Engine troubles please help

[SuperSam]

I have a 1989 supra saltare with the Pcm 351 in it I just cleaned and rebuilt the carb because my accelerator pump was not pumping the needed gas and put it in the water to test it and now the engine is bogging down. I thought it was the fuel filter so replaced that and it ran well for a short period of time maybe an hour or so with no issues then when trying to increase the throttle it bogs down and can choke out. Thought it might be water in the gas so dumped in a bottle of heet and another new filter but same result drove around for 15 min fine then it started to bog down and then u couldn't go faster then an idle in gear with out it wanting to die. What really confuses me is that it runs great in neutral and never chokes or bogs in reverse and so I'm confused if it was gas wouldn't reverse be affected or does it only use a limited amount of gas in reverse so the restriction of gas doesn't affect it. Anyone that can help would be appreciated I am about to bring it to a shop cause idk what to do

[Cusefan78]

Well I would go back to the carb. Take it off and make sure everything is set correctly. Also make sure all the passages are clean

[michael hunter]

What was it doing before you rebuilt the carb?

[wotan2525]

Try to run it off of a aux. plastic gas tank instead of your fuel tank. Sounds like bad gas to me.

[Zim]

Could be debris in your tank also thats getting washed around as you're moving, and then starts clogging up the fuel pickup after a while choking the fuel supply. Have you checked the filter since you replaced it?

[SuperSam]

The reason I rebuilt it was because it was backfiring when throttled and I thought the accelerator pump was not functioning. It was also bogging down before so I was thinking the rebuild would fix both. I have replaced the fuel filter again and it had particles but didnt think.it was enough to.clog a brand new filter but I replaced it again anyways. I have not emptiex my tank of gas anx checked it. Was hoping the heet would take care of the gas but obviously it didnt. Any suggestions how to clean the tank I will have to take out the ski locker today and pump the fuel out. Im not super mechanical so I am trying not to tear it all apart but I am learning as I go so all advice is much appreciated.

[SuperSam]

I still wonder why I can go in reverse as fast as I want and it doesnt choke out but when I put it in forward it does once I throttle it a little. Anyone have any ideas? Does it not take as much gas in reverse or would that mean its not a clogged tank or bad gas?

[Cusefan78]

I still think you have something up with the carb. Did you set the screws properly could be not getting enough gas to throttle it up. Reverse gear has less friction plates so it will go faster in reverse with less power. A few particles in the filter isn't going to clog it.

[SuperSam]

Played with the mixture screws didnt change anything... was told by a carb specialist that if it was the carb he wouldnt think that it wouldn't run fine for a short period of time and then clog if it was clogging the jets would clog within the first 30 sec because of all the fuel it would be sucking not after 15 min to an hour... he thought fuel or exhaust... as we speak I have been emptying the gas tank and am gonna try and clean it I do see particles but not an alarming amount. Is there a good way to clean it? Is there a filter in the tank? I got the float hole open and have been working through that but not a lot of room to work to clean it.

[cadunkle]

When it is acting up when trying to give it throttle pull the air cleaner off and manually work the accelerator pump lever. You should see a crisp stream of fuel out of the accelerator pump discharge nozzles hitting the boosters. If nothing you have a bad accelerator pump check valve or plugged passage. A failed diaphragm normally results in an external fuel leak. If you have a weak dribbly spray you may have a partially clogged passage or discharge nozzle, or the metal gasket at the top and bottom of discharge nozzle is not sealing.

If you VERY slowly open the throttle does it still bog? Lack of fuel is more of a stumble or misfire. A bog is just lack of power or smoothly crapping out. Stumble is lean, bog is rich. Which do you have? What you describe sounds more like it would be a lean stumble related to the accelerator pump not working properly or just delivering insufficient fuel when opening the throttle.

[SuperSam]

Just replaced the accelerator pump power valve, and prior to going out checked the stream of fuel it shot and it was strong unlike before I replaced it when not much sprayed. I didn't check while I was having issues if it was still spraying. I feel like it must be a lack of power that I am describing because of lack of fuel... I keep calling it bogging but maybe it's more a stumble or lack of power... Even when I move the throttle slow it chokes out and has no power except if I am at idle speed... Like I said before right away when I put it in the water after the rebuild I could throttle pretty hard and the boat would take off and run fairly well then an hour later it would die when throttling and would only run in idle

[Broke Pilot]

I don't have a carb'd supra, but does the carb have any sort of a choke mechanism? Sounds like the motor is warming up and the choke is starting to engage. That would explain the idling ok and then choking out as it gets going.
And to answer your question, no the engine doesn't use as much fuel in neutral as it does with a load on it.

