Comp 75/90, to late for decarb? 78 35 HP Rude

[outboardnut]

Picked up a "never heard it run" 35 horse, has no spark, and compression is a low.
Think it's to late for a decarb?

 

[surrender]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

How would you do a decarb with no spark? Or do you mean is it worth getting it to run, THEN do a decarb?

 

[psteurer]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Compression numbers of 75 and 90 are not too good. It might be best to pull the head off the cylinder and take a look. You might just have a blown head gasket but then you would have to find out why the head gasket blew.

 

[tashasdaddy]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

probably ran hot. agree $20 head gasket is worth a try.

 

[outboardnut]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Pulled head and everything looks peachy.
I hosed the pistons with some deep creep and will let it soak in over the weekend.

I guess now I'll have to buy a head gasket or reuse the old one.

Whatch yall think about putting a tack coat of metallic spray paint on the head gasket and reusing for temporary troubleshooting purposes?

 

[R.Johnson]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Don't use metallic spray paint, just put it on dry for now.

 

[outboardnut]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Put head gasket on dry, compression is about the same.

Tried to do a leak down with my POS harbor freight tester and it seems to be OK.

However the POS leak down tester is only calibrated for 15 PSI which doesn't seem like much to me.

I've got a phead from a 81 25 HP rude that I thought maybe I could just swap out, but after a little bit of investigation I don't think it will bolt on. I looked up the gasket between the exhaust housing and block and am showing a different one.

So I'm a little up in the air as to what to do. I think I need to get a leak gauge lined out and see how that goes, then look at the reeds and maybe upper/lower crankshaft seals.

The exhaust cover plate gasket on this motor has been redone at one time, there is red gook squeeze out of it all over the place. I can't think of anyway this would cause it.

 

[outboardnut]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

ok got the leak down tester lined out,

came up with 35% leak on the top and 25% leak on bottom

 

[G DANE]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

The 81 Powerhead will bolt up, but you will need the inner exhaust tube from the 81 as they are different. If pistons and bores are fine, no scorings, I doubt it can be that bad. You must be sure your head gasket is 100 % airtight to get an accurate leak down test. I would spend the 20$ and take new compression readings. Continue with soaking in decarb oil. How did you cranck it, pull start, be sure to give it 5 good powerfull pulls at least.

 

[outboardnut]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Dang, I sold the inner exhaust tube to the scrap man for 55 cents a pound. Got a whopping dollar out of the thing. Ha. That's how it goes I guess.

I'll get a new head gasket ordered.

 

[G DANE]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

Also check with a steel ruler or similar that the head isnt warped. If it is, do a search for it here on ther forum, and correct the warp as described.

 

[outboardnut]

Re: Comp 75/90, to late for decarb? 78 35 HP Rude

I'm using an electric starter, she is spinning plenty fast for a good reading.
Installed new head gasket, actually lost a little ground but it is colder so it's prob the gauge.
New readings are 65/80

only thing I can think of is the rings are stuck.