Misfiring, backfiring

Need help troubleshooting this one. After filling the tank on my 36k mile R100R with non-ethanol 92 octane, the bike started misfiring and backfiring badly. I rode for about 4 miles over 4k rpms and the bike smoothed out. Eventually the problem diminished but never went away even after refilling the tank 3 times with 2 octane ethanol gas. After riding 500 miles to get home I parked the bike and changed spark plugs and replaced the air filter before a month-long pause in my riding.

I started the bike tonight and it took 30-40 seconds for it to finally start (normmally would start in 2-3 seconds). After I got it running I went for a ride and had a bad case of misfiing and backfiring until I was able to warm the engine and run it over 4k rpm. Same problem, misfiring and backfiring.

As background, the carbs were rebuilt 5k miles ago, valves adjusted 6k miles ago, new in-line fuel filters 5k miles ago and carbs synced 3k miles ago.

What should I try next, new plug wires, new coils, new Hall-effect sensor?

Thanks in advance for any and all advice!
Charlie

First, try removing the float bowls and inspect for water. Then check for evidence of water on the jets. Possibility the gas was contaminated and you have some residual moisture.

If you drop the bowls, you might also want to remove the jet stack and look for additional water and/or gunk build up on the emulsifier tube.

Get the smaller can of "Techron" and pour it into a full tank......Ride that puppy as much as you can to let the stuff do it's magic.....It's just fine if you ride maybe 20 miles and let it sit overnight as it "works" on the carbs just sitting also......But RIDE....good luck Bud, it is a total pain to have that happen.....

My wife got a can of fuel for our RTV, a 4wheel utility vehicle by Kubota for doing farm chores and such.....Anyway, poured it in to fill up the tank...Immediately it began to die, run on 2 cylinders (it's a 3 cylinder diesel), run on 1, and then pick up again.....this went on and on and was totally intermittent. Finally drained the tank, fuel filter, and bled the injectors. Put in maybe 8 oz of Lucas and Cetane for diesels mixed into a gallon of diesel and it got much better...... Ok, it got totally almost gone better. Enter hired hand. We were down in the pastures and sent him to the barn on an errand. He came back saying that he ran out of fuel making the 1/2 mile trip to the barn so he put in what was left in that "yellow" can.......NOT knowing that was the can that I drained the junk from the tank into.......lol...he was complaining that the durn thing had started running funny again..........God bless....Dennis

Water in gasas.

Thanks for all the ideas, I never thought water could stay after 3 tanks of gas. I'll drop bowls first thing in the morning and try the Techron idea and will update the group.

174713 said:

Thanks for all the ideas, I never thought water could stay after 3 tanks of gas. I'll drop bowls first thing in the morning and try the Techron idea and will update the group.

Click to expand...

Get a bottle of IsoHeet in the red bottle (Isopropyl alcohol) or Heet in the yellow bottle (methyl alcohol).

Could be the weights in the hall sensor are stuck at a lower RPM. With a stroboscope you might verify this by checking the ignition marks on the flywheel.

Or, blind approach:

- remove battery ground wire
- remove front cover of motor
- connect battery ground wire
- remove front cover of hall sensor (2 screws)
- start engine
- squirt WD40 into the hall sensor
- turn off engine
- remove battery ground wire
- close everything up

/Guenther

Still misfiring/backfiring

Drained the carb bowls, clean and re-installed. Treated gas with iHeet, mixed it in by rocking the bike on the centerstand, let it sit for 3 days. Ran the bike tonight for 20 minutes, problem remains so now on to the bean can.

A couple years ago my 82 R65 started acting up. Everything felt like it was a fuel problem. Could find any reason for the issue. Ended up replacing the ignition leads and the problem went away. Had the same thing on my 75 R90/6 with Dyna III system. Ended up going back to points, replace coils and wires. Just recently had the ignition quit on the R65, replaced it with the ALPHA system.

Don

Hall sensor update

Guenther said:

Could be the weights in the hall sensor are stuck at a lower RPM. With a stroboscope you might verify this by checking the ignition marks on the flywheel.

Or, blind approach:

- remove battery ground wire
- remove front cover of motor
- connect battery ground wire
- remove front cover of hall sensor (2 screws)
- start engine
- squirt WD40 into the hall sensor
- turn off engine
- remove battery ground wire
- close everything up

/Guenther

Click to expand...

Well, still not runnig without misfiring/backfiring even after following Guenther's advice (thanks!). I took a 30 minute ride and the engine ran smoother but still misfired at low and now at very high rpms. I'm now suspecting bad plug wires and/or coils, is there an easy test to confirm their performance?

