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Old 06-10-2018, 09:10 PM   #1
NeverDone50
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More carb problems!

So I have a 292 swapped into my 50 3800 and i recently bought a new monojet for it. Ive adjusted everything to spec closest to the year the motor came from (67 c20) and rechecked everything. But this motor didn't originally come with the monojet, it just came with a rochester B. Anyway, it ran once but hasnt ran since. I've completely disassembled it and cleaned it out. So I put it back on and it started spitting back through the carb. I adjusted it more rich until it stopped and it gets close to starting, but wont. Any ideas? All the vacuum ports are capped except for the vacuum advance and my vacuum gauge. New gas lines and mechanical fuel pump. Another side note, it was acting like it was flooding before I tore it down and cleaned out the carb.
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Old 06-10-2018, 11:01 PM   #2
franken
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Re: More carb problems!

Sneezing back is a lean indicator. Try plugging all the vacuum ports. Got gas quirting from the acell pump squirter? Close the choke?
If it still won't start shoot some b12 down it (or dribble gas) and crank.
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Old 06-12-2018, 09:57 AM   #3
Wrenchbender Ret
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Re: More carb problems!

What makes you think it is the carb at fault? Have you checked the ignition?
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Old 06-12-2018, 01:24 PM   #4
mikebte
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Re: More carb problems!

Do you have another carb to put on? I have purchased brand new and rebuilt carb that would to that, bad out of the box. I about went insane trying to figure out what was wrong. Do you have a history on the carburetor your installing.
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Old 06-12-2018, 01:43 PM   #5
mr48chev
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Re: More carb problems!

Did you have the truck running with the stock carb before you swapped carbs? If you never ran it and swapped parts the part you swapped may not be the issue to begin with.

As Mikebte asked, what is the history on the Monojet? was it a fresh carb or one you just had or picked up from a buddy or ?

My memory doesn't tell me what the base surface of both carbs looks like right now even though I have rebuilt both in the past but might you have the wrong base gasket that is creating a vacuum leak? I've seen that on a couple of other carb swaps where you had to have the correct gasket to make it work.

I'm not found of swapping parts around on an engine I have never heard run until I have run it. It seems that every time one of my friends calls asking for help with an engine not starting they did a wholesale swap of parts before trying to start the engine and you have to sort it out one step at a time to get it to work.
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If you can't fix it with a hammer, you have an electrical problem.

My ongoing truck projects:
48 Chev 3100 that will run a 292 Six.
71 GMC 2500 that is getting a Cad 500 transplant.
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Old 06-12-2018, 08:36 PM   #6
NeverDone50
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Exclamation Re: More carb problems!

The motor ran with the old carb, but it never ran right so I decided to buy a new monojet. It did run with the new carb at first, but after some initial tuning, it wouldn't start at all. All the electrical parts have been checked and I've narrowed it back to the carb. The mounting gasket may be wrong. Also, the monojet instruction manual doesn't list adjustments for '67 c20. It only goes back to '68. Also I think my float level is wrong. It's suppose to be 9/32 and I have it set to 1/4.
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Old 06-12-2018, 09:15 PM   #7
NeverDone50
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Re: More carb problems!

Also, I have a pertronix kit and coil. It was upgraded when the other carb was installed and it ran. I checked for spark on all the cylinders and that's all good. I'm curious i may need to check compression again. I'm suspicious it was flooding the engine while I was trying to diagnose the problem. Can flooding the cylinders too much wash the oil out and lower the compression. Thoughts?
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Old 06-12-2018, 09:21 PM   #8
mikebte
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Re: More carb problems!

To much fuel is never good, can wash down the cylinders, too little is bad as well.

Can you install the old cab and see if it runs? If so, it’s the carb. Maybe just adjusting needed, I’m not real experienced with a monojet, more of a carter/rodchester kind of guy.

Some monojet Gouru will chim in with more info I’m hoping. I always wanted to mess around with them, I hear they can be a good carb when tuned correctly.
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Old 06-12-2018, 09:43 PM   #9
NeverDone50
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Re: More carb problems!

My main issue with the old carb is that it has the wrong accelerator pump installed. It's a story I won't bore with details. It needs the correct arm and pump, but there are two lengths for the accelerator pump and I don't know which one it is. I can post pics of the old carb and look for the model # if anyone can help me figure that out.
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