lack of throttle response under load

need some tuning help here... 85 W350 crew cab, 360 auto.
Truck runs and drives great in normal everyday operation. The problem is when under high load trying to get moving. It just will not move. Engine bogs down and holds idle speed, may quit, but most of the time not. Never see any black smoke when its stumbling. What could cause this?

Truck is mostly stock. I added the 302 casting heads to the stock bottom end, has an older performer intake, and a 9801 aftermarket Thermoquad..I know Thermo bog... Ive used these before with great success on other trucks. Could this be just too lean? ignition issues? Any help or thoughts would be great, Thanks to all.

Sounds like its lean to me. an engine needs fuel to make power, no black smoke means its certainly not rich.

you might block the metering rod tree up & see what that does

With the engine off, make sure the secondaries open fully.

Readjust the air door, make it harder to open.

Does it have a choke and is it fully opening?

Are you running out of fuel?

When the fuel pump on my 273 started to go the first symptoms were similar to what you describe.

i never had much luck with the aftermarket 9800 series TQ's. plus parts are nearly impossible to find. do you have a factory TQ that you can try? if so, swap it out and see what happens

TQ parts are findable

https://buy.walkerproducts.com/carbureto...components.html

http://www.thecarburetorshop.com

http://www.harmsauto.com/

i know you can find TQ parts but 9800 series carbs are completely different from factory TQ's.

OMG http://www.thecarburetorshop.com wants $500 for a TQ strip kit. i have 2k setting in my garage. awesome.

funny story, was at the super chevy show at Maple Grove Raceway a few weeks back and bought a 6322s TQ and an incomplete strip kit for $20.

Thanks for the replies. Will try to answer and comment on all the above.

Have not tried to tie the tree up. But the Thermoquad had an arm under the tree to force the tree up as the throttle is opened. So in this case it is up when this happens.

The secondaries do open with the foot throttle pedal. I did check the air door. I'm not sure I should be in this stage yet... I had my dad watch what was happening in the shop the other day. He said as the throttle was opening he saw the secondaries open. As the vacuum went down the air door slowly opened. As this was happening it just ran worse until it did quit running this time. IT restarted with a tap of the key as always.

These have electric choke. I like this feature on these, works perfectly

Truck has an electric fuel pump and I don't believe its running out of fuel.....No issues on the road pulling, full throttle runs etc.

I'm not sure about being "completely different" from OEM Mopar Thermoquads. Other than the choke they seem to be the same to me...

On the topic of being lean, when I installed this carb a few years ago it was New in the box. Truck would pop out the carb if you needed to hit the gas in a hurry. At the time it was just a daily driver to work and back home. Really ran well on the road. So I found some old Junk core TQ's that my dad had from back in the day. I installed 98's in the front, 137 in the rear and the 2024 rods. (.066 .054 .040) This took care of the popping. Carb came with 95, 125, and 2110 rods. (.069 .061 .040)

I just pick that out from one of the carbs because it's what i had that seemed bigger.... What would be a good base jetting to start with? This seems like it should be in the ballpark.

are the floats set correctly?

This makes me think you may have water in the fuel.. I had a 78 Dodge W250 about 20 years ago that didn't get used much.. Mainly used for bad weather and to get back into a semisecret fishing area.. Me and my boys were going To go fishing so we loaded everything into the truck started it up and let off the clutch started to give it gas and it dies.. Hit the key and it fired right back up again I let the clutch of and give it gas and it dies,,tried it a couple more times with the same results.. I spent the next 4 hours checking everything in the fuel and ignition system multiple times.. Finally decided to pull the carb off and check it out,, it was about half full of water.. Cleaned it out reassembled and went fishing..

The floats were correct when I changed the jetting.

I don't think its water. I have to fill the tank every other week, (20 gal) sometimes every week and as much as twice in the same day. If I had a bad fill it would have been gone by now. The nearest station is 7 miles away and i usually roll in on empty.

Got a cat converter or other exhaust (muffler) that might be plugged up and restricting exhaust flow?

Otherwise I'd go for low fuel flow. Could be a defective fuel line or hose, and an electric pump can still go bad. Check your fuel pressure and the fuel flow to the carb. Gene

I have not checked the exhaust. It looks to be the original system. No converter on this truck. Muffler looks like a replacement. Whats the best way to check this? Take muffler off and run it...

I have not checked fuel pressure either. I will do that.

I think I should clarify that I do drive the truck every day. It runs great and very reliable. I was driving it "to work" and now I am "using it for work" on the farm. I did some testing with it today to help describe what is happening.

I don't have a tach in the truck, but at around 15-20 MPH if i floor it it really goes. No problems at all. As many of you know the TQ is very loud when the secondary's open. I think I could hold it to the floor for miles...

