550 starts hard then opens wide up

[NOSstreetracing2]

I have recently just bought a used 1987 JS550. The previous owner just had the engine and carb rebuilt. I just got done replacing the base gasket which was cracked and leaking. When I try to start it, it takes a long time for it to even start to sound like it's going to fire. After it starts, it revs as high as it can go and then shuts down. After doing that twice, the third time it backfires. Can anyone help me. Thanks.:(

[1fastski.com]

Re: 550 starts hard then opens wide up

sounds like a massive air leak , rebuild it again or do a leak down test .

[Antwon]

Re: 550 starts hard then opens wide up

When it shuts down that's the pistons expanding and sticking in the cylinders. Check compression to see if I'm correct and then rebuild that thing.

[NOSstreetracing2]

Re: 550 starts hard then opens wide up

I tested both cylinders and one has 120 and the other 130. I think it's supposed to have somewhere around 135 but I'm not sure.

[Technical Support]

Re: 550 starts hard then opens wide up

That engine is very damaged if that reading is accurate - it should be about 150 in each.