Super Jet Help me with a odd carb problem

Sasquachcrap

Sasquachcrap

Location
North Carolina
So I just put a set of modded dual 44 carbs in my motor. Im running a r&d manifold, vf3 reeds, ported and decked 760. Ski runs pretty well but I fouled 2 sets of plugs yesterday. Not a lot of full throttle runs. pop off is 20 low jet is 115 high is 132.5. Off idle response is good, 1/2 throttle is good and it pulls hard and fast but it seems like it runs better if I only open the throttle to 3/4 or a touch more. If I pin it it seems to not run as good, but I'm trying to be safe I don't want to lean out the motor , I have ran the screws in but I wasn't sure if I could close the high speed adjusters. I'm at 1/2 turn out now and just want to be sure I'm going the right way. Can some one explain to me why it runs so good at all other throttle positions. I seem to gain more rpms at 3/4 throttle then a full. I am tuning with a tach.
 
Quinc

Quinc

Buy a Superjet
Location
California
If you think you are lean, turn the screw out a full turn and see if it gets better. If not turn it all the way in.
 
CRJ

CRJ

Hibernating
Location
Toronto
Your too rich, when i had a 762 i was running a single 46 with a 150 main and it was almost perfect, and that was a ported motor. you cant divide the jetting by two for each carb though as your venturi speed drops with a twin carb. The adjusters give you about one jetting size to play with. If you are 1/2 turn from seated you need to go down to a 130 or 125 main. Your low adjuster should be set once and left alone. at idle turn it in till the ski stumbles then come out 1/4 turn. its set, only touch it if you adjust the idle speed screw.

I would try 1.5 turns out at 125 main. whats your plug color and whats you piston wash look like? Fouling plugs when the motor is warm means she rich, usually by a fair bit.
 
jetpilot36

jetpilot36

Location
Fort Worth
my experience when good at 3/4 and slower at WOT has been fuel delivery. might want to look into other factors besides carbs. like pick ups, fuel filters, and the vent valve. try running atmospheric pressure in the tank and see if your problem changes. ( just open vent with no valve)
 
Quinc

Quinc

Buy a Superjet
Location
California
Sasquachcrap said:
Yea @Quinc I saw you were working on a blaster with a very similar set up to me. Where did you end up with jetting?
Click to expand...

I am currently tuning my first set of dual 44's too. 771, R&D intake, vforce 2 reeds, blaster mod pipe. Currently at:
122.5 Pilot
21psi pop off
135 mains. But I haven't tested it yet.

At 34psi pop off and 140 mains I had a slight stumble at 0-1/4 throttle and at 3/4 - full throttle she was a little rich.
 
Dartman

Dartman

Location
usa
probably rich
try lower popoff like 2.5N&S 80-95 gram spring
14-16lbs
then reverse jet to:
120-125 low start at 2 turns
105-110 high start at 1-1/4
 
Ducky

Ducky

Back in the game!
Location
Charlotte, NC
@Sasquachcrap , I know it is not the same motor, and you rode my motor, but here is what we are at just so you can compare a little:

125 Mains - 1/4 to 1/2 turn
117.5 lows - 1 1/4 turn
1.5 NS with 65 Gram spring for 32ish pop off.

It is still a bit rich on top, but is hitting night and day different from when you last rode it. Just figured you could use that as a somewhat similar reference for your motor.
 
jo5hi3

jo5hi3

Location
Charlotte NC
Matt Jones said:
@Sasquachcrap , I know it is not the same motor, and you rode my motor, but here is what we are at just so you can compare a little:

125 Mains - 1/4 to 1/2 turn
1.5 NS with 65 Gram spring for 32ish pop off.

It is still a bit rich on top, but is hitting night and day different from when you last rode it. Just figured you could use that as a somewhat similar reference for your motor.
Click to expand...

gonna drop it down to 120 and see what happens
 
Sasquachcrap

Sasquachcrap

Location
North Carolina
Yea. @jo5hi3 save those mains I might give them a try. @Dartman I have tried reverse jetting never really got the results I was looking for but I never went that lower I think it was 110h and 125 lows. Defiantly a softer hit than with 115 l and 132h. I think my total jetting is to high.
 
CRJ

CRJ

Hibernating
Location
Toronto
Dartman said:
probably rich
try lower popoff like 2.5N&S 80-95 gram spring
14-16lbs
then reverse jet to:
120-125 low start at 2 turns
105-110 high start at 1-1/4
Click to expand...
just remember that your low jet and adjuster should be set and left alone, to ease your high tuning. Get your idle and low figured out and leave it alone to make life easier. Your low jet also has no direct relation to your high as they transfer as throttle is applied. So jet the low for good fuel at idle-1/4 but not too rich, so you get a good punch. once your happy there find the right high jet, and once you have the right one dial it in with the high adjuster. you should leave the adjuster at 1.5 turns out till you find the right high jet. i usually swap 5 at a time. it saves time and splitting 5's really isnt needed till you find one that is worse than the one before it.
 
Dartman

Dartman

Location
usa
Sasquachcrap said:
So I just put a set of modded dual 44 carbs in my motor. Im running a r&d manifold, vf3 reeds, ported and decked 760. Ski runs pretty well but I fouled 2 sets of plugs yesterday. Not a lot of full throttle runs. pop off is 20 low jet is 115 high is 132.5. Off idle response is good, 1/2 throttle is good and it pulls hard and fast but it seems like it runs better if I only open the throttle to 3/4 or a touch more. If I pin it it seems to not run as good, but I'm trying to be safe I don't want to lean out the motor , I have ran the screws in but I wasn't sure if I could close the high speed adjusters. I'm at 1/2 turn out now and just want to be sure I'm going the right way. Can some one explain to me why it runs so good at all other throttle positions. I seem to gain more rpms at 3/4 throttle then a full. I am tuning with a tach.
Click to expand...

when you say modded dual 44
what do you mean? stock oem carbs modded? mikuni retail carbs modded?
reverse jetting works good for freestyle setups
pipe water management can play a role why some jetting setups don't work well
 
hornedogg79

hornedogg79

dodgin' bass boats
Don't be afraid to turn those high speed adjusters all the way in. I run full spec 44s with 120 pilots and 120 mains. Low adj (1_1/2 turns). High adj (closed). When I go to sea level I crack them open 1/8. Sounds like you're on the right track.
 
You must log in or register to reply here.
Top Bottom