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gas flowing from carburetor


tcausey

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Hi.

 

So I just picked up an '78 R80/7 that's running, but not terribly well, at least at idle. I start by pulling the valve covers and doing a valve adjustment, new plugs, inspecting everything, changing all the fluids (for my own sanity). Then I start reading about adjusting and synching the carbs, setting idle etc. (in my clymer and haynes books). things seem to go okay until fuel starts pouring out of the left carburator into the bucket I quicky put beneath it. Something's clearly wrong on the left side. If the bike is running and I pull off the left spark plug wire, I can adjust the idle mixture and throttle cables, but if I pull of the right wire (while the left is connected), it dies (so surprise eh).

 

So I have NO IDEA about carburetors, but after all, that's one of the reasons I bought the bike . . . to learn.

 

I've read a fair bit, but there was no section on "gas pours from carb" so any enlightenment on what's going on would be great. I don't even mind being belittled.

 

this should be fun.

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I suppose I should confirm I'm getting a spark to the left side. How might I do that? I dropped the bowl and check the floats and sprayed cleaner making sure all the parts were moving. I'm thinking my problem might be sparks to the left side.

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Paul Mihalka

The most common reason for the carburettor to leak gas is some dirt in the float needle valve. It can happen while you are on the road. Quick remedy: Shut the petcock. Remove the float bowl, it is just a spring clip. Put something under the carburettor if you can. Open the petcock. With the gas flowing jiggle the float up and down shutting and opening the gas flow. This should flush out any speck of dirt in the needle valve. Shut the gas, put the bowl back. Hopefully it is fixed for a while.

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thanks. . Looks like it's fine now and that's basically what I ended up doing . . . . just not sure it is firing on that side now.

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Harry_Wilshusen

Sounds like your petcocks and tank needs cleaning.

 

If you really want to learn about your Airhead check out this site .

 

Scroll down about 1/3 of the page to the links on fuel the system.

More than you will ever want to know.

 

Harry

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Thanks Harry. I have an oilhead too and so I started on this forum. That site looks great . . . . a wee bit harder to navigate, but I'm working on it.

 

I've tinkered some on the carbs (and cleaned but haven't rebuilt yet) and the petcocks seem to be fine now. I've cleaned the jets, etc. but I couldn't figure out how to get the float pin out to clean the float needle. The bike sat for a while so I've drained down the tank and refilled the tank and then tonight I just ran it down the road for 10 or 12 miles to try to run some new fuel through the systems.

 

Now that I've spent more time with it. The main problem is that I can't get a consistent idle with the engine warm and I get a little bit of what feels like erratic fuel flow (hesitation) under acceleration. I'm also trying to learn about lean/rich adjustment as well as the best way to adjust all of that. The injectors on my oilhead are a bit more consistent, but I'm learning. I actually think I like the simplicity of the bike.

 

I think I need to just rebuild the carbs and the replace throttle cables so I'm at a good starting point. The throttle sticks a little bit just before full closed and I can't tell if that's affecting the idle speed or not. something's definitely not consistent.

 

thanks for all the help

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A bit premature on refilling the tank.

 

Perhaps it would be a good idea before getting too deep into carb issues and rebuilding to drain tank and remove BOTH left and right side petcocks from tank. You will find screens attached to the petcocks that stick up inside the tank.Clean these, and if they are ruined, buy new ones. Do not use torn screens.

 

And chances are the tank has crud in the bottom as well. Not to mention water. Water is the nemesis of these tanks. They eventually rust out and leak if not maintained properly. The bottom of the tank both right and left side will collect water that cannot exit the area. You should remove tank from bike and tip upside down with gas cap removed to get out water and crud.

 

Reinstall petcocks, paying attention that threads are different.

Petcocks are rebuildable if necessary, or buy new at about $45 a pop.

 

I also run a small inline filter both right and left side gas lines to carbs as additional insurance. These are clear and

will make it easy to visually see fuel flow quality as well.

 

Good Luck with that 80/7, prob the best model BMW ever made!

 

MB>

 

 

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