Moparts
Carburetor problems with heat soak
Posted By: acesneights
Carburetor problems with heat soak - 06/15/13 04:12 AM
My 440 BB in my Travco had a Thermoquad on it. The acclerator pump was shot and the age of the carb was unknown although it had a Holley rebuild sticker on it. I decided easier to just throw a new edelbrock performer on it. Well since I did the fuel perculates really bad giving an awful gas smell about 15 mins after shutdown. Also makes it diffcult to start. After reading up on this being a common issue with the Edelbrock, I returned it and bought a reman Holley Spreadbore direct TQ replacement. It runs really good but still having same issue. I have an insulator gasket under it. Any ideas ? I was told nothing I can do and that the reason the TQ didnt do it was the plastic bowls but that they are dangerous and can crack and spray gas all over.
I was thinking about putting it back on but the Holley really runs sweet. it gets the gas stink also but will start when hot.
I hav the factory cast iron spreadbore intake ? Would an aluminum intake help ?
I really didn't want to dump a ton of money into this motor as It has 94k miles on it and I plan on replacing it with a Cummins Diesel.
Posted By: GO_Fish
Re: Carburetor problems with heat soak - 06/15/13 06:08 AM
1/2" phenolic or wood spacer between the manifold and carb should help greatly if you have room.
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/15/13 06:11 AM
Electric fuel pump with a return regulator or self learning EFI.
Posted By: RapidRobert
Re: Carburetor problems with heat soak - 06/15/13 06:37 AM
blocked heat riser. non ethanol gas. wood spacer (laminated baltic birch?)
Posted By: goldmember
Re: Carburetor problems with heat soak - 06/15/13 06:48 AM
Insulate any metal fuel lines as well as keeping them away from heat sources,an electric fuel pump with return,heat shield between carb and manifold would be the starting point.
Posted By: Challenger 1
Re: Carburetor problems with heat soak - 06/15/13 12:10 PM
Yes a aluminum intake with either the heat risers blocked or not even there like my victor 340 intake with no heat risers and a air gap underneath. It does great in hot weather and I run a edlebrock carb.
Get rid of the original heavy intake with heat risers.
Posted By: 62maxwgn
Re: Carburetor problems with heat soak - 06/15/13 01:36 PM
Go back to the T/Q and save your $$$$,accelerator pumps are cheap!!
Posted By: acesneights
Re: Carburetor problems with heat soak - 06/15/13 02:12 PM
IS non ethanol gas available ?
I have never seen it around here. It all has 10% in it. I bought some treatment for ethanol from Stabil. Figured it would be good for the generator too as that runs off same fuel tank.
I can say where the choek mounted it get's very hot. I had left the ground wire from the TQ choke laying there and it melted. I think it's the heat coming off the manifold more than the fuel lines. I think it's boiling the fuel in the bowl after shutdown. I guess an aluminum intake is probably the best way to go. A good spreadbore pheolic spacer was like 80$. That is alomst halfway to a new intake. I wish I could find a used one.
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/15/13 11:44 PM
Quote:
IS non ethanol gas available ?
I have never seen it around here. It all has 10% in it. I bought some treatment for ethanol from Stabil. Figured it would be good for the generator too as that runs off same fuel tank.
I can say where the choek mounted it get's very hot. I had left the ground wire from the TQ choke laying there and it melted. I think it's the heat coming off the manifold more than the fuel lines. I think it's boiling the fuel in the bowl after shutdown. I guess an aluminum intake is probably the best way to go. A good spreadbore pheolic spacer was like 80$. That is alomst halfway to a new intake. I wish I could find a used one.
Don't even think about the non ethanol gas use, though it would be nice ethanol is in the fuel pretty much everywhere , finding non ethanol is not easy , or cheap.
Also an Alum intake with the heat riser blocked is not the answer either, there are many still combating the issue wit han alum intake and the heat riser blocked.
You need to sheild the carb from as much heat as possible and get cool air flowing around it to keep it warm.
The electric fuel pump isn't the total answer but it will put fuel in the carb faster than the mechanical on the side of the engine and it will take care of the restart by filling the carb faster.