But below that it will stumble before take off. As long as the truck is rolling. Then as speed increases its the same as above.

The big problem is when the truck is stopped. Like being stuck, or trying to pull a heavy trailer up a steep hill or ditch. I'm talking like grunt work. It just will not turn the tires. Put it in low range to get back on the flat ground. No off idle torque in high.

Here is a real life example. Last winter I was driving behind the yard to look at some equipment. We had about 8" of snow on the ground with some hard drifting. Truck was in 4 high. Well I fell into a hole with the front tire. "stuck" I tried to back out but the truck would not move. Would not spin the tires on the frozen ground no matter how hard i tried to rock it. Truck would just sit there and stumble. It never quit running though. So I shifted to 4 low. Now it would rev sky high as I tried to rock it back and forth, tires spinning. But this isn't helping any as now I'm digging a hole with the rear too. So I shift back to high and try some more to ease it out with out spinning and keep my traction on the ground. Truck just keeps stumbling, but I am moving a little back and forth. After a while I finally roll out of this hole and drive away.
What is the problem here?

Ok, Poorboy commented about fuel pressure.... I think I have a problem here. Truck has a vapor return line. I put a tee on after the filter and before the carb. When running I only had about 3 psi. If I pinched the return I could get about 4 psi. Removed filter and used just the tee and had almost 5 psi. I don't think this is enough. The FSM for the truck states the original mechanical pump should put out 4 3/4 to 5 1/4 psi at idle.
This is an electric pump of unknown brand/quality. When turned on it should be running at full speed, volume, Correct? It did pump a quart in 45 sec. The spec for the original pump was 1 quart in less than a min at idle. Thoughts on this anyone...

As for the muffler and exhaust. I checked the flapper on the manifold and it was free to turn. The muffler I don't believe is plugged and It's not the original as it said Quiet flow on it. The rest of the exhaust is original to the truck.

5 psi is plenty & you're set there if you have a good free flowing filter or whatever part of the line was causing the restriction & yes a pump is pumping out its full potential as soon as it is turned on

If the motor runs well in 4 low, you probably do not have an exhaust flow issue. The fuel pump pressure is in the ball park, a bit low, but probably not enough to warrant replacing the pump. Did you replace the filter? A 1 psi drop through a filter might show a partially plugged filter. I often restricted (but not stopped) the fuel flow through the return line. Are all your lines and hoses in good shape?

So, now the question is, is there a carb stumble, or an engine misfire? How long ago was the motor tuned up, with plugs, cap & rotor and wires? Most engine misfires occur under load, but they are often present at other times as well.

It really sounds like maybe your Themoquad needs a new accelerator pump, to me, but I've been told that Thermoquads are simply out of adjustment when they don't work properly. Yours must need an adjustment. Maybe someone can walk you through that process. Gene

I thought it should have more pressure than that. In its current state I had less than 3 psi at idle. The only way I got close to 5 was with no filter and no return. And it took a while to get there at idle.

The fuel lines and hose look good at the front, (not that old) but i cant see whats on top of the tank. Most likely original under the box...

I have thought about the accelerator pump seal could be dried out, and not ethanol E10 compatible. The height and stroke looks to be correct. The shot is instant. Maybe the nozzles should be bigger??

The plugs, cap, rotor, wires are about two years old. I had a plug out the other day. It looks really grey (lean?) Thought it would have been more brown....

I appreciate the help and thoughts on this to all.

if it doesn't stumble as soon as you hit make throttle adjustment it's probably not yr accelerator pump.

sounds like it's probably lean under partial load, primary side before it pulls the secondaries in...
in holley's i would adjust with the power valve, in an edelbrock i guess it'd be the smaller step on the rod that gets lifted by the spring under lower vacuum conditions.

not sure how to tune that on the thermoquad.

i'd be looking at the primary step up rods...mid and power stages, not econ if it's not surging a little at cruise...

http://www.hotrod.com/articles/mopp-0501-tuning-the-carter-thermoquad-carburetor/

Do you still have the carbon canister in place and connected? Have you checked the float bowl and jets for debris?

Do you still have the original Quadrajet you could install for testing purposes?

Robert

I never had the carbon canister or the original Quadrajet. Truck had an old Edelbrock on it when I hauled it home. I have not opened the top lately. When I changed the jets on it a while back it all still looked like new.

[quote=krautrock]if it doesn't stumble as soon as you hit make throttle adjustment it's probably not yr accelerator pump.

sounds like it's probably lean under partial load, primary side before it pulls the secondaries in...

It does stumble when you hit the gas from idle. As stated above its fine at speeds over 20 MPH. Its the low end pull/torque that's the problem.

Again the lean comments keep popping up. Can anyone comment on my current jets and rods? Am I in the ballpark? If it is the mid and power step on the rod, then how much smaller step would make a difference? Or do I use a bigger jet and a bigger economy step?

