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.