Posted By: acesneights
Re: Carburetor problems with heat soak - 06/17/13 04:46 PM
I toyed with the idea of putting a marine bilge blower in and piping it to the intake area. The problem is that this is a motorhome so it also gets zero airflow.I did it yesterday and even once I got it started it was running funny like idling poor until I drove it for abit.
Posted By: Challenger 1
Re: Carburetor problems with heat soak - 06/17/13 04:52 PM
Quote:
Quote:
IS non ethanol gas available ?
I have never seen it around here. It all has 10% in it. I bought some treatment for ethanol from Stabil. Figured it would be good for the generator too as that runs off same fuel tank.
I can say where the choek mounted it get's very hot. I had left the ground wire from the TQ choke laying there and it melted. I think it's the heat coming off the manifold more than the fuel lines. I think it's boiling the fuel in the bowl after shutdown. I guess an aluminum intake is probably the best way to go. A good spreadbore pheolic spacer was like 80$. That is alomst halfway to a new intake. I wish I could find a used one.
Don't even think about the non ethanol gas use, though it would be nice ethanol is in the fuel pretty much everywhere , finding non ethanol is not easy , or cheap.
Also an Alum intake with the heat riser blocked is not the answer either, there are many still combating the issue wit han alum intake and the heat riser blocked.
You need to sheild the carb from as much heat as possible and get cool air flowing around it to keep it warm.
The electric fuel pump isn't the total answer but it will put fuel in the carb faster than the mechanical on the side of the engine and it will take care of the restart by filling the carb faster.
IMO, if this is the case, then I would predict that they are lean, real lean under power making too much heat. Did the OP richen it up and see if it helped?
Ethanol fuel needs to be run richer to keep the a/f ratio the same as non ethanol fuel. 
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/17/13 05:29 PM
Quote:
Quote:
Quote:
IS non ethanol gas available ?
I have never seen it around here. It all has 10% in it. I bought some treatment for ethanol from Stabil. Figured it would be good for the generator too as that runs off same fuel tank.
I can say where the choek mounted it get's very hot. I had left the ground wire from the TQ choke laying there and it melted. I think it's the heat coming off the manifold more than the fuel lines. I think it's boiling the fuel in the bowl after shutdown. I guess an aluminum intake is probably the best way to go. A good spreadbore pheolic spacer was like 80$. That is alomst halfway to a new intake. I wish I could find a used one.
Don't even think about the non ethanol gas use, though it would be nice ethanol is in the fuel pretty much everywhere , finding non ethanol is not easy , or cheap.
Also an Alum intake with the heat riser blocked is not the answer either, there are many still combating the issue with an alum intake and the heat riser blocked.
You need to sheild the carb from as much heat as possible and get cool air flowing around it to keep it warm.
The electric fuel pump isn't the total answer but it will put fuel in the carb faster than the mechanical on the side of the engine and it will take care of the restart by filling the carb faster.
IMO, if this is the case, then I would predict that they are lean, real lean under power making too much heat. Did the OP richen it up and see if it helped?
Ethanol fuel needs to be run richer to keep the a/f ratio the same as non ethanol fuel.
One car in particular was run on a chassis dyno and the carb adjusted so I don't think it being lean is the issue , but you never know.
The OP , I don't know what he did.
Posted By: dogdays
Re: Carburetor problems with heat soak - 06/17/13 05:32 PM
First of all let's put something to rest.
"I was told nothing I can do and that the reason the TQ didnt do it was the plastic bowls but that they are dangerous and can crack and spray gas all over."
The three most dangerous words on this board are either "I was told" or "I have heard".
Now on to the phenolic bowls. They have been known to warp, but the idea that they should be avoided because they'll crack and spray fuel everywhere is just rubbish.
Now on to ethanol in the gas. Thank you to JohnRR for pointing out that it's almost impossible to buy gas without ethanol in it. It's a federal requirement for areas that cover about 90% of the US population. Also, fuel manufacturers change the evaporation rate "Reid vapor pressure" for summer or winter. So, for example, if your motor home has a load of winter gas in it, it will evaporate faster in the summer and give you more problems. On the other hand, a load of summer gas can mean a very hard-starting car in the winter. Fuel has to be in vapor form in order to light off.
