Posted by: @16813

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I've looked at the service receipts from the previous owner and I think the only carb service done was new gaskets for the float bowls, he owned it for 20 years and rode it a lot until the last 8 or so, so I'm guessing the carbs were fine before that.

There's no photos, so brother, I can only go by what you write.

But I got to tell you that in my head, the Dusty Springfield song "Wishing & Hoping" keeps playing. 

I once got a 1970 Triumph 500 in for service that wouldn't crank. The customer only wanted a very minor tune-up, since it was "running good last week". But there was nothing really way-off about the bike, except that something about the valve timing struck me as weird. So I called the customer and asked if the timing cover had ever been off. "Oh yes, for some other work I was doing last week."

"And tell me", I said, "did you remove the intermediate wheel?"

"Well, I didn't remove it, but it did fall out when I stood the bike up. So I put it right back where it was supposed to be."

The timing marks on a Triumph twin only line up once every 94th crank revolution, and there no way the present setting was even close. And that was his entire problem.

The point is, the devil is always in the details. And with details you can either guess or you can know. I also know that I'm annoying as all get out. But if you want to repair carbs you got to be laser focused, be OCD about every detail, and investigate everything/ leave nothing to chance. That, or you will be doing it again. Which is exactly where you are, friend.

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Moving on... To set Bing float levels, do this...

Replace original parts with the following modern ethanol-proof Bing replacements...

• Float

• Float needle

Then hold the carb [pivot up] at a position where enough of the weight of the float rests on the needle to take out all the free play. Approx 45°. At that point the mold line on the side of the float should be visibly parallel to the bottom of the carb body. Done.

I think the first thing I'm going to check are the petcocks to make sure they're not clogged. From there I'll pull one carb at a time and go over the rebuild.

Funny, when you've only got a little gas in the tank it helps to turn the petcocks to reserve. Got the crossover line between the fuel lines properly fiddled too. It wouldn't fire on it's own on the starter but a little quick start fired it right up. Again it ran up to redline. I backed off the idle screws 1/2 turn to no effect and quickly shut it down. Does my first guess of improper float height make sense?

If I remember correctly the 45º method was what I did to set the float height but that doesn't mean I got it right. 

Posted by: @16813

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It wouldn't fire on it's own on the starter but a little quick start fired it right up. Again it ran up to redline. I backed off the idle screws 1/2 turn to no effect and quickly shut it down. Does my first guess of improper float height make sense?

• No it does not make sense. Your throttle cables are too tight or your slide isn't going all the way down. This has already been covered (with zero feedback).

• Float height can effect the mixture to a small degree and has a lot to do with float bowl leaking at the gasket and overflow tube. (Float height is like #80 on the list of most influential things to check.)

• Again... Either your Enrichener circuit is not working (clogged path, reversed disc, incorrect choke cable setting, etc) OR you have a gigantic air leak (vacuum gauge screws left out, rotted inlet rubber hoses, loose inlet spigot, etc) OR your fuel is very old. In an extreme case the valve timing could have slipped.

We are covering explanations and material previously covered. If this doesn't fix it, then you need to pack up your carbs and mail them to someone who really knows Bings and can help you. 

Looks to be sitting about right to me. 

Slide bottoms out properly. Throttle cables could be an issue, I looked online for a description of how to do that adjustment but didn't find anything. 

Definitely not the throttle cables, I checked and there is a touch of slack there so the butterflies close completely. I backed off the choke cables too so they close completely. New gas so it's not that. 

I guess start looking for an air leak. No screws left out I'm pretty sure. I'm not sure on terminology, what are you calling the inlet spigot? 

The intake spigot is the sleeve on the intake side of the heads where the carburetor fits up. More precisely, the stub that the rubber sleeve fits on. An air leak at this structure will destabilize the idle. 

I would also point out that it is possible to install the butterfly discs in the throttle shaft incorrectly. I've done that myself. The edge of the butterfly discs have a slight bevel to allow the disc to completely close in the throat of the carburetor at full stop. The bevel is so slight that I can not see it without the assistance of a magnifying glass. The undesired effect is to hold the butterfly slightly open which does not allow the motor to idle. It causes the motor to run above idle, but not typically going straight to red line. If you can see any light bleeding around the edge of the throttle butterfly, this might be in play.

Ok, I will check the intake spigot when I get back home. I definitely double checked the butterflies were in correctly, it was easy to see if the bevels were facing the wrong way. I had a look on one just so I'd know. There was a "10" on the outside lower face for reference. 

Turn on petcock, wait 30 seconds, turn off then remove bowl. It should have gas. Raise float, turn on petcock. Fuel should flow when float lowered. Flow stops when float seam line is parallel to carb. If no fuel no run.

Bob

The empty float bowl was my own stupidity not turning the petcocks to reserve rather than "on". I had one start where it settled down to a nice idle but back up to super high again. I'm thinking vacuum leak as I can't get these elbows to go in tight into the airbox.

1. The vacuum leak you need to concern yourself with is between the carb and the cyl head.

2. Is there, or is there not, a screw blocking the end of BOTH vacuum takeoff ports ?

?1

YaaaaY! Thank you so much for pointing me in the direction of a vacuum leak! Turns out the issue was the rubber boot from the airbox was pinched on one side. I cleaned that up and reset the idle screws and now it purrs like a kitten as it's supposed to. Just need to balance the carbs now and it's good to go! Too bad it's calling for rain all week!

"The devil is in the details."

Congrats.

Thanks for all your help Richard! My first run out yesterday was great, decent weather despite a section of fog and reasonable temps. I met up with Tim and Joe Hille our MA Air Marshall. They were coming back from St Pierre ao I met them on the highway for a chat and a bite of lunch. Can you believe neither of us remembered a photo?! 

This bike love running at highway speeds, I'm sorry the speedo only goes up to 80 mph as the bike certainly goes faster! It's definitely got a different feel to any of my other bikes but that's no surprise. My only issue was when I got on to head home my signal lights were not working. Coming from my R65 my first guess is the fuse. I've read it's behind the headlight? How much of a pain in the ass is that?

► I believe the fuse box on an R80 is on the Left side of the frame, under the fuel tank, just in front of the LH side cover. You won't see it at first or even second glance. It's a small, black, plastic box mounted to the frame. If you insist on keeping the German fuses, then I'm going to insist you do 2 things....

1. Go buy some 7A or 8A spares for your tool tray. You haven't been able to buy these out on the road since about 1980.

2. Coat the 2 conical ends of both fuses with a anti-oxidation electrician's paste, such as No-Ox-Id. These are located in a semi-wet location and connector corrosion is promoted. And obviously, if you don't know where they are, then you're not now doing any preventative maintenance.

► I highly doubt fuses are your issue. Like other Airheads there are only 2 fuses. One for ALL the lighting, and another for ALL the remaining accessories.