Time for a new Carb?

[mlebauer]

2001 Challenger with twin 717s. Left engine won't start, no fuel getting to it. It starts briefly with a squirt of starting fluid, but won't run, and will run if I drip fuel directly into the carb, so it's definitely a fuel delivery problem.

I had both carbs rebuilt last year. Right engine works, but it was working before the carb rebuild. I just rebuilt the left engine fuel pump. No holes in the diaphragm, but it was stiff. Still, I'm not sure that's the problem. When I pull the pulse line and run the starter I can feel the pulses (although they're not very strong, are they supposed to be?), and I can pull fuel through the fuel line, and fuel filters are full.

Is it definitely the carb? Should I just get a new one at this point?

One more thing: the accelerator pump isn't squirting gas when I push the plunger either.

One benefit of all this carb work, I'm getting good at pulling them :thumbsup: (although the throttle cable never seems to go easily back on the lever, is there a trick to this?).

 

[Waterluvr]

How much pressure is your freshly rebuilt fuel pump generating when you crank the engine? Did you reuse the same impulse line? Have you checked the impulse line by pressure or vacuum testing it? What about the fuel line to the pump, when you hook a vacuum pump and recovery cannister to it does it flow fuel constantly without interruption?

If the answer to any of those question's is I don't know, start with the fuel line to the pump and work back from there to find the problem.

All of that first, then on to the carb. You may want to re-think using any more starter fluid and only use fuel with oil pre mixed for checking with a spray bottle, new motors are expensive and starter fluid will have stripped the oil film from your pistons and rings.

Maybe give that motor a shot of fogging oil asap from the plug holes and then the intakes before you stick a ring, they don't have to sit long without an oil film for that to happen. Roll the motor over by hand from the pto shaft to coat everything before using the starter motor again.

 

[mlebauer]

Thanks, yes I sprayed fogging oil down the carb and in the spark plug holes before that test with starter fluid. I'll put more in to be sure and turn from the PTO (I used the starter before, didn't know that mattered).

Yes, I reused the impulse line. It is pulsing when I turn the engine over.

I don't know the pressure from the impulse line or the fuel pump, as I don't have a gauge, and don't know how if I did. Nor do I have a vacuum pump, but fuel came out when I sucked on the line. Is there a procedure somewhere? I always search the forums before posting a question, but didn't find anything. Can you point to what tools to use for that and how to do the tests?

The right engine starts and runs, so fuel is going through some of the system.

 

[Waterluvr]

I use a Mityvac silver series as it has the ability to produce both pressure and vacuum for all fuel line and vacuum testing, and it comes with a variety of fittings to connect into different sizes of lines.

As an example, I would remove the impulse line and use a short section of hose connected to a T and then from each end of the T I would use another hose and nipple to pull vacuum from both ends of the impulse hose to check it for leaks. You can turn the valve and pressure test it also. A cracked impulse hose might cycle the pump a little bit but not to full capacity, I find a bad impulse hose on occasion that will run the pump at idle speeds and lean the carb out at higher rpm's.

The shop manual has procedures for fuel pump and carb testing, but it doesn't get creative for testing the integrity of fuel and impulse lines or fuel delivery issues that's just something you have to consider and test for on your own.

 

[mlebauer]

Thanks for the recommendation on the pressure/vacuum tester. I'll look into adding that to my toolkit.

Update, I went back out to fog the engine, turned it, then re-inserted the plugs and cranked it. It sputtered. I thought it was just the fogging oil, but gave it another crank, and it fired up. I shut it down and attached the hose, then ran it for a couple of minutes. It seemed to run pretty well on the trailer, although stalls if I put it all the way to idle, probably need to adjust the throttle cable.

Perhaps it just needed time to fill the internals of the carb. I did notice that the accelerator pump is still not squirting. Also the left tuned exhaust pipe has sprung another leak (I JB welded the last one). Probably need to pull it and get it properly welded.

