Engine stumbling and bogging when you pull away from idle--77 Newport with a 400 and TQ carb

[Pclancy]

I have had nothing but problems with my ignition system and carb. No doubt due to some problems that came with the car, mistakes made by my mechanics and/or bad parts that we have put in. Or some evil combination.

About 6 months ago, we removed the lean burn. Everything worked well for a couple of months, but then the ignition began cutting off at random times. We diagnosed that as a faulty orange box (ICM). Put in a ICM made by standard and that stopped producing spark after a couple of weeks. Completely. Now we have put in a chrome ICM made by Mopar. That problem seems to be solved, and the spark is strong. Starting is either instantaneous (just after shutting down) or after just a bit of cranking when cold. I can live with it. The choke works well.

But the engine runs a bit rough at idle, especially when warm. Barely noticeable, but it is there sometimes (and sometimes not when the engine is cold). Feels like a very tiny rumble/misfire. And the engine stumbles and bogs just a little bit when you accelerate very gently from idle or a stopped position (on the flat). Or when you go up a hill, very slowly, from a stop. As you speed up past 10-20 MPH or so, the engine smoothes out and runs perfectly. At highway speeds, she runs like a champ. Smooth.

To fix this, we have rebuilt the TQ (original) carb. Twice. We have replaced the spark plugs. We have installed a new ICM. We have checked and adjusted the distributor. We have readjusted the choke and the vacuum advance. All wires and connections have been checked. Everything has been gone over twice. I'm sure I am missing some stuff.

You guys know by now that I am not a mechanic. But I choose my mechanics carefully, and the guy I have is good. But he seems to be stumped. And like all of us, he isn't perfect. The latest theory was that we replace the spark plug wires.

Any ideas? Thanks as usual!

Peter

 

[commando1]

Any ideas?

Too easy. Edelbrock.

 

[Snotty]

I've experienced this a few times. Might not be the same for your car, but it sounds to me like there is a small vacuum leak. Check the valve on your Power Brake booster, also look at all the hoses coming off the intake. A slight leak will cause the stumbling you are mentioning.

 

[Pclancy]

Too easy. Edelbrock.

OK, which one? Any issues with swapping carbs?

 

[Pclancy]

I've experienced this a few times. Might not be the same for your car, but it sounds to me like there is a small vacuum leak. Check the valve on your Power Brake booster, also look at all the hoses coming off the intake. A slight leak will cause the stumbling you are mentioning.

Thanks for the tips. Will do.

 

[70bigblockdodge]

Sounds like a vacuum leak, with as lean as a lean burn TQ can be it would not take much. Also make sure the metering rod piston and linkage is working quickly and smoothly, it is kind of flimsy and bends fairly easy with some of the gorillas/ mechanics out there.

 

[Dobalovr]

It's been my experience on Mopar engines that you will never have a glass smooth idle. Everyone I've ever driven be it LA or RB has a small idle drop rumble no matter how much tinkering I do with the carb etc. the TQ was the worst for doing it as mentioned if there was any kind of vacuum leak. It wasn't until the 4.7l came out that I truly found that idle rumble was gone. I could still feel it on 5.2/5.9l engines in the 90's drove me nuts because the GM's were glass smooth. If the feeling is like smooth smooth smooth then rough rough then smooth smooth again good luck finding a fix...Ive tried for 25 years. The bogging off idle is the TQ btw. Its a lean burn carb on a non lean burn application. Get a 1406 Eddy and never look back. BTW did I mention I hate TQ's....

The above is only my opinion - I'm sure several members have glass smooth idles on their rides and if they do....they suck

 

[Pclancy]

I'm going to try and find a vaccum leak in the areas mentioned (again) and if no luck, switch to a 1406 Eddy. Summit has new ones for about $335. Used/remans go for about $250. Assume I should buy the new?

 

[Darter6]

Well, take it for what it's worth....The guys that run the Edelbrock trailer that do the shows and NHRA said that the Edelbrock re-man's are very good.New is assembly line built.The re-man's (That are new that a fault was found on the assembly line) are reworked completely by one person and re-boxed by that same person.It was their opinion that you will get a better and well set-up carb with the re-man. Yes ? NO ? Maybe ? Again, take it for what it's worth.For me, I've been happy with buying the re-man's.

