Issues with Cylinder 3, Vaccum leak?

[mortation]

I'm still thinking pilot circuit. One thing I noticed is that I couldn't possibly do a carb sync when the engine is cold. The vacuum on my #1 cylinder is way high. Once it warms up and is getting gas like the other three the vacuum is very close to the same.

Anyone know when the main jet takes over and the pilot no longer delivers any fuel? I'm thinking between 1500 and 1800 rpm.

According to the instructions you are not supposed to do a carb sync till it is warmed up. Dunno if it matters though...

[mortation]

no other reason....unplug one plug at a time and replace back while the bike is running. Check if the popping stops when the plug is removed ...if it does you know the problem is in that cylinder area. then you can go deeper...may have to increase the idle so the bike does not go off.


make sure you have rubber gloves or something when you do it.

It only pops when riding. Dunno if I should ride it with one plug disconnected...

[simon kuether]

I had same problem with '79 GS1000S. Check vacuum hose from #3carb to back of fuel tap (petcock ?). Previous owner had removed it. I blanked both connections using short pieces of fuel line and zip ties although now run position is now OFF,no reserve and bike runs on PRI. I refuel using trip meter as guide. Good luck

[abates226]

This is a funny situation. I have had something similar, though. Do you have the vacuum-controlled fuel cock? I do. Mine had a vacuum leak, and was only letting enough fuel trickle in to feed #3 adequately. I actually vacuum-sycnhed the carbs and it ran really hot on 1, 2, and 4. Couldn't figure it out for the longest time, but I had the tank off and the carbs, doing the dyno stage 3 kit 'cause of new V&H kit thinking I was just out of whack from the new pipes, but I got to looking at the petcock and tested it, and got no fuel on the PRI position, and a bare trickle on the run position with a large sucking sound around the screw. Theoretically, you're giong to get enough fuel for the #3, and depending on the severity of the problem, you starve everything else. Rich #3 and lean 1, 2, and 4. I've heard the Pingel gravity feed with adapter plate touted highly, but I got original on ebay for $50, so decided not to reinvent the wheel. I'll find out tomorrow if my theory is correct. I'll let you know.