300/440/550 550 has me stumped

[lake-skater15]

It is the head gasket. Or rather just a leak. When I put it back together should I put an actual head gasket on it? Right now it just has black silicone on the mating surfaces.

 

[cookn]

That is an old school trick to just glue the head to the cylinder to get those high compression numbers. The only problem with that is, the two mating surfaces must be perfectly flat to get a good seal, and even then the cylinder wall on a 550 is so close to the case stud holes you will still have problems. I would recommend a copper head gasket, especially if your over the stock bore. It will lower your compression some but will give you less trouble. check your compression again after the install and make sure both cylinders are the same or you have other problems as well

 

[cookn]

Also be sure you get both the head and cylinder clean before re-assembly.

 

[lake-skater15]

Yeah I learned that trick from my friends dad who is an old school 550 guy. It made the ski run good but it didnt seem to last long so I think I'll take your advice and get a copper gasket.

 

[Polish jet pilot]

I am still unsure why would it blow back through the carb...In my opinion your bores are ovalized. Especially if that ski was running 210 psi before!

 

[lake-skater15]

Why would that cause the cylinders to ovalize?

 

[cookn]

well if your compression was reading correctly 210 psi is really high for a 550, thats race gas territory. also the fact that you have different compression between the cylinders may indicate that something is wrong. did you end up taking the cylinder off and looking at your pistons. some pictures will help. my 550 would puff a little smoke out the carb when it had sat for a bit and i had to crank for a while to get it started. i dont think it is any cause for concern but i could be wrong there. i found once you get your piston port fairly moded your carb settings really effect its starting abilities. at one time i had adjusted just the screws and it fired right up when it was cold and ran well but then i would get out to the lake, fall off and would kill the battery just trying to get the thing started again. i believe i made the low speed screw slightly richer and the problem was fixed. when making screw adjustments even 1/8 turn is a big move. you have to do it in small increments. and lastly like droc said the piston port is a slow starter from my experience, especially without a primer.

 

[Crab]

always do a leakdown test on them old iron motors.

 

[lake-skater15]

The crankseals are good and the pistons are good too. It was just a leak around the front of the head.

 

[Polish jet pilot]

So you are back to normal?? Whats the compression now? Did you ride already??

 

[lake-skater15]

I put a gasket in it and now it's 180 psi and back to normal. Thanks for the help guys.

 

[screaming440]

the older bn carbs (pre 89 i think) dump fuel when they sit for a few minutes. if you let them sit for 3 to 7 min they load up and can be hard to start. if you let them sit a little longer the fuel drys out and they start fine.


try and start it with the trottle wide open if it sits a little and don't let it idle right away.

 

[N2 H2O]

1990 was the last year of bn carbs. A lot of times the needle and seat don't seal properly causing it to dump fuel into the engine. I would rebuild it anyway.

 

[screaming440]

they changed the pilot circuit on the 44bn between 88 and 89 the older bn dumps fuel into the engine when it sits.

there is no fixing it. just start them with the throttle open.