So maybe the easiest thing to do would be to rebuild the Thermoquazd one more time.
Your idea of a bilge blower is NOT a bad idea.
An Edelbrock wood spacer would help. Heck, two would help more, and look at heat shields to block off radiant heat between engine and carb.
Blocking off the heat riser under your stock manifold would help.
As far as heat conductivity goes, aluminum conducts best. Then the Holley zinc body, then cast iron, then insulators like wood or plastic. So replacing your cast iron manifold with an aluminum one would increase the heat conducted to your carb.
Check out the new Barry Grant Street Demon with the "space age plastic" bowl. According to a race shop board member, this carb is tremendous. Maybe that's an option, too .
R.
Posted By: Challenger 1
Re: Carburetor problems with heat soak - 06/17/13 05:38 PM
The only reason I suggested aluminum is because one can be had with no heat risers.
Lean is mean and makes heat, do you really need that on the street? Sure on a dyno your gonna go lean to make the most power.
A dyno does not have all the answers, many guys can tell you that after tuning on dyno.
Posted By: Paul_Fancsali
Re: Carburetor problems with heat soak - 06/17/13 07:59 PM
In 1987-88 Dodge installed electric fuel pumps in the B 350 vans that were stalling due to heat or no start after sitting They also used a higher output mech pump on the 360s The carb you are using is a emission carb designed for the 360 of the 80s. You can consider a Chrysler base Rochester carb they have thicker heat gasket that will isolate the carb somewhat. Despite what you may hear the q jet is just as good if not better the the TQ and I have used and have both carbs. The gas mileage on the Q is better on average. By the way if the carb you have is the emission version Holley the sec will never open all the way it comes with a super heavy black spring, in vac pot standard. But for now keep what you have and insulate the lines and get a 1 inch spacer{not metal or aluminum and put a low output electric pump on the van
Posted By: RSNOMO
Re: Carburetor problems with heat soak - 06/17/13 08:08 PM
I run schitznit fuel spiked with 110...
An aluminum M-1 with a thick base-gasket under a 750 Edelbrock AFB...
It's supplied by a 440 HP mechanical fuel-pump...
No vapor separator-a later filter with return to the vapor canister...
The correct non-vented cap...
No problems...
Posted By: acesneights
Re: Carburetor problems with heat soak - 06/17/13 08:14 PM
I think I should clarify, the issue is not while I am driving it. it is fine. It's when I shut it off, the residual heat form the motor appears to be boiling the gas out of the carb. That was why I thought maybe Alum intake would be better becuase I know it conducts heat better but it also cools down quicker. I have room for about 1 inch of spacer before the carb hits the engine cover.
I could probably fix the TQ myself. It just needs an accel pump.
I am not sure which Holley. All I know is it looks like a speadbore version of a 600 vac sec and the guy told me it was a specific aftermarket replacement for the TQ that is no longer made. I don't think it's an emmisions carb but I will take some pics and post them.
This all started after I took the TQ off. The TQ had a major stumble/flat spot. The TQ had a Holley Rebuild sticker on it which I "was told" is a good version of it.
I have worked on carb stuff over the years but I will confess I am more of a diesel guy.
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/17/13 08:24 PM
Quote:
I think I should clarify, the issue is not while I am driving it. it is fine.
If this is your only gripe then put an electric fuel pump on it and be done. No matter how you try to insulate the carb the fuel is going to evaporate long before the engine compartment is cool enough to not cause an issue.
Posted By: RSNOMO
Re: Carburetor problems with heat soak - 06/17/13 08:25 PM
From my experience with my combo over the last 20 years...
Unless yer gonna ice-down the carb, the percolation issue is reduced with the addition of 'real' fuel...
Excessive heat is the enemy...
I have a 6-quart pan, in addition to a deep trans pan w/cooler, and a 3-core rad...
When I shut it down, it's at 180...
Not 195, not 210...
An electric fuel-pump is not a necessity, and not necessary...
It's your call...
I'm only offering what's worked for me...