Short of replacing them? Something we used to do long ago was to run the machine in the dark and look for any glow on/around the wires and other high voltage connections. Check your connections at the coils, including removing and trimming back the wires. Are your plug caps original?

174713 said:

I'm now suspecting bad plug wires and/or coils, is there an easy test to confirm their performance?

Click to expand...

A general test for the wires and coils is to measure the resistance from one spark plug cap to the other. I think it still applies to the later model bikes, but you should get something like 20K ohms from one side to the other. It might check out statically, but since you're having issues when running, it might be a heat related issue. The coils might be breaking down when they get hot...difficult to simulate in your driveway.

Be sure there is no corrosion where the spark plug wires connect to the top of the coil tower. Corrosion inside those connections can create problems.

Have you renewed the heat sink paste under the ignition control module? Could be that this module is breaking down when it gets heated...the paste helps in the transfer of heat away from the module.

20774 said:

A general test for the wires and coils is to measure the resistance from one spark plug cap to the other. I think it still applies to the later model bikes, but you should get something like 20K ohms from one side to the other. It might check out statically, but since you're having issues when running, it might be a heat related issue. The coils might be breaking down when they get hot...difficult to simulate in your driveway.

Be sure there is no corrosion where the spark plug wires connect to the top of the coil tower. Corrosion inside those connections can create problems.

Have you renewed the heat sink paste under the ignition control module? Could be that this module is breaking down when it gets heated...the paste helps in the transfer of heat away from the module.

Click to expand...

Thanks for the ideas Kurt. I'll check the plug wires for resistance and coil connections. I have not renewed the heat sink paste since the bike has this issue no matter whether its cold or warm. Worth a check though. Thanks.

Charlie,

I assume from your response that the timing check turned out OK.

Another reason for back/miss-firing I had was a bad diaphragm in the carburetor. At one point I installed a diaphragm twisted by 30 degrees because I didn't pay attention to the notch/nose there for correct alignment.

/Guenther

Guenther said:

Charlie,

I assume from your response that the timing check turned out OK.

Another reason for back/miss-firing I had was a bad diaphragm in the carburetor. At one point I installed a diaphragm twisted by 30 degrees because I didn't pay attention to the notch/nose there for correct alignment.

/Guenther

Click to expand...

Timing was ok and I replaced the carb diaphragms this past spring but I'l check them anyway. I spoke to Rick Jones at Motorad Electrik, he is 99.9% certain it is the origianl coil based on my description. A new one along with new plug wires is on the way! Thanks to all for your help (and to Rick for his alwasy excellent advice)!
Charlie

Misfiring

Charlie,

The suggestion regarding renewing the heat sink paste really has nothing to do with ambient air temperature. The paste helps transfer heat from the ECU to the bracket holding the ECU. Easy to check and renew, cheap to do so, and you might be surprised by the results. I do it every other year to my 88 RS. I pick it up at Radio Shack, don't need much. I tend to misplace the tube before I use it up. =8^)

Friedle

Friedle said:

Charlie,

The suggestion regarding renewing the heat sink paste really has nothing to do with ambient air temperature. The paste helps transfer heat from the ECU to the bracket holding the ECU. Easy to check and renew, cheap to do so, and you might be surprised by the results. I do it every other year to my 88 RS. I pick it up at Radio Shack, don't need much. I tend to misplace the tube before I use it up. =8^)

Friedle

Click to expand...

Wow, I didn't realize the ECU tests up that quick. Makes me wonder they placed it under a gas tank on top of a warm engine and without a lot of airflow. I'm adding new paste to my routine maintenance list!
Thanks,
Charlie

174713 said:

I spoke to Rick Jones at Motorad Electrik, he is 99.9% certain it is the original coil based on my description. A new one along with new plug wires is on the way! Thanks to all for your help (and to Rick for his alwasy excellent advice)!
Charlie

Click to expand...

I didn't have any misfiring or backfiring, but I did notice some hesitation which was more noticeable in the lower RPM.

You can read more in my "Grey" Ignition Coil - Failure thread.

It is best to analyze an issue instead of throwing a bunch of parts at a problem.

Success!

Installed the orange Dyna Coil and NGK plug wires, started immediately and ran smoother than ever. I suspect the coil has been going bad over time as I noticed a slight miss at high rpms at the beginning of the summer. Now on to adjusting the valves and carbs. Thanks to all for you input and ideas! Charlie

The final chapter

Did the valves, the left cylinder exhaust valve was .22mm vs. the .2mm spec. When syncing the carbs the tech noticed the screw plugging the vacuum port hose was missing so this explains the backfiring. Now the bike starts and runs the smoothest it ever has. Note to file- never overlook the smallest detail!