► A collection of random ideas....

• It is VERY common that high idle has to do with the ignition advance not returning to Full Retard at idle. This can be due to lack of lubrication of the advance mechanism and/or weak ignition advance return springs. When was the last time you serviced your auto advance unit ?

• If you disassembled both carbs at the same time, you could have placed the Enrichener Discs into the wrong carbs. There is most definitely a Left and Right to the carbs AND to the parts of the enriching circuit. Those discs are marked L and R for that purpose.

• Since you had to undo the choke AND throttle cables to work on the carbs, the correct re-installation of the cables is HIGHLY suspect. Do the chokes go to the FULL OFF position on both sides ? Is there 3mm slack in BOTH the throttle cables at idle ?

► Stop guessing at carb balance. Build THIS simple device.

► An explanation of what work was performed and what your experience level is would also help.

All the best.

Thanks for the response Wobbly, you have been a great help to us. As more of a background... the bike came with two different carbs (you might recall I posted a question about this a few weeks ago). The right was the correct 64/32/14 while the left was a carb body from 1995 (which only had 2 cap mounting screw holes) with the 4 mounting screw hole cap that was supposed to be with the 64/32/13 carb that should have been there. We since bought the correct /13 carb, rebuilt it, and put it on the bike. But the original setup with the hybridized carb (although almost impossible to start) did not over-rev like it is doing now. Don't know if this means anything as the choke cables and choke did not seem to be on correctly. I guess this actually increased our confusion as out first startup of the bike after we had reinstalled the rebuilt carbs was great. Engine started right away with no choke and went straight to the correct idle (but as mentioned below, that changed quickly).

The work performed was a rebuild of both carbs(all new seals and gaskets and some replaced jets) with new cables, but they were done one at a time to avoid mixing up any parts. I have some general mechanical experience but have never done carbs before so I did the work carefully after watching many videos and following along with them. There is only one slight difference in the carbs, the left has a #50 low speed jet while the right has a #45 (this is the way they came on the bike when we bought it). I don't know how big an issue this is but I figured I should mention it. As to the cables, the coke lever does go to the fully closed position (lever on the carb rests on the stop) and goes through the whole range normally. The throttle cable currently has ~2mm free play on both sides but I can back that out a bit. Finally, I have not yet done work on the auto advance unit and the bike has been sitting since 1996 so its been a minimum 23 years since its been serviced. Is there a way to determine if the advance is the culprit and if so how do I remedy it?
Thanks again,
Andrew

• The secret to getting any dual carb bike to run correctly is to make all the parts and adjustments identical. I do not think the mis-matched jets are causing your present issue, but I do believe it's not a "good thing". Your next parts order should include a matching #45 for the other side, and fairly soon.

• If you have the single cable at the twist grip, then you have a "2 into 1" device under the tank. That device needs some lube (like ATF) and the 2 lower cables need slack at the adjustment on the carb's top. IOW, ALL the throttle cables need slack at idle if you expect it to actually "idle". The 2 cable systems can be checked at the twistgrip alone, but the 3 cable systems require a lot more work.

• Americans are crazy about cable ties, and that's OK... until you start lashing things like throttle cables hard to the frame. Throttle cables need to be routed such that they make the most gentle bends possible, and are free to move around under tension. I spent an hour or so on my new bike experimenting with different routings to get the best possible. If you head into a sharp turn at speed and expect to shut the throttle and get the required engine braking, then these "small details" seem to matter. The last thing you need is a revving engine when it should be decelerating.

• No Airhead cranks without choke. And the later the model gets after about 1977, the more choke us usually needed due to EPA leaning out the mixture. So the fact that your bike cranks easily without choke is telling me that your mixture is WAY too rich. That's why I'm keying on choke adjustment. Next would be float needle and float height. You can follow that trail for yourself. Do both sides have the manometer ports blocked ? Did you replace ALL the o-rings on ALL the jets ?

Hope this helps.

Adjusted the valves and replaced the spark plugs today and started the bike up, the over-revving issue seemed to get a little better. The bike would not start without choke and idled at 2000 RPM. It would only get "stuck" at 2800 after blipping the throttle. This seems like it could be a weak springs in the mechanical advance issue so tomorrow I will get the front cover off and investigate. The right cylinder is seems to be running very rich as smoke is only coming out of the right exhaust (large amount when blipping the throttle). I have a 2 cable system not the "2 into 1" and there seems to be ample free play in the cables (I don't use ties). When rebuilding the carb, I replaced the 5 O-rings in each of the carb and have just ensured that the manometer ports are blocked. How would the float level cause a "too rich" problem in one cylinder and how might I check the fuel level in the float bowl. There is a lot I still have to learn here and really appreciate your advice.

The physics of the carburetor is akin to drinking liquids through a soda straw. The closer the pool of liquid is to the vacuum source, then the easier it is for a set vacuum to draw liquid up through the straw. IOW, the closer the pool is to the vacuum, the greater the volume of liquid drawn up. So the height of the fuel inside each float bowl is critical when you have 2 carbs you need to run exactly alike.

