Carb / Fuel problem

[SJ636]

So here is my issue that I am just looking for some advice:

I had a ported 701 that I was running with dual 48mm Riva Powerbomb carbs. I last ran the engine last season and fogged it over the off season. I recently upgraded to a ported DASA 850 (came as short block) and swapped everything from the 701 to the 850.

My problem now is that the carbs are not picking up fuel. If I dump fuel into the carbs it starts and runs great but will not take fuel into the carbs on its own. I have done the following checks:

- Fuel lines are not obstructed.
- Both pulse lines from the case have good pressure / vacuum
- Pulled the carbs apart and the diaphragms look to be in good shape.

Is there something I am missing? If I had to guess I would assume that the carbs may need a rebuild and maybe I missed something when I checked them over....

Is there any good way to test the carb to make sure the diaphragms are working properly?

Just looking for any advice you might have.

Thanks!

 

[BruceSki]

Stuck needles is my guess. Did you move them by hand?

The ethanol content in the fuel gums mine up if I don't ride for two weeks with fresh/new needles installed with short run time.

Old worn out needles won't have this sticking problem.

 

[SJ636]

I did move the needles by hand and made sure that they were free of any sticking. I even pulled the plate off of the back of the carb, held the needle open and cranked the engine to see if the fuel would come through with no success.....

 

[jo5hi3]

check your tank pickups for issues....

 

[SJ636]

Did that as well. No issues with tank pick ups. I sucked fuel through both fuel lines with no problem. Both pick ups are clear of any debris

 

[RyanO]

In/Return lines round the right way?

 

[BruceSki]

where are the returns on those carbs? still in them or drilled out? clogged?

 

[SJ636]

In/Return lines round the right way?

Both the in / return lines are in the proper positions.

 

[SJ636]

where are the returns on those carbs? still in them or drilled out? clogged?

I can take a pick of the carbs and post it later tonight

 

[BruceSki]

Just saying cause my xscream carbs have the returns drilled out and a single restrictor in the return line. Works for both carbs. If it's clogged you won't make fuel pressure correctly

 

[Vumad]

Your fuel pumps may be leaking. just because they look good doesn't mean they work right. I put in brand new SBT kits and a stock 50 psi pop-off and the ski ran bad because the o-rings aren't the right size and pumps were leaking.

Check your pop off. Part of checking your pop-off is checking your fuel pumps for leaks. Your carbs should hold 10 psi for... 1 minute? It should also hold pressure at any pressure lower than your popoff for at least a few moments. If you don't hold the 10 psi, or say your pop-off is 35 and you pump slow and the pressure is dropping as you pump, your pumps might be leaking. Spray wd40 on the fuel pumps and see if they bubble air.

 

[SJ636]

So I ended up going through the Carbs again. Didn't find anything plugged and all jets / ports were clear. Diaphragms all looked good and nothing stood out to me. When I put the Carbs back on, I primed the fuel lines and carbs by blowing into the gas tank through the return line. Once fuel had filled the lines, made its way into the carb and out the return line, I fired up the ski and it maintained its fuel pressure.

I'll take the ski out for a test ride and see how it runs but I think the problem is solved. Not sure why the carbs wouldn't pick up fuel when not primed but hopefully this does this trick.