Blaster Tired of going through top ends - HELP

[escore]

So I blew the top end in my Blaster for the 4th time since i built it a while back. Here is a picture of the pistons as they where when the cylinder was taken off. You can see some exhaust residue on the bed plate which was also on the rear cylinder and manifold. When I first put the engine together it went 3 times in 4 hours and then I put double base gaskets on it and it ran a year and a half until this. It has port matching, factory mod pipe, reeds and angled spacer, reed stuffers, MSD CDI, lightened flywheel, stock carbs, dual cooling, and most importantly an ADA head with 35cc domes. any insight based on this picture would be awesome. I'm really tired of this.

 

[superjetguy]

hows your crank

 

[schicks]

is that an exhaust leak or bad seal in the case halves? Did you do a leak down test before installing? did you check the ring gap in cylinder before you installed the rings to the pistons? what was your compression?

 

[amitchell]

Looks a bit lean.

 

[escore]

I believe compression was around 175. The exhaust was either coming from the mani or the coupler i am not sure. Ring gap was checked every time. I plan to do a leak test this time around. Not sure what else to do. Probably going back to a stock head for a while.

 

[MX429]

When you say you are blowing top ends, what is happening? Is it seizing? Is it losing one cylinder? The same one each time?

 

[escore]

It never looks up. Just seems to stick a ring and screw everything all up. This time around it was both which if I remember correctly wasn't always the case but more than once has been. I am at a loss other than lowering compression and being more confident in my jetting.

 

[MX429]

I don't think compression is your issue. I have run much higher than that with a very reliable motor. One thing that is simple and something to look at is your fuel tank. Make sure the vent hose for the tank is clear of obstruction and not kinked in any way. If it is, your motor will run fine until it sucks enough fuel out of the tank to cause a vacuum. after that happens, one cylinder can go lean and seize or stick a ring for sure if you are running it hard. Good luck with your motor.

 

[kevbo]

It never looks up. Just seems to stick a ring and screw everything all up. This time around it was both which if I remember correctly wasn't always the case but more than once has been. I am at a loss other than lowering compression and being more confident in my jetting.

Dont tune with expectations of what is should be. You have found the limit of your fuel more than once. Just back off the timing and compression. Then spend more time with break in and carb tune.