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Should I shim jet needles

  • Thread starter Thread starter Black 550 L
  • Start date Start date
B

Black 550 L

Guest
bike is running lean would shimming help or should I shim? I'm cleaning the carbs this week installing new Orings just wanted to know if I should try this while it is apart 1980 550 L 21000 miles premium fuel Thanks
 
Go ahead, clean the carbs, change the o-rings, set everything back to normal, but please ... GET RID OF THE 'PREMIUM' FUEL. :eek:

Unless you have done things like increase compression and/or change cams, you do not need 'premium' fuel. 'Premium' fuel has fewer BTUs per gallon, is harder to light and burns slower, so why would you want to use it in a stock engine? Only when compression has been raised to the point that the mixture heats up enough to auto-ignite do you need fuel with higher octane to resist the auto-ignition. It resists the auto-ignition because it is harder to light, meaning it will wait for the spark before it lights. Because it is slower burning, the spark needs to be advanced, too, so it will be finished burning in time to exert maximum pressure on the piston.

Too many people think it's the higher-octane fuel and/or the advanced ignition that provides the power, but it's really the increased compression. The fuel and timing changes are only there to compensate for problems that the higher compression introduces.


So ... if your bike is stock, you will likely not need to shim your needles. Put everything back stock, set the mixture screws out about 2 turns to start with, then warm up the bike with a ride around the block and then fine-tune the mixture screws when the bike is warm.

.
 
I'm a shim the needles advocate. It made a very positve improvement on driveability on both my old 550 and my current 850. No real downside I can notice since the bikes were so lean from stock.

Agree about the premium fuel, waste of money. As a side note, many modern cars have adjustable timing systems so using premium can actually increase mileage since the ECU can switch to a more aggressive timing map which will both make more power and save gas.
 
What octane fuel do you recommend? I thought the manual said 90 thats why I am buying the more expensive fuel
 
Nessism said:
I'm a shim the needles advocate. It made a very positve improvement on driveability on both my old 550 and my current 850. No real downside I can notice since the bikes were so lean from stock.
Click to expand...

Don't forget we're at sea level, it might not work out so well for someone who lives at elevation. Your shim is probably similar to 3 or 4 thousand feet of elevation I would think as it should run richer throughout the range...

I'm a regular man too. :)
 
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