Advise on carburetor rebuild

[Einar]

Hi everyone.

My newly bought R65 (1981, 115k miles) is requiring work to be brought back to a better life so I'm hoping to occasionally bounce some ideas off you guys. It will be a steep learning curve for me.

First up rebuilding the carburetors, and a few associated questions:

1) There seems to be dirty oil inside the carb as well as inside the piston. Is this normal? It doesn't smell distinctively like gas hence the question.

2) The long needle that goes from the diaphragm appears to be slightly bent as do the jets that it goes into. I am unsure of the effect this has on the carb-operation. Both carbs have the same signature.

3) The threads on the screws attaching the butterfly to the rod are damaged. Are these screws meant to be replaced each time they are undone? I heard something about "1-fitting-only" screws somewhere in the Bing carb to prevent a faulty screw ending up in the engine.

4) The floats seem to be in decent condition. Is there a simple way to test them? I don't have an electronic weight that can measure down to 13 grams.

5) Is the float needle in decent condition?

6) Is the fuel hose misaligned?

As can be seen from one of the pictures, the carbus have a lot of oil smear as do the engine block. I might have several leaks (piston block, drive train, right carbu). Currently in the process of identifying them, cleaning up and replacing seals.

Both carburetors are currently in pieces waiting for the rebuild kits.
Your input will be much appreciated.

[Barry]

I'll answer 4. for now.

Test them in a jar of fuel and if they look like this you need new floats. I'm supporting the float at the pivot just like they are when installed. New floats would have approx. 1/3 above the surface of the fuel.

[Einar]

Great. I can do that no problem. Thank you for the reply.

[montmil]

1)  Note the plastic tube exiting the air box. This is a component of the crankcase ventilation system. It often pukes an oily mist into the air tube, on into the carb and intake tract. Overfilling the crankcase can exaggerate the issue. Myself and numerous other Airhead owners maintain the engine oil level at the halfway point on the dip stick. BTW, measure oil levels with the cap unscrewed and resting atop the oil fill opening.

2)  The needles and needle jets are among the major players in carb operation. Any damaged or worn parts should be replaced. The needle n' jet control carb ops from just off idle until the main jet comes into play at close to WFO. Yes, theslide cutaway has its part but it doesn't cause problems unless someone makes it a problem. The needles can wiggle a bit. The constant movement of the steel jet needle againstthe brass needle jet means wear is inevitable. If they are suspect, replace them.

3)  The small screws securing the butterfly disc to the rod are supposed to be peened to prevent their backing out. Remove them if you must but use caution not to booger up the threaded holes in the shaft. A Dremel tool is handy to grind off the exposed threads... As is a prayer to the gods of Bing.

5)  A worn float needle seat will have a "wear ring" that should be visible and felt during examination. If questionable, new bits are cheap and easily replaced.

This next bit of advice is too late for you... Disassemble one carb at a time. Some parts are handed and are designated L or R even though they can be fit to either the left or right carb. Mix ups become a tuning nightmare until the root cause is discovered.

[Einar]

Great feedback! Thank you once again Monte!
I have now rebuilt the two carbs and will install them tomorrow.

1) I will drain the oil and refill to no more than half. I will use a synthetic oil as well, I have a feeling they will create less fumes.
3) I do not recommend to remove the butterfly screws. I damaged the threads in the process and was lucky to be able to put them back in place. They are now permanently damaged and will need to be replaced on next occasion.

Will keep you posted once installed. I was fortunately aware of the right/left non-compatibility and the risk of dismantling both at the same time, so I hope I managed to keep the relevant parts separated.

Thanks for your input guys.
Einar.

[mrclubike]

Like Monte said
If you would have ground off the exposed thread of the butterfly screw you could have easily gotten them out.  
The screws should be replaced anyway after that.
the big question is did you damage the throttle shaft.
It is a good thing you took the shaft out
The O rings on the shaft probably need replacing anyway.  

[Justin B.]

The butterfly screws are, as previously noted, to be used only once.  When the screws are installed and tightened (after plate is aligned) the protruding threaded portions are physically "peened" or deformed to make it impossible for them to get loose and get eaten by the engine!

You could probably just re-peen them but it would be safer to put in new ones.  I think your shaft is probably OK as it is steel and the screws are brass, IIRC.

[Einar]

Installed the carburetors this evening. Did a 5k ride and all seems smooth after some needle friction in the beginning that sorted itself out with Carb Cleaner.

Next up is the cylinder seals. Will do my research and surely return with more questions.

Thank you for your valuable input. This is a great forum!

[montmil]

A note regarding synthetic oils in old Airheads. Odds are that most, if not all, seals throughout the engine, gearbox and final drive components are OEM. Syn oil is amazing stuff. So thin and slippery, it can even sneak past the oil seals that's retrying to keep the oil where it belongs! You may get lucky. Then again, you may notice oil weeps, seeps n' leaks. A return to conventional lubes usually cures a case of "the runs."