I rebuilt the stock 2bbl motorcraft carb for the 302 in my '82 F150. Since then, I have had a couple of problems. 1) it is idling very high (around 1500rpm) and I cannot back out the idle screw anymore. I tried adjusting the timing also with no luck. 2) it is not always easy to start, even if it is warm and was just turned off a few minutes ago. It doesn't fire right up like I think it should. It seems to like lots of gas to start. 3) if it sits for a few days, I think all the gas drains out of the carb- you have to crank it for 45 seconds before it fires up. Maybe I have mutiple issues here....

Any help appreciated! Thanks,

Phil

 

I always set the timing 1st then adjust the carb. The timing has an effect on the vacuum signal seen by the carb. When you say you can't back out the screw anymore, are you referring to the idle speed screw or idle mixture screws? If the idle speed screw is backed all the way out, make sure it's not resting on the fat part of the fast idle cam. Also make sure there is'nt anything that is blocking the linkage from closing or causing it to bind. Did you remove the throttle blades when you rebuilt the carb? If they were removed, they could be slightly off center, causing them to bind against the throttle bores and not to close all the way. If you have air conditioning, there should be a fast idle solenoid to raise the rpm when the a/c is on so the engine won't stall. This may need to be readjusted or make sure it's not froze in the on position. Make sure there is'nt a vacuum leak that may have been "tuned out" while you were adjusting the carb. Wiggle the throttle shaft front to rear, if there's a lot of play between the throttle shaft and throttle body, that might be the source of the vacuum leak. If none of this does the trick, I'd take it back off and recheck that every adjustment is to spec according tho the instruction sheet in the kit.

 

Thanks for all the things to try. Yes, I was talking about the idle speed screw. I can back it out more but its' no longer in contact with the throttle. I will check the things you suggested today. Also, the rebuild kit I used had the wrong fuel pump so I reused the original. I will get a new one today.

Phil

 

Well I had time to work on this and I think I found the problem: The choke mechanism is sticking open a little. I can push it with my finger and it frees up and the idle drops. Next I need to figure out where it's binding. I also replaced the accellerator pump but I don't think that was causing any of these problems. Also I adjusted the float up- hopefully this will help keep the gas in the bowl if it sits for a while.

Thanks,
Phil

 

Okay, more info on my high idle. I'll try to explain this but pardon my ignorance... The choke mechanism is sticking. The choke sets correctly but doesn't kick down unless I push down on the choke mechanism manually. Then, it kicks down and I have a nice low idle, at least untill the throttle is advanced again, then it kicks back up to a high idle.

I checked a few things: The electric choke is getting power- 9.5 volts when the engine is running. I can't find anything obviously wrong with the mechanism. The choke plate mechanism doesn't seem to be sticking, but the mechanism that also opens the throttle a little bit is sticking. There is an adjustment screw underneath the choke (fast idle adjustment?) This is what is not kicking down if I tap the gas or whatever, even if it's warm. Where this adjustment screw hits a little cam, there seems to be too much friction- if I hold this open the mechanism kicks down.

I hope this makes sense. I can post dig. pics if necessary to show what I am talking about.
Thanks! Phil

 

Some pics would be good. With out being there, it's kinda hard to interpret what's taking place. How does it run once it's warmed up? With what you're saying, I'm thinking, the choke coil may need to be adjusted / leaned out. Loosen the 3 screws on the choke coil cover and rotate it a few degrees to relieve some coil spring tension. If this does'nt help, remove the choke coil and cover and check to see if the coil spring is installed properly on the lever inside the housing. There's a little loop on the spring that goes over the lever. With the choke coil removed, check to see if the fast idle cam / linkage operates freely. If so, you know it was too much coil tension. If it still sticks, it's definitly something bent, twisted or too tight in the linkage itself.

 

Thanks again for all the info. I think I have resolved the original problem. I observed that the high-idle kick down worked properly if I held the choke open manually, so I figured the choke thermostat wasn't working properly, even though it looked okay. So, I installed a manual choke. (This mechanism was obstructed by my air filter so I bought an aftermarket air cleaner and breather cap. It's always something...). Anyway, with the manual choke it works okay and the fast idle releases now.

('m learning as I go...)I realized that the choke hot air tube from the exhaust manifold was not hooked up. Since the original tube was damaged I made another one from a brake line and now have it hooked up. So now I am thinking of putting the electric choke back on and seeing how it works. Thoughts?

Finally, I mentioned earler that it's hard to start if it sits for a few days, like the gas is leaking out of the bowl. I checked the float and it seemed low to me, so I bent the float up some. Now, it's harder to start: warm or cold I have to pump the gas or hold it down to get it to fire, and it runs rough for a few seconds after starting. Could this be the float adjustment?

Thanks again,

Phil

 

I would go back and set the float level exactly (to the letter) as described in the instructions in the rebuild kit. Carbs are very sensitive to these types of adjustments. If the float level is off, it can create all sorts of problems.

As far as it being hard to start after it has been sitting for a few days, everything I've ever owned that has had a carb and a mechanical fuel pump has been like that. Especially if the fuel enters the carb at the bottom of the fuel bowl like the autolite/motorcraft 2bbl. After you shut off an engine, it's very warm. A certain amount of fuel evaporates due to the heat a lot more can leak past the needle valve over a period of time and drain back through the pump, causing a low fuel level in the float bowl and the pump loosing it's "prime". It takes a few moments of cranking for the pump to prime itself and replenish the fuel bowl. One way around this is to install a low pressure electric fuel pump (with a regulator). Turning on the pump just prior to starting, should eliminate that problem.

As far as the manual vs electric choke I'd go with whatever works best for you. I like my electric one. Once they're set up properly, it's a set it and forget it thing. It runs smooth when cold and I don't have any driveability issues. With a manual one, I don't like doing the little tap dance on the throttle on a cold morning, it can hesitate/stall when you drive off, you can forget to push it off causing a rich mixture and washing the oil off the piston rings. Just my 2 cents.