Thermo-Quad help

[Glenn E. Cozad]

Hello to all my fellow Mopar enthusiasts. I need answers from a good carb man, preferably one who knows T-Quads very well. Running a 1979 Ply. Trailduster. 360 all original parts but been rebuilt (by me). I cconsider myself a darn good Mopar mechanic having 40+ years in the field but.... The T-Quad is absolutely great, Good Cold start (one pump touch the key) great cold operation as well as hot, great idle quality, great mileage when you drive it "Nice", great throttle response and performance throughout the R.P.M. range. Truck is an absolute joy overall. Shining example of a Mopar. One thing,After it is warmed-up, you can walk away for a minute or two and you have to crank for a five second count before it "lumbers" back to life, blows gas smoke, clears up and goes back to normal. Got to looking after I shut it down and noticed fuel dripping from the end of the primary throttle shaft. I am thinking, 1. Fuel pressure problem.2. Bad needle and seat. 3. Float level. I rebuilt it using all tests and specs from 1979 Dodge Manual. Did I miss something? Wanted someone to verify my thoughts. Thanx, Glenn.

[440roadrunner]

I think you are in the "right area." This seems to be a pervasive problem nowadays. One other couple of things you might consider

Is the vehicle fuel vent system working OK? Does it have the carbon can system?

Also consider implementing a vapor return system. You may have to run an additional line back from the engine to tank, but if the carbon can system has been removed, you may have a line you can use, IF you vent the system properly

Wix makes a few filters with the vapor return port built in. 33040, 41 are 5/16, 3/8" fuel with the 1/4 return orifice port.

This does a couple of things. Constantly recirculates a tiny amount of fuel which helps keep the fuel moving past the exhaust, returns any vapor bubbles, and VERY quickly allows the pressure to bleed off back to the tank upon shutdown, and if the fuel tries to boil in the line after shutdown, allows a place for pressure to escape, rather than forcing past the needle/ seat

You can either mount the filter vertical as shown, or horizontal so long as the 1/4" port is at top

[John Kunkel]

Fairly common problem with the TQ:

http://www.offroadexchange.com/tquad.htm

[Glenn E. Cozad]

John Kunkel, very informative website you steered me to, thanx. Did all that. Have perfect metering rods and adjustments. I love this carb, I only need to find out why the fuel is presuring after shut off. It is apparent to me that something is not releasing pressure at the needle and seat after engine stop. Do I dare to remove carbon cannister return system? Is there a way to check the fuel return system with "blowing through the line"? By the way, I stated that I got this carb from a junkyard after being fed up with a Holley. This carb came off of a 1978 360 but was the "lean burn" carb. I don't know if that answeres any questions, this carb is absolutely great for the application it runs, just want to resolve the peoblem. I appreciate your input and it is very good to know such a perfectionist who really understands what the word "Troubleshoot" really means. My Mentor, Lloyd Purcell would be very proud of you. Thanx, Glenn.

[John Kunkel]

The only practical way to relieve the pressure on the needle valve after shutdown is with the vapor return filter 440roadrunner mentioned. Of course, this is useless if the return path to the tank isn't open so, yes, blowing through the return line to see if it's open is wise (be sure the fuel cap is removed when testing)

[Mroldfart2u]

Your T-quad is a lean burn carb... Does the vehicle still have the lean burn system? If not thats why it is not venting... You will need a pre-lean burn carb if the lean burn has been deleted.... I have a thread on a lean burn delete on another forum....

[chirorod]

I think you're getting a fuel pressure build-up after shut down. Engine temp does increase after shut down. Perhaps, in this case, underhood temp is increasing more than it should. This may be causing the increased fuel pressure, which forces fuel past the needle and seat. Probable boiling of fuel in the line.
Check cooling system.
Check operating fuel pressure.
Check fuel pressure after shut down. (with hood closed)
Check fuel line routing.
Check heat riser.
Check intake manifold for cross flow heating.
Wrap fuel line with proper insulation.
Another possibility is percolation in the carb bowls. Although the phenolic body is supposed to eliminate this. Again, that would be caused by too high underhood temp or plugged intake manifold heat cross.

[Glenn E. Cozad]

Mroldfart2u, as far as I know my 79 Trlduster was not equiped with the lean burn system. This T-quad has an electric fuel bowl vent that is not hooked up but there is a fuel return line hooked up at the rear of the carb. I ran it yesterday to normal engine temp, took ajumper wire and energized the vent before shutting down, still had the problem. With engine stopped, I connected and disconnected the solenoid several times and could not hear any movement from it. Not sure if it works. Will remove and test. If I can get the vent to work, will it possibly solve the problem and can you tell me how to hook up the solenoid. I am guessing it will have to be on some sort of a timer type of curcuit, energizing the vent after engine shut off. Thanx, Glenn.