There's just enough daylight to take it to the river and give it a real test.

 

[mlebauer]

Post-river run update. Both engines started up quickly. But once I opened it up, the left wouldn't rev more than 6K RPM, while the right would do over 6.5. It held a steady 6K for a while.

After about 45 mins of riding, the left started fluctuating between 4K and 6K. At that, I brought it in, idle felt ok, but tried opening it up again, behaved the same.

Any ideas?

As aside, last summer I replaced the wear ring and rebuilt the drivetrain with new carbon seal and stainless ring to fix a cavitation problem (then ran into the left engine carb problems and wasn't able to verify is the other work fixed the cavitation problem). Well, the cavitation is still there and the same as before all that work.

This boat is getting frustrating!

 

[Waterluvr]

Post-river run update. Both engines started up quickly. But once I opened it up, the left wouldn't rev more than 6K RPM, while the right would do over 6.5. It held a steady 6K for a while.

After about 45 mins of riding, the left started fluctuating between 4K and 6K. At that, I brought it in, idle felt ok, but tried opening it up again, behaved the same.

Any ideas?

As aside, last summer I replaced the wear ring and rebuilt the drivetrain with new carbon seal and stainless ring to fix a cavitation problem (then ran into the left engine carb problems and wasn't able to verify is the other work fixed the cavitation problem). Well, the cavitation is still there and the same as before all that work.

This boat is getting frustrating!

A sudden fluctuation in rpm's like that after hard lean running is what you will experience when the piston begins to shed aluminum and score, it goes through a series of lean seizures that fit your description perfectly. Removing the Rave valves and inspecting the pistons for damage on your port (left) engine would be a good idea along with compression testing.

If your throttle cables are adjusted properly you're not getting enough fuel through the carbs, that sort of *testing* is destroying your engines at 45 minute intervals running them at WOT leaned out.

Obviously water tests are needed for evaluation but when you can't make rpm's with the throttle open all the way and it's not loading up from a rich condition your simply murdering your engines from leaning them out and continuing to operate the boat.

 

[mlebauer]

Well, that's aggravating. I sent the carbs off to be professionally rebuilt by a SeaDoo tech. How are you supposed to these boats working right? There's nobody in my area that works on them. I may have to drive it someone for the winter to get a professional, or throw in the towel on it and sell for parts. It's in good shape except for the left engine problems (and the cavitation).

 

[Dr Honda]

As above... the large fluctuations in RPM isn't good. I would start with a compression test on that engine.


Also... holding the throttle open full is hard on the engine. And, if there is any issue with the fuel supply... it's a fast way to melt a piston.

When working on carbs... you have to be VERY methodical. Checking/verifying everything. And, when in doubt... never use any parts other than OEM Mikuni. A lot of the aftermarket rebuild kits and parts look great... but don't work. And on these regulator carbs... there no middle ground on getting them to work.


As far as... "How are you supposed to these boats working right??.... well... that's a hard one to answer. For most of us, it's a labor of love. If you have to pay someone to work on these older boats... then it will get expensive, and they will never run right. AND... to be 100% honest... you are better off with a new boat. This isn't just a SeaDoo thing... this applies to any boat or watercraft.


Sorry for the issues.

 

[mlebauer]

The cruise stayed at 5-6K. I only used WOT for brief moments to check for maximum RPM. At first it was cruising nicely, although it wouldn't go above 6K, previously 7K was WOT, and the cavitation isn't solved.

The fuel pump rebuid kit was from OSD Marine, which many people recommend here. Their site says it contains Mikuni OEM parts. Where would you recommend to get the kits?

It is a labor of love, but an occasional reliable boat ride would be nice!

Compression test: task for next weekend.

One hint from a post I found: could the fluctuations be related to the leaking tuned exhaust pipe? I read someone's post that such a leak can cause intermittent overheating and partial shut down. Doesn't sound likely, but...