Hello, I hope by chance someone here can give me a hand.

My truck (1985 F150 302 holley 80457) all at once started idling hard in park, and killing out if put into gear, I thought the choke might have been sticking so I removed the choke thermostat, and installed by instructions a manual choke.

This did not solve the problem, same idling problem and dying in gear.

"I did notice that if I put it in gear while engine was running, used emergency break, I could pull down on the choke and it would smooth en out as the choke neared closing.

So assuming a vacuum problem I decided to pull the carb and rebuild it.

I bought the kit number "37-119" (which is what this carb calls for) and spent some time rebuilding it. Once finished I reinstalled the carb on the engine and hooked up the vacuum lines and throttle cable, as well as fuel line, then turned it over, the engine started right up, but at an rmp that I would consider extreme, and dangerous.

I adjusted the adjustment screw behind the throttle, turned the mixture screws completely in and then reversed 1 and 1/2 turns on both sides. Started the engine again and same thing, very high rpm.

So I unhooked the throttle cable and left it hanging, started the truck and again it started right up, but this time at a very low rpm. I then lifted the throttle to give it gas and it would cut out and then pick up and rev almost like normal, but as soon as I let off the throttle it would go back to very low poor idle.

A little information.....I did not bother the throttle at all during the rebuild, the throttle arm is now where it was b4 the rebuild.

the carb is a 4 barrel, and my 302 is 2 barrel, I have installed a 4 to 2 barrel base plate which is what the truck had when I bought it and at that time it ran great.

I have also used a flashlight to look down into the secondary barrel and they appear to be completely closed.

At this point I am at a complete loss for idea's. any help would be great.

Thanks

Doug

 

guess i found a problem that even stump the experts, 132 views and zero replies. wow. Thanks anyways, junking the truck tomorrow

 

Just to make sure, it ran fine before. Correct? It has trouble idling, but can you still drive it down the road?

 

This could be a fuel pump problem too. Maybe you are not getting enough fuel pressure (5 to 6 psi). Is the fuel good (not 3 months + old)? Also what is the vacuum reading at idle (or as low an rpm close to idle that the engine will stay running)? Does the vacuum gauge remain steady or bounce around? Are you getting at least 17 " vacuum or better at idle?

so your applying choke (meaning richening the fuel mixture) and it starts to run better. But "nearing closing"? Was the engine warmed up when you were doing this? If the engine was cold then this would be expected. If the engine was hot, then that would signify you are running very lean. Could be low fuel pressure or a vacuum leak (I'll assume not a carb issue since the problem is the same before and after the carb rebuild).

Sounds like you put the throttle cable attachments on the wrong spot on the carb linkage - or something was sticking in your throttle cable. You should be able to attach the throttle cable without any movement of the carb linkage/throttle plates. Did you have the throttle return spring installed (some throttle cables has a built in spring)?


So this shows that the problem is with the linkage or how you attached it to the carb. With the cable detached you should adjust the idle speed with the screw.


Be sure to check all the vacuum lines and look around the engine good (maybe a sparkplug wire came off, etc.). Change the fuel filter, and then pump a little fuel into a container and take a good look at it. Is it clear, does it smell right, any signs of water?

I am thinking your original problem may not be carb related and you jumped the gun a little by rebuilding it. We need to get some stats on the engine first.

 

That's what I was thinking too. When my fuel pump went bad it barely pumped any fuel at idle. It was easy to see with a clear fuel filter between the pump and carb.

 

Thanks for the replies everyone, Since the original posts I have taken the carb back apart and checked for any problems, found none. I did notice that the secondary throttle plates were just barely opened, called the Holley Tech guyy and he said it should be completely closed and then backed off 3/4 of a turn, so I did this and reinstalled the carb with no change at all.


The engine is a 302 2 brl motor, the carb is 4 brl, but has a 1 inch spacer converting to 2 brl.
As far as vacuum readings I have none, I don't have anything to gauge the vacuum with nor anything to gauge the fuel pressure with. So these two things I don't know.

I did notice that once I closed off the secondary throttle plates, the engine runs at about 2k rpms with the throttle cable unhooked, not sure if this is because of the secondary plates being closed.

