# Need help with engine problem



## mcguiremcd (May 23, 2012)

I have 389 tri-power.On the way home from a cruise night i goosed it a few times playing with a Mustang and as i got to the next stop light the engine died. It cranked up and ran fine to next light and died again. It cranked up, ran fine to next light as i stopped the RPM's would just keep dropping.{Like when you unplug vacuum but keeps dropping till dies].I had to turn idle screw up to keep it idling.I tapped on center carb,checked timing,checked for vacuum leaks,all was ok. Out of nowhere it started idling fast and i set idle screw back. A few weeks later i had to move it out of shop,all seemed ok. When i cranked it to put back in shop it wouldn't idle again with out setting idle screw up.I never know when it will die at idle or be idling too fast.I changed PVC valve and that didn't help.One guy says its the fuel pump and another says no its not fuel pump.Need help on what may be the problem. Seems to run fine except for this problem.
Thanks,
Larry


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## bigD (Jul 21, 2016)

Is there a choke on that center carb ?

Sorry !'m not familiar with Tri-power carbs. 

I do know that some Q-jets have a high idle screw, connected to the choke. It's supposed to hold butterflies open enuff to idle, when cold, then release the butterflies, when engine warms & choke opens completely. The screw adjusts this mechanism. So, there can be some sort of malfunction of the choke mechanism. 

Again, this may not apply to your carb. 

Since adjusting the throttle screw increases your idle speed, that pretty much rules out a fuel supply to the carb problem, IMO, since if the problem was fuel supply, just turning the screw would not increase fuel supply to the carb.

I just read a post that said when you are chasing an idle problem, it's best to remove the end carbs & seal off the holes with block plates. Then solve your idle problem BEFORE putting the end carbs back on. Sounds reasonable to me.


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## Lemans guy (Oct 14, 2014)

I would check for any vacumn leaks at base of carb or intake runners,.....squirt some carb cleaner around base of carb and intake see if idle speeds up, a smoke machine is better, but however you do it check.

Also make sure your fuel filter is not blocked. I would add a bottle of Redline S1 Complete fuel system cleaner to a full tank of gas, nothing better, and it will help clean any gum or clogs..

Then I would clean the center carb with gumout and like big D said you can block off secondary carbs. Even just tightening the throttle plates up a bit so you have no leaks there

reset the center carb back to basic setting, 1 1/2 turns out throttle to just showing the transfer slot. And begin again.

Sounds like a lean stall at the lights, maybe from a vacumn leak or through secondary carb throttle plates, when you open the throttle screw you are increasing the mixture being pulled through, 

It is faster more vacumn pulling through the idle and transfer slots and it overcomes the leaner mixture which was stalling.....Maybe

Those are a few things to check, but weak coils and ignition can cause similar stalling. To start with I would be working with the mixture and if the car sits a lot the gasoline phase separates and water makes for poor running. That is where that Redline will help.

Also make sure your choke linkage is not sticking, causing a stall and then causing it to run fast it can do both if it sticks.

You will get it!


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## PontiacJim (Dec 29, 2012)

mcguiremcd said:


> I have 389 tri-power.On the way home from a cruise night i goosed it a few times playing with a Mustang and as i got to the next stop light the engine died. It cranked up and ran fine to next light and died again. It cranked up, ran fine to next light as i stopped the RPM's would just keep dropping.{Like when you unplug vacuum but keeps dropping till dies].I had to turn idle screw up to keep it idling.I tapped on center carb,checked timing,checked for vacuum leaks,all was ok. Out of nowhere it started idling fast and i set idle screw back. A few weeks later i had to move it out of shop,all seemed ok. When i cranked it to put back in shop it wouldn't idle again with out setting idle screw up.I never know when it will die at idle or be idling too fast.I changed PVC valve and that didn't help.One guy says its the fuel pump and another says no its not fuel pump.Need help on what may be the problem. Seems to run fine except for this problem.
> Thanks,
> Larry



Flooding.


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## mcguiremcd (May 23, 2012)

Choke seems fine.
Fuel supply makes since.thanks
I have the end carbs unhooked but like the idea of blocking off.
Thanks


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## mcguiremcd (May 23, 2012)

Thanks guys for all the info.
Post above for BigD. I'm still working on how all works on here.
Not the best with computors.
Will look at all things mentioned.


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## BearGFR (Aug 25, 2008)

Check and verify your float levels in all 3 carbs. Make sure the pivots/hangers for all the floats are installed correctly and are situated how they're supposed to be. If you're not sure about the condition of your needles, and seats - consider replacing them in case they're leaking. If you've got brass floats, check them for leaks (pull them out and shake them - listen for sounds of gasoline inside them. Submerge them in a container of gasoline and look for bubbles.) If you got polymer floats, look for signs of nicks cracks that might be allowing them to soak up fuel and sink. If all that checks out ok, check your fuel pressure at the carb inlets. If it's too high it can force the needles open and allow flooding. 

I'm a big fan of using wide band air/fuel meters, either permanently installed or one of the hand-held types like the ones from Innovate. Knowing for certain what your air/fuel ratio is under all conditions is extremely valuable information.

Bear


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## PontiacJim (Dec 29, 2012)

Do you have power brakes?


