1991 650 Carb/Fuel problems

C

Cyprus_

Location
Calgary
I have been trying to get my superjet up and running consistently after changing the carb internals.

Bought a new ski and previous owner mentioned it had sat for 1.5 years or so.

Ran it as is for a week or so before it would shut off randomly at full throttle so I decided to stop running it as I believed it was leaning out at full throttle due to the old carb internals.

Fast forward to the last few days and after buying a car rebuild kit and adjusting the carb screws (1.5 and 2.5) as well as replacing the fuel filter and cleaning the petcock/fuel selector the ski started good but could not get past 1/4 or 1/2 throttle without dying. If I used the primer it would get up to speed for a few seconds and then die down again.

I re-inspected the carb and everything seemed to be in good condition and installed correctly.

I put the carb back on and now there is no fuel getting to the carb at all as seen through the clear fuel filter.

I'm at a loss for what could be the problem at this point. Any suggestions would be great! Thank you
 
SteveC

SteveC

Location
West MI
Cyprus_ said:
I believe at some point the fuel lines have been replaced since they are not rock solid. Pickups inside the fuel tank were inspected but didn't seem to have any issues
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Can you draw fuel through the lines using something like a primer or vet syringe from farm store? Also during carb rebuild did you replace fuel filters inside the carbs? Maybe check them again. Might have clogged!
 
C

Cyprus_

Location
Calgary
SteveC said:
Can you draw fuel through the lines using something like a primer or vet syringe from farm store? Also during carb rebuild did you replace fuel filters inside the carbs? Maybe check them again. Might have clogged!
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Ya good idea I'll give that a try tomorrow
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Okay I am probably going to get some pushback on this because I haven't come up with an explanation for it yet but here goes, in the last few years I have run across one Superjet with a 701 swap and two 650SX's that just wouldn't rev, hand choke them or hit the primer and they revved up, most were so bad they wouldn't rev on the trailer.

The fix for all three was a substantially larger pilot jet , I don't remember what size I had to go to on the Superjet but on the 650SX's I went from a 75 pilot to a 95 on one and a 100 on the other one , on the first 650SX I did a pressure test to check the crankshaft seals for leakage , it passed the test with flying colors , neither gave any indication of an air leak while running.

I also sanded the bottom of the carbs with sandpaper and a surface plate and installed new thicker fiber type carb to manifold gaskets to rule out any kind of a leak there.

I put the biggest pilot I hadl on the first one which was a 95, on the second one it took a 100 pilot to get it to run properly and I also fooled with the popoff spring a bit, the one with the larger pilot jet ran and cranked better than the one with the smaller pilot did but both cranked much better and had way better takeoff and bottom end power with the bigger pilot jets.

As I stated I don't have an explanation for the need for the huge pilot jet size increase, nothing changed on any of these from the way they were set up before , my guess is possibly lower compression from normal wear and tear but it did not show that on my compression gauge.
 
JC-SuperJet

JC-SuperJet

Location
Texas
WFO Speedracer said:
Okay I am probably going to get some pushback on this because I haven't come up with an explanation for it yet but here goes, in the last few years I have run across one Superjet with a 701 swap and two 650SX's that just wouldn't rev, hand choke them or hit the primer and they revved up, most were so bad they wouldn't rev on the trailer.

The fix for all three was a substantially larger pilot jet , I don't remember what size I had to go to on the Superjet but on the 650SX's I went from a 75 pilot to a 95 on one and a 100 on the other one , on the first 650SX I did a pressure test to check the crankshaft seals for leakage , it passed the test with flying colors , neither gave any indication of an air leak while running.

I also sanded the bottom of the carbs with sandpaper and a surface plate and installed new thicker fiber type carb to manifold gaskets to rule out any kind of a leak there.