[SuperSam]

Has electronic choke that seems to be working fine opening up as the engine gets warm... Also know that it neutral doesn't require as much gas as under load the question was about reverse which was answered which the boat runs great in both of those and usually starts right up so don't think it's the choke

[cadunkle]

Fuel filter(s) new? With all the crud you mentioned in tank pull the primary bowl off the carb and see if any junk in there. Also check at carb inlet to float valve if there is a screen in there that may be plugged. You may have some crud that got through and has plugged up some passages in your metering block.

Also you mentioned idle mixture screws do nothing? Screwed all the way in (lightly seated, don't tighten beyond where they just bottom) should stall the engine. If not you have extra fuel getting in from somewhere. Check your timing and that is is advancing. 10* initial should be good. Do as below to adjust idle mixture and RPM then recheck timing.


There is a brass screw on each float bowl. With the engine running, remove it and observe fuel level. Should be right at the bottom of the hole or just below, if fuel comes out when you remove the screw the float level is too high. If it's pouring out and nothing else has changed you probably have junk in your needles and seats. On each fuel bowl there will be a large flathead screw and a 5/8" nut near the fuel inlet. Remove the screw and remove the nut, removing the needle and seat assembly. Clean with carb cleaner. Reinstall to approx the same position as before, better installed deeper than previously if in doubt. Reinstall the nut and screw.

To adjust, remove the screw from side of bowl and observe fuel level below the opening. If above, loosen the screw and tighten the nut until the fuel level is just below the hole but no fuel comes out. If below, loosen the screw and then loosen the nut until fuel level is just just below the opening.

Other things that came cause a rich condition are plugged air bleeds. Take a can of carb cleaner with the straw in the nozzle. Put the straw in each air bleed one at a time, and give a burst of spray to dislodge any obstructions. The air bleeds are the small brass plugs with small holes in them that you see when looking down the air horn. There will be 8 of them.

After doing all this adjust your idle mixture with the mixture screws on teh primary metering block. Screw in until you get a stumble/misfire/RPM drops then screw out 1/4 turn. Do this once twice per side, alternating sides. After that set your idle speed with the idle stop screw if necessary and repeat the idle mixture screw adjustment. Repeat as necessary until idle speed is where you want it, generally 700-750 RPM in neutral will get you 600-650 in gear.

[CJD]

The chance of bad gas hitting right when you rebuilt the carb is extremely small.

The obvious is that something didn't go back together right in the rebuild of the carb. If it were me, I'd pull it off and double check the following ( I'm assuming you are working on a Holley):

1) make sure you set the the float levels correctly.
2) remove and blow into the power valve to make sure it has not blown. One back fire is enough to blow a brand new power valve...and the symptoms you describe are exactly what a bad valve would cause.
3) if you have the old power valve, double check that you did not replace it with a different number valve. The number can make large differences in the way the carb delivers fuel.
4) make sure your bowl gaskets were installed right side up, blocking some of the idle and power passages.
5) look at the jets for mangling and that they are snug.

A trick...if you use silicone or WD-40 on the bowl and block gaskets, they will not shred when you take the carb apart, so you can re-use them several times.

[michael hunter]

Have you checked the ignition system [Dist cap ,rotor,wires, points and coil] Misfire under load is a sign of ignition failure. If you have points what is the dwell set at?

[SuperSam]

Here is where I am at... I have removed the tank and the gas inside and there was not much debris in it blew out my fuel lines between the tank and the filter replaced the filter checked pressure on the fuel pump which is functioning ( believe it was 10psi is that normal?). Carb has been rebuilt minus the needles and the vacuum diaphragm for the secondaries. Took it out on the lake ran well a little lean with hard acceleration but not bad drove for about 20 min thought I fixed it. Put the boat in the next day ran fine again for about 20 min then back to not being able to give it any throttle without it dying. Let it sit then took it out again later and it ran alright for a bit and started to die after 20 min or so. Because it has ran well at times I think it is unlikely a problem with the carb or fuel because if that was the case it would be more apparent. I'm guessing it has something to do with the engine warming up. Engine itself doesn't run too hot usually around 150 and maybe will spike up to 160 or 170 but rarely. My best guess is the coil might be bad and that it is heating up from resistance and not functioning properly and once it gets to that temp it isn't able to make a charge that would be sufficient for driving under load but is still strong enough when it's in idle... I also plan to check my timing in the near future... All input is appreciated cause I'm struggling to be able to figure this out

[Cusefan78]

It could be the coil but my best guess is your carb is either still dirty or not set properly. Pull the plugs and make sure you have bright even spark across all the plugs. But I still bet it's the carb. There could be small particles that work its way into the carb then when you shut it off the back out only to get pushed back through.

[SuperSam]

Thanks for all the help I replaced the ignition coil and spark plugs and she is running perfect now!