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View Full Version : Help..Fuel starvation or flooding???



Boat_Mon
07-19-2002, 07:28 AM
Ok, so I'm in the boat cruising along at around 3000 rpm, as I accelerate everything is smooth, no missing, no backfire, very smooth. But...like clock work, I get to 4500 rpm's on the nose and the engine cuts out and will not accelerate anymore, when I back it off just a hair, it picks right back up like nothings wrong, anyone got any ideas?? Oh one more thing, I have watched the voltage meter as this occurs and it never changes, I guess that kinda rules out electrical (i think)also this is a Rochester quadrajet carb.

Rootsy
07-19-2002, 07:46 AM
is this a new problem which just began to occur? are you saying that it is still running but just falls on it's nose? does it lose rpm or just hover at 4500?

might want to give a few specifics on the motor setup...

initial gut feeling would be to say its going lean or it could be ignition related but without all kinds of good info and specifics it's difficult to say for sure...

Rodger
07-19-2002, 07:47 AM
Fuel starvation is a possibility but I've been fooled before into thinking I had a fuel problem when it really was ignition. To isolate the problem you could have someone dribble gas or spray carb cleaner down the throat of the carb at the point where it hesitates and see if it helps. If it does, that tells you it is indeed fuel starvation. I've used this method before. I just remove the engine cover and flame arrestor and go to it.

Boat_Mon
07-19-2002, 07:57 AM
Ok as far as the engine goes 350 - 4 bolt main, forged crankshaft, pink rods,(full floating) forged pistons, fuelie heads with one piece Manley S.S. valves, Crane roller rockers, Rhodes lifters, balanced and blueprinted.

This just started happening, and when it hits the 4500 it will stay there but will significantly lose power and speed, and again, if I ease back to 4400 it picks right back up. One other thing, when there is no load on the engine it doesn't have any problem. You guys mention ignition, why would it be an ignition problem? I thought that would be a more random cut out. This is like clock work.

blackhawk
07-19-2002, 09:11 AM
If you have a water seperator check that. My friend's boat was cutting out at about 4000 rpm and we popped the seperator that night and it was half full of water.

Boat_Mon
07-19-2002, 09:25 AM
ok, I'll check that. I just got this boat, so I'm not entirely sure I have one. If I do I assume it would be between the fuel pump and the carb? Looks like an Oil filter?

Jamesbon
07-19-2002, 09:40 AM
Do you have a rev limiter? If so, check it. I'd also take a look at the weights and springs in your distributor if you're not running an electronic ignition module.

Boat_Mon
07-19-2002, 09:48 AM
I don't believe there is a rev limiter, but in terms of a description, the symptoms are very similar to what one would see I believe if there was one..I'll pull the distributor today.

Rodger
07-19-2002, 09:53 AM
Yes, the fuel-water separator, if it is the original type Merc, looks like an oil filter.
If you have an ignition problem, it isn't the type you mentioned where it cuts out. It's where the ignition is marginal, for some reason, and will perform OK, to a point. When the demands on it overcome it's ability to perform properly, perhaps trying to go beyond 4500 RPM, then it might cause symptoms your experiencing. This is why you have to isolate the problem; fuel or ignition. Of course some things are easy to check such as the fuel-water separator so that might be worth the trouble before setting up tests where you need assistance.

Boat_Mon
07-19-2002, 10:01 AM
Hmm, good thoughts Rodger, I'll keep you updated as I check these things out. In terms of the ignition though, what areas would you troubleshoot first? I hate to just buys things to buy things.....

Rootsy
07-19-2002, 12:57 PM
I went for a ride in an 18 a few weeks ago.. he's runnning a pretty stout sbc w/ alpha SS... generally he says that his combo will run around 5800 rpm... we could only muster 5200 out of it and it sounded fine... he posted on here a few days later that just by replacing his 20 dollar ignition coil he managed to pick up 400 of the missing rpms...

really to think about it... something is really going on somewhere... you said that it stays right at 4500 but it loses speed until you back off the throttle a wee bitn and then it picks up speed????

Boat_Mon
07-19-2002, 12:59 PM
Hey, no one has said fuel pump yet. I've noticed that when I rev the motor between 2500 and 3500 rpm's I am starting to get fuel in the "green Line" the clear tube that also runs from the fuel pump. I guess in the event there is a hole in the diaphragm the fuel dumps up through that hose into the carb to burn off as opposed to getting dumped into the bilge. anyway, I'm on my way to get a new fuel pump.

By the way, I checked everything else you guys recommended also, thanks for the advice. I'll keep you updated on if this works or not.

Rootsy
07-19-2002, 01:04 PM
leaky diaphram huh... bad problem to have in ANY situation... eek!

nick
07-19-2002, 04:31 PM
when is the last time you changed the fuel water fliter sep. my money is on the simple things first. my engines have two on each do you have two? if it is fuel i hope you did not suck up crap in to you carb. what type of ignitiopn do you havealso? are you or have you at any time blown a fuse or circuit breaker lately? just some things to also check loose wires clean grounds etc.

Boat_Mon
07-19-2002, 08:16 PM
Scooter,

Those are all great suggestions, I went through and checked everything you said. It was all looking normal. I pulled the fuel pump off and the only way it would push full when I moved the actuator arm was out the green line fitting,not the main fuel line.

Now the big question... I put the new fuel pump in and I can't get gas up to the carb. I know there is fuel in the new pump and in the fuel filter, and I know fuel is moving from the tank, it just seems the new pump isn't pumping. So then I take it off again, compress the arm and whoosh, gas comes flying out the "out" fitting. So I know the pump works, did I or is there a way that I installed it wrong??? Anyone????

Long Island Boater
07-20-2002, 12:08 AM
Do you have a electric or mechanical fuel pump? If it is mechanical (Run off a lobe on the camshaft), make sure the arm of the fuel pump is resting on the small steel rod that acuates the pump. On the small block chevy, the rod sometimes slides down when you remove the old pump. Easy to miss this when you are contorted in a small engine compartment. If this is your problem, you can put a small amount of grease on the rod, to hold it up in block until you get the new pump in. Good luck, Rob

nick
07-20-2002, 10:21 AM
make sure the fuel pump is installed correctly.on asbchevy check 1.the rod make sure it not bent etc. use grease to hold it up 2. get or borrow a fuel pressure guauge install it up near the carb check fuel pressure at high rpm 3. also watch you DONOT loose you hatch wnen going fast with it up, maybe remove the hatch temp.4.your fuel filter is it before or after the pump. 5what type of ignition are you running?nothoing wrong with changing fuel pump check for leaks with a white clean paper towel when done. you might have a ignition or carb problem if it still is there .

Boat_Mon
07-20-2002, 04:24 PM
Long Island,

Thanks for the info on the steel rod, made all the difference!! She's in and running pretty good. Now I'm getting a little bog under load over 5000, I'll check the ignition I guess.

Also thanks for the list scooter, sounds like you been here before!!!

Long Island Boater
07-20-2002, 10:06 PM
Glad I could help Boat-Mon.