1998 GTI starving for fuel

[John Locke]

My craft runs great for about 4 to 5 miles, then it starts starving for gas. Initially it slows down from 49mph (top speed) to ~43mph, then ~40mph, then it just bogs down to practically no power and can't plane. Sometimes even with the choke on 100% and the throttle wide open, it barely keeps running to do 5mph, when normally if I pull on the choke it kills the motor because of too much fuel. However it will idle forever, like a champ, so small amounts of fuel are provided to adequately support idling. You can putt around wakeless at idle forever. Both times I've taken it out in the last week, it runs great for about 4 or 5 miles, but after warming up it starts to starve for fuel, ending the day. The cooling water is flowing fine out the squirt nozzle in the rear like normal, so that eliminates potential overheating.

I've done the following:

1. Replaced the carburetor, it's brand new as of 3wks ago. The original carb was toast inside after leaving it in storage 4yrs. However, before I replaced the carb, 4yrs ago, before I put it in storage, the craft had the IDENTICAL problem that I never solved, which is why I haven't ridden it in 4yrs (along with other reasons). I thought maybe a new carb would fix it, but no joy. It has the exact symptom as 4yrs ago with the original carb. That seems to indicate it's not a carb problem.
2. Replaced all fuel lines, including both breather lines and the fuel pump pulse line from the crankcase.
3. Checked the pop off valve and the one way intake air valve to the gas tank, they seem to work fine. When the symptom starts, I've also taken the gas cap off to eliminate the possibility of a vacuum in the gas tank, verifying the one way air intake valve was working OK.
4. I disassembled the petcock gas selector valve and cleaned it out really good. With a full tank of gas, the bogging symptom exhibits itself in both positions, ON and RESERVE.
5. I removed the internal gas tank intake tower to inspect the integrity of the internal tank filter, looking for possible obstructions, but no joy.
6. After installing the new carb, and failing on my first lake test, I removed the brand new carburetor and checked the internal tiny filter located in the diaphragm pump. It was 100% clear.

I think my fuel starvation problem has something to do with heat, but that's only a guess because it runs great for about 10 or 15 minutes after sitting all night. It's consistent at exhibiting the fuel starvation symptom from one day to another day. However this problem cannot be duplicated in a shop, as it take a long time (15-20 minutes) for it to fail at full throttle. I don't think a test tank can accommodate such a long full throttle test.

Does anyone know of something else to check?

I'm getting really good at removing the carburetor, but it's getting a bit old, having no positive results.

 

[POPPS]

Almost sounds electrical,,not carburation,,,that happens right away,,,,i would load test the battery,,check that is charging,,,,i would then test for spark,...could be a coil breaking down after getting warm,,,could be cdi breaking down,,
, ,,i would check compression,,also...run water thru it on the trailor,,,you could have an exhaust leak,,,the gases slowly sufficate a motor,,,you remove the seat,,the air gets back in,,,and you repeat the cycle,,,it is remote,,,but with skis,,,anything is possible,,,

 

[Rabid]

Could it be a fuel system vent issue?

 

[POPPS]

Well,,just ride with the gas cap loose,,,and see what happens,,,

 

[John Locke]

Thanks Popps for the suggestions. It's not electrical, I know what an electrical issue feels like. It never misses a stroke, it's not a sudden engine off scenario. It doesn't have a miss at all, plus the plugs are new. I forgot to mention I did do a compression test and it's consistent between cylinders at 130. Since it idles so good, it seems like it's something to do with heat or fuel. I've looked for exhaust leaks, but nothing. I think there would be water in the hull after a lake run if there was an exhaust leak, since water goes through the exhaust pipe. The inside of the hull stays quite dry.

 

[John Locke]

Could it be a fuel system vent issue?

Thanks for the reply, but I covered that in my #3 bullet. It tested good, and the removal of the gas cap confirms it's not a venting issue.

 

[John Locke]

Well,,just ride with the gas cap loose,,,and see what happens,,,

Yes, I did that during today's lake test, as mentioned in my bullet #3. But no joy, no change at all in the symptom.

 

[POPPS]

Doesn't 130 seem low?

 

[John Locke]

Doesn't 130 seem low?

130 is a little higher than my 1994 GTX, which runs like a champ. So it's better than my older craft. Maybe my gauge isn't accurate, but I always thought 130 was pretty good. I'll borrow a friends compression gauge to confirm, but being low on compression shouldn't exhibit the symptoms I'm having of running great for 15 minutes, then slowly bogging down to practically no power. Low compression would not idle well either, and mine idles great. If I let it sit with motor off for 10min in the water, then restart, it takes off good, but not for long, as it starts to bog down again after about 30 seconds.

 

[Rabid]

Just some ideas.I have had issues with plugs where they start the foul after a good run at high speed. I will replace the plugs and all is well. Even after cleaning the fouled plugs I still have issues. The new plugs fixed it. I have this issue every year on the first ride.

I have had an issue with the exhaust coupling had disintegrated on a long run on high speed. I noticed the engine noise changed but it was running fine until I got close to the dock and slowed down. I popped the seat and it ran fine.

just keep at it you will figure it out. Remember to enjoy the journey.

 

[John Locke]

Just some ideas.I have had issues with plugs where they start the foul after a good run at high speed. I will replace the plugs and all is well. Even after cleaning the fouled plugs I still have issues. The new plugs fixed it. I have this issue every year on the first ride.

I have had an issue with the exhaust coupling had disintegrated on a long run on high speed. I noticed the engine noise changed but it was running fine until I got close to the dock and slowed down. I popped the seat and it ran fine.

just keep at it you will figure it out. Remember to enjoy the journey.

