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Carb Maintenance

Once you have put your ignition system in good order, adjusted your valves and made sure that your compression is good you can move on to the carburetor. The only two adjustments that can be made is to the idle speed which is done by turning the screw on the throttle arm or on the later 34 PICT by turning the big by-pass screw on the left side of the carb.

The other adjustment is the idle volume control screw on the lower left side of the carb recognizable by the spring around the base on the older carbs and just below the by-pass screw on the later. This adjustment is simple. Warm the engine and make sure that the choke plate is wide open in the top of the carb. Adjust the idle speed to what sounds about normal (600 -900rpm). Turn the volume control screw in until the engine starts to noticeably slow down. Now back it back out until it smoothes out again and then turn it an additional ½ turn out. You may want to readjust the idle speed.
The most common problem to carburetors is dirt. This often comes in through the fuel line from the bottom of the fuel tank. A fuel filter in the line leading to the fuel pump can usually stop the dirt before it gets to the carb but be sure to check the filter occasionally. If the filter is getting full quickly you may need to clean or replace the tank. The other place dirt can enter the carb is in the air so always run an air cleaner. The first place dirt will usually cause a problem is at the needle and seat valve. It will either stop it up cutting off the fuel or make it stick open flooding the motor. Sometimes a temporary fix is just to tap on the top of the carb to dislodge the dirt. Usually you will need to clean the needle and seat by removing the screws from the top of the carb (and the throttle spring on 34 PICT). By lifting off the top you can see the brass needle and seat valve screwed into it.
Unscrew it and spray out the dirt with a can of choke or carb cleaner.
Sometimes fine particles can get past the needle and seat and later clump up and get into the main jet in the bottom of the bowl. In the later carbs there is a brass plug 13mm on the left side of the carb. The main jet can be removed by inserting a screwdriver through this hole. In the older carbs the main jet is actually in the end of brass plug (14mm). Again spray it out with carb cleaner. Wipe out the bottom of the bowl if needed. If there is crusted on junk in the bottom of the bowl the carb may need to be cleaned and rebuilt. Another jet that may need to be cleaned out at times is the idle jet on the upper right side of the carb. You will find two on the late carbs.
Unscrew the jets and spray them out being careful not to get the spray in your eyes. Spray into the hole in the carb as well.
Another thing that may get clogged with dirt is the accelerator spray nozzle.
You can remove it by pulling straight out and twisting at the same time. Clean out the small hole in the end.
Pump the throttle arm a couple of times to clear the line. There must be some gas in the bowl when you do this. Be sure to tap it back in tightly. It could fall into the motor. Attention to these few areas will usually solve most of your carburetor problems but in time the carb may need to be dismantled cleaned and rebuilt. Or maybe even replaced. But try these few things first and you may be surprised and save a bunch. You can see this done in detail in our Vol.1 General Maintenance video available from Bug Me Video.

Rick Higgins and Crew
Bug Me Video, Inc.

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