Low Low Idle
 

After getting my '48 f3 running & out of my yard for the first time in 2 years I can't get the idle up. I rebuilt the carb- pulled it off 2 times after to get sludge out of it from bad gas & even with the idle screw all the way in it barely idles. I took the vacum hose that works the wipers off & with the extra air going in to the carb it idled good but ran lousy at higher rpms.
I'm sooooo close to being able to take it on the road again & the only thing thats holding me back is the low or no idle thing it's driving me nuts!
Any ideas?

I'm certainly no expert but it seems to me that if it runs at all with the mixture screw all the way in you have a vacuum leak somewhere. Are you saying you removed the wiper hose and left the port open? That port needs to be closed off and perhaps the mixture screw opened more to let in more air...:)

I played around with the idle mixture screw & it didnt seem to make it run any better. The idle screw on the linkage is all the way in, usually this would make it idle fast but it barely idles. I took the vacum hose off for a moment & when it was off there was more are going in to the carb & it idled well but with that hose off it dosnt run at higher rpms. I'll have to play around with it more on my next day off- which may not be fore a while!

Your terminology is confusing; the "idle screw" you refer to is the throttle stop screw. It sets idle speed. I think Vern and I both assumed you were talking about the idle mixture screw.

It sounds like your slow speed/idle fuel system is plugged. Have you adjusted the idle mixture screws on the back side of the carb? Try starting out with them 1-1/2 turns out from closed (all the way in).

Sorry for the confusion. Yes the thottle stop screw is all the way in & I did try to adjust the idle mixture screws on the back of the carb. I 'll take apart the carb again & see if the slow speed/idle fuel system is clear. Thanks for the advice.

something to look at is the fitting that threads into the intake manifold and sends vacumn to dist and wipers. sometimes they crack on the thread going into manifold and you can't see it! don't know if your engine has this setup, but maybe. otherwise you still have crap from fuel tank getting into carb!

If you have the stop screw all the way in, the idle/air screws won't affect anything (as the plates are cracked way open now)....I wouldn't think it'd be a vacuum leak, or you have (generally) a situation where idle is too high.

What's the timing set at?

Beautiful truck, by the way!

Pull out the idle mixture screws and squirt lots of carb cleaner in thru there. If you don't see it squirting out of the holes in the throttle bore, it's seriously plugged. (PS -- wear a face shield -- that stuff REALLY burns your eyes, and it WILL squirt back into them!!) Use a thin copper wire if the cleaner won't clean it out.

Only thing that keeps me thinking, is if the idle stop screw is all the way in, means the throttle plates should be cocked way open...so I don't see the reason to squirt anything into the air/fue bleed screws, since if the screw is all the way in, there should be no way the carb is/can run on the idle cuircit?

If anything, then the idle jets (not imulsion tube) are plugged...but my guess (and pull your plugsto verify) is you';re running real fat and the plugs are black...means you need more air somewhere...but anyway...

What's the timing set at?

Holley 94's have pretty short throttle stop screws, but I see your point. Actually your comment makes me wonder if the bellcrank is slipping on the throttle shaft?! (screw isn't doing anything)

Ya, could be, kinda becomes one of those thing you might need a visual on. Ofcourse, if the timing is good and the idle is still low, he'll probably have to go ito the carb...also...anoher off the iold-age-memory thing here...I just won0der if the truck ever ran/idled well before?

A partially restricted exhaxuast could become an issue too...sooo many things onold trucks, like they say...90 % od\f carb problems are ignition related and 90% of ignitioin problems are carb related.

Pick you poison:)

Thanks guys, The truck ran great when I parked it away in my backyard a few years ago. the bad fuel issue, that I took care of when I got it running this spring, really plugged up the carb. When I rebuilt the carb it had a lot of a white hard build up in the fuel bowl & in the cast tubes at the bottom of the accelerator pump area & even in the fuel pump. After soaking the carb & picking & scrapeing it cleaned up well. I got a day off tomorrow & will check all the things you pointed out. Cant wait! Hopefully it will be up & running by Friday & I'll enjoy a nice ride to work on Friday!

If there is a carb shop in your town, they can boil it out in a mild caustic solution that gets that white stuff out. May be worth it.

Now that I think of it, the plugs were definitly black after maybe 1/2 hour of running.

Power valve leaking, or float needle not holding...