cracked head

I have a 78 bravo that I just got running. Sealed tank, rebuilt carb, the whole works. It starts right up, runs and idles great but has no power. I get power for about 10 seconds and then it gets slower and slower to the point where it is just at idle. I have a feeling that the cylinder may have a crack. Is there a way that anyone knows to test for this. I put my hand down there and I do feel air but I cannot tell if it is the cylinder or the exhaust.

Re: cracked head

Richard Wisniewski /

head gasket replacement???base gasketr???

Re: cracked head

No head gasket on a bravo. It has compression because it is really hard to start. The head is fine. Is it possible that there could be a small hairline crack? or would I be able to see exhaust coming out of the crack?

Re: cracked head

should I use aviation sealer? Permatex? Fabio told me not to use anything but he is MIA now

Re: cracked head

No..........sounds like what Rich said about a BASE GASKET leak. They will show good compression usually, but not run worth a hoot,or run lean and burn your piston.

The reason it starts is the choke is on,richening the mixture...........when the choke comes off,the extra air from the leak is too much.

Anyway,that's whaT IT SOUNDS LIKE. You can cut a new base gasket with the dark gasket material from an Auto Parts place. You can't use cork or really thin paper,though. Don't use permatex or silicone. Torque the cyl.back tight in an `X' pattern progrressively up to 11 ft.lbs. with new lock washers or blue(NOT permanent type) loc-tite on the threads of the bolts. don-ohio (:^)

Re: cracked head

What is the dark gasket material you speak of? is it like a thick paper roll that I will cut? or a tube of chemical gasket material?

Re: cracked head

If I remove the piston from the cylinder to re-do the base gasket (I am assuming by base gasket you mean the gasket between the cylinder and the block) do I need a ring compressor to put the piston back?

Re: cracked head

the "black paper" is paper that you cut into your pattern with scisors

nick

Re: cracked head

You can get it at Auto-Zone.It's gasket material. I cut it with a razor blade, but a modeling blade would be even better.don

Re: cracked head

My problem that I thought was a cracked cylinder turned out to be a carburetor problem. The rubber tip on the end of the needle had broken off and was preventing fuel from entering the bowl fast enough. That is why I had good power and then it slowly tapered off after a few seconds. I let everyone know in a different post but I didnt want to leave this post up in the air.

Gratzie

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