Thanks for the ideas. The plugs are new, but I replaced them anyway last week. That didn't change the symptom, which is what I expected. I've ridden two stroke motorcycles, snowmobiles and PWC for over 30yrs, and rebuilt motors too, from motorcycles to dune buggies. I recognize what a plug problem sounds and feels like when a cylinder is missing. I'm 100% confident it's not an electrical problem or HV delivery problem to the plugs. A plug problem would exhibit itself at high speed all the time, not intermittently like my symptom does, plus it would be obvious with a miss on one cylinder. Two plugs can't fail at the same time, gradually, coming and going like my symptom. My craft doesn't miss, it's dies gradually of fuel starvation, I just can't figure out why after replacing the carburetor, hoses and filters, only to result in the same symptom that my original carburetor had, with the same timing of running great for 15 minutes, then starving for fuel to the point where it can't even plane the water. It will only idle, and it idles great with no hand on the throttle. What's telling is, during the failure, at it's worse point, full throttle with the choke on full, the motor can do about 5mph. What normally should happen is the motor would die with full choke on, flooding from too much gas because the choke is 100% on. This proves to me it's fuel delivery, a failure to pump adequate gas to the carb, because with full choke it doesn't die, and it should. It's really odd two carburetors, having two different pumps exhibits the identical problem when all the hoses have been replaced, even the pulse hose to the crankcase. All the filters have been cleaned or replaced, and fuel line valves check good.

I'm missing something, somewhere. I'm baffled.... like the fuel, and I'm running out of gas (mentally) trying to fix it.

 

[POPPS]

Did you rectify the burnt xhaust coupler???...exhaust fumes in a hull, will slowly sufficate a motor,,

 

[John Locke]

Did you rectify the burnt xhaust coupler???...exhaust fumes in a hull, will slowly sufficate a motor,,

As mentioned, if there was an exhaust leak there would be water inside the hull. I have no water accumulating in the hull, hence no leak.

 

[POPPS]

5 miles is a long way on a jet ski,,,carb issues occur very quickly,,,not down the road since you have ruled out ventilation as an issue,,
Electrical causes misfires,,,you can't even get to full speed, ,,
What do the plugs look like,,,i would do a plug chop,,.go WOT. for 30 seconds,,,pull the seat...and see what the plugs look like,,,
I am now thinking,,,physcal,,mechanical,,,part/s getting hot,,,binding,,,carburation issues are not linear...its,,sputtering,,,sometimes seems like a misfire,,,electrical failures occur early,,,you can't get to WOT for 5 miles,,,I am thinking physical/mechanical,,,
Just thinking outside the box,,,yours seems like,,,a partial slow seizure,,,something is overheating,,,getting hot,,,expanding,,,binding,,,and you said you have no exhaust leaks,,,which could cause your symptoms,,,
This will be an interesting diagnosis.

 

[John Locke]

I am now thinking,,,physcal,,mechanical,,,part/s getting hot,,,binding,,,carburation issues are not linear...its,,sputtering,,,sometimes seems like a misfire,,,electrical failures occur early,,,you can't get to WOT for 5 miles,,,I am thinking physical/mechanical,,,
Just thinking outside the box,,,yours seems like,,,a partial slow seizure,,,something is overheating,,,getting hot,,,expanding,,,binding,,,and you said you have no exhaust leaks,,,which could cause your symptoms,,,
This will be an interesting diagnosis.

Yes, I was thinking that too. I was concerned about a slow seizure, but I've taken the craft out 4 times now trying to diagnose this issue. Each time it runs great for about 5 miles, then it starts bogging down, starving for fuel (presumed). I would think if it was seizing the compression test would change with each trip, and it also wouldn't idle like a kitten. Usually an overheat situation the motor won't idle so sweet. The plugs look good, coco brown, but I haven't pulled the plugs right after it's bogging down, because I'm out on the lake. Although it's possible to do on the water, I haven't because I'm 90% sure it's fuel. Plug reading won't help much to locate the cause of lean fuel delivery, but it would confirm weak fuel if the plugs are white.

The puzzling part is the old carb and the brand new carb exhibits the exact same symptom, which leads me to believe it's not carb or fuel pump related.

I'm considering a test setup using a small electric car fuel pump, connected to the battery with an on/off switch temporary. If the fuel pump solves the problem, then it's not seizing (which I doubt is the issue), and the fuel lines are then suspect, even though I replaced them. I already have an ideal fuel pump for that test, which I bought to pump out all the old gas that was sitting in the tank for 4yrs during storage.

I think my next step is to double check the crankcase pulse line to the carb. I've already checked it to be clear when I replaced the hose, but I need to check that again to ensure the integrity of that fuel line is delivering a good push pull pulse to the carb diaphragm.

 

[John Locke]

By the way, I didn't mention that I have taken the gas tank fuel baffle out for two purposes. 1. To repair the blown fuse in the fuel sending unit, since the fuel gauge didn't work. That was fun. 2. To inspect the inside of the tank to ensure there's nothing inside that tank causing an intermittent free flow of gas to through the hoses.

I found the design of the fuel pickup tower to be very cleverly designed. The method of measuring fuel with floating magnets changing the resistance as it passed up and down near a circuit board is pretty interesting. When working on that fuel tower, taking off the internal fuel filter, I found no debris on the fuel screen/filter. I looked inside the tank as best possible when I had the fuel baffle removed and couldn't see anything in the tank that would hinder fuel flow. It appeared clean.

 

[POPPS]

Is the fuel/water separator "O" ring on properly?
Maybe a crack in the fuel baffle?
No exhaust leaks?
Are you at WOT for the 5 miles?
Dumb question.is the battery up to snuff?,,,connections,,,