Manual trans truck dies in drive

[Mac2Night]

I searched for this but couldn't find anything like my issue so here goes.

I have a GREAT running 302 on my '74. I just had the carb professionally rebuilt and it will idle beautifully. Step on the gas and it purrs like a lion, but, put it in 1st gear and it stumbles and dies. I have been able to keep it running by staying in 1st gear and giving it a lot of gas, but shift to 2nd and it dies.

Part of me feels like it leans towards a vacuum leak, but I've checked and can't find anything. Ideas and experience appreciated.

 

[redtail]

check for intake to head leaks. Also check your timing.

Also, check your ignition system, I have had issues like this with weak spark.

 

[Slowleak]

It sure sounds vacuum related. It could be a bad vacuum advance diaphragm causing a vacuum leak or maybe its getting too much vacuum advance assuming it is on ported vacuum. I would plug the vacuum advance line and take it for a spin.

 

[Broncobowsher]

Did it do this before the carb rebuild?

I've had bad ignition that does the same thing. Once you get a load on the engine, cylinder pressure builds, spark is too weak to light off in high cylinder pressure and it feels like the engine shuts down. Get it boarderline and some cylinders are too much while others can barely still fire. Slightly more throttle and it is too much and shuts down but light slightly and it runs perfect. Bad coil or coil wire come to mind, also had a bad rotor once that did weird things.

 

[jckkys]

A basic engine scope can diagnose ignition issues quickly and easily. Even service stations can often do this for little money. It's a better approach than replacing parts. A vacuum leak would cause more problems at idle. So if it idles well without turning the idle mixture screws out more than a couple turns, an idle leak is unlikely. 2100,2150s are designed to idle well with the mixture screws turned out approximately 1 3/4 turns.

 

[Slowleak]

A ported vacuum leak would not cause any problems at idle, only when the throttle was partially open. That is why they are often overlooked.

 

[jckkys]

Leaving the hose off the ported vacuum nipple wouldn't cause any issue with the engine. It would just loose the slight benifit of vacuum advance. All of Ford's performance engines in the '60s had no vacuum advance. I've neglected to reattach the vacuum advance hose with no noticeable change.

 

[broncnaz]

Might want to check your timing as well. sometimes to much or to little can cause driveability issues.

 

[Slowleak]

Ok, well I sure know when my vacuum advance is not connected. It stumbles when I put it into gear and I also notice a big decrease in performance due to the lack of timing advance. Maybe it stumbles because it doesn't have the timing advance it is expecting but the end result is the same.

 

[67RT]

Do u see a steady stream of gas when u look down carb throat and move throttle?

 

[dave67fd]

Maybe a dumb question but have you or did you make any adjustments to the carb after it was rebuilt? Good chance the carb builder may have just left the mixture screws at a reasonable or not so reasonable position. I would confirm that the carb is tuned properly if you havent already. What carb are you running?

 

[DirtDonk]

I have to assume this is all while trying to drive it Mac. Correct?
It almost sounds like you're saying that just shifting into those gears is what kills it, but if that was the case, then it would be the shift lever(s) hitting some wiring and cutting out your ignition.

If it's doing it only when you try to take off from a stop, putting it under more of a load, then I'm with the others that it's either a weak spark or retarded timing.
Could still be a really lean mixture, but like was said, if it was due to any decent kind of a vacuum leak, it would probably have a crappy idle too.

Maybe you re-connected the vacuum advance to full vacuum? If you adjusted the timing and carb this way, it would stumble as you open the throttle. More load means more retarded timing as vacuum drops.
But if you didn't touch your distributor, and put the hose back on correctly, then I don't know what you might be suffering from.

Other than perhaps the lack of a decent squirt of fuel from the accelerator pump, like was already mentioned as well?
You didn't say, but did you do anything else during this carb rebuild? Mess with the ignition or wiring or intake manifold for instance?

Good luck.

Paul

 

[Mac2Night]

Thanks guys for all of the ideas to track down. I moved a few vacuum lines around and only made the idle worse. Gonna try to undo the damage there. One of the biggest changes to the vacuum that worsened the idle was hooking any line to the vacuum advance (none were hooked to it originally). It totally screwed up the idle. Why would that happen?????

