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carb trouble

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alleycat

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I've gone and done it now. I have a 67 250 in my 51 pickup and just had the carb rebuilt. Put it on and started it up and have to keep it idled up fast to keep it running. The exhaust manifold glows cherry red for about a foot down it (not good). I've adjusted the mixture screw in and out and it made no difference. Before I had it rebuilt it would idle fine but sometime it would spit gas out by the throttle. Now I would guess it has to idle about half throttle just to keep running. When I put it back on it seemed like it was loose but the bolts were tight. any suggestions what I did wrong????????????
 
that's what I thought so I checked the vacuum line and finally just blocked it off. Is it possible to suck air between the carb and intake? I have the gasket in but am hesitant to put silicone between them. Like I said the bolts are tight but there is movement between the carb and intake. It feels loose.
 
Movement between carb and manifold is bad. Don't fix it with silicon. Take it apart and figure out why it won't tighten up properly. Maybe you are running out of thread on the carb mounting studs before the carb gets tight.
 
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Checked the treads and had plenty left. checked top of intake with straight edge and it looks fine bottom of carb looks fine. Nothing looks warped That I can find.
 
Did you put the lock washers back on the carb studs after you installed the carb on the studs? Did you forget to put the spacer back between the carb and the intake? It's going to be something silly. If there is movement between the carb and intake and the carob nuts are tight then you have reached the bottom of the threads on the studs. Try some washers under the carb nuts.

Andy
 
Stop guessing; buy a vacuum gauge (probably 10 bucks at HF) and hook it up. If it doesn't show at least 17 inches of vacuum at idle and more likely 18-20 then that's the problem.
 
If the exhaust is cherry red...would that not be something a lot more serious than vacume...Are there puffs coming out of the exhaust, butterfly open, valves ok, no blockage, etc? What about spraying some carb cleaner around that gasket...does it change anything? I would not run it toooooo long being cherry...it can cook a lot of stuff and I am not limiting it to the head...Is the water temp way up too?
 
If you have a lean running condition it can turn the whole manifold red. Some think it would mean too much gas is causing it but raw gas carries heat away. Think of a cutting torch---the oxygen/acetylene mixture will heat up the metal to red hot but the instant you press the trigger the metal burns itself up and is blown away by the pressure. Same thing happens with a vacuum leak where extra air is introduced into a system; it gets real hot. It probably doesn't apply here but retarded timing can also make a manifold glow. This is because the spark doesn't occur till the exhaust valve is starting to open so some of the combustion cycle is happening in the manifold.
 
as soon as it warms up a little I will try spraying a little carb cleaner around the base and see if it speeds up. The only thing between the carb and intake is a thin little gasket. It has always been that way. Checked the timing, spot on Valves set right. It has to be to lean from sucking air someplace. It doesn't pop spit or anything like that. It has to be something simple question is what.
 
I just noticed that this is a 250.....does the vacume have the equal importe effect on a 235? The reason is that I have seen, in the long distance past in a galaxy far, far away, some pretty big leaks or hose fallen off my 235 and never seen it cherry. I have heated it up by accident many other ways and blown the head and other parts.

Thanks Evan...for reminding me. What you say? I still have an old gas welder/cutting torch that I have not recently opened. I had better do that, so that my gray matter cells do not forget everything about it. The last time was probably years ago...and the last few times were only to heat up parts, bolts and stubborn stuff. I need to do that just for the fun of it.

rod
 
I don't know where this situation stands, but if the leak testing with carb cleaner did not reveal something(careful there), I have had a similar thing happen a couple of times, but without the cherry hot exhaust. It turned out that crud had partially plugged the jet at the bottom of the acc. rod. I have never figure definitively how that crud got there...filter right outside. The last time I replaced the bowl gasket and am still waiting to see, if anything does not happen.

rod
 
Finally got out to hanger today and messed with the carb for a while. It wasn't where the carb mounts to the intake that was loose but where the float bowl mounts to the base. So I took it off and tightened the screws, they were only finger tight. makes me wonder if they didn't tighten them what else inside could be loose. Put it all back on ,cranked it up and same problem. If the choke is about half pulled it will idle slower but still way to fast. I have turned the idle mixture screw from seated to 5 turns out and no difference. I sprayed carb cleaner around everything and no difference. So I guess it has to be sucking air someplace but don't have a clue where. It will idle about half throttle with choke pulled about half way but that is about as slow as it will idle.
 
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