[Glenn E. Cozad]

chirorod, I have installed a five row radiator in the 79 Trlduster and never had any temp problems, 195 degree thermostat, engine never gets above 1/4 on the guage, rubber fuel line runs up from pump and is routed across top of intake manifold in original clamps on rocker cover, fuel filter is also on top of intake, removed intake last fall and changed all gaskets, did pay particular attention to crossover ports to make sure they were free of any deposits. Should I reroute fuel line or raise it off the manifold? I believe fuel pressure from pump is ok as I do not have any problems while engine is running. While engine is running, I can look into venturis and see no drip from accelerator pump nozzles. Idle quaility is excellent and all other carb functions are excellent. Please see my post to Mroldfart2u. WE (thanks, team) are slowly but surely narrowing this down. WE will prevail. Thanx, Glenn.

[Glenn E. Cozad]

John Kunkel,I removed fuel return line from carbon canister and tried to blow through it and encountered a lot of resistance (popped my eardrums). Took a small portable air compressor and inserted a nozzle into the hose. Removed fuel cap, started air comp. pressure on guage jumped to 30 psi then went to 0. Listened at tank and could here air moving through vent system. Might have had some kind of blockage but seems to be free-flowing now. Also removed fuel return from cannister to carb and blew through that with 0 resistance and could see that it blew fuel out the top of the carb. Still checking and my thanks to you. Please see posts to Mroldfart2u and chirorod as they have been of great assistance. Thanks, team. Glenn.

[chirorod]

I believe, but don't know for sure, that the carbon canister has a replaceable element. But I don't think a venting problem would cause a boil over. It could cause a fuel flow stoppage and/or collapsed gas tank but not your problem. Did you check the heat riser? It may be stuck closed. Did you check fuel pressure after shut down?

[Glenn E. Cozad]

chirorod, glad that we are on the same page. I have a set of headers so do not have a heat riser. Sorry, should have stated that before. I do not have access to a guage to check the fuel pressure after shut down. It is a Auto zone replacement pump and there have been numerous mentions on this site about fuel pressure. As a matter of fact, sounds pretty stupid, what kind of guage could I use to measure fluid pressure? Never had to perform that particular task. Lots of plumber friends here, would the average plumber have such a guage and would gas ruin it? My thanx again, Glenn.

[Glenn E. Cozad]

440 roadrunner, I am really starting to like the idea of the Wix filter alternative. Concern: I already have the extra "purge" line hooked up to the carb. If I use such a filter, I am assumming (we all know what that means) that the "purge" line will have to be hooked-up to the extra nipple on the filter instead of running to the carbon cannister. 2. Is there a check valve in the fuel pump that would stop this redirection of the fuel as I am once again assuming that the bleed off pressure would be fed directly back to the post pump fuel line. Thanx, Glenn.

[Glenn E. Cozad]

From Glenn, 1. Thank you all. 2. Let's get simple, Mopars like that. There is nothing wrong with anything about this situation except where the fuel goes after I shut it off. Reading the Dodge manual, I checked out the fuel bowl vent solenoid. Manual shows it should be open after shut off. It is. According to what I see, and Knowing that the recurculating lines all the way through the carbon cannister to the tank are open, why is the fuel not going back through the venting system to the cannister and back to the tank like it was designed to?In the open position, the fuel bowl is vented to the vapor cannister. Manual does not show where fuel bowl is vented to diaghram. There has to be an oriface connection between the fuel bowl and the vent diaghram. Could this be plugged? Everything else checks out. Simply, why does the overflow fuel not follow specified and designed routes from fuel bowl to bowl vent solenoid and back through cannister to tank. Everything that was put in place by the designers to take care of this is working as specified. This has to be something very small and stupid. I have the feeling I am going to have one of those "DUHH' moments. Oh, well. Thanx, Glenn.

[chirorod]

Again, that is not a symptom of a venting problem. It sounds like a flooding problem after shut down. Again, I would like to see a fuel pressure check after shut down. You will need a fuel pressure gauge. No, anything a plumber has will not work. The rubber parts in a fuel pressure gauge are made from a rubber that is impervious to gasoline. Fuel pressure gauges are cheap, if you do have to buy one. The gauge goes in series in the line. If you are careful, you can put the gauge in so that you can safely drive the trailduster until it is good and warm. Then shut it down. Let it sit a couple of minutes. Then open the hood and check fuel pressure.
On re-reading your post, I noticed you did salvage this carb. There may be some warpage of the phenolic body, which shows only after shut down. Small problems with TQ's can be hard to deal with. When they work right, they are fantastic, but there are those times. Unfortunately, the bodies are expensive.

