1976 R90/6 questions

[Mcdrugs]

Hello all,
I bought my first motorcycle, a 1976 R90/6, that had been sitting in my neighbor's storage unit for 30 years. It is ready to go after rebuilding carburetors and putting on new fuel lines, tires, and brakes. I've had it out on a 5-mile ride around streets in my area.
I would love some advice.
#1 What fuel should I be using in a 1976 Airhead? Back when I was a little kid in the 70's, they sold leaded gas. Do I have to use some kind of additive in the tank, or can I get away with purchasing premium gas? (I live in the USA in Salt Lake City.)
#2 One of the carburetors is dripping gas. Could it be the fuel switch that needs to be replaced? Do those stop working or functioning correctly? Or is it a problem with the carb that was rebuilt?
Any advice is appreciated!

[Kurt in S.A.]

Welcome!

1) Stock compression is 9.00:1 so getting up there. I would think you need at least the middle grade unless you begin to hear pinging. If you do, then you will need to go to the highest grade.

2) Fuel switch aka petcock. Could be that since it was sitting for years. But if it has failed, how come only the one carb is leaking? I think you should pursue the leaking carb first. First thing to try is to turn the petcock on, let the bowls fill, then turn off the petcock. Drop the float bowls. Using a ruler or something that you can stick into the middle of the bowl, how high is the fuel level? I forget the number but likely something like 20-22mm high. If much more than that, your float is not set right or it could be the float is actually sinking, allowing too much fuel in the bowl. Next would be to see if the float on the leaking side actually shuts off fuel flow. Put the opposite side bowl back on. Then holding the float carefully with your finger, raise it so that the line on the float body is parallel to the carb flange. Turn the petcock on. Does gas flow or not? If gas starts streaming out, then your needle valve is not seating or has some debris on the seat allowing gas to flow. If gas doesn't flow, how much do you have to let the float down before you finally get gas flow?

Kurt

[Rob Frankham]

If fuel is leaking from the carb, then there is a fault in the carb... but... make sure where it's leaking from first. Many people have spent hours stripping out the carb only to discover that the fuel line is leaking.

One thing is for sure... leakage from the carb isn't really due to a fault with the petcock. The needle valve in the carb should stop leakage even if the petcock is letting fuel through... for that matter, even if it is left switched on. Mind you, if the carb is still leaking, even when the petcock is off, then it applies that it (the petcock) is also leaking even if it's not the reason fuel is escaping from the carb.

Did you replace the fuel lines? If the lines are old, it's a good idea to replace them as the inside lining of the old lines has a habit of disintegrating and allowing debris to clog the needle valve in the carb...

Are the line filters in the petcocks in good condition? If there are no filters or they are defective, any debria that has accumulated in the tank over the last 30 years will find it's way through and clog the needle valve in the carb...

Did you replace the floats? The hard plastic floats will eventually absorb fuel and become too heavy which means that the float valve doesn't work properly.

Did you replace the float bowl gaskets... did you get them in place correctly? If the fuel level is a bit high, a defective gasket will allow fuel to escape at the bowl/body join.

Rob

[Tom H Ca]

As mentioned, it depends on where the carb is leaking from. I had a float bowl that was leaking from the tube that is soldered or whatever into the bowl. Read about that somewhere and sure enough it was that letting gas get on my boot. New bowl solved my problem.

Tom

[SteveD]

Re the leak...run the tap open with the bowl off (container underneath), lightly jiggle the float p and down. The idea is to flush something that might prevent the valve from closing correctly. It's not unknown to have junk on the seat causing that.
Inspect the gasket whilst you're there.