligan]

Apr 4, 2016 19:56:23 GMT 1 hudtm60 said:

This is interesting stuff- would anyone suggest running larger than 220's on completely bog standard 4L0 at sea level?

No. The 220's should actually be a bit rich. Yamaha did that intentionally so the engines wouldn't melt down under normal use. You could prob go at least one size smaller and still be safe.

[arrow]

Apr 4, 2016 16:43:26 GMT 1 robj said:

What notch did you have the needle on and how many turns of the screw out ,just to give me a fair starting point thanks arrow

Sorry I missed this. Standard clip position according to the manual, can't remember which groove that is sorry (it was a while ago)! Just one turn out on the air screws worked best for me and 210 mains.

[twostrokebrit]

I had spec11 pipes .fibre reeds,and a hi flo airbox top and ran 260s