Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Did you check the adapter between the carburetor and cylinder head? Common for them to crack and let air leak in! What engine do you have? 350/400?
Two cycle engine, water cooled. Front cowling should be marked with 350/400. Or engine cylinder head has cast number in it. But the adapter that carburetor connects to, is the most likely cause, other than the carburetor itself. Idle is set by the throttle cable adjustment. On the handle bar, the cable connection has a lok nut under the rubber boot, that has to be unlocked , then the cable can be rotated to change idle speed. Too fast, and you will not be able to get in gear without clashing gears.
250 or 300 air cooled engine? Does engine run ok just will not idle? The smaller engine carburetor attaches differently. Can still leak, but not as common.
Any leak in the air intake , between carburetor and cylinder head will affect idle. Did you try to adjust the throttle cable to raise the idle speed?
Yes ,adjusting the cable length should affect the idle. Take the three screws out of the top cover, and see if all is well inside.
Cable goes direct to the butterfly in the carburetor and adjusting the cable . making it shorter, should raise the idle.
Just another place to check! But it can affect idle. Idle can also be adjusted at the carburetor end of the throttle cable. But it is same cable that you adjust on handle bar.