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Sluggish acceleration when warm

8K views 45 replies 11 participants last post by  76 Powerwagon 
#1 ·
Looking for some knowledge. Got a '76 W-200 318 2 bl that has sluggish acceleration only when engine has warmed to operating temp. When the engine is cold or warming it runs great! It seems to only be an issue at low RPM. If I ease into the gas it will accelerate fine but under load (when I am towing or accelerating "quickly") the engine is choppy with no power??? Carb rebuilt 9 months ago, cap, rotor, wires, plugs replaced 2 years ago. The truck was running good till about a month ago when this popped up. Wondering if the carb needs some type of adjustment?? I can't understand why is runs like nothing is wrong when the engine is cool??

Any suggestions.
 
#2 ·
Im going to say ignition. A lot of times the "warmed up" issue shows itself because the pick up plate needs to be adjusted. I'd also check your timing and check the choke on the carb.
 
#3 ·
Choke.

Sounds like it's running great when choked, until it warms up. Make sure the choke is fully disengaged after warm-up, then check for adequate fuel delivery and/or adjust mixture screws... :)

...or it could be a vacuum leak as well...
 
#4 ·
Thanks for the quick reply's folks!! I Checked the choke after experiencing the sluggishness and it was wide open. My Dodge has the Carter BBD carb, and the Chilton repair manual states that adjusting the the mixing screw does not significantly alter performance......? I will have to do some investigating regarding the potential vacuum leak. The pick-up coil suggestion is intriguing. The drop off in power is most noticed when the truck shifts from 2 to 3. After shifting there is noticeable sluggishness so I would compensate by pressing on the gas, which caused some choppy engine behavior until I press the gas pedal down to the point that the tranny kicks down then rpm's jump up and the sluggish behavior disappears. So it seems to be rpm related. Also, for the entire time I have been driving this truck (~2 years) I have experienced hard starting when the engine is warm which led to the rebuilt carb, which improved performance somewhat but not the hard starting. I am wondering if I should replace the entire distributor? After replacing the pick-up coil and reluctor, it wouldn't be that much more for the whole unit.

I hope my lengthy description makes sense and thanks for sharing any information.
 
#5 ·
Adjust the pick up plate. If that doesn't work, im still going to say its an ignition issue. My truck had similar behavior when I first got it. I threw in a new HEI distributor, coil, plugs, and wires. It ran awesome after that.
 
#6 ·
My two cents would be to look for a vacuum leak, especially since it runs ok when choked. That includes checking the carb mounting bolts, and the vac advance diaphram on the distributor. Also REMOVE and check all the vacuum lines, on a 76 there aren't that many, and they always develop leaks underneath where you cant see them for some reason.
 
#7 ·
usnavyvet, that is a pretty good suggestion. if its running fine with the choke on (pulling air from the leak) and not with the choke open (pulling air from the carb and the leak), the engine would be running lean and not getting enough gas. that goes with what he said about the high rpms. more rpms, more gas, runs better.
 
#8 · (Edited)
checked the hoses (only three) and they all looked good. How would I test for leaks in the vacuum control? I will adjust the pick-up coil next and see what happens. Also, how much circular play should there be in the distributor? I was looking inside the dist. to check on the condition of components and noticed that the rotor would move back and forth ~1/8 of a turn. Is this normal??
 
#9 ·
Best way to check for vacuum leaks is to hook up a vacuum gauge. If I recall correctly you should be get like 12+ on the gauge.
 
#10 · (Edited)
I don't think I completely agree with this. A small leak in a vacuum line or diaphram wont make that much difference on the gauge, but will still affect the carburetor significantly. at least it did on my truck. I think the best way is to unplug and cap at the carb for everything except the vacuum advance, and you can verify the diaphram on the distributor with a vacuum pump. you can also check the dist advance action with the vac pump.

The three hoses to the carb are, I'll guess, the dist vac advance, the pcv valve, and the egr valve. No power brake booster? Anyway you can remove all but the dist adv line and cap the carb inputs. Then see if it runs ok when hot.
 
#12 ·
I was looking forward to trying some of the suggestions but the truck died on me this evening and wouldn't start. I am planning on replacing the entire dist. and hope that resolves the problems. I will post back with an update.

in reply to the most recent post, the three vac lines are the pcv, vac advance assist and choke vac assist. brake booster is hooked direct to the intake manifold and I don't think there is a EGR valve??

