Hoping one of the FI Gurus can help with this.

98 Ultra, stock engine. MM fuel system. Runs great on the road, no miss, backfires, etc. Am kind to it, no revving above 3400 rpm, normal hiway speed 62-65. Occasional 70's, and have run into 90's a couple of times

Sudden problem occurring is that when hot, occasionally will suddenly run up a hundred or so rpm at a stop, and when I give the throttle a "rap", it'll misfire pretty badly. Slame starting back up and same thru every upshift. But does not always happen at every stop.

So did a total reset of the MM system thinking that would solve it. Nope.

Never a problem when warming up. Only thing negative I don't like about the MM system is the gas mileage: 33mpg 1-up, 29-30 2-up.

Like to keep it stock, but if I can't resolve the issue, will consider CV carb conversion.

Inside tank is very clean, filter, fuel delivery is fine.

 

One of your sensors or a ground would be my GUESS. I do EFI, but not the MM. Common problems I see here are the crank position sensor and the temp sensors. Maybe the air intake temp sensor? The cylinder head sensor is a frequently listed cause of issues too. It sounds like the ECU is leaning out the mix, so it may think that something is too hot. Can you pull codes?

 

Sounds like the head temperature sensor is on the way out. If you know how to retrieve the code it will be a 14. As it gets worse the bike will buck and start/stop on you while riding. When you give it the gas there will be nothing there like the engine isn't running, then it will run again. Riding with a bad temp sensor is no fun and pretty dangerous. The p/n is 32446-95A. The last time I checked, Surdyke had them for roughly $100. Ronnies HD was out. Some last for a long time, others go quick. I have a theory that a lean running motor causes them to prematurely go bad. I also keep a spare one in the shop.

I would

 

No codes are available. It defenitly sounds like something is leaning it out. Will check grounds (again ) and connections to FI and ECM.

Not acting finicky enough for ETS, but who knows.
Thanks.

 

ETS was my first guess, replaced about 15k ago. But it was immediately obvious by wild rpm swings. Think that will be my first fix and go from there. Surdyke it is. Thanks,Carl.

 

You typed:
"Sudden problem occurring is that when hot, occasionally will suddenly run up a hundred or so rpm at a stop, and when I give the throttle a "rap", it'll misfire pretty badly. Slame starting back up and same thru every upshift. But does not always happen at every stop."

Generally the engine temp sensor will cause a wild swing in idle response and not just 100 RPM.
100 RPM is very little...is that a typo??
If correct then it does not lean towards temp sensor.
If you "rap" the throttle...guessing that means that you twist throttle....you get a misfire.

I think you might have a combination of problems:
-The manifold gaskets (2) at throttle body are probably worthless if original and that is allowing unmeasured air.
They are about $10 total and are easy to change if you use the allen wrench from your garbage disposal unit to turn the 2 bolts.
-The idle control arm and assembly is probably loose...the one nut on that bracket located at throttle body behind air cleaner(remove air cleaner and back plate) can become loose and make things sloppy.
-The idle control motor is dirty and getting stuck.
-The CRANK position sensor wire connector under right side painted cover (under seat). That push and turn connector is loose.

 

The 100 rpm up-idle was not a typo, which is why I did not think it was the temp sensor. The ICM motor screws were actually loose on the mounting flange to where I could wiggle it on the flange...tightened that up, but did not fix the problem.

Checked the assembly nut and it is tight, linkage is cleaned and lightly lubed regularly.

Pretty sure everything is original., so changing the intake gaskets is a good idea. If available, think just replacing the ICM is a good idea.

The crank position sensor connection is something I've never checked (and should have long ago).

Thanks for the input, Im... sounds like I've got a few minor things to check and do. Like I said, I would really like to keep everything original. But I do NOT like the stated gas mileage. Not much I know of I can do about that. Probably will replace fuel lines for new while I'm at it on the conversion I did in one of my older posts. It has worked flawlessly.

Intermittent problems are always the bitch. Ken

 

Perhaps i was reading too fast and missed something...but you write "But I do NOT like the stated gas mileage" ???
The gas mileage on your bike if engine is more or less factory is anyplace between 30-45mpg on a 2 wheeled bike with no side car or trike.
The mileage goes down at higher speeds.
The higher mileage number is basically going down hill with the wind at your back for ever.
If you have a trike then a guess about 27-28 MPG of mixed condition riding and that is probably on high end if you ride above 55mph.
The crank position sensor connection is something that very few people check and it is a simple fix with a figure 8 tie wrap and maybe a few extra ones.
Sensor connector will visually look tight but a slight vibration will cause motor to studder, miss....a higher reving motor or a bump in the road will cause a studder/ tumble/ miss if loose.
When connector is loose...with engine running, bike in neutral and stopped.. Just hit bike with a rubber hammer on hard parts and engine will stumble
I would not put dielectric grease on those pin wires as the connection is tiny.
The manifold gaskets (2) total at throttle body (available from dealer) are probably worthless if original and that is allowing unmeasured air but are easy to change..you can move the throttle body when they are bad and you can also hear a puff/puff with engine running.
The manifold gaskets are just a fancy black rubber band / rubber bracelet looking thing. You need two #26995-86B
The Garbage disposal allen wrench in your kitchen drawer has the correct angle to make removal of bolt easy.
One bolt requires removal on each head and the other bolt can just be loosened.

 

Thanks, I'm. Yep, with a trike body there is the added weight and added friction of the rear axle/ snyder gears....complaining changes nothing. Just needed to vent. Staying inside today, been out in the yard working for 3 weeks and it's beginning to get hot. Fortunate the humidity is still in 70% range. A few weeks and it'll be in the 90's % range . Then it's HOT.. Ken