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## mcguiremcd (May 23, 2012)

Thanks Bear.Will put on list to check. Mike W rebuilt carbs 4yrs and 1300 miles ago.
Jim, no don't have power brakes


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## 40flier (Nov 5, 2010)

Have you held your hand over the throat of the end carbs while running?


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## PontiacJim (Dec 29, 2012)

mcguiremcd said:


> Thanks Bear.Will put on list to check. Mike W rebuilt carbs 4yrs and 1300 miles ago.
> Jim, no don't have power brakes



OK, thought it could be a bad check valve going into the power booster, or bad booster.

Have you checked all rubber fuel lines and fittings? The rubber lines should all be replaced with ethanol friendly rubber lines. The factory, or older type, rubber lines will deteriorate quickly. IF you have a small split in a fuel line, or cracked in a steel line, you could be sucking in air, rather than draw in fuel.

Just another thing to check.

Is it possible something is floating around in the gas tank and it periodically plugs the gas pick-up tube in the tank. I had that experience when younger. It was frustrating as the car would run out of gas, then sit for about 5-minutes, and fire back up. There was a red rag floating around in the gas tank that someone must have once used for a missing gas cap. So as it floated around, it would plug the pick-up line. Then when I sat, the rag would sink down to the bottom of the tank uncovering the pick-up tube and I was good to go. Took months to figure out.


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## mcguiremcd (May 23, 2012)

40flier---Yes,was one of first things i checked.

Jim---All fuel lines and tank was replaced 4 yrs ago.

Thanks


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## Gtowally (Jan 19, 2019)

I’ve Had a similar problem with my tri powered car when I opened them up. The throttle plates on the end carbs hung up and didn’t close all the way


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## mcguiremcd (May 23, 2012)

Gtowally--I unhooked end carbs to take them out of play.
Thanks


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## mcguiremcd (May 23, 2012)

Well guys.I think i found the problem and not in a good way.On Monday was trying some different things. Coming back from second run 
I smelled something burning and thought it was coming from outside somewhere.As i stopped to back it in shop smoke was coming from under hood.I shut it off lifted hood and rear carb was on fire.That little Element put it out quickly.I think that rear carb was leaking fuel was the problem all along.Iwas so pis--- at myself for not checking it.I had checked the front and center but could't get my old body in far enough to look in rear. A couple guys helped me get it in shop.Yesterday i went to Cruising the Coast for the day.Today will see how much damage done.


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## geeteeohguy (Feb 2, 2008)

That sucks....hope everything is okay. As a long time tech, and now as an old guy, I've learned that it's always the ONE component that you don't check because it's buried, hidden, hard to get to, or whatever, is going to be the component that is going to fail. Every time. So the answer is to turn on the radio, grab a cup of coffee, relax, and check out EVERYTHING at a slow enough pace that you don't wear yourself out. These cars are now well over a half- century old, running on new, crappy fuel formulas that like to boil off and flood engines. We have to be careful.


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## PontiacJim (Dec 29, 2012)

That sucks, but I did say flooding. Have had that experience more than once. The flooding of the carb dumps too much raw fuel in and the car slowly dies away on you at a stop/idle because you don't have enough RPM's to keep enough air entering - which is why it ran when you bumped up the idle to sorta compensate for the extra gas. I have managed to limp home by making sure I had one foot on the brake and the other on the gas to rev the engine up so it would not stall out when I came to a stop. 

Good news is, you found the problem and your car didn't torch up on you. Fire extinguisher in the trunk?


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## mcguiremcd (May 23, 2012)

geetee--You are correct.I've been kicking myself for not finding a way to check that carb. Lesson learned.

Jim--Yes you did say flooding, and after thinking about it the last few days, it made since that that was what it was. I had to heel/toe it a few times myself [Had almost forgot how to do that]. 
The fire extinguisher was the Element 50. It had the magnet, so it was stuck to the pass. side seat foot {hidden]
That little thing worked great. I was able to get to it very quickly.

Many thanks to all,


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## geeteeohguy (Feb 2, 2008)

Yet another classic car saved.....because a fire extinguisher was handy. Their importance and value cannot be overstated. 
Had a classmate in high school in 1978 who had a mint orange '69 Judge. Ram Air 4 speed car. Only 9 years old, it looked like new. Out cruising one night, it had an engine fire (caused by faulty MSD wiring) and the car burnt to the ground...and was a total loss. He had no fire extinguisher, and neither did anybody else. Two years later, he had built himself a mint '68 GTO that was a sort of a Judge clone, and you can bet that car was equipped with a fire extinguisher. Glad to hear no real damage was done, mcguire!


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## PontiacJim (Dec 29, 2012)

Looked into the Element 50 fire extinguisher. Never heard of it. It is quite small, and compact, so a plus. Video shows how it works. https://elementfire.com/


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## mcguiremcd (May 23, 2012)

Jim--I really liked how small it is and with the magnet[extra cost] you can put it in a lot of places. Easy to move from one vehicle to another.
Its about the size of a flare.
I will buy another and hope i never have to use it.


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## LATECH (Jul 18, 2018)

Looks like a Halon extinguisher

Glad that your car did not turn into a crispy critter


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