Carb Tuning

[pearsonbe]

This weekend I drilled the factory plugged idle mixture screws and took a shot at syncing the carbs. I don't have a sync tool yet, so I used my infrared gun and set them by header temp. It didn't go well. Based on the videos I've watched syncing with a tool (vacuum pressure or fluid), the plan was to bring the two carbs with the lower temps up to the same temp as the carbs with the higher temps. I didn't touch the "good" carbs; they were 450+ degrees. Seemed reasonable. However, the motor was not happy when I leaned the mixtures. It only improved slightly when I enriched. And I couldn't get the temps close across all four carbs. The good news is that the mid-range was a little smoother. But the idle got worse. I will buy a sync tool a try again.

[DonTZ125]

Syncing the carbs and setting the idle mix is two different things. Syncing is done using a vacuum gauge or manometer by adjusting the screws on the throttle linkage between the carbs. The idle mix is set after sync using the idle mix screws; a temp gun is a quick and easy way to determine the results.

[pearsonbe]

Aaahhhhh. The carbs were synced last fall by a pro shop who said they were close. While the carbs were on the bench, I did see one screw in the linkage between each set of carbs - two screws total (iirc). Does the idle mix only affect the idle?

[DonTZ125]

There are 3 sync screws - 1-2, 2-3, 3-4. The 'idle' mix affects carburetion at closed throttle, which can include cracked-throttle operation.

[pearsonbe]

Ok. I must have missed one. When adjusting the screws, does the order matter?

[DonTZ125]

Not really.

[pearsonbe]

Thanks, Don.

[pearsonbe]

The sync tool arrived yesterday so I synced the carbs today. After calibrating the guages and setting the dampers, I got the carbs pretty close to each other. Checked the header temps and saw 400+, 390+, 150+, 130+. Setting the idle mixture on the cylinders that arent firing didnt help and the low end is still rough. However, the idle is a little better, and the bike is much smoother over 75 mph. Had it up to 90 and it wanted to keep going.

I dont know why cylinders 3 and 4 arent firing at idle. Its weird because I remember having problems with 1 and 4 - not 3 and 4. The next step is a plug and compression check. Unless someone else has a better idea.

[LuckyStriker86]

I would check the spark. I have no idea why spark plug boots just screw into the wires. I feel like there is a probably a better way to make a connection. After reassembling my bike, I was moving the wires around to plug them back into the plugs and one of the boots pretty much fell off the wire. After that, I just snipped a little bit off each one and re-screwed all 4 of them in. You will definitely need to re-sync again after you get those cyl firing.

Although if they are not firing at idle ONLY, probably your pilot jets are clogged....?

I usually Sync 1-2 and 3-4 (either one first), then sync both sides (middle screw) to eachother.

[pearsonbe]

Thanks. Will check the ignition connections before continuing. Hope it's that simple. The pilot jets were replaced recently (stock #) on the two carbs that were giving me problems #1 and #4. Now, I'm having issues with #2 and #3. Doesn't make sense to me unless the plugs are fouling at idle. I've also wondered about the condition of my coils, wires, and caps. They tested ok last Summer when I got the bike, but it has never idled well for me. None of the ignition components are new except the plugs.

Today I learned that the engine may not respond to adjustment of the idle/mixture screws if the pilot jets are too small or large. Or if the the needles are damaged/broken. Mine we still plugged, so that's not likely. I have another set of carbs that I am checking and cleaning that may go in if I still have reason to believe the problem is fuel related.