cool head dome info?

[j450rking]

i need to know what size dome i should run so i can still use 93 pump gas. i don't want to be on the limit so i want to run the dome one size down from the limit. i need to know asap.

[j450rking]

nobody? oh also i am running a stock thickness cometic head gasket.

[C-LEIGH RACING]

26 to 28 cc, might could get by with a 21cc on a pv cylinder depending on intake & case volume.
Neil

[Buttermilk]

I would think that you could run a 23-24cc dome on an OEM cylinder with stock port timings and be OK with pump 91 gas.

[j450rking]

ok so the more cc the less comp?

also i got my 38mm air striker and the jetting it came with was almost spot on but it won't idel so i switched the 55 pilot for a 60 and it still won't idel. i tryed messing with the air/feul screw and it didn't chang anything as far as the idel and i tryed messing with the idel adjuster screw and that didn't chang anything. the only diference that i saw was that when i had the 55 pilot in there there would be white smoke comming out of the exhaust and with the 60 there isn't so i know the 55 was too lean but i don't thing that it would take more then a 60 pilot but i don't know.

by the way it's a stock cylinder so you think the 26cc dome would be ok? i just want to be safe couse i really don't need to have to tear down the engine and rebuild it.

thanks alot

[Buttermilk]

Correct on the cc's. More dome cc's equals less compression.

If your carb won't idle with a 55 pilot, it most likely is too rich and then putting a 60 pilot in is most likely going the wrong way.

Another factor that most people don't consider is the slide you have in the carb. The slide will have a number on it which tells you the cutaway angle. This angle can be changed for a richer or leaner slide also. The slide number will also be a factor in what jetting you ultimately run.

You may need to change the pilot out to a smaller pilot. My own rule of thumb that I use: less than one turn out on the air screw, bigger pilot, more than two and a half turns out on the air screw, smaller pilot. I let the engine tell me what size pilot it needs based on that. That's just to get a decent Idle.

www.sudco.com has a downloadable catalog. On page 112 of the 2007 catalog, there is a diagram showing what each of the jetting circuits control. Very useful information.

In my 38mm A/S carb I run a 55 pilot and a number 7.0 slide (throttle valve). On my 41.5 PWK carb I run a 55 pilot with a number 6.0 slide. The 6.0 slide is richer than the 7.0 slide. My AFR is nearly identical with the two carbs on the same motor.

[j450rking]

it's a #7 slide. so i'll try the 52 pilot but i would think with white smoke i would want to run richer

[j450rking]

you were right about the pilot jet the 52 works great! so i'm still not sure on the dome just to make sure you know it's the older style head that uses a head gasket. i just want to double check so i don't mess anything up.

[Buttermilk]

I would think that if you kept the compression on a guage to around 150 psi or so you'd be ok with pump gas.

a 23cc - 24cc dome should be in the ball park.

I'd call Pro-Design and see what they recommend.

[j450rking]

yeah i will when i call them to order one. thanks

[C-LEIGH RACING]

You can go to at least 180 lbs compression & still use pump gas. I wouldnt use any less than prem 92 though, even if it didnt have but 100 lbs compression.
87 pump gas is junk & thats saying it kindly.
Neil

[machwon]

It depends on how thick the head gasket is, bore size, etc., but you will likely want a 22-23 cc with a .040" head gasket.

[j450rking]

i always use 93 octane in everything with or without high comp. i'm not sure how thick the head gasket is all i know is it's stock thickness

[Buttermilk]

Stock head gasket thickness is 0.060".

You can improve your performance some by running a thinner head gasket.


OEM cylinders with stock strokes were set up with a fairly large squish area, and can be improved upon considerably.

[j450rking]

yeah i know i could but i got a like new cool head for $75 off ebay and i just need a dome for it.