Airhead bings

[Corvus]

I would be grateful of airhead wisdom, if anybody can help:-

'83 R100 with standard bing carbs.

I set the tick over and sync and the bike ticks over fine until it gets up to full temperature. After a good workout the bike won't immediately offer engine braking upon shutting the throttle. It feels as if the butterflies aren't fully returning to throttle stops, yet they seem to return fine when I've come to a stop and the bike settles to idle speed.

There is plenty of free play at the twist grip. The cable junction seems free enough. Cables in excellent condition.

It is definitely associated with a fast run.

I have some k&n style filters fitted to each carb.

Anyone?

Cheers.

[cornishflat]

First i take it the plugs are good, timing set up and valve clearances correct.I take it the choke cables are set up ok with slack in them. Then you mention the tick over is fast when at full working temperature. You did or should have set up the carbs with the bike at full working temperature, ie not 5 minutes round the block. If not I,d go down that route first. If that does not sort it, what are the colour of the plugs. I did all the above on my R80 with K & N style filters and set it up with a Morgan carb tune and the tick over is fine when up to temperature. As you say its not a big issue and if the bike runs well you,re not far off.

[Corvus]

Thanks Cornish flat.

Plugs are not new but look good. Good colour.

I've not checked the valve clearances. Don't sound too bad to me but I will go through the motions anyway. The ignition is electronic, can it be tinkered with?

I've ordered a set of vacuum gauges as my synchronising method so far has been to insert a 3thou feeler under each stop screw and very carefully watch to see they drop at the same instant. Not really textbook I suppose. Idle screws underneath are set to 1/14 turns out.

Cheers.

[slparry]

are the slides in the correct carbs?

[cornishflat]

I did similar when setting up to give me a base setting. When I had the bike up to temperature I tweaked each mixture screw to give the fastest tick over for that carb the Carbtune being more accurate than my ears/ eyes required a tweak to balance the values of the carbs and that was it dead easy. Now you have a synchroniser on the way you should be able to fine tune things ok. Its common knowledge I believe that the Bings can be a little finicky to set up. Float heights being one area that needs to be spot on. Daft question, but there are no splits holes in the rubbers to cause a vacuum loss.

[Corvus]

Siparry, do you mean have my carbs got the right slides, or are they in the correct side?

Cornishflat, I wondered if the float heights might need a look at.

Thanks guys. I can feel a carb strip coming on!

The bike has 88k miles on the clock + who knows what else for good luck!

I wondered if the slides are worn? I don't have much experience with cv carbs. Maybe it is due some new needles and jets.

Regarding splits in the diaphragms, I haven't looked. The thing has quite reasonable performance, but who knows. There could be a problem there I guess.

Another symptom is that the thing stalls a lot and stutters blipping the throttle from tick over. In the old slide carbs I suppose you'd look at the pilot system for that problem or maybe the slide cutaway. But I'm not sure with the cv carbs. The principle doesn't seem to use a cutaway.

Thank you for suggestions. Please keep it coming!

[slparry]

Siparry, do you mean have my carbs got the right slides, or are they in the correct side?

Cornishflat, I wondered if the float heights might need a look at.

Thanks guys. I can feel a carb strip coming on!

The bike has 88k miles on the clock + who knows what else for good luck!

I wondered if the slides are worn? I don't have much experience with cv carbs. Maybe it is due some new needles and jets.

Regarding splits in the diaphragms, I haven't looked. The thing has quite reasonable performance, but who knows. There could be a problem there I guess.

Another symptom is that the thing stalls a lot and stutters blipping the throttle from tick over. In the old slide carbs I suppose you'd look at the pilot system for that problem or maybe the slide cutaway. But I'm not sure with the cv carbs. The principle doesn't seem to use a cutaway.

Thank you for suggestions. Please keep it coming!

I mean are they in the correct sides

[Corvus]

I mean are they in the correct sides [/quote]

Ah, gotcha. I don't know. I've not worked on the carbs yet, but I know they were cleaned up by the person I bought the bike off. I suppose it is possible they were mixed up.

How would one know?

(You're going to tell me there is L and R stamped on them, yes?).

Cheers.

[Dai wiskers]

Have you got a inline fuel filter fitted that has blocked or got contaminated with water?
To me it sounds like either a air leak on the inlet stubs or fuel starvation mabee a fuel line trapped or cable tied up a touch tight

[slparry]

oooo while I think of it, my R80 mono had a running problem that turned out to be the tiny thin gaskets that seal the choke cover plates, they'd popped out and snapped .... don't know how as they were never dismantled.

Anyway replacements fixed it

Along with replacement coil because the original cracks

[Corvus]

Thanks guys.

I'm going to strip the carbs down and see if anything jumps out at me (slide spring jokes on a postcard).

The air leak theory might be a good one. I'll treat it to some new rubbers.

Anyone tried the squirting of engine start spray technique? Never tried it but I hear it works to show any air leaks?

Cheers fellah's

[Dai wiskers]

Classic sign of fuel starvation won't settle down to tickover after a thrash turn it off let it cool right down it will start warm up fine tickover not a problem but give it a thrash tickover up classic!

Spray either easy start wd40 or anything in an arasol[spelin] [not chain lube save that for all your pivot points taking care not to clog up micro switches] if you have an air leak the revs will pick up unless it's realy bad then revs will drop

Hope this helps Dai

[Corvus]

Thanks dai W.

Yes, that helps a lot. The symptoms certainly seem to fit, on the face of it.

So your thinking fuel starvation caused by the addition of air post mixing? As opposed to straightforward fuel starvation upstream, by a block of some sort?

Both, knowing my luck.

Why does the tick over rise after a good workout? What's the technical explanation? Do you know?

Cheers.

[Dai wiskers]

Check fuel filter in the tap first then work your way to the carbs if you then still find no blockage check for air leaks with wd or easy start if you find no air leak my final check would be float levels as float levels set too low can give the same symptoms

I will appologise now i said running weak what i meant was fuel starvation it could be something as simple as a fuel pipe trapped somewhere or even a air lock in the fuel line
EDIT
Worthless appology i had it right last time

where are you ? perhaps some one could nip over to give a hand

[Corvus]

Thanks again Dai W

I'm pretty sure the tap filters are ok as I had the tank off about a month ago, but I will check down the list as you say.

The carb to head rubbers are very hard so I need to be ordering a new set. I'm going to pick up a can of easy start spray this weekend.

The vacuum gauges have arrived so I can check my mechanical settings method. While I'm at it a check of the floats and general condition internally too.

The symptoms do seem to fit the air leak scenario. Stutters when blipping or trying to set off and tick over rises for short time after a good workout.

Thanks again.