[Glenn E. Cozad]

chirorod.I am starting to follow your drift here as I can find no problem with the venting system, Thanx for restating your case. Old hard heads sometimes take a little longer to penetrate. I am aware of the possibility of a flaw in the body. One reason why these carbs did not stay in production for that long. I will find fuel pressure guage somewhere and perform the tests you require. My understanding is that nominal fuel pressure should be between 12 and 15 lbs. Is this correct? If I find a boil over situation due to the increased pressure after shut down, please advise on how to correct as my Dodge manual does not adress that problem. The reason I never had to test fuel pressure with a guage is, disconnect the fuel line at the carb and have someone turn it over. If it pumped solid fuel into your catch container for more than five rotations of the motor, The fuel pump wasn't the problem. Do understand your concern, will test and advise. Thanx for your expertise. Glenn.

[Glenn E. Cozad]

chirorod, Please excuse me, I've been out in the sun running th weed-eater and very hot. Think I just answered my own question. I am sure there is a pressure regulator available to install in the fuel line. Will still test as you directed and get back to you. Would you have any leads for the pressure regulator. (SUmmit racing, etc.) Please excuse the DUHH factor, Hard day. Thanx, Glenn.

[old woolie]

Originally Posted by chirorod

I think you're getting a fuel pressure build-up after shut down. Engine temp does increase after shut down. Perhaps, in this case, underhood temp is increasing more than it should. This may be causing the increased fuel pressure, which forces fuel past the needle and seat. Probable boiling of fuel in the line.
Check cooling system.
Check operating fuel pressure.
Check fuel pressure after shut down. (with hood closed)
Check fuel line routing.
Check heat riser.
Check intake manifold for cross flow heating.
Wrap fuel line with proper insulation.
Another possibility is percolation in the carb bowls. Although the phenolic body is supposed to eliminate this. Again, that would be caused by too high underhood temp or plugged intake manifold heat cross.

This is where I would be looking. This is a very common problem on the old flatheads and could be giving you grief as well, don't know about thermoquads but on the flatheads, using a spacer between the carb and manifold (I made one out of a piece of 3/4 plywood for mine) and lowering the float a bit will make a world of difference.

Rerouting and insulating the fuel line is a good idea too.

[old woolie]

Originally Posted by Glenn E. Cozad

chirorod.I am starting to follow your drift here as I can find no problem with the venting system, Thanx for restating your case. Old hard heads sometimes take a little longer to penetrate. I am aware of the possibility of a flaw in the body. One reason why these carbs did not stay in production for that long. I will find fuel pressure guage somewhere and perform the tests you require. My understanding is that nominal fuel pressure should be between 12 and 15 lbs. Is this correct? If I find a boil over situation due to the increased pressure after shut down, please advise on how to correct as my Dodge manual does not adress that problem. The reason I never had to test fuel pressure with a guage is, disconnect the fuel line at the carb and have someone turn it over. If it pumped solid fuel into your catch container for more than five rotations of the motor, The fuel pump wasn't the problem. Do understand your concern, will test and advise. Thanx for your expertise. Glenn.

With a mechanical pump fuel pressure should be roughly in the 5 to 7 lb range in my experience. 12 to 15 is way too high.

[Glenn E. Cozad]

old woolie, Thank you for your response, Again I will test and advise. Thanx, Glenn.

[chirorod]

Agree, 5-7 psi. Shouldn't need a pressure regulator with a mechanical pump. Old woolie's suggestion that a spacer might help is a good one. But the phenolic body was supposed to take of this. However, it just dawned on my old brain that you are running headers. This might be raising underhood temperature significantly. First, do pressure checks. Since it doesn't do this while running, probably not a pressure problem until shutdown. I would like to know if it is boiling the fuel after shutdown. Let's table the possible solutions until we know exactly what the problem is.

[Mroldfart2u]

I havent posted due to just absorbing and seeing which way the suggestions go. I do agree that you are getting 'heat soak' after shut down. Headers do increase the underhood temps. If you can determine that it IS a percolation problem causing it to 'boil over' there is going to be only a couple of options. 1 Using an insulating carb spacer as was mentioned, or the thick gasket that comes in the kit if it wasnt used. 2 A SMALL lowering of the float can help, but also keep in mind that under heavy right foot use you may get into a lean condition.

Not knowing what other mods you have performed, I could suggest one more if applicable, and that being IF you are running an electric fan have it run for 3-5 minutes after shut off... Just tossing out more "solutions"...

[chirorod]

The electric fan didn't occur to me, somehow. That is an excellent idea.
If it is percolation, another possibility is a slightly cooler thermostat. We had to do that on Datsun (now Nissan) 240Z's running in the desert in California.

