Single carb tuning question

BMWtech

BMWtech

Location
SWFL
Looking for some assistance here for a friend's ski, was hoping you guys could help out.

94 B1
Motor is a 61x
Single 44
B pipe
ADA head...though compression is a bit low on this motor. (~130?)
145 high/120 low, 95g spring, 1.5 n/s.

Ski was dying while using it. Rebuilt the carb and was acting similar. Swapped in a fuel pump from a spare carb and now it runs well.

The problem I'm having is from 3/4- wide open throttle it's dying, as if there isn't enough fuel. From idle to 3/4 it runs just fine. The jetting is the same as it was originally, the only thing changed was the guy had what looked like an 80g spring in it before. I have the high adjuster all the way out and it still dies up top. Have tried it in all positions.

I think the 145 jet is the right one to use, so I'm confused. Any ideas on where to start? I'd think this is a simple one for some of you. Thanks!
 
Quinc

Quinc

Buy a Superjet
Location
California
I would start with a 2.0 n/s 80gram spring and maybe a 150m and 125L but start with changing just the n/s and spring. Is the compression low because it is ported or tired?
 
BMWtech

BMWtech

Location
SWFL
Quinc said:
I would start with a 2.0 n/s 80gram spring and maybe a 150m and 125L but start with changing just the n/s and spring. Is the compression low because it is ported or tired?
Click to expand...
Tired.

Jetmaniac gave me the carb parts recommendations.
 
Nate_D

Nate_D

Location
Houston, TX
Pressurize the carb on the pump side and check for leaks. Like a pop off test, except well below pop off pressure.


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CRJ

CRJ

Hibernating
Location
Toronto
i run a 150m/125p with 2.0 ns and dull grey spring. if the ski is dying on the top end, you either have water ingestion (happened to me when my cooling line came off) or the N/S isnt flowing enough. with the setup im running theres power for days. Id also look into the compression, as stock is over 150psi. tuning will be all over and never seem right if the motor has low compression.

whats your piston wash look like?
whats the CC size of the motor?
whats the dome size of the ada head?
 
BMWtech

BMWtech

Location
SWFL
CRJ said:
i run a 150m/125p with 2.0 ns and dull grey spring. if the ski is dying on the top end, you either have water ingestion (happened to me when my cooling line came off) or the N/S isnt flowing enough. with the setup im running theres power for days. Id also look into the compression, as stock is over 150psi. tuning will be all over and never seem right if the motor has low compression.

whats your piston wash look like?
whats the CC size of the motor?
whats the dome size of the ada head?
Click to expand...
I do understand the compression is a bit low but before the fuel pump went out the ski ran fine which is why I'm confused. Haven't opened up the motor, no clue. It was hard to read the old n/s size, maybe I will try and throw the old one back in. We thought it was a 2.5 at first and then I went with a 1.5 on the new setup. Maybe it WAS a 2.5 before.
 
Quinc

Quinc

Buy a Superjet
Location
California
BMWtech said:
Tired.

Jetmaniac gave me the carb parts recommendations.
Click to expand...

43psi is really high, by lowering your pop off you will get more fuel...
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