Fuel Starvation problem got me stumped

[vdimenna]

I've got a 1996 200HP Johnson Carbureted. It's been having intermittent problems getting on plane. If I squeeze the primer it'll pick up and plane. Once it planes it will have trouble getting over 4000 RPM (surges).

I hooked up a feeder tank to the primer bulb and it still has the same problem.

I hooked a vacuum gauge up to the fuel inlet side of the VRO it reads about 2 inches of vacuum around 2000 RPM when I accelerate it will go to 0 when the surging starts, sometimes it will creep back to 2 inches and the surging will stop.

The VRO is 1 year old and has maybe 50 hours on it. The fuel lines between the primer and the VRO are all pretty tight. I did notice when the air box was off that the gas that was puddled in throat of the carbs looked milky (like it could be getting aerated). I can't find any air leaks. I took the VRO off to inspect it, so far so good. I plan on picking up a vacuum pump tomorrow in order to test it. The only other thing I haven't looked at is that thing that's T'd on the inlet side of the VRO, it has a 1/4 inch fuel line going to it. I think it's the pulse limiter (not sure though).

Any ideas would be greatly appreciated.

Thanks
Vic

 

[jonesg]

Re: Fuel Starvation problem got me stumped

milky deposits sounds like water in fuel, draw some and let it settle out, see what you have. If you don't have a water seperator then thats why, todays fuel is a problem if you don't take precautions.

 

[tashasdaddy]

Re: Fuel Starvation problem got me stumped

dirty high speed jets?

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

I do have a water separator. I ran it off a 5 gallon can that I know was clean and it still did the same thing.

How could it be the main jets?(even though I emptied the carbs and flushed them with carb cleaner). The vacuum gauge that's inline on the fuel inlet is going to zero.

 

[jonesg]

Re: Fuel Starvation problem got me stumped

You need to remove carb, then remove jets to clean, run wire through them, use a rebuild kit, you can order them here on iBoats.

How is compression?
Unless humidity is very high that moisture is coming from somewhere.

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

Carbs were disassembled and cleaned, then flushed a second time.

Does anyone know why the vacuum on the fuel inlet would go to 0 then back to 2? I have good compression, 105 across the board.

Is there a way to test if the engine sending a good pulse to the VRO?
Also what does that sensor that's T'd into the fuel inlet near the VRO do?

Thanks
Vic

 

[Faztbullet]

Re: Fuel Starvation problem got me stumped

The milky looking fuel is due to humidity and condensation in carb throat when running. The crankcase makes vaccum when piston is on up stroke and pressure on downstroke this will explain your pressure going to zero. I have seen this on the 1989-92 motors due to skirt worn on piston causing low internal crankcase pressure.

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

What would be an acceptable range at the crankcase?

So does that mean a compression check won't pick this up?

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

Tested the VRO using the instructions from:
http://www.boatpartstore.com/vrotable.asp

It passed all the tests.

 

[noelm]

Re: Fuel Starvation problem got me stumped

just flushing carbs with anything does not clean them, you need to fully dismantle, buy kits and rebuild properly (as explained on the other site) buy a genuine manual, pumping the primer in effect bypasses the fuel pump, so it too could be suspect,try a complete remote tank and complete hose with primer.

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

I disassembled, cleaned and rebuilt them. I flushed them as a second precaution.

Wasn't able to run it on a secondary tank, will do that today if the weather holds up.

Vic

 

[Faztbullet]

Re: Fuel Starvation problem got me stumped

Worn skirts will not show in a compression check. I have one here at shop and will check crankcase pressures and post back results, I dont think they will mean much as wear on crankcase seal rings and piston will vary. This one will be high as I just overhauled it for customer.

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

Sounds good. At least it will give me some sort of starting point.

Thanks Again
Vic

 

[vdimenna]

Re: Fuel Starvation problem got me stumped

I figured it out.

Pulled the plugs again and found the port top cylinder was fouled.
Took it for a ride, pumped the bulb to get it on plane dropped that cylinder and the engine wouldn't change tone.

Swapped coils with another cylinder, it still stays on 1.

Now I'm stumped.

Popped the airbox off an wouldn't you know, kinked fuel line to the starboard top carb.

I would have never guessed it. It still baffles me how it could foul the plug when it must have been starving for fuel.
These two strokes are something.

Thanks everyone for the ideas, it really helped me stay the course with this thing
Vic