coolhead and rebuilding help

[streetbanshee]

so wen i bought my coolhead i was told that i could run 21 cc domes so i did and on the second run my right piston goes out so i though it was the cool head but i decided to still run it i bore it and put .20 over wiseco pistons with 22 cc domes i break it in and it runs good for about 6 months then im riding it in 6th gear wit the power on at about half throttle and all of a sudden blows out again and turns out it is my right cilinder the piston had a hole in the top so the question is am i doing something wrong or is it the coolhead my mods are esr pipes,k&N pod filters ,boyesen power reeds280 mains 30 pilots temperature 90-100 elevation 650 ft any help would be apreciated

[b33rs]

That is an awful long sentence btw, but maybe you need to mix your gas a little or play with your jetting some more :shrug:

[jbooker82]

I run 19cc's at 2500 feet elevation. That should be around the same compression as your 21cc at sea level. I also have my ignition timing advanced 3 to 4 deg. Runing on premium pump fuel.

 

Your jetting sounds lean to me. Maybe that is why your buring holes in your pistons. You might aslo check for an air leak. What does the other side look like that isnt melting down?

Edited September 14, 2006 by jbooker82

[BigRed350x]

You are lean or getting some bad detonation. Jetting and some higher octane fuel might be in need.

[streetbanshee]

the left piston looks perfect normal wear but with my stock head i had no problems at all with that jetting

[BigRed350x]

If that's the case, sounds like you might have an air leak somehwere making the cylinder lean. Or you might have a warped head or warped cylinder letting something past it shouldn't. I always blew up my 87's top ends in like a week. It has a cylinder that was an oval shape and the head was warped come to find out. Some guy wanted the chassis for a hill shooter so I scraped the whole thing and sold it.

[streetbanshee]

how would i find out wer the leak is

[LiftdT4R]

You have pods with stock carbs and your running 280 mains?? If so, you ARE LEAN!! I ran 320s with FMF pipes, and no lid on the airbox. With pods you should be around 330-360, somewhere in there. I would say start with the jetting, it's definately too too lean, and then go from there, you can't re-use the o-rings for the cool head, I don't know if you did or not, but they won't seal up right. So I would also check for an air leak too. Good luck bro!

[streetbanshee]

yea i had read somewhere that it was to lean as for the o-rings i put new ones in it last time i rebuilt it also how would i know wen im too rich and if im running too lean while breaking it in will it mess anything up ?

[LiftdT4R]

yea i had read somewhere that it was to lean as for the o-rings i put new ones in it last time i rebuilt it also how would i know wen im too rich and if im running too lean while breaking it in will it mess anything up ?

I'd post in the jetting forum, they will be able to give you a more exact main size there. You can plug chop, which is in a FAQ at the top of the jetting page. Generally after I have about 3 or 4 horus on a pair of plugs, I will pull them, if they are too light, it's too lean, if they are the same color as a paper bag they are perfect, if they are too ddark it's too rich. This isnt very accurate, but it suffices if you know you are in the right area. Sounds like you really leaned the thing out with a possible air leak, and defiantely from being too small on the mains. I run 260s on an airbox with a lid, so I know you are too too lean on the mains. Good luck, hope you can get away with just pistons this time. Also check BigRed350xs splitting the cases thread, it shows you how the pistons should look when the bike is setup right. Very very accurate picture.

[streetbanshee]

awsum thanks for the help everyone

[platinumjason]

I am having the exact same problems with mine. It was stock with the exception of the VF3's a airbox with K&N setup and +4 timing, I added all of the other stuff at the same time. I was running a Noss head with 21cc domes at the time and 300 mains, 27.5 pilot and clip on 4th position. Blew up after about 45 minutes of ride time total, the right piston that is.

 

Rebuilt it again, thinking it was too lean, went to 320 main, 27.5 pilot and 4th on needle, ran it at silver lake for about 3 hours, right side leans out again.

 

So now getting it narrowed to detonation this rebuild will consist of all of the same upgrades but am switching to 19cc domes and running race gas. Hopefully it works this time.