351 PCM full throttle bogging. Help!

[Highgeer]

I have a 21ft supra Mariah. New edelbroch carb last year and new fuel pump last year also. Currently boat will fire up idle fine. With a full tank of gas the boat will run fine. As soon as it gets to 3/4 full the motor will start to bog when going over 3500 rpm. Put into neutral and will idle fine can open the throttle up will run for a min plain out then start bogging again. Sounds like its starving for fuel. Once the tank is half empty I'm unable to even get it to plain without it bogging down. Has been at a local marina for 2 weeks now. He has checked fuel pressure which is running normal, have changed the distributor checked and tightened all fitting. Even ran off a spare tank and would do the same bogging issue. Does anyone have any ideas? The marina has just about given up and doesn't want to just start throwing new parts at it to figure it out. Please help.

[jasun]

Sounds like a timing issue, but if they changed the distributor, then I hope that would have fixed that...
you know it is not a fuel issue to the pump and carb, so i would think it would be a spark issue.. What distributor did they put on it?

[Highgeer]

It was direct replacement. The points ignition. They did mention possibly swapping it out to direct electronic ignition. Marina also said that the actual distributor had a lot of play in it. Was very loose.

[Jetlink]

Have the plugs and plug wires been checked or replaced recently? What year boat?

[jasun]

It was direct replacement. The points ignition. They did mention possibly swapping it out to direct electronic ignition. Marina also said that the actual distributor had a lot of play in it. Was very loose.


So they just changed the points or the whole distributor???

I had the same issue recently and was about to rebuild my distributor (points, cap, condensor, rotor) but it turned out that my rotor on the distributor would not "Spring" back in place (it as loose and had "Slop"). the weights and springs under the plate were shot. Traded the whole distributor out for a used one from a buddy on here and it worked just fine then. If the weights and springs in the distributor are bad it will mess up your timing not letting it advance when it gets to higher RPM's.

Is the coil orginal?

[CornRickey]

sounds like the primary jets are clogged to me.

[lively]

couple things .. the carb works fine when your gas tank is full ? runs great ? the same as your used too ?

distributor- you need to check dwell and point gap .. or just spend 120$ on electric conversion and set timing @ 5-10@ 900-1000 rpm degrees BTDC and total timing around 36-38 degrees @4300 rpm .. is that the original distributor? have you lubed the mechanical advance weights ? changed the springs? reason why is that if the weights that spin out to advance timing stick or dont return they will cause this issue as well .. check compression , spark , vacuum and you will find the answer

[cadunkle]

Ensure timing is correct. Should be 6*-10* initial and 30*-36* total by 3000 RPM. If that is good, bogging is rich, stumble is lean. So I'd say you're rich at wide open, lean out your secondaries and maybe primaries.

[rideevol]

Things that are common to high RPM - Is the choke opening completely. A carb change may cause choke to flame arrestor mechanical interference. Ignition Coil and coil wire/ends. Low voltage on ignition RUN wiring. Ballast resistor is in use during RUN mode. Old fuel lines, the insides can develop restrictions ( I have seen this twice). Old spark plugs. Look at one immediately after BOG condition, wet or dry tells a lot. Good luck.

[rideevol]

Your problem fits the fuel line problem area. A full tank of gas is less work for the fuel pump. As the fuel level gets lower there is more strain on the delivery system. If the small separate source gas can was placed on the floor of the boat and used the same boat fuel line , same problem. Use a separate gas can plumbed to the inlet of the fuel pump to prove this theory of what section of the fuel line is at fault.

[Highgeer]

This is exactly what has been done. Forwarded from my mechanic.

Things checked: Draw tube and pick up screen, anti syphon valve, timing, carb float levels, fuel pressure at 4.5, carb cleaned, secondary valves open fully, vacuum until surging

Things adjusted: points filed and set, idle mixture screws, accelerator pump linkage, run on a remote tank hooked to the fuel pump removing fuel water separator, replaced fuel water filter, run on remote tank to remove fuel line as a problem, tried different step up springs.

I guess jets and rods could be an issue. But why now and not last year?