Does everyone agree that the low fuel pressure is fine? Or should I do something about that?

It makes me think of two things which is a clogged exh system or a bad torque converter. Ron

i had a thermoquad that acted super lazy like the symptoms mentioned by the OP, and it turned out to be a plugged bowl vent. that prevented the fuel from filling the bowls no matter how i set the floats. could that be the same thing occurring here ?

When you say plugged bowl vent, Are you talking about the 3 small pipe's sticking out the top of the carb, Or the one on the side? Some other spot?

Ron, About the torque converter, About a year ago i had an issue where something broke in the converter. It would squeal only during stall. Like idle, in gear, rear tires stopped. OR slow speed brake applied, Or a squeal between shifts. At the time not sure what it was. Asked a bunch of questions here. No real answers...

I figured it had to be the converter. I replaced it, problem solved. BUT, I tried to ask here what I should be using and people said I don't need anything special. When I ordered a new one they asked me If I wanted a "high stall" I didnt think so, so i ended up with a "LOW stall"
I don't know how low this is or how high the high is... It seems very tight. Did I get the right one????

How about a convertor that has the lock up stuck in the on position.
In low range it will scoot through it with the ratio.

Well you could have but it depends on what your combo is. Is your car all stock or is it built up some ? That will make a big difference as well as what gears are in it and the cars weight also just to start. Do you know what kind and stall was in it at all before ? Ron

When I say bad converter what usually happens is a problem in the stator where it has no stall speed anymore. Seen it before and on a stock converter it makes the car feel like a clogged exh as when you hit the gas it has no rpm since no stall and it feels like a dog until the car gets rolling. Then you can hit it from a 40 mph roll and it may feel ok but from a stop it would be a pig.
Now if a lock-up converter would lock-up way early in a low gear it could feel sorta the same but the lock-up would have to be unlocked at idle or the car would stall at an idle. They can fool you to look at other things like the eng for a lack of power. Course a clogged exh system can also feel almost the same when it wont let the eng rev up much. Ron

Depends on the carb. All carbs have internal bowl vents (in the air horn) and many use an external bowl vent. I have never seen a bowl vent keep the carb bowls from filling as the fuel would still go in the bowls and just vent out the venturi and air bleeds as it would still have atmospheric pressure getting in the bowls and it would have enough room in the bowls to still fill up.
What should happen with an external bowl vent is they are open at idle and should close right off idle. Many newer emission carbs use electric external and sometimes internal bowl vents that use a solenoid to open and close them and some are vacum assisted. Some emission carbs will just have the external vent open with the eng off and closed once the eng starts. Ford had a TSB one time on their 4 barrel carb that if the external carb bowl vent did not close right off idle that the car would run rich when on the gas driving down the road. Thats because it should vent on the internal bowl vents when on the gas since the internal bowl vents are in the air horn the pressure will change from the air running through the carb air horn. Basically the carb should have outside atmospheric pressure from the external bowl vent at idle but driving down the road it will have the pressure on top the fuel change from the internal bowl vent in the airhorn as the airflow through the airhorn will cause less pressure on the fuel because the pressure is rushing into the eng in the airhorn. If you run the correct air cleaner for the car it will work right. The Ford TSB said the car will flood and load up going down the road if the external vent does not close as soon as the car comes off idle as it needs to be closed off idle. Thats basically what they call a balanced carb. But when racers run no air cleaner that does not work so well and the carb has to be jetted accordingly. It can also depend on just where the internal vents are positioned on the carb. Ron

just like ron describes above. however on my instance, the carb in question had an electric bowl vent [1978 E-58 cop carb] that wasn't working. i tried everything under the sun to get that to work without success. i changed out that vent and it ran great there after, including better gas mileage ! if your carb has a mechanical vent, i can't think you would have issues. just my experience.

It's a 85 Dodge W350 crew cab truck. Has its original 360 and 727, I added the 9801 aftermarket Thermoquad, I added the 302 casting heads and an older Performer intake. Truck has 4.10 gears and around 33" tires. At the time i listed the numbers on the OEM torque converter here but no one could tell me what i had. Just that it was original to the truck. How many different stall speeds could have been installed originally? Did they have a low and a high stall in 85 for the trucks???

I dont know for sure what came in the 1985 trucks. I would think John Kunkel may know that as he is very familiar with what converters were in many Mopars from the factory. Maybe he will chime in and let you know. I would have to look up that info myself. How did the truck run with the old converter as compared to the new one in it ? Ron

Truck ran fine, but at the time I was just driving it around on the street. No real work being done. Not long after I started pulling with it is when the converter broke. Even currently, truck drives fine. Its when you put a load on it trying to get moving it stumbles or wont move.