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Discussion Starter #1
I'm no mechanic, but two real ones haven't been able to figure out what's happening with my bike, so I'm trying to figure some things out on my own.

Bike sat for a couple years, and I had carbs cleaned. Bike would backfire a lot, and the mechanic couldn't figure it out.

I let the bike sit another couple years, and I took it to another who cleaned the carbs and fixed the backfiring problem (I think a gasket wasn't seated properly), but now the max speed is about 50 mph, and it has no guts any more. It also stalls a fair amount and is sometimes difficult to crank back up.

A third mechanic told me to check the temp of the exhaust pipes, and I found the rear one was cool. After the bike has been warmed up, I did a compression test:

  • Rear cylinder: Exhaust pipe is cool and compression is 120. Bike easily started while running test on this cylinder. (Yeah, I know I should have turned off the fuel.)
  • Front cylinder: Exhaust pipe is hot and compression is 130. Bike did not start while testing this cylinder.
Spark plugs look good on both. What could be the reason the rear cylinder isn't working?

Thnx for your help,

Dave
 

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Is the rear plug wet? If you're not getting spark you can have compression and fuel but still no fire. Or, and I know you said just had the carbs gone through, but if the rear cyl is not getting fuel, the plug will look great because there's no fuel to foul it, but no fire. Also, but unlikely if you haven't been in the engine, timing could be 180 out on the rear cylinder. You'll have compression, but the spark will be coming in at the wrong time. Just some thoughts, other than that it doesn't make sense.:eek:
 

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you should check your boots, and ports to make sure they are airtight. if you have a leak in the vacuum system, you could not be getting any fuel to the cylinder. also check your ignition system. you could have a grounded wire, or bad coil.

i helped my brother swap an engine on my old cb750 (1977.) for some reason, the bike would only fire 1&4, or 2&3. turned out to be bad points, a grounded wire, and the timing was off. the hassle was going through the system with a multimeter to find the trouble.

on the plus side for you: no points, and only 2 cylinders!
 

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Discussion Starter #5
'92 Virago Horrific Performance (Max Speed of 50 mph, No Guts) Reply to Thread

I pulled the plug on the problematic rear cylinder and ensured I have spark. After reinstalling the plug, I started the bike, turned it off, and pulled the plug again. The plug is dry.

As for thoughts on the carburetor, vacuum system, or timing, these are going beyond my meager skills. :( If it's not something simple, I'll have to take it back to a mechanic somewhere.

Thank you very much to everyone who was kind enough to take time to reply with their ideas!
 

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dont be scared dave! get a haynes manual (or similar) and diy. it make take some time, but you will save $$ and learn your bike better. jmo. :)
 

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size and Year? Have you removed the plugs, put the boot back on, grounded the plug then crank her to see if there is spark? Try that. If no spark then it could well be the spark plug boot. Not the wire. If no spark, swap boots (unscrew the boot from the wire, don't pull it off) If you now get spark then buy a new boot.
If still no spark, get your coils tested.
If you are getting good spark at both plugs then it is the carbs. If it is an older modle, then most dealer mechanics don't know [email protected]*t about them.
Good luck
 
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