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Old 05-04-2009, 04:26 PM   #1
upsman OP
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airhead is driving me crazy , help

I have a 78 R80/7 that i have been bringing back to the street. I rebuilt the carbs, changed fluids, syched carbs, set timing and valves and thought i was going to have a sweet running bike, always has worked before.

Well it hasn't quite gone like that, it starts hard, hesitates off idle and seems to miss or surge at speed. I would appreciate any help with this problem.


Thanks Greg
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Old 05-04-2009, 05:04 PM   #2
outfit
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What did you notice when doing the timing, say to the Z mark (full advance)?

Safe riding Karl.
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Old 05-04-2009, 05:05 PM   #3
Wirespokes
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When did this problem start? Before all the work was done, or after?

More data is necessary! Give us some history. What was done to rebuild the carbs? Is there an RPM range where it misses or surges?

There are quite possibly multiple problems going on here. For one, it's quite possible the throttle cables aren't totally synched causing the hesitation off idle.
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Old 05-04-2009, 05:25 PM   #4
upsman OP
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i have had the bike for a few years and just put it on the road this year. the carbs have been synched twice, it hesitates off of idle and seems to surge or hunt in the mid-range. starts hard, choke , no choke, wants to run on one cylinder at first. thanks greg Karl i didn't notice anything out of the ordinary when timing the bike, or when setting the valves. carbs were rebuilt including choke circuit, they aren't switched i checke that this weekend. thanks again
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Old 05-04-2009, 05:31 PM   #5
Boon Booni
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Quote:
Originally Posted by upsman
i have had the bike for a few years and just put it on the road this year. the carbs have been synched twice, it hesitates off of idle and seems to surge or hunt in the mid-range. starts hard, choke , no choke, wants to run on one cylinder at first. thanks greg Karl i didn't notice anything out of the ordinary when timing the bike, or when setting the valves. carbs were rebuilt including choke circuit, they aren't switched i checke that this weekend. thanks again

How many turns out are your idle mixture screws?

Did you have both carbs apart at the same time?

Did you put the enrichener roatary valve in correctly. It can be put in up side down.
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Old 05-04-2009, 05:32 PM   #6
jtwind
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Still need more info. Did you check/replace diaphragm? Replace needle jets and seats? How are the points? Was timing set at full advance? Have you checked fuel flow and float level? Valved adjusted? The more info you can give the more folks can help>
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Old 05-04-2009, 05:35 PM   #7
bgoodsoil
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I had similar problems. It turned out to be 20+ year old spark plug wires. Flex 'em back and forth a little. If you see cracks they could be the problem.
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Old 05-04-2009, 05:39 PM   #8
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I'd start by asking: When the last time you rebuilt your carbs?

You'd probably be absolutely amazed how much better fresh carbs will make the bike run. I know I was...!

Do a top down, checking the ignition, wires, timing and the carbs. If you get everything spot on, the bike can't help but run well.
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Old 05-04-2009, 06:12 PM   #9
upsman OP
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thanks for all the answers. brand new carb rebuild with diaphrams, everything new in carb. new points. valves set. i will check spark plug wires. thanks again
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Old 05-04-2009, 06:18 PM   #10
Renner
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maybe more than one problem

Quote:
Originally Posted by bgoodsoil
I had similar problems. It turned out to be 20+ year old spark plug wires. Flex 'em back and forth a little. If you see cracks they could be the problem.
+1 new plug wires if you don't know how old they are/provide light-show in the dark/are stiff, crack-prone or brittle.

If you have access to compressed air, blow air back through the jet in the bottom corner of the float bowl. Those are easily obstructed and the procedure is simple.

Your description may be of a bigger problem than can be fixed by these steps but they are in the right direction and should be performed to eliminate at least these two variables, plus they're cheap and easy.
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Old 05-04-2009, 06:39 PM   #11
Wirespokes
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1. Has it alwasy been hard to start the whole two years you've owned it? I see you've had it two years, but only running for the last year.

2. Why was it not running the first year you had it? Was it running fine when you got it?

3. Were the carb passages blown out with a compressor and carb cleaner?

4. Are these the original plug wires with the metal capped ends?

5. How many miles on the bike? What's the history of the bike a year or two before you got it?

6. You say the chokes are together correctly... L is in the left side, R in the right? The punch mark on the end of the shaft points to the end of the lever?

7. Are the coils wired up correctly? I believe terminal 15 is + and 1 is -. +12V goes to 15, then a jumper lead travels from #1 coil at terminal 1 to terminal 15 on #2 coil. Coils can go bad. Also, any little bit of corrosion on connections can cause the spark power to drop drastically. Make very sure there's minimal voltage drop to the coils for this reason. Clean, and Shiny!

Barring any real clues from the questions above, I'd second the recommendation to do a full tune up, or at least verify everything already done. If that doesn't resolve the issues, then start checking out other related areas.

If you're new to these bikes, it may be a good idea to have a knowledgeable airhead guy take a look. It can be difficult to spot the trouble sometimes if you don't know how things are supposed to look.
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Old 05-07-2009, 06:54 PM   #12
upsman OP
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airhead

update on the airhead, it was a spark plug wire, went to the local auto parts store and bought a cheap replacement and the bike runs great. thanks for all the help and advice.
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Old 05-07-2009, 07:50 PM   #13
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Old 09-15-2010, 01:28 PM   #14
Ed~
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Quote:
Originally Posted by upsman
update on the airhead, it was a spark plug wire, went to the local auto parts store and bought a cheap replacement and the bike runs great.
Good going! My GS exhibited strange hiccups during humid or rainy weather on a long trip. My friend helped me trace it back to the cracked insulation of both spark plug wires with a water mister at night. What a light show that was! Tiny electrical arcs grounding down to the pistons rather than reaching the plugs.

I made it home just fine with electrical tape wrapped along the whole of the wire and then changed them out with new ones: fancy Split-fires. Yeah, electrical gremlins can be tricky to suss out.
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