[Glenn E. Cozad]

chirorod, Mr oldfart2u, old woolie, thank you all for your help. I have the "thick" carb gasket installed. By thick I mean about 1/4". I can't say that the headers are raising the underhood temps, probably so but I can run the engine to normal op temp with the hood opening in the shade with a breeze, shut it off and watch it start dripping. if there is boil over happening it is due to either the location of the fuel line or manifold heat affecting the carb bowl or fuel line. It is an aftermarket fuel pump which I have not yet tested because I live so far from town. I am running a 5 blade flex fan with a 2" spacer to introduce the fan futher into the cowl. This in combination with the five row radiator has always given me excellent cooling capability even in AZ with temps over 100F. When I shut the motor down, I can count to 5 and have a drip. This seems to me that is a little soon for heat to cause a boil over situation, especially with hood open in the shade. I do not have to drive the vehicle to get these results.As a matter of fact it doesn't even have to come up to full temp. As far as mods, original bore 318, stock 360 cam, dual roller timing set, original oil pump checked to factory specs with "Hemi" spring, 40+ psi on oil when hot. Fully ported 360 heads w/ 360 dual springs, stellite seats, new guides and valves with teflon seals. Original cast iron manifold w/EGR curcuit removed, headers, Mopar "Orange Box" ECU and Champion Truck plugs 7mm wires and electronic ign. I am aware the the plastic body was designed to take care of some of the problems I have been explaining. It seems clear to me that now that the vent problem has been solved, I have one of 2 problems. Fuel pressure too high or I have a slight warpage in the plastic body,Excuse me, Phenolic body.This truck is affectionately refered to as the Beast. It will start, run and take you through places most people would rather get out and walk. It has the ability to obtain excellent driveability, 15MPG with full time 4WD and really scare the beegeebers out of you if you put your foot in it. Shifts full throttle at 5 grand with agreat powerband from 2-5 grand. Truly a great mix. Just drips gas. I have overcome the hot start problem by putting the pedal to the floor letting more air into the fuel sitting on the manifold floor. Don't like to fire it like that as I know the extra fuel isn't doing my rings or oil any good. Thanx, Glenn.

[Glenn E. Cozad]

Gentlemen, based on what I just posted, I went out at 65F hit the gas once and as usual it roared to life. Left at idle for 10 seconds, shut off, and pinched off fuel line. Drip occured at 5 seconds and did not stop. Moved the truck. Let cool did same test. It does this if vehicle is facing uphill, downhill or level. Obviously fuel boil over is not problem. Warpage of phenolic body does not seem to be feesible. If motor performs under normal conditions perfectly, Vent problems overruled, I am thinking...1. bad needle and/or seats 2. float set a litlle to high. Am I overlooking anything else? Thanx, Glenn.

[chirorod]

Since it's leaking at low temps after shutdown, most likely candidate is the float level is too high. But still could be warp or crack in phenolic body. You have to do most of a disassembly to set floats on TQ, so you can also inspect phenolic body at the same time for warpage and cracks. It's also necessary to check for leaks at the bottom of the phenolic body where the primary well is expoxyed.
I usually use the little plastic rule included in the carb kit to measure float level. One I had was not zeroed, so be careful.

[Glenn E. Cozad]

chirorod, Iguess I'm going to have to buy another rebuild kit and go through the TQ again. Don't plan to change anything but float setting but would be wise to use new gaskets.In one of your posts you stated that the phenolic bodies were expensive. I did not know they were available. As I read the service manual, I see nothing about how to check the body for warpage. Logic says to find a FLAT surface and use a feeler guage to check. Any other ideas besides straightedge? Also, this is my sole transportation during the day so if I am going to dissassemble, I may go ahead and try to have another body, as well as gasket set, on hand ahead of time. I read somewhere that you can lay body on flat surface with light sandpaper and lightly sand to correct small warpage. I did not think think this to be a viable remedy, What say you? Can you give me any leads on finding "straight" or new fuel body? I have a good lighted magnifying glass to check for cracks but am concerned that unless body is under normal fuel pump pressure I may not be able to spot that small hairline crack that could be the problem. Standard check for leaks would be to fill dissassembled body on level surface and fill with fuel and observe. Please advise and I thank you for all your help. Thanx, Glenn.

[chirorod]

The interior of the carb is not under pressure, so you can easily check for leaks in bowls by observation. You will see 2 epoxyed caps at the bottom of the body. This is a common site of leakage. If it's leaking there, it's easily fixed with new epoxy. These bodies do crack, and a crack could be a source of leakage. I suspect some of the cracking might be due to improper torquing. Some warp can taken out with sand paper. As you said, check with a straight edge, feeler gauges, and eyeballs. I will try to find the source of new bodies. The most important part of a tq assembly is new well seals.

[Glenn E. Cozad]

chirorod, thank you for the response. The manual is very specific about the well seals.and at last rebuild I did pay particular attention to making sure they were properly located. I am also aware that the epoxy seals are very important. I did use the manual specs for inch lb. torque upon reassembly and this problem did not occur until about 6 months later. Again, Thanx, Glenn.

[chirorod]

You do have to go over the phenolic body with a fine tooth comb.