Running Race Gas...problems

[jeepmark4x4]

What is the right octane for 200 psi? I have done on the Kawi fresh port work/bored 760, ADA head running 200psi with a single Mikuni 46. I went and got 110 leaded race fuel and mixed it 50/50 with 93 and came up with 101.5 octane. I took it out and it ran like crap, it would not rev up but started up great.

Took off the head and saw the front cylinder was clean and the rear was covered with un-burned fuel :dunno:
Both plugs are giving good spark.

THEORY. The stupid o'rings are letting water in the cylinder
OR
SEEEMS like light detination, but no perminant physical signs.

AGAIN

My 650 SJ running 195psi will not rev up?! Before the super duper aftermarket head, it ran great with an aftermarket ROGO and i was running 180psi with 93

So how much octane do you have to run in comparrison to compression?!

 

[blaster800]

FYI ....Its not the fuel ! I do the same mix on 210 psi in a 701 and it screams !

 

[Speedfreak]

There are alot of thoughts about this but it has alot to do with your motor setup. What is your squish clearance?

I have ran one summer with 230 PSI and a squish clearance of about .055. I ran a mixture of 3 gallons of 93 octane and 2 galons of torco 104. The ski ran great and the next year I ran straight 93 ocatane with 200 psi. All of this with an MSD enhanser. I might be just lucky but never had any problems.

So with your problem it sounds like something else.

 

[SUPERTUNE]

50/50 on the fuel your mixing should be good enough at 200 psi if you have conservative timing curve and not too much exhaust port duration, Try glueing your head o-rings with 1211 threebond and check top of cylinder block for any imperfections around bore and sleeve height (not dropped down).

 

[jeepmark4x4]

Well when i was out there first looking at it, the sleeves did not seem even with the top of the cylinder block. I figured this would have some bad repercussions with using o ring head gaskets and un-even sleeves, it did not act like this using the stock head gasket. the quinch does not seem to be an issue here with the Kawi and with the SJ I'm using a .040 metal headgasket. Has any of ya'll used a copper gasket for an o'ringed head, I can get them made to spec.

I'm going to take pictures after i get home from school. thanks for the comments.:biggthumpup:

 

[SUPERTUNE]

If you have any deck problems, it's best to tear it down and have it resurfaced and adjust head domes as needed. (if you can get away with less than .005 thou. milling then your most likely ok on the domes).

 

[jeepmark4x4]

Yeah, .005 taken off should be alright, but that was enough to have water intrusion it seems. It was showing good compression while cold but I guess while it was starting to heat up it was leaking. Also, do you have to adjust the carb because of the slower burning fuel? It would seem that running leaded 100 octane would be too rich on a stock carb tune.

 

[crammit442]

Yeah, .005 taken off should be alright, but that was enough to have water intrusion it seems. It was showing good compression while cold but I guess while it was starting to heat up it was leaking. Also, do you have to adjust the carb because of the slower burning fuel? It would seem that running leaded 100 octane would be too rich on a stock carb tune.

Race fuel is not necessarily slower burning. The octane rating denotes ONLY the fuel's resistance to detonation. Normally you will not need to tune much if any differently for leaded fuel. If you have the compression and/or timing to need race fuel your carbs will actually be a bit more forgiving. The exception would be if it is heavily oxygenated.

Charles

 

[jeepmark4x4]

Well back to the issue with the Superjet, its acting funny with the leaded 100 octane. The carb was dialed in perfect with 180psi and 93. But than after the bump to 195psi and 100 it bogs at about half throttle and seems like its running wwaay rich. Thats why im scratching my head at the carb tune.

Well after diagnosing the Kawi its officially confusing. The front cylinder with the lower sleeve height is firing correctly, and the rear cylinder with the right sleeve height isnt...GRRR

 

[ANT]

Usually you run richer from race gas. You might not have to worry about it though since you cut down your mixture. Test ride it you might be able to get some extra power by goin a little leaner if it does run richer.