 

[70bigblockdodge]

Well, take it for what it's worth....The guys that run the Edelbrock trailer that do the shows and NHRA said that the Edelbrock re-man's are very good.New is assembly line built.The re-man's (That are new that a fault was found on the assembly line) are reworked completely by one person and re-boxed by that same person.It was their opinion that you will get a better and well set-up carb with the re-man. Yes ? NO ? Maybe ? Again, take it for what it's worth.For me, I've been happy with buying the re-man's.

That's a good point. Friend of mine rebuilt a Eddy carb that ran okay but it had sat a while, he is just like that. Found one float shutting off early, or adjusted low, don't know when this happened but it never was a issue the other float was adjusted correctly. So there may be some validity to one person giving a special touch to the carb.

 

[Ripinator]

I have had nothing but problems with my ignition system and carb. No doubt due to some problems that came with the car, mistakes made by my mechanics and/or bad parts that we have put in. Or some evil combination.

About 6 months ago, we removed the lean burn. Everything worked well for a couple of months, but then the ignition began cutting off at random times. We diagnosed that as a faulty orange box (ICM). Put in a ICM made by standard and that stopped producing spark after a couple of weeks. Completely. Now we have put in a chrome ICM made by Mopar. That problem seems to be solved, and the spark is strong. Starting is either instantaneous (just after shutting down) or after just a bit of cranking when cold. I can live with it. The choke works well.

But the engine runs a bit rough at idle, especially when warm. Barely noticeable, but it is there sometimes (and sometimes not when the engine is cold). Feels like a very tiny rumble/misfire. And the engine stumbles and bogs just a little bit when you accelerate very gently from idle or a stopped position (on the flat). Or when you go up a hill, very slowly, from a stop. As you speed up past 10-20 MPH or so, the engine smoothes out and runs perfectly. At highway speeds, she runs like a champ. Smooth.

To fix this, we have rebuilt the TQ (original) carb. Twice. We have replaced the spark plugs. We have installed a new ICM. We have checked and adjusted the distributor. We have readjusted the choke and the vacuum advance. All wires and connections have been checked. Everything has been gone over twice. I'm sure I am missing some stuff.

You guys know by now that I am not a mechanic. But I choose my mechanics carefully, and the guy I have is good. But he seems to be stumped. And like all of us, he isn't perfect. The latest theory was that we replace the spark plug wires.

Any ideas? Thanks as usual!

Peter

What about the thermostat ?!? Did you check the thermostat ?

Seriously. . . I'm in the camp with those who are betting on a vacuum leak. Put a good vacuum gauge on the engine and eliminate or block off all the accessory and other vacuum ports to obtain a baseline, and then start hooking them back up. You may also want to check your coil - coils going bad are insidious beasts that can display all kinds of different symptoms.

 

[Pclancy]

What about the thermostat ?!? Did you check the thermostat ?

Seriously. . . I'm in the camp with those who are betting on a vacuum leak. Put a good vacuum gauge on the engine and eliminate or block off all the accessory and other vacuum ports to obtain a baseline, and then start hooking them back up. You may also want to check your coil - coils going bad are insidious beasts that can display all kinds of different symptoms.

The coil was replaced when we removed the lean burn. My mechanic doubts it's the coil. I also think the problem is a vacuum leak. My mechanic said they put a smoke machine on it and checked carefully. Found nothing. But these vacuum leaks can be hard to find. I will have another mechanic look at vacuum leaks. Then I will replace the spark plug wires. Then I will replace the carb. I swear, I will find the problem.

 

[Pclancy]

Well, take it for what it's worth....The guys that run the Edelbrock trailer that do the shows and NHRA said that the Edelbrock re-man's are very good.New is assembly line built.The re-man's (That are new that a fault was found on the assembly line) are reworked completely by one person and re-boxed by that same person.It was their opinion that you will get a better and well set-up carb with the re-man. Yes ? NO ? Maybe ? Again, take it for what it's worth.For me, I've been happy with buying the re-man's.

My mechanic resists for the moment in switching carbs. Says his experience is that you end up with a different set of problems, even with Eldebrock. But is it true that a TQ with no lean burn attached is always going to be problematic?

 

[Darter6]

The O.E. TQ has no prevision for the vacuum advance hose. Where are you getting the signal from ?

