Hey All,

So been having a hell of a time getting past this final hump of an issue to finally get my pickup back on the road.

The engine has a DSII dizzy with a new cap and rotor and a 500cfm Holley 2bbl (can't remember exact model, sorry) with manual choke. It starts right up and idles fine, when sitting you can give it gas and it sounds just as it should. When you put it in gear, it'll move about on it's own and feels as it should, that is until you put your foot into it. It'll produce almost no power at all and then die. You can start it back up but it will barely even move before dying again. Eventually once I get it parked again I can get it to idle consistently, but for maybe the first 10 minutes after re-parking it, it'll want to die off (this seems to be intermittent). The engine just completely chokes on itself when you give it gas while in gear/under load.

The carb is almost brand new and was mated to this engine in its previous vehicle. We've pulled the distributor three times now, moved the oil pump rod, rolled the engine back to TDC and put the distributor back in and have gotten the same result each time. My good buddy thinks its timing but I think we have something in the vacuum system not hooked up correctly, there is a loud vacuum hiss coming from the carb/intake; It's on the throttle side at the front-bottom of the carb. If you plug this port at idle it will die off but my friend thinks its for the charcoal box and not important. All of the other likely 'bonehead' stuff is accounted for; the plug wires are running to the right plugs, vacuum advance is hooked up and adj, verified TDC on the compression stoke is 0 degrees on the balancer, etc etc.

I'll be going back out again this weekend to try and get it right. Anybody have any direct experience with something like this and any suggestions? I can get some detailed pictures of the carb and how it's currently been set up tomorrow.

 

Do you know for sure the choke is coming off? If so, the. It sounds like you are running out of fuel. Have you checked the fuel filter? I would put a clear one on between the pump and carb so you can see that you have fuel at all times. And, a fuel problem can easily be due to the rubber fuel lines having gone bad. They can allow air in and cause starvation.

 

Thanks Gary!

I know the choke is coming off but didn't think it could be starving for fuel! I've got a glass filter I can put on there to check that this weekend. Would this be consistent with being able to gas it while parked but not under load?

Man, this place is just the best. Ford Truck Nirvana!

 

Gary is right. Those old fuel lines can corrode over time and leak air or collapse under pressure. I think it's probably collapsing.

Something else that kind of bothers me is, you said when you block off a port on the carb it dies. It should be getting plenty of air in through the Venturis. Have you checked the carb to see what the plates are doing at idle? There should be an idle circuit there that leaves a gap (1/64" I think) for air to get past the plates. If those plates are completely closed then you won't have any air getting in. I could be completely wrong about this but I think this is the case.

Also, it sounds like you are timing the truck to 0*. I know on mine it liked to be at least 10* BTDC (advanced). I have a slightly bigger cam than stock so you might want to try 6* or so.

If you think you have a vacuum leak somewhere you can spray starting fluid around the carb base and intake. If it surges you know you have a vacuum leak.

I think that about covers it. If I'm wrong about something I know someone will chime in.

 

Yes, that is very consistent with it running fine w/o load and not under load. It doesn't take much gas to spin the engine itself, but it takes a lot more when loaded. Depending on what year your truck is, it may well have rubber fuel line from the tank to the metal line on the frame, again at the fuel valve under the cab, and again at the pump. The rubber is almost certain to be rotten and porous by now and any leakage can allow air in and that keeps the fuel pump from being able to move the fuel.

 

what if I am not visibly leaking fuel? Could I be allowing air in without allowing fuel out?

 

Yep. Sure can. Mine did. When the pump tries to pull fuel in it can get air as well and then it can't pump.

 

If you're talking about the line between the pump and the carb, it would be leaking fuel out while the engine is running. The fuel lines at the suction of the pump could be sucking air in.

I had the same question Jeremy had about timing....you mention you've pulled the distributor and reset it...but have you timed it with a timing light?

that may be an issue, but I'm with Gary and Jeremy...I think you got a carb problem. I'm not sure what port your plugging (probaby just a general vacuum port at the base of the carb) but if you plug it and the engine dies....that is screaming at you..."hey, we got a problem here".

Like stated above, that is probably all the air the carb is getting to the idle circuit and when you plug it...it chokes.

Try this...when the engine running at idle....try to block off all the air going into the thoat of the carb. You should be able to choke the engine to the point of it dying. If you close it off, and it keeps running, then that's an issue.

