I just did a rebuild on my 90 YJ's carb and it was a miracle it even ran. It was blocked up pretty bad. My question is to do with the mixture screws on the front of the carb. Going all the way in and then back out, one was out 1 turn and the other was out 4 1/4 turns. I put them back to that position after I cleaned them up, but it doesn't make sense to me that they should be so different. After all the vac lines etc. are hooked up it started up, but it isn't running smoothly and I want to have a starting point as far as the screw settings before I go back at it tomorrow. Any other tips on dialing it in would be appreciated.
You said you have all the computer crap working, correct?
The adjustment is totally different with the computer in or out of the circuit. Those plugs that blocked the screws shouldn't have been removed, but when the computer or carb fails, folks try to 'fiddle' with it to make it run.
You basically need to find the happy medium idle mix then the computer takes over via the stepper motor and mixture pins.
I like to start rich and work my way lean like on a normal carb. I start at at least 5 turns out on both screws, usually 6 just for good measure.
You need the idle to be close and you will likely have to adjust the idle as the mix sets, then set the mix again. This will happen 2 or 3 times likely before it centers.
You want to 'carefully' look down the carb throat so you can watch the stepper motor's metering pins move. You turn the mix screws in 1/4 turn at a time each, then rev the engine. As you get close to the balance, you will observe the pins moving in and out. You are trying to get them to stay in the center of their travel in the opening. This should have the screws somewhere around 3 1/2 turns out.
The pins pull out when the screws are too rich and push all the way in when the screws are too lean. They are trying to compromise for the input from the screws so full in on the pins is computer rich.
As the idle changes, you will have to adjust it and continue on.
The reason they were so far off is likely because that carb had a plugged up idle tube or two so the mix was fiddled with rather than fixing the blockage. The idle tubes are those 2 long skinny brass tubes in the center of the venturi. The block up and need to be 'physically' reamed out. Chemicals will not clear them. I have seen several 'professionally' rebuilt carbs that still had blocked tubes because it really is a no no to ream out carb parts. Except for those damn tubes....
Here is a good link on cleaning and reaming the idle tubes:
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I can clear those tubes on the trail if needed. The choke plate just has to come off and the venturi cluster can be pulled up and twisted out.
One major cause of blocked up tubes is that loop of steel gas line between the gas filter and the carb. It has a loop so gas can evaporate in there leaving hard scum that gets put back into the carb. I recommend this tube be removed and cleaned well.
Then just FYI, make sure the gas filter in in right side up. It has 2 outlets, the center outlet goes to the carb and the top outlet goes to the return line. If the return line is lower than the carb line, gas will syphon back to the tank when it sits.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
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