I put the biggest pilot I hadl on the first one which was a 95, on the second one it took a 100 pilot to get it to run properly and I also fooled with the popoff spring a bit, the one with the larger pilot jet ran and cranked better than the one with the smaller pilot did but both cranked much better and had way better takeoff and bottom end power with the bigger pilot jets.

As I stated I don't have an explanation for the need for the huge pilot jet size increase, nothing changed on any of these from the way they were set up before , my guess is possibly lower compression from normal wear and tear but it did not show that on my compression gauge.
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Probably because the Carburetor Throttle Plates and Shaft Bushings are worn allowing more Air to pass at Idle and Low Throttle, thus requiring more Fuel...
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Pull your pulse hose loose from the carb, spin it over and see what kind of pulse you have going to the pump, after that I would say pull the outlet hose from the petcock loose attach a long piece of hose to it apply suction to the hose and see if you can siphon fuel out of it, try this on the on position and on reserve , if you can't pull a siphon on it there is no way the fuel pump can either, find out why, bad pickups, sucking air where the fuel lines attach, cracks in fuel hoses , bad primer etc.
 
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C

Cyprus_

Location
Calgary
WFO Speedracer said:
Pull your pulse hose loose from the carb, spin it over and see what kind of pulse you have going to the pump, after that I would say pull the outlet hose from the petcock loose attach a long piece of hose to it apply suction to the hose and see if you can siphon fuel out of it, try this on the on position and on reserve , if you can't pull a siphon on it there is no way the fuel pump can either, find out why, bad pickups, sucking air where the fuel lines attach, cracks in fuel hoses , bad primer etc.
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I got it running with the hand trick. I'll send another update when I check new plugs on it for colour and check to see if it works in the water above the throttle amount I was getting before.
 
C

Cyprus_

Location
Calgary
I've had the chance to take it out now and I got running for a short amount of time until it completely died again. Seems like it had the gas from when I covered it with my hand long enough to start and run and now it just will not pull gas from the fuel filter at all. Again it runs fine from little spurts from the primer. I checked the spark plugs and they looked basically dry so no fuel getting in. Looks like it's fuel pump related so I'm going to pull it off later today and reinstall everything again to make sure.
 

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C

Cyprus_

Location
Calgary
Since I was able to use the primer to get gas flowing from the on fuel line I can rule out a complete clog from the tank up to the petcock/switch which I already cleaned and has no clog.
 
C

Cyprus_

Location
Calgary
I figured out the first problem about the fuel. The carb rebuild kit came with two gaskets for the pump along with the plastic screen. I used both gaskets but apparently you are not supposed to use both. So after i changed that out the fuel started flowing no problem.


Now I am back to having the issue where if I go over 1/4-1/2 throttle or high the ski falls on its face and dies pretty much immediately.

I have the high speed screw at 2 turns and the low at 1 1/4. It will rev fine out of the water or for small bursts after hitting a wave and the impeller comes out of water.
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Then you need to pull the carb back apart and see if something was left out of the fuel pump , all 44 carbs are not the same, Yamaha carbs use gaskets that a regular 44 doesn't use . First pic is a basic Mikuni 44 carb, notice there is no gasket between the fuel pump body and carb body , just a rubber pump diaphragm and a funny shaped o-ring part number 6a , now look in the second pic that is a pic of a Superjet carb notice part number 39 , the gasket goes as pictured, then the pump body etc , etc just as pictured , any other way and it won't work at all..

Look at the carb bodies and the gaskets, you will notice a tab sticking up on each one , that rubber pump diaphragm can be put in backwards but it won't work that way, make sure all the tabs on all the gaskets and all the pump bodies face the same way upwards.

Sorry it seems you posted while I was posting.
 

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WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Cyprus_ said:
I got it running with the hand trick. I'll send another update when I check new plugs on it for colour and check to see if it works in the water above the throttle amount I was getting before.
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I had no idea where you had the tee for the primer at , some people run them in the return line, I usually do that and make the return line dip down where the tee is at the bottom of the dip.
 
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