Next I'm going to check the spark and replace the coil if things look weak. New rotor cap and button probably needed as well.

Paul, the wire issue is interesting. I noticed some spliced wires in the engine bay harness. I'll look at those and see if any are touching or are near the linkage.

I'll keep y'all posted!

I have to assume this is all while trying to drive it Mac. Correct?
It almost sounds like you're saying that just shifting into those gears is what kills it, but if that was the case, then it would be the shift lever(s) hitting some wiring and cutting out your ignition.

If it's doing it only when you try to take off from a stop, putting it under more of a load, then I'm with the others that it's either a weak spark or retarded timing.
Could still be a really lean mixture, but like was said, if it was due to any decent kind of a vacuum leak, it would probably have a crappy idle too.

Maybe you re-connected the vacuum advance to full vacuum? If you adjusted the timing and carb this way, it would stumble as you open the throttle. More load means more retarded timing as vacuum drops.
But if you didn't touch your distributor, and put the hose back on correctly, then I don't know what you might be suffering from.

Other than perhaps the lack of a decent squirt of fuel from the accelerator pump, like was already mentioned as well?
You didn't say, but did you do anything else during this carb rebuild? Mess with the ignition or wiring or intake manifold for instance?

Good luck.

Paul

 

[Slowleak]

Stick a hose on the vacuum module and suck on it to see if it has a leak. It should hold a vacuum. If you are hooked to full manifold vacuum, like Paul mentioned, a bad vacuum module can cause a vacuum leak at idle or could cause too much advance. It should be hooked to the ported vaccuum on the side of the carb so it gets no vacuum at idle.

I had a bad pickup coil on my 77 once. Any amount of vacuum moved the pickup coil enough to kill the engine.

 

[broncnaz]

Do you have the dual port vacuum advance cannister? They use one ported hookup and one that runs thru a temp switch. If you have a single port cannister it normal for it to be hooked up to ported vacuum which at idle shouldnt have any vacuum at all so your timing shouldnt change at idle.
Changes to timing affect idle quality. adjustments would be needed to get the idle back in check and sometimes to much timing at idle just wont allow for adjustments.
Some pics of your setup may help as well.

 

[Mac2Night]

Do you have the dual port vacuum advance cannister? They use one ported hookup and one that runs thru a temp switch. If you have a single port cannister it normal for it to be hooked up to ported vacuum which at idle shouldnt have any vacuum at all so your timing shouldnt change at idle.
Changes to timing affect idle quality. adjustments would be needed to get the idle back in check and sometimes to much timing at idle just wont allow for adjustments.
Some pics of your setup may help as well.

So Broncnaz, funny you mentioned the "dual port" advance. I have never seen one that I know of, but my distributor has one on this truck (see photo). When I bought the truck, neither port had anything attacked to it and it ran crappy. I now have the vacuum line in the front port like I am familiar with but I have not driven it since I added the vacuum. It seems to idle well and revs up nicely though. What should I do to the top port?

 

[Slowleak]

I'll jump on and tell you what i did with that on my 77. I left the back one open and all was well. Drove it like that for years. It was originally intended to retard timing when the engine was hot and plugged into a heat controlled vacuum port. I later replaced it with a single port when i did a Crane spring conversion.

 

[67RT]

So wait, your subject says "Manual trans truck dies in drive". Is it auto or manual? How does it idle in neutral and/or drive now?
I had an idle issue that was just cleared by pulling idle mixture screws and blowing compressed air thru them. You can use carb cleaner.
Did you try spraying a little brake cleaner or ether (be careful) around carb base and vacuum lines to see if revs pop (vacuum leak)?

 

[Broncobowsher]

So Broncnaz, funny you mentioned the "dual port" advance. I have never seen one that I know of, but my distributor has one on this truck (see photo). When I bought the truck, neither port had anything attacked to it and it ran crappy. I now have the vacuum line in the front port like I am familiar with but I have not driven it since I added the vacuum. It seems to idle well and revs up nicely though. What should I do to the top port?

Port on the left goes to ported vacuum
Port on the right (closest to the cap) leave open so it can breathe and not fight the vacuum side. Don't even cap it. Just leave it open.

That will do a halfway decent way of converting a dual port distributor into a single port. Won't be perfectly tuned, but it will be pretty close.