Anyone know Ford 351's?
 

Motor: Indmar 351 w/ Holley 600
Hrs: 1190
Issue: Surging between 2700-3K rpm's, and a minor stumble at initial throttle tip.

This happened rather suddenly about a week ago, running across the lake at about 3500r's. Took a couple of big wake and about 3min later she stumbled very hard and forced me to bring it off plane. As soon as the r's dropped below a grand, she died. On and off this year, it's had a surging problem around 3K, but it has been intermittent and not a big enough issue to pull the boat. Well after it stalled, it refused to restart. Was able to get home off plane, but boat wouldn't idle. With carb tweaking I got it to roughly idle, but power was gone completely. Tweaked more the next day and got it to run up to 3K but feeling gutless out of the hole. So far: new accell super coil and plugs, minor change if any. Fuel is pretty fresh, and she has seen 30hrs this year so at least 150gals. I'm leaning towards the distributor as the issue since it is a consistent surge at a set rpm. One side note, was able to tune the carb once and get it to run to about 3500r's(no higher), then brought it off plane and tried again, it wouldn't do it.

Well I'll update this for the hell of it. Heads are 2 seasons old, and brand new rather than reman'd. Carb is 5yrs old and was a reman to begin with, so ordering parts today to rebuild it. Looking for the cap and rotor as well. Coil and new plugs along with carb tweaking made limited improvement. Interesting/frustrating note, I can't get a vacuum gauge about 11min... My understanding is that I should be more like 18+

Surging sounds like a lean issue, combined with low vacuum readings maybe a vacuum leak? Sounds like that or its not getting enough fuel

Maine, I would agree but.... Holley 600's have the screw on the outside of the floats to check fuel levels, when I pulled it, fuel poured out. Indicating floats are stuck open (I think) putting too much fuel into the motor and flooding it. Am I off base? plugs are coming out looking more carbon'd up then lean... More to come when I'm back in town

Ive got the 351 PCM set up in the wifes ski boat. Pretty damn reliable engines. Sounds like time for a simple carb cleaning/rebuild. Make sure all of the air pasages are completely clean.


Darrell.

Some of the 600's have a primary metering block power valve. Sounds like yours is ruptured. Get a kit for it and tear it down...re build it. They are pretty simple.

moore and John thanks, Kit came in the mail today. Guess what I'm doing tonight :angry-smiley-038:

And I got the marine specific kit with the proper power valve, etc.

Carb is rebuilt. Fresh power valves, gaskets, etc. Goes on tonight with a base tune for the test run. Fingers crossed

Best of luck. I've had to rebuild the carb on mine twice in the last ten years. It seems the newer fuel blends are just rougher on the gaskets and seals the the older blends.


Darrell.

sounds like a fuel delivery issue to me..ck filters/water separator, even the anti-siphoning valve in top of tank...

EZ tell me if I'm wrong here, but I rebuilt the carb and put it on. Boat runs substantially richer than before. So I pull and re-adjust floats. No change. Idle screws, no change. Nothing makes a difference. I broke down and ordered a reman from national carburetors. Any one have any other thoughts?

something would have to be done wrong if rebuild and now way rich, bad power valve(had that happen recently out of the package and were holley) wrong gaskets blocking a passage, leaking needle & seat...or excessive fuel pressure...also make sure ignition is ok...on some cases some ignition issues seem like a carb issue...points closed up for one thing..

The powervalve is new and installed correctly. And the carb was running rich prior to the rebuild. Now it is just worse. I've heard of the powervalve's being damaged by a backfire, but my carb has the check ball, so even though it back fired on initial start up, I'm inclined to believe I'm alright. Part of my problem is that the floats refuse to set properly. The motor is angled down towards the rear, so naturally the back of the carb is lower. I've adjusted the floats up and down, and messed with A/F screws and idle mix to no avail

Forgot to mention, my floats don't match. One is very old school metal and one is newer plastic. Also the fuel tube that runs between the bowls is slightly bent. I doubt it matters, but figured it bears mentioning.

i recomend checking your ignition system,if it is weak it cant fire the fuel ,that can be confused for carb problems.

I've got new plugs, wires, and coil. The dizzy is a mallory and maybe 3yrs old...

if you pull the float bowl and look at the power valve dia side, should be dry, if it's wet or damp it's leaking, or if the well area behind the metering block where the power valve gets it's vacuum signal is wet, it's leaking, makes no difference how old/new your dist is, new parts fail to...pull site plugs off side see where they are(not running) fuel should be below hole edge, no concerns of the floats as long as they float...

I did the site screws. One is good, other is pouring fuel

You should be able to set your float levels "to the sight port" by adjusting the float screw on top of the bowls. If you cannot get one to stop pouring fuel regardless of the setting, then you have a bent float tab or the needle is not installed correctly. You keep saying fuel pours out of the level port, and you keep saying it runs rich.

When you rebuilt the carb, did you not check the float tab and make sure the float would fully close the needle before hitting the top of its travel?
There's a lot more to a carb rebuild than throwing in some new gaskets and powervalve. You should be cleaning all passages, looking for gasket mismatches, looking for malfunction of the float/needle mechanism, realigning your butterflies, etc.

MC

also the float may not float. all the adjusting in the world won't help a float full of gas. while you are at it, do a compression test.

Did the problem ever get resolved????