 

[70bigblockdodge]

. But is it true that a TQ with no lean burn attached is always going to be problematic

Always problematic no, can be and if you do not want to really tinker with one the Eddy might be a good way out.

 

[Dobalovr]

The O.E. TQ has no prevision for the vacuum advance hose. Where are you getting the signal from ?

Very good question.....pictures needed.

 

[saforwardlook]

Thermoquads have in the past been very easy to rebuild and generally the results are great. Although I have not had problems in the past, in the last 10 years I have had some I simply am unable to rebuild and have them run OK. I have checked everything that I can on the ones that won't rebuild properly and have concluded that something happens that warps the plastic bowl that I have not been able to find. In the past, I have sworn by TQs as great carburetors but not any more. Time and temperature cycles does something to them that causes just the problems you are seeing. I have even had a couple carburetor experts that are in the business and they couldn't get them to run right, just like yours.

I now lump the TQs in the same group as any early Holley 2 or 4 bbl carburetor. They all seem to warp over time and can not be fixed in any simple way. With the TQs, I find problems in perhaps 2 out of 10 of the ones I have rebuilt over the last 10 years, so I still try to rebuild one that might need it. With the Holleys though, I won't even try to rebuild those since my failure rate is usually 100%. The castings in the 2bbls (specifically the airhorn) is usually warped visibly and short of heating and putting them in a press on them to get them flat again, you will not succeed in getting them to run right. The Holley 4 bbls warp in the bowl and the metering blocks, making them throw aways.

New Holleys seem to run fine and most Edelbrocks do run fine as well. If I were you, I would opt for one of those latter options and strop trying to make the TQ you have work. You could try another TQ and rebuild it and have some chance of success if you are really stuck on authenticity, but otherwise, cut your losses and change to something more reliable.

I have sold some 32 cars in the last 5 years or so, so I have had to deal with this multiple times, so I have some clue as to what I am talking about.

Good luck

 

[Pclancy]

Thermoquads have in the past been very easy to rebuild and generally the results are great. Although I have not had problems in the past, in the last 10 years I have had some I simply am unable to rebuild and have them run OK. I have checked everything that I can on the ones that won't rebuild properly and have concluded that something happens that warps the plastic bowl that I have not been able to find. In the past, I have sworn by TQs as great carburetors but not any more. Time and temperature cycles does something to them that causes just the problems you are seeing. I have even had a couple carburetor experts that are in the business and they couldn't get them to run right, just like yours.

I now lump the TQs in the same group as any early Holley 2 or 4 bbl carburetor. They all seem to warp over time and can not be fixed in any simple way. With the TQs, I find problems in perhaps 2 out of 10 of the ones I have rebuilt over the last 10 years, so I still try to rebuild one that might need it. With the Holleys though, I won't even try to rebuild those since my failure rate is usually 100%. The castings in the 2bbls (specifically the airhorn) is usually warped visibly and short of heating and putting them in a press on them to get them flat again, you will not succeed in getting them to run right. The Holley 4 bbls warp in the bowl and the metering blocks, making them throw aways.

New Holleys seem to run fine and most Edelbrocks do run fine as well. If I were you, I would opt for one of those latter options and strop trying to make the TQ you have work. You could try another TQ and rebuild it and have some chance of success if you are really stuck on authenticity, but otherwise, cut your losses and change to something more reliable.

I have sold some 32 cars in the last 5 years or so, so I have had to deal with this multiple times, so I have some clue as to what I am talking about.

Good luck

Thank you for the very thoughtful reply. I don't care that much about whether the carb is a TQ or not, I just want the engine to run well. So assuming there is no vacuum leak, and will check again, I will switch to an eldebrock 1406 reman, which seems to be the consensus choice. Anything in particular that one should know about how to make this switch? My mechanic is very good, I think, but he does not have the deep formal experience you guys have. Thanks again for all your support.

 

[cantflip]

I'm not disputing any of the other excellent advice in this thread, but I also notice a huge difference in manners when I run non-ethanol vs cheap(not really) readily available gasoline. See if you can find a place that sells it and try a tankful.

 

[MoPar Maniac]

That may be a good idea. Those carbs were lean back then and E10 makes them even leaner. That could explaon the off idle stumble. Its been 35 years since I have been in one of those carbs (I can work on Dellortos in my sleep). Maybe different metering rods or raising them would help.