Super Jet Weird compression problems

[SJ 701X]

Hey guys I just rebuilt my engine (new crank, rings, hone, seals, head). I am running into a problem with the compression. I am running an ada head with 37cc domes. The front cylinder is running at 170 psi while the rear cylinder is showing 190. Any clue as to why this is happening? only thing I can think of is a pinched o ring or a dropped sleeve. I have about a tank through the rebuilt engine. I wouldn't be concerned if the numbers were even.

 

[ProSouth]

the rear seems high, with that size domes. i have 195 psi on a pretty fresh motor and 33cc domes. but you could be running a thinner head gasket than me. so.... i would yank the head and check o rings first.
does it run good?

 

[Matt_E]

^^As mentioned, 190 is too high for those domes. Even 170 is higher than it should be. What gauge are you using?

Possible reasons:

1. Wrong spark plug in one of the holes
2. Uneven wear (pull head and check)
3. Domes are not the same
4. Shop f'd up the boring & honing and one side has way more piston-wall clearance than the other
5. Oil in the 190 psi side.

 

[DAG]

Did you check ring gap? Are they the same?

 

[SJ 701X]

Matt, there was black sludge coming out of the plug hole on the 190 side because gauge wasn't seated properly. I'm running 32:1 as well.

Sent from GS3 Synergy

 

[ProSouth]

i would change that to atleast 40:1 what kind of gauge were you using? and like dag said, was ring end gap measured?

 

[Poizen]

Regardless of what gauge was used there is a 20psi diff in pots

A ty gauge should still read equal

Like they say check ring gap
Check squish

I assume you are holding the throttle wide open when testing

 

[SJ 701X]

Throttle is about 3/4 open because of the slop in the cable I can't make up. I will run it and see if there is a difference. There appeared to be oil in the rear cylinder. It wasn't bored and before it was 170 even. I just ran a hone through it. Ring gap wasn't measured. Both new sets of rings. Squish was fine with old crank, haven't checked new one.

Sent from GS3 Synergy

 

[glennbbautomachine]

Throttle is about 3/4 open because of the slop in the cable I can't make up. I will run it and see if there is a difference. There appeared to be oil in the rear cylinder. It wasn't bored and before it was 170 even. I just ran a hone through it. Ring gap wasn't measured. Both new sets of rings. Squish was fine with old crank, haven't checked new one.

Sent from GS3 Synergy

Just sayin you got a lot of iffy stuff going on and you need to check and do it right.

 

[SJ 701X]

Oh I know I'm just thinking it's the oil. There's no way it can possibly be 190 with 37cc domes. Squish was .040 last time I checked. I will check it all again but I don't feel like pulling the head, again. It starts and runs fine.

Sent from GS3 Synergy

 

[SJ 701X]

Just checked it after running about another half tank through it and they are both 170 even now. Most likely there was some unburnt oil in the rear cylinder because I had the low speed adjuster and high speed adjuster really rich for tuning. Thanks guys.