2002 Challenger 2000 240 - will not go over about 10mph

[nchiotti]

Replaced impeller 2 years ago, wear ring still in good shape so I did not change that. Last year it ran fine one day and then the next it would not go above 10mph, but the engine revs to over 4k.
Idles fine and sounds great. Starts up immediately.
Last night I changed the front gear oil, and removed the stator to replace oil and re-check the wear ring. Impeller looks like the day I installed it and feeler gauge is right is tight at about 0.038 all the way around, no gouges.
I have read that maybe my exhaust hoses might be an issue, but can anyone else think of anything else I should be checking?

 

[Tim75]

Replaced impeller 2 years ago, wear ring still in good shape so I did not change that. Last year it ran fine one day and then the next it would not go above 10mph, but the engine revs to over 4k.
Idles fine and sounds great. Starts up immediately.
Last night I changed the front gear oil, and removed the stator to replace oil and re-check the wear ring. Impeller looks like the day I installed it and feeler gauge is right is tight at about 0.038 all the way around, no gouges.
I have read that maybe my exhaust hoses might be an issue, but can anyone else think of anything else I should be checking?

If you had the stator off, it would be hard to miss debris in the impeller or stator. A plastic bag or small stick is all it takes to cause issues. Perhaps a vacuum/air leak on the intake side of the impeller.

If the engine revs to 4000rpm, you should get about 30mph. That's the rpm we wakeboard at.

If you can get to 4000rpm, I don't think your exhaust system is the problem. What is your max rpm in the water?

 

[nchiotti]

At full throttle in the water, it maxed out at 4000rpm and less than 10mph. It does seem like I have a bunch of cavitation behind the boat. My next course of action I am guessing will be to replace the wear ring just to make sure.

I removed one of the exhaust hoses last night and the inside seem intact, but they are softer than I was expecting. Replacing with OEM hoses is actually not possible anymore, so I am looking for other options for that too.

 

[ripcuda]

One day it ran fine, then the next it wouldn't... hmmm.

So you've inspected the jet pump and there is no debris trapped in there. 0.038" impeller to wear-ring gap is pretty big. You will definitely be loosing some thrust because of that... but that wouldn't prevent your engine from reving beyond 4k. In my experience, a "loose" jet pump will make it easy for the engine to rev to the rev-limiter... all the while thrust from the jet pump is mediocre or barely any... like how a slipping clutch in a car will let the car engine rev way up... but the car won't really be moving.

Side note: if you are going to repair your jet pump... it is more likely a worn impeller causing the large gap, and less a worn wear-ring. The 'JBWeld' skim coat on the wear-ring can help "fill the gap" as a semi-short term fix. But if you buy a new wear-ring, I'm betting your gap will still be big (cause the impeller is more worn than the wear-ring).

In my Challenger 2000, at 4000 rpms, I am able to get up on-plane and get to ~27mph (gps).

Cheers!

 

[Tim75]

One day it ran fine, then the next it wouldn't... hmmm.

So you've inspected the jet pump and there is no debris trapped in there. 0.038" impeller to wear-ring gap is pretty big. You will definitely be loosing some thrust because of that... but that wouldn't prevent your engine from reving beyond 4k. In my experience, a "loose" jet pump will make it easy for the engine to rev to the rev-limiter... all the while thrust from the jet pump is mediocre or barely any... like how a slipping clutch in a car will let the car engine rev way up... but the car won't really be moving.

Side note: if you are going to repair your jet pump... it is more likely a worn impeller causing the large gap, and less a worn wear-ring. The 'JBWeld' skim coat on the wear-ring can help "fill the gap" as a semi-short term fix. But if you buy a new wear-ring, I'm betting your gap will still be big (cause the impeller is more worn than the wear-ring).

In my Challenger 2000, at 4000 rpms, I am able to get up on-plane and get to ~27mph (gps).

Cheers!

Ripcuda is correct. Excess clearance will allow engine to rev higher than it normally would. Think of the excess clearance an an "internal leak". The water is moving thru the pump, but not contributing anything.

More important is your max RPM. I suspect you have 2 cylinders not firing. If you have injectors not spraying, you are not getting any oil into those cylinders. I would start with a compression test. All plugs out. WOT. Then I would replace the non-firing spark plugs with new. I have had good plugs go bad from one outing to the next. And they were NGKs. Cheapest I have found is Rock Auto about $5.25 each in a box of 10.

Just to be sure- using a flashlight, look UP into the tunnel from under the boat. Anything out of place? Like a rock, stick, bag, weeds, rope on the shaft? These are more common issues than a vacuum/air leak. While you are there, what is the condition of the leading edges of your impeller blades? They should be smooth and even. About .010-.020 thick. NOT razor edge. They are too easily damaged.

 

[nchiotti]

Thanks for all your responses. I have found a shop near me that routinely works on her boats and am throwing my hands up and letting them have at it.
Impeller is new, but I didnt replace wear ring when I replaced impeller, and i should have.

 

[Tim75]

Thanks for all your responses. I have found a shop near me that routinely works on her boats and am throwing my hands up and letting them have at it.
Impeller is new, but I didnt replace wear ring when I replaced impeller, and i should have.

Do you know what it means to B.O.A.T. ?

I think you may find out soon.... or later. Some shops keep your boat 3-4 months before working on it.

 

[nchiotti]

Oh believe me I know.
This is my backup boat, I have a 27' Regency Tritoon with a 300 verado as my main fun boat. I am just trying to get the jet boat sold, have had it for years.