kaizenator : Backfiring thru carb on 230, adjustment screw Qs

Re: Backfiring thru carb on 230, adjustment screw
Post by kaizenator on Jul 10, 2006, 10:18am

...new points with gap right.

Once rpms get past the 800-1000 range, the engine is very strong and smooth, and has nice responsive throttle. From idle to this point, however, I have to ease the pedal, I can't stomp it, or it does pop out of the carb.
hummm? Seems like timing or air/fuel mixr to me, but everything is new or like new, and the timing is set to 5 deg BTC, points set to .020?, plugs gapped right @ .030"..etc...etc.

Re: Backfiring thru carb on 230, adjustment screw
Post by hiker on Jul 10, 2006, 11:10am

Backfiring out the carburetor on acceleration is a lean mixture. Somethings wrong with the accelerator pump circuit, most likely. Diaphram torn, missing check ball when rebuilt? With the engine OFF, look down the carb throat and check for a good fuel squirt when you open the throttle.
good luck, Robert- CA

Re: Backfiring thru carb on 230, adjustment screw
Post by kaizenator on Jul 10, 2006, 11:40am

Its got a new accelerater pump and diapham, the check ball was moving nice and freely upon reassembly. There is a nice and steady stream of fuel being pumped into barrel when I rotate the trottle lever.

I am going to re check the timing. would the vaccum advance have anything to do with it or a disconnected vaccum line or leak?

Re: Backfiring thru carb on 230, adjustment screw
Post by brute4c on Jul 10, 2006, 12:00pm

If it is a stock ignition, there is no vacuum advance. Stock has the screw onto the plugs ttype metal braided spark plug wires. Even though there is no vacuum advance on the stock military setup, there are 2 vacuum lines connecting to the ignitor assembly, thats the coil/distributor housing. These are strictly for venting.

Leaving any vacuum line open would cause it to run funny...I would make sure all those lines were hooked up properly before proceeding.

Re: Backfiring thru carb on 230, adjustment screw
Post by jeepistdougiowa on Jul 10, 2006, 12:32pm

I keep thinking "lean pop"

Have you tried partially pulling the choke while accelerating? make any difference?


I know, Intake instead of exhaust, but so hard to tell over the net...LOL

Re: Backfiring thru carb on 230, adjustment screw
Post by kaizenator on Jul 10, 2006, 2:51pm

brute, yes I have a 24v distribr, I typed before thinking, it has no advance, but I need to check over all the vaccum lines. The one going to the master cyclinder may not be sealed well enough, it is makeshift. What should I do with it once I install a different MC that has no vaccum atachment? Can I just plug it?

More choke makes it run better than with no choke! seems lean.

Re: Backfiring thru carb on 230, adjustment screw
Post by jeepistdougiowa on Jul 10, 2006, 2:58pm


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More choke makes it run better than with no choke! seems lean.

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Vacuum leak, or crap in the jets...that's my final answer...LOL.

Easiest way I've found to find a vacuum leak is with a small hand held propane torch. Turn it on, but don't ignite it Probe around any possible leaks and you'll here the engine speed change when you find one.

Re: Backfiring thru carb on 230, adjustment screw
Post by hiker on Jul 10, 2006, 3:00pm

I like Doug's idea of slightly pulling out the choke while driving and see if that improves things. Years back when I first got my truck, the mixture was way lean causing some of the problems you discribed. Pulling the choke, temporarily helped it run better. Turning the mixture screw, only helps near the idle range, not midrange or acceleration. I rejetted the carb, in stages, each time test driving to see any improvement. I finally got to the point where performance increased and slightly pulling the choke out didn't help anymore. I was too cheap to pay anyone to put an exhaust analyzer on it to check mixture. Better to be too rich than lean. If you decide to rejet, I'd jump the jet size by at least 4 numbers to see any difference.

You can test your mechanical ignition advance by using a timing light and checking for the marks to advance when increasing engine speed.
Robert-CA

Re: Backfiring thru carb on 230, adjustment screw
Post by hiker on Jul 10, 2006, 3:18pm

Jetting info from a previous posting:
If the float level is correct, then look at your main jet size. I ended up replacing a #58 with a jet #69 (Holley, larger numbers means richer mixture) that did away with the lean mixture . Good Luck, Robert

Also, Vacuum leaks are common on the vacuum windshield wiper lines, or a torn vacuum pump diaphram.

Re: Backfiring thru carb on 230, adjustment screw
Post by brute4c on Jul 10, 2006, 4:25pm

As far as the master cylinder vacuum hose....that is just a vent. It is not, or at least stock it is not, drawing any vacuum. It should just be hooked to the air cleaner snorkel so that it just allows for venting of the master under normal circumstances. If a fording kit is installed on the truck, then all the vents get pressurized when the fording valve is closed....

If the line on the master is hooked to a vacuum source, it is incorrect and should be rerouted.