I'm not sure this explains why it won't go off idle though. That seems to me like you're just not getting any fuel. Check the operation of the accelerator pump. with the engine off, look down the throat of the carb and stroke the throttle...you should see a good solid stream of fuel down each throat.
Have you checked the float levels in the carb?

 

Probably wouldn't hurt to stick a vacuum gauge on it and check for leaks either. That'll let you know real quick whether or not there's a vacuum leak.

 

Thanks for all the great suggestions! It gave me a lot to go off of, more money to spend (my girlfriend loves that part ) and Im still having no luck. I just want to put it to pavement already and get it out of my buddy's shop.

I checked through the following:

- Choke is coming off (the vent gap at idle looks just about perfect). I was able to kill all air going to the carb and the truck died out. The only port that is odd is a vacuum port I referenced earlier where the carb meets the manifold and it draws air in. If plugged, it'll die off.

- replaced all rubber fuel line on the truck and verified Im getting a healthy spray of fuel down the carb. checked float levels, accelerator action, etc.

Some of the line was weathered pretty bad, but was in remarkably better shape than I thought it would be overall.

- my friend is still convinced we haven't found the sweet spot on the distributor/timing. We've tried at 10 BTDC and dead on with the same symptoms. Could be we aren't getting the oil pump shaft turned to exactly the right spot before setting the distributor?

Since he decided to fuss with it, it's now worse off than it was before (he pulled the distributor to turn the oil pump and reseat it). Before, I could get it to idle normally and move around under compression. Could gas it at idle with some hesitation; now it just dies when you even look at the throttle. Back to Square 1.

 

I'm not sure what you mean by "Vent gap" when referring to your choke. If it's a manual choke, the choke plate should be completely vertical and not impedding air flow at all.

The vacuum leak you speak of at the base of the carb is still an issue. I don't know for sure if it is the cause of your problem for sure, but it is not normal. The only air that should be going into your engine is through the carb. If you have that big of a leak that when plugged, it causes the engine to die, then you got something seriously wrong with that carb. That must mean that the majority of the air getting to your engine for combustion, is through this leak, and when you plug it...your engine chokes and dies.

So if you engine is depending on this leak to run, then is it also a guess that it may just be the only air it is getting under load.

Be sure that manual choke is WIDE OPEN. Without the engine running, look down the carb and stroke the throttle....do you see both throttle plates opening? With the choke open, you should be able to go to WOT and see right into the manifold.

It is also possilbe that your throttle plates are not adjusted correctly for idle. Not familiar with what particular carb you have but the fuel should be flowing through the idle circuit and just enough air to mix with it. I have heard of some people actually drilling holes in their plates for this....I'm not suggesting you do this. But air as to get in there, and not through a leak

Can you get us a number off that carb?

 

Kevin, I think he may be referring to the choke plate. Do you have an electric Choke OP?

On mine, with electric, there are instructions for setting that gap. Engine off with the choke engaged you bend the choke lever to set the plate open just a hair. Something like 7/32" for me comes to mind.

OP- Does your engine stall with the idle mix screw all the way in, or continue to run with a high pitched whistle?

 

I think he stated he has a manual choke. Just make sure that is wide open

 

I assumed he was talking about the bowl vent, and guessed it is an old style Holley. But, Kevin is right - the port that causes the engine to die is a problem. Don't worry about the timing until you get that sorted.

 

Looking really good guys, thanks for all the help. We timed it back to 10 BTDC and plugged off that open vacuum on the intake and it started right up. Set the mixture and realized it was the exhaust robbing me of all my power. Cut that sucker off (it was completely rotten), everything after the catalytic converters came off and welded a glass-pack muffler on, after making sure the converters weren't plugged up as well. Now it has power galore and sounds great to boot!

It now runs and drives just as it should, better than I expected actually. Ran across a whole new problem though on the last test drive. We can't get the back rubber seal on the oil pan to close all the way and it's losing oil at a pretty good clip. Jacked the engine back up, took the pan down, resealed it with a new gasket kit and RTV black and it still leaks out the back. Maybe a very slightly dented pan? Pain in the ***!

Thanks again for all the advice and information guys! I cant wait to get it finished and post up some pics once I have it cleaned up. Here's my engine bay before we plugged off that vacuum port on the intake.