Intermittent loss of throttle. (Feels like I'm running out of gas)

[Desperado]

Hey guys

1985 K100RT

I've had this issue over the last few hundred miles and have tried various fixes. It feels like I'm running out of gas even with a full tank. I lose any throttle response and the bike becomes jerky. It's doesn't feel mechanical. It feels like a fuel/air/mixture problem. If the bike is cold, it will take 35-40 highway miles to start showing symptoms.

Attempted fixes:

-Fresh air filter
-Fresh fuel filter
-A few rounds of injector cleaner
-New fuel pump (purolator 2042 mod well documented here: http://www.motobrick.com/index.php/topic,2058.25.html)
-Checked electrical going into the tank

I'd love any suggestions. Home is Los Angeles but I'm currently in Yakima, Washigton. I'm going to start checking the fuel rail and injectors and I'll update when I can.

[The Mighty Gryphon]

I'm thinking coils or hall effect sensors.  Could possibly be the spark plugs.  35-40 miles is about what I would expect it to take to get the Hall Sensors hot enough to be a problem. 

If you let things cool off a bit does the problem go away until the engine gets hot again?   

If the problem was a lean mixture I would think it would be worse when the engine is cold.

[Desperado]

It does go away when the bike cools off. The plugs are relatively new but I plan on checking them out. Thanks for the tip

[Laitch]

Review this article, especially #6 and the text following. It affirms the suggestions that have been made already.

[Martin]

Get a can of freeze spray, when the bike starts to act up spray the area where the Hall Effect sensors reside. If this fixes the problem you will know. Do it a couple of times to make sure. I have diagnosed an overheating crank sensor with a bag of crushed ice, but freeze spray would be easier.
Regards Martin.

[Desperado]

Ok I'm back. I tried the freeze spray test as well as a hair dryer and it doesn't seem to have any affect. Like I said before, I'm 1100 miles from home and don't have quick access to a heat gun, but I just went on a 60ish mile ride and stopped three times to test the freeze spray. I also tried riding with the gas cap open to make sure it isn't a tank venting problem.

I'm not completely sure the Hall Sensor isn't the issue. The freeze spray seems like a vaguely crude way to test so that may still be at play.

I'm going to let the bike cool off a bit and then take the fairing and the tank off so I can start checking things there. I'll check plugs then as well.

Any other suggestions are fully welcome.

[The Mighty Gryphon]

On your test ride, you got the problem to happen and you were able to get the cover off and shoot some freeze spray on the sensors.  Is that correct?

How long did you have to wait before the engine would run correctly?  Did the freeze spray shorten the time to get running again?

[Desperado]

Would it be safe to spray directly on the sensor? I only sprayed the cover, hoping that by proximity, the sensor would cool down.

If I let the bike sit for 30 minutes, I can generally get another 30 highway before the issue returns.

[Laitch]

I just went on a 60ish mile ride and stopped three times to test the freeze spray.

Does this mean that the bike cut out and stopped three times but started up again after freeze spray was applied?

[Desperado]

The bike doesn't completely shut off. It gets jerky to the point that you can't safely ride it. The throttle becomes unpredictable.

[Laitch]

The bike doesn't completely shut off. It gets jerky to the point that you can't safely ride it. The throttle becomes unpredictable.

The freeze spray got you restarted?

[Desperado]

No. It is not a problem of starting the bike. The freeze spray did nothing. I can start the bike at will, it just runs like crap.

[Laitch]

No. It is not a problem of starting the bike. The freeze spray did nothing. I can start the bike at will, it just runs like crap.

What I should have written was "does it run smoothly after the freeze spray?" Apparently it doesn't. It just has to cool off without help. Have you checked off all of Eilenberger's other five suggestions? Fortunately or unfortunately, there are several other problem sources to check. You just need to be patient and methodical.

[Laitch]

Here an approach to the hair dryer method.

Could it be the Hall Effect sensor? 

Yes.............to test: remove the T-shaped cover in front of the engine (be careful with the gasket).
With a cold engine, heat up both HES with a hair drier....start, then the engine should stop much
earlier...if it's one of the HES that is the problem.