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nbooij

Joined:

Apr 13

Posts: 11

nbooij says:

Yamaha XJ900s fuel consumption

Dear reader,


Synchronised carburettors and got another bike, perfect. However fuel consumption increased. Went through following steps:
1. Cleaned carburettors and nozzles (of which two were filled with dirt).
2. Outer spark plugs are black and the inner two normal.
3. Pilot screw is on 2,5 turns instead of 1,5. This controls lower ref region. Is this responsible for fuel consumption? Probably not.
4. Synchronized again. 

Q: What things could I try in order to optimize the fuel consumption?

Thanks,
Nico Booij
Netherlands

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  • Posted 2 years ago (24 June 2013 19:01)

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fogie

Joined:

Jan 04

Posts: 851

fogie says:

fuel consumption

Did you check/set the float levels? Were the needles and main jets in perfect condition, ie. needles scored, and jets worn oval? Float needle valves in perfect condition? Floats in good condition, ie. not punctured or bent?

Hope this helps. 

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nbooij

Joined:

Apr 13

Posts: 11

nbooij says:

Yamaha XJ900s fuel consumption

Dear Fogie,

Thanks, will check your suggested points next saturday.
Bougth the XJ900s with extremely low milage1995 with 28000km. Bike looks wonderful, but did quite some jobs to get everything smooth running. Especially maintenance on the forefork paid back in better steering and braking. Replaced the brakes by 4 cilindered brakes from a Fazer: amazing result. Last but not least are the carburetors. Looking foreward to the results. 

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nbooij

Joined:

Apr 13

Posts: 11

nbooij says:

Yamaha XJ900s fuel consumption

Dear reader.
Did quite some cleaning regarding the carburettors. Lots of fuel "gum" on the needles and other places. Replaced the nozzles of the inner cilinders from 100 to 110. Outer Nozzle should go to 95, but could not get them.
Needles have three possible positions. Outer cilinders now on lowest position, middle cilinders highest position. 
Result: fuel consumption dropped a little. Engine runs better. However bougies of outer cilinders are still black. That means the 100 nozzles should be replaced by 95 or even smaller.
Best regards.
Nico.

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smidget

Joined:

Nov 07

Posts: 2423

smidget says:

Hi

High fuel consumption bike from 1995 with low usage.

I would first off ensure the inlet side of the engine was clean, and airtight before considering altering anything in the carburettors, this means before and after the carbs. 

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nbooij

Joined:

Apr 13

Posts: 11

nbooij says:

Yamaha XJ900s fuel consumption

Dear reader,
Finished and tested the modifications:
1. Replaced the nozzles of the inner cilinders from 100 to 110 and the needle in the upper position (of 3).
2. Nozzles of outer cilinders from 100 to 90!! Needle in lower position. Spark plugs went from black to milk coffee.  
Result was fuel consumption drop from 1:13,4 to 1:16. Total investment of 7,50 euro's was quickly earned back.
Engine feels more responsive than before.
Thanks for reading.
Nico

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ranorthe

Joined:

Jul 10

Posts: 157

ranorthe says:

Yes but?

Sounds fine but you've now got quite a non-standard carb set-up. The bike wasn't designed to run with the carbs set-up as you now have them. The bike has an underlying problem which you have not cured, you've adjusted your carbs to get around it.
Have you checked the compression?
Have you checked the float height (the proper way with an external tube)?
Have you tried a new coil? Since the problem is on 1 and 4 you could have a weak spark.

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