RPM's surge, gas mileage dropped, runs hot - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 11 Old 01-19-2011, 10:19 PM Thread Starter
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RPM's surge, gas mileage dropped, runs hot

When shifting (warm or cold) it takes up to 5 seconds for the RPM's to drop below about 3000 - kinda tough on the gear dogs... I also noted that I'm hitting the reserve tank at 200 miles instead of around 230. Finally, the engine seems to be running hotter. I bought this bike a year ago with only 1000 miles on the odometer. After buying it I did all the suggested maintainence except adjust the valves. I haven't pulled off the cap and adjusted the air screw, but I don't see how that would cause surging. Other than that the bike runs great. (I sold a BMW R1100RSL to get the KLR and I LOVE it!) Thanks, Barry
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post #2 of 11 Old 01-20-2011, 02:02 AM
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Does the air butterfly snap to when the throttle is closed?

If not, the throttle linkage may be boogered; I'd check the spring and the two throttle cables (i.e., the OPEN and the CLOSE cable) for free travel of the air butterfly.

Air butterfly snaps to, but the problem persists? Then, I'd check the slide for free up-and-down movement; slide could be sticking in its grooves, or slide spring compromised.

If the final idle speed is within specs, doesn't sound like idle adjustment screw is out of whack, or serious jetting problems exist.

Assume the "choke" (starting enricher) plunger seats fully in the carb when the choke lever is in the OFF position.

When the throttle is closed, so should the air butterfly close, immediately. With the intake airflow cut down, the slide should drop from the force of the slide spring very soon thereafter, since airflow vacuum alone raises the slide, uncovering needle and main jets providing fuel to the engine.

Here's how your carb works: http://www.gadgetjq.com/keihin_carb.htm

I consider adjusting the fuel screw fundamental (although it dominates only the idle air/fuel mixture); I'd recommend 1.75 turns out as a starting point for a stock bike.

Valve clearance should be of no consequence to your open-throttle-to-idle transition problem, seems to me.

The unknown magnitude and conditions associated with running "hot" make prospective diagnosis difficult, for me.

Last edited by Damocles; 01-20-2011 at 02:10 AM.
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post #3 of 11 Old 01-20-2011, 09:26 AM
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Read post #2 twice.

The overheating may be related to a lean factory carburetor setting. A lean mixture tends to burn too slowly and causes hesitation to throttle input, reduced mileage, intake backfiring [“POP!” up the intake tract], exhaust after firing ["pop-pop-pop" on deceleration], surging at steady throttle cruise speed, and / or engine overheating. Much of this can be remedied by adjusting the air / fuel mixture screw as mentioned above.

Does this bike have a set of after market hand guards on it? A good "bump" can restrict the the throttle housing from returning freely. Is there anything restricting the movement of the throttle assembly at the handlebar? Cable free of kinks, properly routed, the right cable? If that all checks, you might consider disconnecting the throttle cable at the carburetor and try blipping the assembly by hand and check the response. That should narrow down the location of the problem to either external or internal to the carburetor.

It would be useful to know if this bike still has the stock air cleaner and exhaust on it, as these things will affect the balancing act going on in the carburetor, which will highly affect operating temperatures.
Aftermarket handlebars, risers, grips, "timber moments", all could contribute to the throttle response issue, in addition to the internal possibilities mentioned by Damocules. BTW, what year is your bike?

And welcome to the forum!

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post #4 of 11 Old 01-20-2011, 09:46 AM
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+ 1 on the freely-rotating throttle "barrel" on the handlebars, vatrader!

A lean mixture indeed burns hotter than one nearer stoichiometric air/fuel ratio, but . . . as mentioned, the nature of this "hot" condition isn't known.

If running "hot" at higher throttle openings, conceivably, a partially-occluded fuel jet could be in play. If at idle, the fuel screw may need opening (I think the fuel screw dominates the mixture at idle).

Otherwise, if the air butterfly closes upon command, and the slide moves freely, and the "choke" plunger seats fully; oughta come to idle quickly when the throttle is closed.
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post #5 of 11 Old 01-20-2011, 11:40 AM
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All great replies...

A surge or hanging idle also could indicate an air leak on the intake side. With the bike idleing spray some starting fluid or carb cleaner around the carb's intake, cylinder base and the head gasket area. If the RPMs pick up there's a leak at that area.

No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him. 1 Cor 2:9
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post #6 of 11 Old 01-22-2011, 10:11 AM Thread Starter
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Thanks for the replies. The reason I traded my BMW for this bike is that I wanted to get wrenching again - so this is more fun than PITA! The bike is a 2006 - 100% stock. I checked the cables and butterfly and they all work just fine. This weekend I'll check the choke plunger and check for air leaks by spraying some carburetor cleaner around the intake fittings. I'll also dig into the reference on how the carb works. As a kid I had a TR-4 with CV SU carbs and they appeared to be magic. It wasn't until Keven CAmeron explained the basic idea that I got it. Thanks Again.
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post #7 of 11 Old 01-22-2011, 01:39 PM
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I assume you checked the obvious, clutch plates slipping?

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post #8 of 11 Old 02-17-2011, 12:08 AM Thread Starter
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Just wanted to thank you guys for the input. I ended up taking the carb off, drilling the cap off the air screw, forging a little screwdriver out of a nail, and loosening the screw 1/4 turn. I also checked the valve clearances, found them all to be tight and spent big bucks on 4 new shims. Finally, I replaced the spark plug and did the T-mod. Now the bike runs great and it kept me out of trouble for a week or so. Thanks again!
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post #9 of 11 Old 02-17-2011, 12:27 AM
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Originally Posted by BarryDorr View Post
I also checked the valve clearances, found them all to be tight and spent big bucks on 4 new shims!
Next time you need to change shims, remember your old BMW dealer.
The shims are the same ones that are used in BMW 2 valve K-bikes, and are usually cheaper at the BMW dealer. If he's closer than the Kawi dealer, it'll save you time and money.

Hard to believe for a company's name that stands for Bring My Wallet, eh?
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post #10 of 11 Old 02-21-2011, 03:59 AM
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B-D----"More fun than PITA?? "People For The Indulgence of Tasty Animals??

Enjoy the enthusiasm.

~Things work out best for those that make the best of the way things work out~
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