Carb tuning problems

F

Fins

Location
Saskatoon, Saskatchewan, Canada
I have just put on some 46mm buckshot carbs and i cant seem to get the ski running again. If the ski is out of water as soon as i start is (prime it to start) the engine races to WOT with out me touching a thing. When i put it in the water the only way i can get it to run is off the primer, as soon as i touch the throttle it dies. So i figured it was getting too much fuel, But when i drained the fuel lines and started the ski it ran decent for a bit.

I have gone throught the cabs and they are clean and free of any debris, and the jets move freely. I blew through the lines and they are clean.

I was thinking that maybe my pilot jets are too small so i have to pump the primer to get enough fuel for it to stay running, but as soon as i give it throttle it leans the mixture out too much to run. Does that make sense?

I am running a polaris octane with:
High compression pump gas domes
Dry pipe
aftermarket cdi from watcom
135 main jets
70 pilot jets

Any thoughts on what else it could be?
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
Who told you to run those jet sizes in a Buckshot carb?
It's no wonder it won't run...way too small of low jet.
Do you know what needle valve and gram spring you have or know the pop pressure?
Buckshot won't even run without at least a 120 or larger on the low jet and about 105-115 on the high depending on the pop-off. I don't know Polaris engines real well, but I do know Buckshot carbs pretty well from back in the day running them on our race Superjets.
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
Fins said:
I have just put on some 46mm buckshot carbs and i cant seem to get the ski running again. If the ski is out of water as soon as i start is (prime it to start) the engine races to WOT with out me touching a thing. When i put it in the water the only way i can get it to run is off the primer, as soon as i touch the throttle it dies. So i figured it was getting too much fuel, But when i drained the fuel lines and started the ski it ran decent for a bit.
I have gone through the cabs and they are clean and free of any debris, and the jets move freely. I blew through the lines and they are clean.

I was thinking that maybe my pilot jets are too small so i have to pump the primer to get enough fuel for it to stay running, but as soon as i give it throttle it leans the mixture out too much to run. Does that make sense?

I am running a polaris octane with:
High compression pump gas domes
Dry pipe
aftermarket cdi from watcom
135 main jets
70 pilot jets

Any thoughts on what else it could be?
Click to expand...

Fins sent me a PM, So I wanted to post my reply to him for added info to this open thread...
His reply was the Buckshots came to him with this jetting and have 1.5 needle valve and the gold spring in them.... (by the way, is a 115 gram spring)
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With what jetting that you have in them including the 1.5 needle valve and gold spring (115 gram) are the jets that come in a stock Superjet! (a 135 main is the jet Factory Pipe supplies for a b pipe) So somebody just threw them in there just to sell and get rid of them.

You need to understand what pop off does... it controls the fuel pressure on the jets, just like a fuel pressure regulator. The smaller the needle valve with a higher pressure spring gives you very low fuel pressure. So the higher pop off is... the lower the fuel pressure is, the less fuel the jets meter.
A larger needle valve with a weaker spring, lowers the pop off, this gives more fuel pressure on the jets so they spray more fuel.
The overall jetting can be made by changing the pop off.
Higher pop off the carb runs leaner, lower pop off the carb runs richer.
So your way off with the pop off for large Buckshots carbs as they have a weaker vacuum signal than a much smaller stock carb.
I would start with 2.3 needle valve and a 80 gram spring and start with 125 low and 110 high.
Set high adjuster @ 1 1/4 turn, set low adjuster @ 1 1/2 turn.
Because these Buck shot carbs are race bred carbs they are straight bored all the way through, this lower the low speed jet signal a lot, this is why you need bigger lows than the high jets.
This will get you down the right path to getting these carbs to work. Remember that these are race carbs and will have the tendency to load up through slow wake zones and are not the best for freestyle riding.
If you have any problems locating parts we do have all Mikuni jets and parts in stock and ship worldwide here at X Scream Inc.
Call or email Chad at the shop and he will take care of your needs in a timely manner. (See my sig below)
Just let us know how we can help.
Chuck
 
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