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4 months 1 week ago #4749 by 14979
If the carbs are crud, you'll need carb cleaner. The problem is likely to be the jets, needles and float valve, any part with brass. When I did my CV carbs I just bought a rebuild kit from CapitalCycle, new floats and float valve, etc. I haven't had a Mikuni apart in 40years so I don't know the details of that carb. Just in general Ethanol is very hydroscopic and old carbs have parts the don't like water.

I'd just pull the oil plug and let it drain overnight. I would not run it if you have a gas smell since the thins the oil and you can cause bearing damage.

1981 R100RT

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4 months 1 week ago #4754 by dretek
While I'm at, do I replace the gaskets and clean the oil pan while I'm changing oil/filter. I only ask because I see this residue and tiny leakage near the bolts on the pan?


As for fuel draining here is what I understand:
Remove the line going to the filter from the petcock

see if anything comes out after 12 hours..

THEN, remove the entire fuel tank and empty.

Finally, remove carb floats and inspect/clean the bowls.

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4 months 1 week ago #4756 by dretek
Actually.. after reading p.354 in Clymers, its much more clear. Basically I take off the fuel tank.. and then I see if the petcock is holding fuel in the OFF position for 12 hours, and then I can empty it!

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4 months 1 week ago #4760 by Wobbly
• Yes, do it with the old fuel because IF the petcock leaks it is easier to repair while the tank is empty. To empty means the tank will need to get turned completely up-side-down.

• I would always ride the bike BEFORE replacing any gaskets. This because the ride might show that you need to take the part back off again, requiring another new gasket. However, your gaskets simply appear to be sweating and not leaking. That oil could be the result of 10,000 miles, 5000 miles, or 5 miles. You have no idea at this point.

• Remove and inspect the bottom inside of the bowls. If the bowls are clean, then you can stop there. What happens next depends on what you find. It's not a Yes/No finding; it's more like a scale of 1 to 5.

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4 months 1 week ago #4766 by dretek
Fellow airheads, I finally got my hands dirty and got to take off the fuel tank and remove the carbs. Nothing complicated by any means, but, let me tell you, it was exhilarating!

First off, not seeing leakages from the petcock!
:)

Looking at the right carbs, its definitely looking green and crusty. Replace?
Right Carb Float Bowl:



Left Carb Float Bowl:




Can I just use this Fuel Defense Engine Protection Carb Cleaner if cleaning will suffice?

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4 months 1 week ago #4767 by Wobbly
► Good report on the petcock.

► The first photo with the green cast in the bottom of the float bowl seems to indicate you might have avoided a lot of work. Your carbs don't seem to have gotten to the varnish stage, which is typically brown in color. Regular use of a fuel additive, such as StarTron, might clean thing up for you.

► To know conclusively there are 2 tests to perform.....
1) Unscrew the top of the carb and pull out the slide. Protruding from the bottom of the slide will be the "needle". (And it looks just like a big sewing needle.) Look very closely at those needles (one each side) and you should see nothing but bright shiny brass. If you see a green ring (like a bathtub ring) some where along the length of the needle, then that has to be removed with a carb cleaner and a cloth. DO NOT use an abrasive, like sand paper.
2) Down inside the round well next to the main jet is the low speed jet. You need to find or buy a flat screwdriver that precisely fits the full-width of the slot in that jet, fully and completely. Unscrew that jet. Gently blow on it, then hold it to the light. Can you see daylight through that jet on both carbs ?

If there is no blockage on the slow speed jets and no ring on the needles, then everything else should be OK. "OK" meaning not excellent, but a good fuel additive and a great deal of riding will clean the remainder of the scum out over time.

Carefully remove the idle mixture screw, spring and anything else down that hole, then spray your carb cleaner in there. Reinstalled the idle mixture screw 1-1/2 turns out. You can also spray the low speed jets, needles, and main jets.

Check and adjust the float levels per Mic instructions.

► Carb cleaner is carb cleaner.

Hope this helps.

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