Misfire above 2000 RPM


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hazarika
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Joined: Wed Jul 01, 2020 7:36 am
Location: United States
Motorcycle: 1980 GL1100

Misfire above 2000 RPM

Post by hazarika »



In 2009 bike went for a long ride got home shut it off. Next day it would start but backfire/misfire. Pops both in the air cleaner and exhaust. Can rev it up to 2000 rpm after that the popping starts and will not rev up.
Checked spark and decided to rebuild the carbs. No change. Sat like that for 11 years.

2020 - Decided to revisit the problem one more time.
- Rebuild the carbs, jets were clogged cleaned them up using the drywall screw to extract
- Made sure all the air cutoff lines were clean
- Cleaned the tank
- Cleaned the lines
- Rebuilt the petcock
- Cleaned the Fuel pump
- Changed the coil
- New Air Filter

Started but the problem is still there.

Primary Coils - 3.2 ohms
Secondary Coils - 14K ohms
Resistors in the boot - 5K ohms
Nice healthy spark
Pulse generator - 546 & 576 ohms
Spark Units getting 11.25 V. Cleaned the contacts and ground.
Compression Cold engine/dry - 1(137), 2(140), 3(145), 4(147)
Got the Timing belt cover off, both sides are on the mark.
Checked the Valve clearance 1(I), 3(E),
2(I) and 4(E) was tight. Made the adjustments

Is there something I have missed?



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ct1500
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Re: Misfire above 2000 RPM

Post by ct1500 »

hazarika wrote:
Wed Jul 01, 2020 7:55 am
Is there something I have missed?
Some observation and diagnosis. :)
With air filter box removed and using sight, sound and feel at flame arrestor screens which cylinders are causing the popping or is it the whole crew? A lean running issue can cause the symptoms you describe and I would start with fuel flow. Disconnect fuel pump outlet hose and attach short section of fuel line to outlet barb, start engine up and watch for good pressure and flow out of pump into a container for a little bit or until carbs run dry. How long can the engine run/idle with no fuel supply while on center stand? What are the fuel pump specs supposed to be? 8-)
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hazarika
Posts: 6
Joined: Wed Jul 01, 2020 7:36 am
Location: United States
Motorcycle: 1980 GL1100

Re: Misfire above 2000 RPM

Post by hazarika »

I think it all 4 at random but will check.

It maybe a day or two before I get to putting the radiator back and do the fuel pump test.

Specs for the fuel pump are 2.0 psi @ 5000 rpm, 15 oz per minute at 3000 rpm

Thanks

hazarika
Posts: 6
Joined: Wed Jul 01, 2020 7:36 am
Location: United States
Motorcycle: 1980 GL1100

Re: Misfire above 2000 RPM

Post by hazarika »

Sorry for the delay, had to wait for an O ring to come in before I could put the radiator back.

The volume is around 430+ml per minute. The ambiguity is because, I didn't realize that fuel would continue to flow after I shut it off. Fuel pressure is around 3 psi. My pressure gauge is old and may need calibration. But definitely 2+ psi at around a 1000 rpm. The float adjustments seems to be fine since after putting the fuel lines back I forgot to open the petcock and the engine ran for a while.

Any other areas to check?

Thanks

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WingAdmin
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Re: Misfire above 2000 RPM

Post by WingAdmin »

The higher the RPM under load, the more power it takes to spark the plugs. Your ignition system might be fine at lower RPM, but are falling down on the job at higher RPMs, causing misfires. I'd be looking there before looking at fuel. If it happens especially (or only) when under load, then I'd especially look at an electrical issue as the source.

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ct1500
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Re: Misfire above 2000 RPM

Post by ct1500 »

Do you think it is running too rich? Black smoke out exhaust, heavy gas smell, loping idle, slightly slow to rev up, black spark plugs. What are the color of plugs if not new.

I was under the impression the engine problems you describe are occurring during idle and revving the engine while stationary or is it only under a load, which one? One more thing to try before ruling out the running lean idea. Grab a can of carb clean and spray directly into the throats of carbs at the screens while the engine is running and acting up. Start with a very light application of spray such as droplets increasing ever so slightly until either the engine seems better or the engine begins to falter from too much (fuel) spray. Have the straw on the can moving the spray around noting any change for the better. This is not a 5 second process. :)
Local and need repair help with your 1500, Valkyrie or ST please click contact
Nothing leaves my shop till its' perfect
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hazarika
Posts: 6
Joined: Wed Jul 01, 2020 7:36 am
Location: United States
Motorcycle: 1980 GL1100

Re: Misfire above 2000 RPM

Post by hazarika »

It may have been electrical. I ended up tracing all the wiring and found the second ground, the one from the rectifier was broken. Fixed that and also cleaned out all the connectors to the coil. The other thing I did was turned out the idle jets, three rounds out. The combination of all three makes it difficult to understand what fixed it? Possibly, the ground since the miss started after a ride. Prior to that is was running file. Also, the rebuild of the carbs then, 9 years back, didn't help. The rebuild this time didn't help either. Thoughts?

Yes, this was happening while the bike was stationary. Idling and miss during acceleration. Haven't got to ride it as I am rebuilding the rear master cylinder.

Thanks for the help.



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