Harms Rebuilt '71 Thermoquad - Wondering Idle, Stalls when Put in Gear

-
F

Frank Cole

Active Member
Joined
Jun 20, 2019
Messages
35
Reaction score
10
Location
New Jersey
Ok. At my witts end. I have a Harms rebuilt (2018) 1971 Thermoturd that was never run. Bone stock 1971 340 except has electronic ignition. Installed carb with new base gaskets (twice) and I'm only getting about 9-10 inHg vacuum. All external manifold and carb vacuum ports have been plugged. Timing currently set at 16 degrees BTC with total 35 degrees all in by 3000rpm. Good throttle response on road but stalls or nearly stalls when I stop the car at a light. Carb responds to air-bleed adjustments (stalls when turned all the way in) and I have them out about 4 turns for best vacuum and rpms. Idle wonders from 880 to 980rpms. I've tried various timing combos and adjustments, air bleed adjustments, etc. without success. Car stalls or runs about 350rpms when I put it in gear. I sprayed WD-40 all over the intake runners but no help. Thing is, I had a new Edelbrock 750 cfm with 1inch square bore to Thermoquad bore adapter and old base gaskets and I didn't have this problem immediately before installing the rebuilt thermoturd. Motor doesn't run hot and plugs look good. The rpms pick up slightly when I cover the air horn with my hand. Replaced coil - no help. Plugs, cap, wires, rotor all replaced within the last 500 miles. Anyone have any ideas what to try next?
 
Seems like rebuild isnt up to snuff. It likely needs to come apart and checked over. First clue is when you swapped good running carb for the thermoquad.
 
Have you tried adjusting the metering rod tower? Sounds like the primary side needs leaning out.
 
Frank Cole said:
I have not. Where is the adjustment and which way to adjust to lean out?
Click to expand...
Right in the center of the metering rod tower. There's a small flat head screw. On the 72 and later carburetors, clockwise raises the tower (leans) and counter clockwise lowers (richens). I have very little experience with the 71 carburetors, but I think they are the same.
 
Tooljunkie said:
Seems like rebuild isnt up to snuff. It likely needs to come apart and checked over. First clue is when you swapped good running carb for the thermoquad.
Click to expand...
The Eddy carb ran better and didn't stall when I put it in gear but the idle still wondered but not nearly as bad.
 
RustyRatRod said:
Right in the center of the metering rod tower. There's a small flat head screw. On the 72 and later carburetors, clockwise raises the tower (leans) and counter clockwise lowers (richens). I have very little experience with the 71 carburetors, but I think they are the same.
Click to expand...
Thanks I'll try that. The meter rods (tower) drift up and down slightly as the idle wonders up and down.
 
1971 was a one year only model of the TQ. It should still work. Correct gaskets used?
Float level? Do the metering rods stay down at idle [ they should ]?
Four turns out on the mixture screws seems a lot. Maybe one idle jet is blocked.
 
Bewy said:
1971 was a one year only model of the TQ. It should still work. Correct gaskets used?
Float level? Do the metering rods stay down at idle [ they should ]?
Four turns out on the mixture screws seems a lot. Maybe one idle jet is blocked.
Click to expand...

Correct gaskets, not quadrojet gaskets. I didn't check float level. New rebuilt so I just installed it as-is. Metering rods move up and down slightly at idle. Regarding mixture screws, engine stalls out when either screw is turned all the way in so i don't think idle jet is blocked. All good points though.
 
How many miles on engine. Cam walking from loose timing chain, vacuums leaks, base gasket leaking. Lots of stuff could be going on but carb may have gotten a small bit of junk or maybe those epoxied pots at the bottom broke loose. Hard to fix over internet. Lots of questions.
 
at idle the rods have to stay down.
in Neutral the rods should stay down with gently increasing rpm, to over 2000rpm or more, so long as the manifold vacuum continues to increase.
If the needles pop up when you put it into gear, the engine will flood and stall.

Here's a trick; Just take the springs out. At idle and in neutral, this should cure both problems. If it does, then you know to install weaker springs.
 
Something not right here, getting drip fed info....
Now you say the Edel wandered at idle.
And the engine is 'bone' stock?
Stock engines will have 16-19" of vac at idle, not 10-11".
A stock engine should idle at 5-600 rpm, not 900....
Since this problem has occurred with TWO carbs, & from what you have done so far, I suspect the engine has had a larger cam fitted. That would also explain the 16* init timing [ which is good, not a problem ].
The high idle rpm could be activating the centri curve in the dist, especially if the springs are stretched. This could explain the varying rpm & needs to be fixed first. Check by monitoring the ign timing with a timing light.
One last thing to try: initial timing is at 16*. Loosen dist, engine idling, turn dist slowly CCW; keep going until rpm stops increasing & THEN see what the timing is.
I suggest you try the above & report back.
 
There are little black approximately 1/2 inch o-rings under the top cover ,Down in the base of the plastic body. Very hard to see because these are also black. Many who rebuild these carbs forget these. Just something to check. These o-rings leaking will cause your problem. Someone showed me this years ago.
 
Oldmanmopar said:
There are little black approximately 1/2 inch o-rings under the top cover ,Down in the base of the plastic body. Very hard to see because these are also black. Many who rebuild these carbs forget these. Just something to check. These o-rings leaking will cause your problem. Someone showed me this years ago.
Click to expand...

Not on a 71 TQ
 
Your 340 is not stock, or you have a vacuum leak, something is off in the carb, or your tune is way off. Those carbs are great. Had a 71 340 4 speed Duster and it was fast, idled fine, dual points distributor and all.
 
I'm thinking the high idle is starting to pull advance . Check your timing at idle. Should be rock steady. If mark jumps around make sure your advance springs aren't stretched or too weak .
And putting your hand over carb and idle increases is an indication of a vacuum leak. Could be a leak on the bottom of the intake runner to head port. WD won't find that.
 
I'm just wondering what it is wondering about? Sorry, that was not nice.
Good luck, looks like you have some great advice here.
 
abodyjoe said:
for what he charges it should install itself and run perfect.
Click to expand...
$500 according to the receipt but it wasn't me who had it done. Carb came in the shipping box with the car. Pretty though.

carb.jpg
 
66Valiant528 said:
I'm thinking the high idle is starting to pull advance . Check your timing at idle. Should be rock steady. If mark jumps around make sure your advance springs aren't stretched or too weak .
And putting your hand over carb and idle increases is an indication of a vacuum leak. Could be a leak on the bottom of the intake runner to head port. WD won't find that.
Click to expand...
Timing was steady at idle, maybe plus or minus 1/2 degree. I had a vacuum gauge hooked up to both manifold pressure and the carb advance port time. Manifold was 9-10 and fluctuating, vacuum port pressure was 0-3 degrees depending how I was playing with idle screw but even at 3 degrees, timing was steady and did not move. Advance started pulling in when I got to about 5 inHG at vacuum port.
 
You must log in or register to reply here.
-

Back
Top