Some new updates on the situation: I took the right carb off the bike and took it apart again and inspected all the O-rings and see if the choke is on correctly. Comparing what was on my carb to Snowbum's notes, my choke is oriented correctly and all parts looked good. I also checked the float height and it was the same as the other side. Once reinstalled, I checked the throttle cable tensions once more and made sure the choke cable was functioning properly. The only thing I noticed was wrong was there was a small crack in the rubber boot that goes over the tube that connects the carb to the air filter housing but I don't believe that had much of an effect as I sealed the crack with duct tape and it didn't change anything (will replace the boot soon). I took the front cover off to check the advance mechanism (though I wasn't really sure what I was looking for/ what to do) but there was some free play until the springs started to pull the arms back and when pulled out the springs pulled the arms back in. The bike still is smoking from the right cylinder only so I am unsure if the right cylinder is running rich or burning oil (I think it is oil). It smokes very lightly or not at all at idle but gets heavy when the throttle is blipped while the motor decelerates to "idle". Finally, I took the bike for a ride to see if it got better when the bike was warm, and at the end of the ride, the bike would only smoke after decelerating from heavy acceleration but the idle had crept up to ~4000 rpm at the end of the ride. Am I right that the carbs have to be synchronized at a "standard" idle? I haven't synchronized because of the high idle. Any ideas what could be causing this? I am going to take off the left carb tomorrow and take it apart too, just to check. Thanks for all the help.

• Due to the length of time it takes to heat the engine oil, engine idle changes after lengthy warm-up. It's only when the engine is fully warmed that you can properly adjust and balance the engine idle (~1000 RPM), and/or balance the throttle cable pulls (~1800 RPM). I highly suggest you fully warm the bike and then completely re-adjust all the idle and cable settings using a manometer, such as the one previous suggested. Any attempt to adjust the carbs without a 10 mile warm-up ride and a manometer is simply a waste of time.

• Too much fuel is always black smoke. Burning oil is always white smoke. You went into great detail on "smoke" but never categorized it by color. Additionally, BMWs are extremely efficient engines, and also create lots of water vapor in their exhaust that can look like oil smoke.

• Here's a good video that explains the Bing part marking and placement....
https://www.youtube.com/watch?v=hDsJH1Y9W_U

Hope this helps.

Fixed the idle issue today. Turns out that is was the left carb throttle blade not returning to fully closed because the return spring was too short. The bike idles like normal now. Will sync the carbs tomorrow. However, there is still the issue of the right cylinder emitting white smoke constantly and especially when blipping the throttle. I am going to try to ride for ~10 miles today to warm everything up to see if that does anything for the smoking. What issues could cause the right cylinder to burn oil at such a rate (it wasnt smoking like this when we bought it a month ago)? And again thank you for all the help you've given while we try to sort out these issues!

Glad to hear you're making progress. It can be slow going on a new-to-you bike, especially if you need to undo several PO bodges AND overcome a pre-existing condition to get the bike to run like you want.

What issues could cause the right cylinder to burn oil at such a rate (it wasnt smoking like this when we bought it a month ago)? And again thank you for all the help you've given while we try to sort out these issues!

• You say you've only had the bike a month, but have you tried changing the engine oil ?

• What is the condition of the air filter ?

• Which cylinder receives the oil from the engine breather ?

Thank you for the encouragement... it has been slow going but I have been enjoying learning about the bikes. I have not yet tried changing the oil but can do so very soon, the air filter is brand new (I installed it relatively early on), and the right cylinder has the engine breather tube in it. I saw that the breather could be causing the oil to get into the cylinder, so after running the bike to confirm it still smoked, i shut the bike off and pulled the boot from the airbox to the right carb off and stuck my finger in the breather to see if there was an oily residue. Not sure if that is a legitimate test but the breather tube was dry.

• If the bike is new to you and you are unsure of the type and weight of the engine oil, then most definitely start with an engine oil change. There are several oils available at your LAPS that are within the Airhead spec: Valvoline 20W50 VR-1 "Racing Oil", Mobil-1 15W50, and any other 20W50 with an API spec of SF/SG (or even SH). What you do not want is car oil rated at SM or SN.

• Often times engines that have been in long-time storage simply need a 100 mile ride with the correct oil to re-seat the rings. If something is worn on the rings, then a 100 mile ride is not going to make them any worse. One way to tell the rings are re-seating is that the idle speed will need to be lowered (because the compression has risen).

• It's good that there is no oil residue inside the breather, but that is not conclusive. Over the RH cylinder, but under the black engine name plate, is a small, curious hole in the engine case. That hole is not mirrored on the other side. I'm wondering if oil is dribbling out of that hole and down the side of the engine ?

All the best.

Thanks Wobbly! I rode the bike for ~10 miles yesterday and the smoking slowed to almost nothing. Today I started the bike for a quick ride and the smoking had stopped completely. Will change the oil and sync the carbs after this July 4 weekend and take the bike out for a nice trip!

Your Official Airhead Owner/ Mechanic certificate and decoder ring are in the mail !!

Congrats.

One more issue has popped up just as I was getting excited to get back on the road. Yesterday, I almost ran out of fuel and had to go on reserve. Put in a half gallon of high test fuel to get ready to do carb sycn the next day. Forgot that this was the first new fuel in the tank for over 10 years. In the morning I turned on the petcocks and did a rough adjustment carbs. Turned off the gas and went to get the stuff for the carb syn. When I got back, I turned on the petcocks on and Fuel gushes out of the left carb when both petcocks are turned on. Following Snowbum's advice, I removed the float bowl and let fuel flow out quickly to clear any debris that could be on the float seat. Once I did this, the leak stopped. The left carb gushing fuel only happened after I put half a gallon of new high octane fuel in the tank, and the float bowl looks like there are a couple small chips of paint on the bottom of the bowl.

I think this is crud in the gas. I can put screens in the petcocks, temporary filters in the fuel lines or just swish gas through the tank (but I have no place to put waste fuel so not keen on this one). Appreciate your suggestions/input... Thanks