[Highgeer]

The boat will run up to full throttle but then after about 20 seconds will start to bog. If you cut it back down to 3000 rpm it will run fine. But open it back up will run at full throttle momentarily then back to bogging. But will run fine down at 3000 rpm and will run at idle fine also.

[Highgeer]

Also. Advance wieghts move free and no broken. Also compression was tested and a new coil installed.

[CornRickey]

do you have another carb you could put on it to rule out the carb?

[cadunkle]

The boat will run up to full throttle but then after about 20 seconds will start to bog. If you cut it back down to 3000 rpm it will run fine. But open it back up will run at full throttle momentarily then back to bogging. But will run fine down at 3000 rpm and will run at idle fine also.

Fuel delivery problem. You get WOT until it sucks the bowls dry then it can't supply enough fuel. Go through the fuel system again. replace fuel filter, check carb inlet for a filter screen and clean if applicable, pull fuel pickup from tank and check sock filter at end of pickup, fuel line could be suspect if none of those, possibly fuel pump on the way out, lastly it may be carb itself needing a rebuild. Definitely sounds like fuel delivery problem though.

[lively]

Fuel delivery problem. You get WOT until it sucks the bowls dry then it can't supply enough fuel. Go through the fuel system again. replace fuel filter, check carb inlet for a filter screen and clean if applicable, pull fuel pickup from tank and check sock filter at end of pickup, fuel line could be suspect if none of those, possibly fuel pump on the way out, lastly it may be carb itself needing a rebuild. Definitely sounds like fuel delivery problem though.
yes this sounds more towards carb , so have you verified under load that fuel is coming out of ventures @3000 rpm??? take the flame arrestor off and take peak while driving the boat and you should see primaries ventures and some of the secondaries spraying fuel .. now when it starts to bog look down there again ? what do you see?
: if you see no fuel when it bogs: then go to auto parts store and get gasket kit for the bowls .. (on the holleys 4160 you can do this on the water with some simple d tools ) BUT since you have a ELDLCOCK lol you will need to make sure floats and needle seat are set per the manufacturer spec .. youtube will have rebuild HOW TOO's and this will have a major affect on performance if the floats are not set right .. ( too much fuel will make it bog also , so will not enough ) i set my holley floats alittle tight so the fuel is Constantly flowing throughout the system ... hell take a video / pictures lets see some model numbers on that ELDLCOCK !

[Highgeer]

yes this sounds more towards carb , so have you verified under load that fuel is coming out of ventures @3000 rpm??? take the flame arrestor off and take peak while driving the boat and you should see primaries ventures and some of the secondaries spraying fuel .. now when it starts to bog look down there again ? what do you see?
: if you see no fuel when it bogs: then go to auto parts store and get gasket kit for the bowls .. (on the holleys 4160 you can do this on the water with some simple d tools ) BUT since you have a ELDLCOCK lol you will need to make sure floats and needle seat are set per the manufacturer spec .. youtube will have rebuild HOW TOO's and this will have a major affect on performance if the floats are not set right .. ( too much fuel will make it bog also , so will not enough ) i set my holley floats alittle tight so the fuel is Constantly flowing throughout the system ... hell take a video / pictures lets see some model numbers on that ELDLCOCK !

Currently the carb is a 1410 edelbrock. Marina switched the carb with another boat same motor that was running fine with a 1409 edelbrock. Swapped out he carbs and seems to work fine now so was something with my carb. Does it need to be completely changed out to a 1409 or can it be modified with new jets to get to be running properly or should the 1410 work and there is something wrong with it i.e. defective.

[Highgeer]

The carb that's on now is a 1410 edelbroch. The marina tested a 1409 off another supra with same motor and ran fine. So not sure how to fix other than getting another new carb? Or possibly rejetting? Any ideas

[chris young]

Definitely not a jet problem. I agree with cadunkle, it's a delivery problem. When you say the marina tested another 1409 from another supra, do you mean that with a different carb it ran fine? If so then just get that baby properly tuned. Sounds like a float issue to me. I don't know a thing about that carb but it's just not getting enough fuel.