2 seized engines, need help with jetting.

C

ClassVgear

Location
Boise, Idaho
So, I have taken the engine from a yamaha waverunner gp 3 700 and put it into a hull that I have fabricated from aluminum. This hull straps to the bottom of an inflatable whitewater vessel, called a creature craft. I have seized to pistons in the tuning journey and am frustrated to the max.
Here's what I have powering it.
61x case and cylinder
new crank and seals
83mm WSM pistons
ADA girdled head w/ 35cc domes
Single SBN 44
Factory B-pipe
Solas 1013 prop (I think)
Stock ignition
I started with the jetting that was recommended by riva and it was a quick trip to the lake.
Pilot 120 screw 1-1/2 out
main 145 screw 2 out
2.0 N/S 95 gram spring 20 psi pop off.
Ski idled fine but had serious bottom lag and wouldn't hit full throttle. SEIZED
I then tried.
pilot 130 screw 1 out
main 170 screw 1-1/2 out
2.3 N/S 115 gram spring 18 psi pop off.
Ski idled great after adjustment. same bottom lag. was able to hit WOT it just took a bit. SEIZED
Im now at 145 pilot 180 main 2.3 N/S and have tried all the springs. No Change in performance. Please help
 
jetx

jetx

Location
Midland, Ontario, Canada
What brand crank seals did you use? I’d start with a leak down test and make sure everything is sealed...if your seals were leaking and you jetted up it would offset the added air being sucked in and marginally run better until you were wot.

Also how heavy is this alum hull?
 
C

ClassVgear

Location
Boise, Idaho
Not sure of the brand. The seals came in a gasket kit for the complete engine. I thought about an air leak since I was getting no change in adjustment to screws or jetting. Wouldn't it "take off" when started or "sputter" when shut off at some point? I can get the engine to idle reliably. With adjustment to the low screws I can get it to fall on it's face at intial throttle, Then adjust out 1/4 no hesitation , but a kinda surging bog. adjust out another 1/4 even worse.
Hull weights approximately 250lbs. if you're interested I can post pics. Thanks for the help. I greatly appreciate it!
 
Quinc

Quinc

Buy a Superjet
Location
California
Clean your carb. Take it completely apart and let it soak in Chemdip for a few hours then blow it all out with carb cleaner and compressed air.
Leak down test. Engine should be able to hold 10psi for 10 minutes without dropping. Spray the whole thing down with soapy water and look for bubbles. (take off the flywheel cover)
 
C

ClassVgear

Location
Boise, Idaho
Quinc said:
Clean your carb. Take it completely apart and let it soak in Chemdip for a few hours then blow it all out with carb cleaner and compressed air.
Leak down test. Engine should be able to hold 10psi for 10 minutes without dropping. Spray the whole thing down with soapy water and look for bubbles. (take off the flywheel cover)
Click to expand...
Carb is new along with everything else. I'm process of leak test now.

Sent from my SM-G930V using Tapatalk
 
smoofers

smoofers

Rockin' the SQUARE!!!!
Site Supporter
Location
Granbury, TX
Just wanted to add that the leak down test is the most important part of a 2-stroke motor build. I've probably rebuilt 20+ jetski motors at this point and have never had one pass a leak down on the first try.
 
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C

ClassVgear

Location
Boise, Idaho
smoofers said:
Just wanted to add that the leak down test is the most important part of a 2-stroke motor build. I've probably rebuilt 20+ jetski motors at this point and have never had one pass a leak down on the first try.
Click to expand...
just performed the leak test. Its been 15 minutes and still holding 10psi. I was really hoping to find a leak cause that would explain the problem. Now what? Truly at a loss here.

Sent from my SM-G930V using Tapatalk
 
Quinc

Quinc

Buy a Superjet
Location
California
Spray the engine down with soapy water around the crank seals (including behind flywheel cover) Do you have pictures of the siezed pistons?
 
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