Harley engine

[CourierDriver]

My ancient Harley engine started dieseling when I turn the engine off...long story short, I added about a half oz of Marvel Mystery Oil to the tank,,,started riding ,came home in about an hour and turn engine off,,,,,no dieseling anymore after that...maybe these types of things have happened to you...its ,a 1996 Sporster carbed engine.

 

[Propflux01]

More like your hour of driving blew out the carbon that was causing your dieseling.

 

[Greasymechtech]

yes... often back in the 1980's with my carb's cars.... was too cheap to run good fuel in the ol' jalopies

I recommend a good fuel additive cleaner and hopefully enough carbon will be cleaned out to avoid needing MMO(which started some cleaning already). Start with a small bottle of Techron at your next fuel fill up. They have 4oz and 10oz bottles at wallyworld so you don't have to worry about what to do with the 20oz or 32oz bottles while at the station.

Another option is the spray thru intake cleaners... more common now because of GDI issues...

 

[MRC01]

I wonder if you could run an aviation oil made for piston engines. Most aviation piston engines are large displacement, air cooled, low revving like a Harley. Aviation oil is "ashless" meaning it resists deposit formation by limiting the amount of metallic additives like calcium or zinc.

 

[Propflux01]

Never run aviation oil in a Harley. The oils are manufactured for different applications.

oh, and calcium is not metallic.

 

[MRC01]

... oh, and calcium is not metallic.

Calcium is an alkaline earth metal.

Calcium - Wikipedia

en.wikipedia.org

Ashless oils have very low calcium, compared to typical car oils that have plenty of Calcium as it helps neutralize combustion acids. For example, in UOA reports for my airplane (ashless oil), Calcium is around 100 ppm. For my cars, it's around 2000 ppm, or 20 times higher.

 

[hank2]

Decent chance that the MMO will continue to clean up the combustion chamber and valves. Don't overdose. Perhaps some of the other FI focused cleansers would do the same. Assuming that's the source of the preignition. Many years of use along with possibly wrong carb float setting or badly done rejetting could have caused quite a bit of carbon/ oil blowby deposits. Sometimes, the cylinder heads just have to come off for a proper cleaning.

 

[Propflux01]

Calcium is an alkaline earth metal.

Calcium - Wikipedia

en.wikipedia.org

Ashless oils have very low calcium, compared to typical car oils that have plenty of Calcium as it helps neutralize combustion acids. For example, in UOA reports for my airplane (ashless oil), Calcium is around 100 ppm. For my cars, it's around 2000 ppm, or 20 times higher.

I stand corr3cted on the calcium. But stand by the non recommendation of use of av oil.

 

[MRC01]

Does an Italian tuneup apply to an American engine? Perhaps it may help to get it up to full operating temperature, then apply some open throttle / mid-high RPM operation.

 

[PontiacHO]

My ancient Harley engine started dieseling when I turn the engine off...long story short, I added about a half oz of Marvel Mystery Oil to the tank,,,started riding ,came home in about an hour and turn engine off,,,,,no dieseling anymore after that...maybe these types of things have happened to you...its ,a 1996 Sporster carbed engine.

Is it idling too fast? That can cause it. Is it overheating due to late ignition timing? That too can cause it.

 

[BigCahuna]

There's a bunch of things that could cause your problem. Old gas, stale gas, riding slow in hot weather for long distances.Leaving the choke on longer than needed, will help build up carbon in the cylinders, which will cause dieseling. If your oil level is low, the motor will run hotter. If everything is on the money, it will run right. I doub't mmo actually solved you problem. Just a happy coincidence it stopped after you used it.,,,