I have a ford f150 inline 6 that has been converted to a carb. All of the emissions have been removed. I am having a hard time getting the carb adjusted properly. I have recently rebuild it and it was running, but the fuel/air mixture wasn't perfect. I would run well at around 2500 rpm's but rough idle. I tried the mixture screw several times without luck. Was told it might be the accelerator pump. So I replaced that again. When I put the carb back on. It will not idle, even with the screw all the way in. I adjusted the float bowl to the specs on the paperwork in the rebuild kit. Any ideas or suggestions?

 

Hi Treedoctor!
For starters, what carb are you working with? I'm assuming the stock 1bbl?

One of the best tuning tools you can get is a vacuum gauge. They're not super expensive and they can tell you dozens of things about your engine that you just can't tell without one. I can't stress their value enough, even while driving.
Hook the vacuum gauge up to DIRECT manifold vacuum. If you have an unused port on the intake itself, that's the best spot, but a port below the throttle plates on the carb works too.

At idle, you should have about 18 - 21hg of vacuum with a good, healthy engine.

From there, while it's idling and all warmed up, turn your idle mixture screw outwards until the vacuum needle doesn't increase anymore. Then, slooowly turn it in until you get the maximum vacuum reading possible. Normally, as you turn it in, the vacuum will slowly climb, and then suddenly drop dramatically. Once it does that, back it slowly out and find that sweet spot. That's your best idle.

Next, set the timing on the distributor with your vacuum gauge. Loosen the distributor and advance it until the vacuum stops increasing (it'll start to run rather rough), then retard the timing slowly until the vacuum drops to about 1 1/2hg below the maximum reading you were able to get.

Next, set your idle RPMs to what they should be (about 700).

Repeat all the steps again to see if any changes were necessary. Continue until no more adjustments can be made. That'll set your engine really nice.


Now, this is taking into consideration that there aren't any other problems with your engine. But, the biggest one I'd assume would be vacuum leaks. Get one or two cans of the cheapest carb cleaner you can find. Then, with the vacuum gauge in hand, spray around all of your carb/intake/head connections. Areas to pay extra attention to are where the carb bolts to the intake, all six runners of where the intake bolts to the head, and the throttle shafts on the carb. Also, spray around your vacuum trees and lines. If, with any of these, you see the vacuum needle waver and stumble, you've found a vacuum leak. The leak will need to be addressed before you can really do anything else.

Hope that gets you started in the right direction.

 

I'm wondering...if you changed from EFI to carbed did you also change the ignition system back to a carbed system like DS2? If not, that's where at least part of your problem might be.

And X2 on what AB said about vacuum leaks.

 

Also, to add to what Harte3 was addressing, what fuel pump are you using? The EFI had an intank electric pump which would have way too much pressure for a carburetor.

 

Thanks for all the input. It does have a 1bbl. I think I found the problem. The intake/exhaust gasket seems to be blown. I just replaced it a couple of weeks ago, which I'm wondering why it would blow so quickly. After I replace that again, I will go through the steps listed above. Thanks again everyone for the input and time you spend to type all of that out for me.

Treedoctor

 

Be sure to retorque the mounting bolts after you've brought the engine up to operating temp and let it cool down after you install the new gasket. That's probably why it blew out.

 

When you replaced the gasket, did you resurface the intake/exhaust manifold? If not, they have a tendency to warp with age and you'll never get them to seal. Leave them bolted together when you have them resurfaced.