Bonneville America Forums Forums Technical Forums Performance Mods Help- Idle mixture screws not working equally.

Okay oh guru's of all things vaccuum. I know this will be close to impossible, but I need to start somewhere. My left and right idle mix screws do not have the same results when turned. The left carb (shifter side) will kill the engine when turned all the way in. The right carb (chain side) will not- it barely makes a change in idle speed. I have the aftermarket thumbscrews that are exact copies of the stockers from newspeedmaster.com (not the Harley pieces that will "work"). I also just synced the carbs a couple weeks back with no change. Other bits of info- no air box, K&N Pods, 45 pilots, 150 mains, 2 shims on thruxton needles.

My knee-jerk assesment is a leak on the right side. Any "look here first" or "how to find a leak" advice is greatly appreciated.

I can only help on the "look here first" kinda stuff. Vacuum caps? Carb boots/band clamps? You can try wetting down the rubber parts and looking for bubbles, that sort of thing.

One other thing to check is that all the parts are in the right order and lined up on the screws..... those teeny little o-rings are easy to lose.

I had a problem with my 06 America after installing a set ot Staintunes, re jetting to 135 mains and replacing the air screws to the after market ones from Brent. My choke quit working completely, the bike would "stumble" at wot and was very hard to start. I went back to 130 mains that I had in with the replaced set of D & D's and continued to have the same problem. I then replaced the 130's again with the 135's and removed the after market thumb screws and noticed that the "new" thumb screws seemed to have some sort of coating on them. I used some low pressure compressed air to blow out the holes where the air screws go and replaced the after market screws with the stock ones and it cleared up the problem. It seems that when I seated the "new" thumb screws to get to a start point for setting the number of turns out that something "rubbed off" of the new screws and clogged up the passages inside of the carb. After installing the original screws the bike runs great. I did notice that after installling the new thumb screws that the tips and the threads did look a bit more of a "brass color" whereas the rest of the new screw had a more "orange " color...like something was rubbed off from installing them. Anyway the bike runs great now and I only assume that the new screws were the problem.

I'll double check the o ring and run a guitar string thru her to make sure the passage is clean (guitar strings make great tools for cleaning passages ) . Thanks for the advice, friends...

IF you find the coating is peeling, maybe you could actually rub the screws down a bit to try to take the rest of the coating off. IT's not like they'll corrode, they are covered in gas Sounds like zinc plating from what LArry said.

You did not say in your post, but

Whenyou replaced the original scre3ws with Brent's you should have pulled the little washer and rubber seal out at the same time.

Then take the new screw install the washer and then the rubber washer then run it up until snug. Then back each one out three turns to start.

Almost everyone runs 3 to 3 1/2 turns out. What happened I think is you crushed the rubber washer or ended up with the washer and rubbber cocked eyed.

Once you get the thing straighten out make sure you balance the carbs.

John

I agree with Big Poppy.When you replaced the screws with Brents you have to make sure you get out the very small ss washer and the o-ring.If you don't it could cause the issues you are having. I had a bit a trouble when I changed to Brents(lost a o-ring)did'nt notice losing it until I started her up and she ran like crap.I had read a thread about watching out for the o-ring and washer. I took them out and found I mas missing the o-ring.Replaced it and every thing runs great its a whole lot easier to adjust with Brents screws.

Pete

Well, no dice. O-ring in place and accounted for, as is the washer. I rebalanced the carbs and no change. The right carb is not responding to the air mix screw.

On a test ride today, I realized the lean pops on deceleration are only on one side- the left side.

Looks like I'll be pulling them and going through them bit by bit. I was thinking of rejetting up any way. I guess this is a good excuse to try some 48 pilots and 155 secondaries.

What is the chance that I have a float out of adjustment? If memeory serves- I pulling from high School here- high float levels cause rich idle conditions? Anyone know the correct stock float height?

Any chance you have a balance hose between the manifolds? That will really weird the idle mixture adjustments. Are you sure the right cylinder is running at idle?

No hose and no I'm not. It idles well. Nice and smooth. The bike runs very well and there are no indications that there is a problem- except the idle mix screw doesn't work and there is a lean pop on decel in the port bank and not in the stbd side.

I like your float theory. Not sure of the spec tho. Got a manual?

No. No manual. I need to get a shop manual, but I keep spending my corn on accessories-

Hopefully someone will speak up. I am not sure where my manual is at the moment.

Since you're going to pull the carbs try using the old adjustment screws and see how she runs....Angelis

Replace all your vacuum caps, just for giggles. They're cheap enough.

Many thanks on the float height. I'll try that this weekend. I also bought a set of vac caps. I tried the soapy water trick and saw nothing, but at this point I'm just throwing parts at it. If this doesn;t work, I'll be looking at the 35mm CR's.

Another way to find a vacuum leak is to use a spray of something flammable(WD-40 for example), with the bike idling spray small bursts at possible leak points(vacuum caps, manifold/head mating area, couplings, etc), if the idle jumps you found a leak.