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Old 07-06-2011, 07:36 AM   #1
SMR
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Join Date: Jul 2011
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Default Only runs smooth on 94 octane? Help

1993 Virago 750
Only runs smoothly with 94 Octane. Why? On 91 premium octane bike idles poorly, backfires on downshift, occasionally stalls at stop lights. At speed in 4th or 5th, 4,000 rpm seems to run smoothly. Initially thought it was rust or dirt clogging carb. Used carb cleaner. Ran fine til next tank of gas. Fuel treatment smoothed it out again, til next tank of gas. Tried 94 octane. Ran smooth. Back to premium 91 octane - same problem. Back to 94 octane runs smooth. That should mean it is not dirt clogging the carb or jets - no?
How do I troubleshoot this?
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Old 07-06-2011, 02:02 PM   #2
Easy Rider 2
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Quote:
Originally Posted by SMR View Post
Back to 94 octane runs smooth. That should mean it is not dirt clogging the carb or jets - no?
How do I troubleshoot this?
Where are you located?
Most places in the US, you can't GET 94 octane.

What kind of carb cleaner did you use ?

Get some Berrymans B12 Chemtool and run a tank at twice the recommendation; that would be 2 OZ per gallon, IIRC. While that is in the tank, open the drains and drain the float bowls once.

How's your idle speed; if it's too low it can contribute to low speed problems.

Have you attempted to adjust the low speed jets??

How long since the plugs were changed ?

Any major mods made.....exhaust.....air intake......heads, cams, etc. ??

If I were in your situation and the bike will just be used locally AND you continue to be able to get 94 octane gas........I'd be tempted to keep doing that and not worry about it.

Before resigning myself to that, however, I'd spend at least a little bit of time trying to run down the previous owner(s). Sounds to me like it might have been "juiced" and needs the extra octane.
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