The engine has not been run to temp since this problem began, With the throttle cable hooked up it runs far to high to allow it to keep running so I always shut it back off as soon as I hear the high rev, and without the cable i have to keep feeding the carb using the throttle to keep it running.

While fooling around I have come to the conclusion that it wont start at all unless I give it gas first (pushing throttle 2 times) and once its running it will die in about 25 seconds unless i hit the throttle again. If I play the throttle and slow pump it, it will keep running but only so long as the throttle is active.

Yes, b4 I rebuilt the carb it would start up at a slightly slugish idle, and when put into gear hesitated and would try to die. after rebuild it dont idle at all on its own.

The fuel in the tank is right now about 5 weeks old, I put gas in it on my way home the last day it ran.

The throttle cable seems a bit to short, I know its not, but the linkage would have to be pulled about 1/2 inch to reach the cable. During the rebuild I didnt remove the linkage or anything that had to do with the throttle outside of the adjustment i did on the secondary after talking to tech support.

I can hook the throttle cable to the linkage using different holes on the linkage, but even at the setting where the throttle is relaxed, the engine will not idle even when I raise the throttle using the screw, it revs for a sec then peters back out.

Fuel looks clear/blueish, as it always does..

Hope this helps you better see my situation

 

With a 2 barrel to 4 barrel adapter there are at least two gaskets involved, one under the carb. and one between adapter and manifold. Any chance one or the other of these gaskets is causing a large air leak?

Any chance that some part of the carb. linkage is hanging up on the adapter?

 

Not that I have been able to find, I sprayed ether around the carb while running but didnt get any change at all.

 

The carb linkage arm is supposed to sit on the idle speed adjustment screw on the side of the carb. If you take the linkage off, it should spring back and sit on this screw, and that's how you adjust your idle. If you are pulling the carb arm off the idle screw to get the linkage hooked up, and it does not come back and rest on the screw, then that is not right.

I know you said it ran ok with this adapter, but they are nothing but trouble. It would not surprise me if you could loosen all the bolts on the bottom and top of the adapter, and move the carb around to make the linkage work better. They are pretty much a rig. I know a intake can be expensive, but I would put that on your priority list to get the proper 4bbl intake.

 

While installing the carb several times I have noticed that a lot of play can be found once bolts are in place but not tightened. This could be part of the problem with the throttle linkage. Thanks for bringing that up.

I am somewhat leaning toward changing the fuel pump out as it is only around 25 bucks or so. So it may be worth trying, wondering if pounding on the tank would help give an idea if the pump is going bad, I know it works with the starter but not sure about the fuel pump.

Completely off subject, but if I am going to change the fuel pump, Ive never been a fan of removing the tank in a truck and I always lean toward raising the bed, wondering if I can install heavy hinges near the tailgate of the bed and making it a kinda light duty dumper.

Would have to raise it by hand and that would be fine, I at some point plan on building a flat bed on it anyways as the wells are rusted out in a bad way.

I am going to try the fuel pump and see if it makes any difference at all, hope it does, if not, does anyone on here have a decent carb they would sale at a cheap price?

Thanks again and I will update tomorrow when I install the new pump and let everyone know how it went

 

The bed construction is not strong enough to support hinges and tilting. You would need to make a frame (like 2x2 square tube) for the bed to rest on and to attach the hinges.They make kits for this, Check out Northern Tools.

 

Unless the truck was EFI you shouldn't have to pull the tank. The $25 pump would be a lift pump that bolts to the block.

 

yes your right, it mounted straight to the motor, but after installed, still the same problem. I loosened the carb and pushed it back, now the linkage lines up as it should.

Started the truck....started up just as always does, still at an rpm that is dangerous.. i now have no other options....

At this point I have spent more than the truck is worth and have been over a month trying to figure this out. any more ideas?

 

Is the linkage arm on the side of the carb resting on the idle set screw?

 

The problem started suddenly... you've done an awful lot of messing with the fuel system with no real change... which tells me the cause of the problem is most likely not in the fuel system.

Sudden changes in behavior are often caused by something electrical having failed.

A 1985 302 would have been computer-controlled... I am assuming you removed all of that and are now using something like a Duraspark (or other) electronic, non-computer-controlled ignition?