Fuel issue??

[Russ46]

Hey guys, so my 1997 challenger 787 stars and idles perfectly in the water, will rev up to 3000rpm then fall on its face. If I spray premix into the carbs I can get it to rev out all the way to 6500 and if I stay up aboove like 20mph I can let off the gas then accelerate back up to 6000rpm but once I get too slow or come to a stop it just cannot get past 3000rpm again without help!

I cleaned both carbs, set the mixture screws to factory, replaced plugs (after driving the boat and pulling the new plugs they look perfect, the fuel mixture looks awesome), I replaced the accelerator pump diaphram as it was leaking and I really thought that was going to fix the problem..

The boat has all black fuel lines, new in line fuel filter and new premium gas. It starts up instantly and will idle at 1500rpm in the water forever with no issues. Does anyone know what it could be? The only thing I didnt do was check the carb pop off pressures, could this be a symptom of that? Or could there be a fuel pump issue?

I am going to order a vaccuum pump and check my pop off pressures and I am even going to pressure test my fuel pump diaphragm.

 

[rusty nail]

could be your safety neutral switch is broken. the boat has a built in saftey to not allow the boat to go over 3000-3500 rpm in neutral. i do not know if there is a test for this.

 

[Russ46]

could be your safety neutral switch is broken. the boat has a built in saftey to not allow the boat to go over 3000-3500 rpm in neutral. i do not know if there is a test for this.

It isnt that because if I try to start it in forward it wont let me. Also if I spray fuel into the intake while accelerating it will accelerate.

 

[Russ46]

Ok so I found a couple things last night after testing it with no success again.

The fuel pump wasn't working, I replaced the check valve discs and proved they held, I thought for sure that was my fix. I also set both carb pop off pressures to 31-34 psi.

Took it out and it does that same bog at like 2500 to 3000rpm. So.. the only thing I havent checked yet is the fuel selector valve and fuel pick up tube screen. I am going to try it with the selector valve bypassed and inspect that pickup tube.

One thing I noticed last night though was i installed a voltage meter and when it was running around 6000rpm it was making like 17 volts?? That cant be right, but I unplugged the voltage regulator and the boat actually ran worse with it unplugged? I am guessing it needs a new regulator though.

 

[Russ46]

So an update, the fuel pickup filter was spotless, i bypassed the fuel selector valve and in line fuel filter as well. I also replaced the voltage rectifier.

When I first put the boat in the lake it would still bog at 3000rpm, I then checked if the accelerator pump was primed and it wasn't since i had the carbs apart. So i got it primed up then that basically fixed the 3000rpm bog! It will kind of stutter at 3000 but it wont die any more and it will accelerate through.

Now my next issue is it wont rev past 5000rpm. If I spray fuel into the intake I can get it to rev up to almost 7000 and it takes off very quickly!

I know my carbs are clean, I have both pop offs set to 34ish psi, and I know my fuel pump works. I have a couple carb rebuilt kits from a friend but cant tell if they are genuine mikuni so I havent replaced my diaphragms in the carbs but now I am tempted to try replacing them.

The diaphragms in my carbs are VERY flimsy, extremely soft and pliable and the new ones in the kits I have are quite a bit more rigid/stiff. I am wondering if my diaphragms are the issue? As I have basically nailed it down to a fueling issue now. I will try replacing them and going for yet another test run

 

[FlyboyX]

Mikuni kits actually say mikuni on the package. Also, the big diaphragm for the internal fuel pump has an anodized red tab in the center of its genuine

 

[Russ46]

Ok I ultrasonic cleaned the carbs and went through them again, didnt find much but I just test drove it and it doesn't seem to have a fuel issue anymore. If I pull the choke when its stuck at 5000rpm it will die instantly. It seems the engine is running perfectly fine?

I am now thinking it has the wrong pitch impeller. If I have a passenger it is really hard for it to get on step but it eventually will then it's fine until it comes off step again.. I remember the previous owner also mentioning it has a "race" impeller installed and they gave me an old impeller with the boat.

Anyone experience a wrong pitch impeller in a boat before?

 

[Russ46]

Does anyone know what the pitch should be for a 1997 challenger 800?

 

[Russ46]

Haha! I think I found my problem now! Pulled the pump off just to inspect it, the impeller looks awesome. It's a brand new solas and the wearing ring looks brand new, less than 0.015" clearance between the two.

But! There is a slight radial bearing play, and I can totally see how that would give me reving issues. The bearings are slightly rough to spin also.

Does anyone know what the bearing numbers are? I'd like to just order the bearings from a local parts store instead of buy a kit.

 

[FlyboyX]

i would just buy the complete kit. the bearings run directly on the shaft. a nice new surface is the way to go. you should be able to buy the complete kit for about 100 bucks or so. anything less is probably just false economy. have you even taken apart what you have to see what kind of wear you really have? rough bearings probably means water got in there and caused rust. that shaft would be rusty as well. also, those components take a lot of abuse. its money well spent if you ask me. anything less and you will be fixing it again next year too. you will also need a special tool to spin off the impeller. you can get it for 10-15 bucks on ebay or amazon.

 

[Russ46]

i would just buy the complete kit. the bearings run directly on the shaft. a nice new surface is the way to go. you should be able to buy the complete kit for about 100 bucks or so. anything less is probably just false economy. money well spent if you ask me. you will also need a special tool to spin off the impeller. you can get it for 10-15 bucks on ebay or amazon.

I just ordered bearings only. I cant find any kits that include the shaft. I can find new shafts on ebay though so I will measure the old shaft when it's out and hopefully it is in good shape.. the shafts alone are like $150 canadian

Luckily a friend of mine has an impeller tool!

 

[Russ46]

Got it apart, looks like the thrust bearing wasn't set on the shaft properly when it was assembled or something, its bent and wrecked. Thankfully the shaft looks mint!

I'm surprised that the thrust washer just sits against the pump housing any doesnt have any sort of anti rotation device? Seems odd how that disk could spin against the pump housing if that bearing ever seized..

 

[Phuck_boi]

So did this fix your rpm issue?