Mixture screw

[darrell3001]

83 11e (Blue)
Carbs professionally rebuilt about 6 month ago - 47.5 jets installed
Pods
Boots replaced
Vacuum synced
ColorTune adjusted

The idle just sucked after i reinstalled the carbs after rebuild. I have tinkered with this for the better part of 4 months trying to stabilize the idle. After tons of reading and trial-error, i finally got things dial in. Mid/Top-end power was fine from day one, but idle was way off. Could not keep it from stalling. In addition, it was very hesitant on starts at low rpm.

Here are my initial conclusions:

The carbs came back from the rebuild with 47.5 jets installed to compensate for the pods being installed. The mixture screw was setup with the standard 5 (1/2) turns. My assumption, at the time, was that i needed to adjust all 4 of the screws the same on each adjustment. ie, i would adjust all 4 screws by half turn increments trying to smooth things out. This ended up being a mistake.

I ended up reading an article where one of the forum gurus suggest doing a "lean best" setup. This ended up being the key to solving the mystery. What i found was that three of the carbs were running extremely lean and one was running rich. The mixture screws settings are wildly different. Three of them are set to 11 (1/2) turns out and one carb (#2) is set to zero turns (ie all the way in). Ive checked and re-checked this using the lean best method. In addition, the idle is smooth at 900rpm. Also, hesitation at <2000rpms is not almost non-existent. Also, ive been checking exhaust temp with infrared sensor. All of the pipes are within 10 degrees of each other now. Before i figured out that number 2 was running very rich, the exhaust on number 2 was running very cold (ie ~60 degree C) while the other three were well over 130C. Also check plugs and they are bone dry and white now. Bottom line, i think ive got things dialed in now.
One other thing to add. In my troubleshooting steps, i ordered a set of pilot jets from Amazon. I put in a set of 50's and set the mixture screw to 5 (1/2) turns. Wow, this totally ruined the idle. It ruined so much that it fouled up the plugs. I even turned the mixture screw completely in (zero turns) and it still just ran like crap.

So three questions:

1) is it viable that the mixture screws between carbs could be this far off from one another? I mean we are talking about 11 half turns vs 0 half turns. This seems pretty extreme.

2) It seems like the three carbs that are running with 11 half turns need to be setup with a bigger pilot jet. Seem like i remember reading that 3 half turns = 1 jets size. Is this viable?

3) The pilot jets that i got from Amazon seem to be completely the wrong size. Has anyone else experienced this? Based on my findings, i think i need to go up at least one size on the carbs running with 11 half turns and probably down 1 size on the one running at zero half turns. Can someone recommend a good source for pilot jets?

Best Regards,

Darrell

 

[Nessism]

Anything beyond 8 half turns open doesn't have any effect on a normal bike. And it's not normal for one of the carbs to run with 0 turns.

It seems that your carb "professional" didn't do such a great job on them.

Did you perform a vacuum sync? Adjust the bikes valves?

 

[darrell3001]

It seems that your carb "professional" didn't do such a great job on them.

LOL!!! I am starting to agree.

Yes, vacuum sync done (about a million times)
Yes, valves adjusted. That was first thing I did 4 months ago.
Also, checked for vacuum leaks with wd40

I’m going to try going down to stock 45 jet on the number 2 cylinder tomorrow and see what that does.

 

[Guest]

Go to the stock pilot jets on ALL carbs. There is absolutely no need to increase the pilot jets for pods. Any jetting increase is because airflow is enhanced. Removing the airbox will definitely affect jetting on the main jets and maybe into the needle, but will have no affect on the pilots. By the time you get lower than half-throttle, your restriction will be the throttle slides, not the airbox, so there is basically no change due to the lack of an airbox. Again, stock pilot jets are all that should be necessary.

 

[darrell3001]

Go to the stock pilot jets on ALL carbs. There is absolutely no need to increase the pilot jets for pods. Any jetting increase is because airflow is enhanced. Removing the airbox will definitely affect jetting on the main jets and maybe into the needle, but will have no affect on the pilots. By the time you get lower than half-throttle, your restriction will be the throttle slides, not the airbox, so there is basically no change due to the lack of an airbox. Again, stock pilot jets are all that should be necessary.

Christmas came early this year!!!! So i went back to the stock pilot jets on all carbs and 5 half turns on mixture screw then BAM!!! just like that. Smooth idle and ZERO hesitation on start. I really cannot believe that in 4 months of messing with this i never thought to put the stock jets back in.

Anyway, Huge thanks for the suggestion on going back to stock jets. It just goes to show you, "Dont mess with perfection!"

Very Best Regards!!

Darrell

 

[Guest]

"Five half turns" on the mixture screws is a decent starting point, but you should really do some fine-tuning from there.

With the engine warmed up, slowly turn one screw out to see if the engine speed changes. As it richens up, it should slow down. Now turn that screw in slowly, the engine should speed up slightly, then slow down. At the point where it slows down, back up 1/4 turn. Repeat for the other carbs.

When you are done, stop the engine, grab a note pad. Turn each screw IN, while counting the turns. Record that number, then turn it back OUT that same number. Repeat for each carb. You may find that not all the screws are out the same number of turns. That is no problem, as each screw is out the proper amount for its carb.

Oh, don't confuse yourself or anybody else with "five half turns". Just call it "two and a half turns" like everybody else.