This dodge is an old military truck that was passed on to the national forest service in southern Illinois then passed on to IL dept of nat resources then to me. Who knows what type of mods have been done to this truck. But, I like it regardless.
 
#13 ·
vaccum should be near 20 on a vac gauge and steady. you can check the dist can by sucking the hose connected to the can with the cap off and see if the plate moves. usually with a vac leak the motor will idle ok but cough and be powerless when the gas is applied. check your timing while under the hood
 
#15 ·
well my duster idled normally but had no power to move
 
#17 ·
OK, I got the distributor installed and engine runs good. I want to check the timing but I cant find the timing marks and the repair manual doesn't offer any description of the location. Where are the timing marks on the 318 5.2L? I haven't driven it yet to see if the original problem has been fixed. As soon as I check the timing I will give it a test drive.
 
#18 ·
I have timing tape on my harmonic balancer but thats it right there. Solid line on the balancer will line up with the numbers that were cast on the timing chain cover. If you are looking at the crank pulley from the front of the engine, the numbers are on the upper right hand side.
 

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#20 ·
Another question. When I was adjusting the timing I discovered that the timing was WAY off. If I had to estimate I would say it was set at ~20-25 BTDC (The timing marks only go to 10 BTDC - 10 ATDC, like pic above). Repair manual states that it should be between TDC and 2 ATDC. BUT the engine was running very well after replacing the ICM (before I adjusted timing). So I set the timing as stated in the manual and it runs very differently. At idle speeds it's fine but if I accelerate quickly there is a dramatic loss of power and the engine almost stalls. If I accelerate very gradually the engine runs decent?? What does this mean??

Thanks for all the help in the past. This forum is awesome!
 
#23 ·
I only mention it because I have done this before but make sure you were hooked to the #1 wire when you adjusted your timing.

If that checks out then make sure your vac advance is hooked up and working. Also verify that the accelerator pump is working in the carb.

carb was replaced about 5 weeks ago. I assume that it was adjusted to manufacturer specs at the shop. Isn't the engine getting more gas as I push on the accelerator?
Pushing the gas pedal is giving you more fuel but the adjustment screws control the air to fuel ratio, the more you open the needles the richer the truck will run. I believe a rough "get you running" setting is 1.5 turns out from lightly seated. Then slowly turn each needle clockwise until the engine starts to labor and then back them out 1/2 turn. Start with the Left hand screw first, passengers side of the engine. I know this method will work on many carburetors but you may want to check a shop manual, a Haynes manual or Google search may even produce the info.
 
#34 ·
In over 60 years of working on my own and a few years of dealership mechanic I've never seen a carb adjusted just right out of the box.
All require some adjustment.:gr_patrio
 
#24 ·
I hooked up to the front driver side plug, according to the repair manual that is #1 plug. I don't have access to a vac pump, is there a way to test if vac advance is working without one. I will double check the screws. How would I verify that the accel pump is working?

I don't see how the truck was running at all with the timing setting it had??

Thanks for all the help
 
#25 ·
That 4* timing is for the computer controlled stuff. Don't use those numbers. 20-25* is a bit high but more like what you need. Mine ran great at around 12-14*. Try that and see how it runs.
 
#27 ·
Btdc.

It will run. But performance will drop off the farther off it is. If you're running four degrees right now, that could be why its sluggish.
 
#29 ·
make sure that you unplug the vac advance when you do the timing. plug the port that the vac advance hose was on. forgot to mention that earlier
 
#30 ·
now that the weather has gotten really cold new issues are emerging. When the truck is started first thing in morning it will start and run for 1-2 seconds then stall. It will do this a couple of times then it will keep running. After it runs for a few minutes I put it in gear and it stalls. It will this every time until it has warmed up a bit. Then when I come to a complete stop then push on the gas to go again the engine bogs down and stalls sometimes unless I feather the gas till the truck is moving again. All of these symptoms go away when the engine warms.

Any ideas???
 
#31 · (Edited)
Welcome to owning a Dodge. Every Dodge that doesn't have Fuel Injection will do that. Sometimes you can ease it up some in tweaking the carb and fine tuning the timing but not much. My 79' Dodge does the same thing when it gets cold. Doesn't matter what carb size you use. 4 or 2 barrel it will be hard to get going in the mornnings. I have been driving them for a decade and learned to wait for the truck to warm up before going any where. My advice is give yourself a little extra time in the mornings before you leave to get the truck warmed up.
 
#32 ·
i saw another thread with this same issue. everyone suggested "let it warm up".

make sure your choke is working properly. about all i can suggest
 
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