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Author Topic: fuel economy down the drain  (Read 999 times)

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Offline ClausN

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fuel economy down the drain
« on: August 06, 2012, 08:36:32 AM »
Hi
My 750K6 is now going 25% less distance on a tank of fuel then usually ! And it seems to have less power also.
Engine is rebuild recently and have been running great for 2000km. The carbs where only taken apart and checked. Electrics have not been touched apart from a new ignition plate. Timing is spot on.
Suggestions:
Ign coils ?

Regards.
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Offline flybox1

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Re: fuel economy down the drain
« Reply #1 on: August 06, 2012, 09:04:12 AM »
We need more details about your bike setup.
exhaust, intake, carb, jetting, new plugs? change gas? clean tank?...etc

dont go to the Dentist, and not open your mouth  ;D
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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"Knowledge without mileage equals bullsh!t" - Henry Rollins

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Offline Gordon

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Re: fuel economy down the drain
« Reply #2 on: August 06, 2012, 09:15:01 AM »
Check to see if all cylinders are firing.  A dead cylinder could easily explain a simultaneous drop in power and increase in fuel usage. 
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Offline lucky

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Re: fuel economy down the drain
« Reply #3 on: August 06, 2012, 09:43:54 AM »
Check the oil level.
Just in case a float is sticking and draining into the crankcase.
Make sure all of your float bowl drains are clear.
Do you have the same air filters and exhaust after your rebuild, as before the rebuild?
« Last Edit: August 06, 2012, 09:45:34 AM by lucky »
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Offline ClausN

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Re: fuel economy down the drain
« Reply #4 on: August 06, 2012, 10:11:45 AM »
Sorry guys. A bit more info:
It hasn't just happened after the rebuild of the engine. It has been running great for two years or so (2000km).
Spark on all cylinders. But seems a bit weak I think?
Foats are good.
Std carb and jetting (same as before rebuild)
Std air filter (same as before rebuild)
Marshall 4-1 exhaust (same as before rebuild)
Clean tank and fuel (same as before rebuild)

Is there a DIY guide to check/measure condision of coils ?

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Offline 2wheels

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Re: fuel economy down the drain
« Reply #5 on: August 06, 2012, 05:20:59 PM »
Is the front brake dragging?  I guess the rear could drag as well but that is unusual.  Tire pressure?
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1970 CB750 K0 (I can't believe I tossed my duck tail seat in the trash 30 years ago)

Offline Stev-o

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Re: fuel economy down the drain
« Reply #6 on: August 06, 2012, 10:24:24 PM »
When did you lady do a full tune up? (plugs, caps, points, condensers, valve adj, time and carb sync). It may be time...
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........
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