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/17/13 08:53 PM
I run a stock carter AVS on my 69 383 dart , I haven't driven the car in 7yrs but I never had a problem with gas percolating ...
Posted By: dOc !
Re: Carburetor problems with heat soak - 06/17/13 09:09 PM
Quote:
This all started after I took the TQ off. The TQ had a major stumble/flat spot.
THERE you go !
The flat spot was a bad accel-pump.
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/17/13 09:14 PM
Posted By: dOc !
Re: Carburetor problems with heat soak - 06/17/13 09:38 PM
Quote:
Quote:
Quote:
This all started after I took the TQ off. The TQ had a major stumble/flat spot.
THERE you go !
The flat spot was a bad accel-pump.
Huh ?.....
If he fixes the accel-pump in the TQ carb and puts the TQ back on .... his present-PROB is solved 
Posted By: acesneights
Re: Carburetor problems with heat soak - 06/25/13 02:06 PM
think I may have t do that. I drove the RV in some pretty high temps.
down the highway no problem. If I stopped for a few mins like at a rest area it idled ok but themn when I went to take off it was stumbling and backfiring through the carb under acceleration for a good 10 mins then cleared up. I'm thinking this Holley is just not the right carb . Where is a good place to get a kit for the TQ and how much different is it than anAFB to rebuild ? I have successfully done AFBs. Won't touch Holleys. Just don't know them well enough.
Posted By: dOc !
Re: Carburetor problems with heat soak - 06/25/13 02:20 PM
Quote:
think I may have t do that. I drove the RV in some pretty high temps.
down the highway no problem. If I stopped for a few mins like at a rest area it idled ok but themn when I went to take off it was stumbling and backfiring through the carb under acceleration for a good 10 mins then cleared up. I'm thinking this Holley is just not the right carb . Where is a good place to get a kit for the TQ and how much different is it than anAFB to rebuild ? I have successfully done AFBs. Won't touch Holleys. Just don't know them well enough.
NAPA has kits IIRC ....
Posted By: RapidRobert
Re: Carburetor problems with heat soak - 06/25/13 02:35 PM
there's 2 little O rings that are located deep in the wells in the phenolic bowl. Be sure & take them out when you clean the bowl & I'm sure there's new ones in the kit. I always make a note of current settings (float/pump etc) as I tear one (any type) down just for a good reference point since settings dont change just cuz a carb needs cleaning/rebuilt & if a setting doesn't match up to what's on the white sheet then I have to checkout where the mistake is. I lube all screws going into the body especially on carbs where I will be opening them up frequently for rod/jet changes etc
Posted By: dOc !
Re: Carburetor problems with heat soak - 06/25/13 02:39 PM
RR adds some good points about the Orings and the floats BUTTT I would also like to add about the floats ....GET some BRASS floats .....NAPA has those too.
Posted By: acesneights
Re: Carburetor problems with heat soak - 06/26/13 03:57 AM
I took some shots on it after it was good an hot. Bowls on the Holley were about 145f. The Intake Manifold was about 220 except where the exhaust pases through. It was a little over 300f.
Also if I decide to get an electric lift pump what GPH and PSI do I want ?
Not looking to break the bank ...
Posted By: JohnRR
Re: Carburetor problems with heat soak - 06/26/13 07:39 AM
You want a 6psi pump , GPH isn't your concern.
Posted By: acesneights
Re: Carburetor problems with heat soak - 07/30/13 12:50 AM
Well it's been awhile but the problem for the most part is solved. I used a Felpro intake set that had the heat riser ports blocked and used a 2191 Edelbrock performer manifold I got off the bay. It runs much much better and starts fine hot with no weird idling or backfiring.
I do now have another issue but I will start a separate thread on that.
The Edelbrock intake bolted on with minor issues. The biggest being getting the bolts started. They were very tight and difficult. I think it was because the new intake/valley gasket was two paper gaskets sandwiching the metal one and it spaced the manifold up a tiny bit.
I got them all started but it was not easy. I also had to adjust the linkages as the new manifold sat a little higher and redrill the bracket for the cruise control so it sat higher. The fuel lines do feel very hot as well so I will be re routing them and insulating.
