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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: pinhead on June 26, 2023, 03:28:39 PM

Title: Declining fuel mileage and won't idle 1985 KRT100
Post by: pinhead on June 26, 2023, 03:28:39 PM

I have noticed my fuel mileage decline from about 48 mpg to now about 36 mpg.  Is the decline in mpg normal with age?  Bike has around 90K miles and runs good at speed but when I pull up to stop it will always stall unless I allow rpms drop below 1500 before I pull in clutch.  Then it will idle at stop light without a re start.  Any ideas?

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Laitch on June 26, 2023, 05:58:08 PM

Quote from: pinhead on June 26, 2023, 03:28:39 PM

Is the decline in mpg normal with age?

No, except in Bricks that have not been well maintained.
Remove the air filter; tap the intake side of it on pavement for a while to see what comes out of it. If a pile of particles doesn't form beneath it, something else is the problem.  :laughing4-giggles:

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Martin on June 26, 2023, 06:27:46 PM

When was the last time it had a complete tune up/service. The fact that they can remain in tune for long periods and the valves rarely need adjusting often leads to neglecting them.
Regards Martin.

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Chaos on June 26, 2023, 09:32:55 PM

The fuel injectors get dirty over time and can cause poor running and bad mileage.  Run a couple tanks with you favorite cleaner (or Chevron Techron) and see if that helps. 

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: pinhead on June 27, 2023, 04:09:57 AM

Quote from: Martin on June 26, 2023, 06:27:46 PM

When was the last time it had a complete tune up/service. The fact that they can remain in tune for long periods and the valves rarely need adjusting often leads to neglecting them.
Regards Martin.

What constitutes a tune up?

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Martin on June 27, 2023, 05:14:24 AM

Servicing and tune up procedures are in the handbook or manual. However check and gap or replace spark plugs, check and adjust valve clearances, check and clean or replace A/C element, replace fuel filter if needed, check fuel hoses for softening ,hardening or cracks and replace if needed using the correct specification hoses, check and or adjust TPS, balance throttle bodies, check and adjust mixture. Add a cleaner if injectors haven't been serviced  or get them serviced. Once all this has been done you have a solid starting point to just follow the servicing/tune up intervals and procedures in the manual.
Regards Martin.

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Laitch on June 27, 2023, 05:34:37 AM

Quote from: pinhead on June 27, 2023, 04:09:57 AM

What constitutes a tune up?

:thisplacewhack

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: frankenduck on June 28, 2023, 01:48:02 AM

Failing coils are a likely suspect on an early K100.

Title: Re: Declining fuel mileage and won't idle 1985 KRT100
Post by: Past-my-Prime on June 29, 2023, 10:06:24 AM

Also potential leaky crankcase breather hose (Z-tube) gave me similar symptoms (I didn't notice fuel consumption change, but poor running and stalling, fixed by replacement of this $12.00 part or whatever the cost was).