Pulsing from intake

9

95 shaw

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Anyone had difficulty with fuel delivery, pulsing the fuel pump for a 38 mm keihen watercraft carb from the intake?

Have a high rpm stutter on open stroker animal.
Also, slight dead spot on drop of green. Cannot duplicate in pits.
 
I run a Mikuni SBN from a Jet ski on my yz144... I pulse it from the intake... haven’t had any issues...
I am not familiar with the Keihin... if it’s a similar carb... are you running a return line?
If so... I put a stock Clone jet in return line to keep fuel pressure up so the pressure doesn’t drop at high rpm...
also to make it meter correct I had to do reverse jetting on the carb...
But again not sure if they are the same carb or not and I am running it on a 2 stroke...
 
Tuning is recommended similar to SBN. No pump stack.
Has a really large bore tapered down to 1.25 intake valve. Thought maybe signal is lost, as vacuum drops at high rpm?
No return line. Methanol fuel.
Pulls good midrange, just stutters on top.
Going to change fuel pump, and pulse from crankcase to see if that helps.

Define reverse Jetting?
 
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Often times a miss on top end is because the carb is too rich.
If it runs good on acceleration that tells me it has plenty of fuel.
The engine requires more fuel to accelerate that it does on top end.
What jets are you using?
 
Plug is white, to light tan.
No aluminum balls.
Geared to get off corner, so turns pretty hard at end of straight.
Took off several teeth, no change in stutter. Rpm dropped. Lost corner advantage.

Bought this setup with a broken rod. Reassembled same basic combo.
Has high and low needles. Acts lean, unless high is 2 turns open. Low open about the same.
Cannot find a number on jet. Did not measure last time i had it apart.
 
Needles should be each at one turn out each... adjust jetting to obtain needle settings...

Reverse jetting is just the pilot jet is larger than the main jet...
But I am running gas...
My pop-off is set at 19psi...
And low jet is at 120 and main jet at 100... both needles set at 1 turn out give or take for tuning...

At 2 turns out or just past the needles loose effect as well as tuning and metering...

What temperature is it running at when sputtering occurs???
On Alky I like seeing 325-350*f
 
I should have read the first post more carefully.
A 38 mm on an Animal is way too big.
A 28 would be more appropriate.
The signal you are losing is for the idle and the main jet.
 
There are 2 easy methods to determine if you are to rich or too lean.
1. Ues exhaust gas temp.
2. Use a wide band O2 sensor.
If you already have a Mycron the EGT would be the cheapest.
 
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