M900 Misfire

Jam911 · 02-05-2022, 02:10 PM

I fired up my M900 this morning...took a bit to start but fired up ok...

..after a few minutes, when warmed up a bit, it misfires / backfires when revved.

...now it had not been run for 8 months and during storage I was advised to coat the inside of the tank with a mixture of petrol and two stroke oil...

...I drained the tank and then filled up with super unleaded before starting...

....would the residual two stroke oil be causing the missfire?

Thanks

Flip · 02-05-2022, 04:48 PM

It is possible the oil may be giving you a bit of trouble but I would of thought it would blow through relatively quickly as it's so soluble in petrol -did you not flush the tank out before filling it with fresh?

More likely in my opinion though is residue from the old fuel which dried out in the carbs over the time the bike was laid up has gummed up the jets.

These old carburetted bikes were never a fan of long periods of inactivity but that is magnified further as modern fuel has got worse over the years.

Jam911 · 02-05-2022, 06:23 PM

No in my haste to get it running I forgot to flush the tank...

Jam911 · 02-05-2022, 06:24 PM

It ticks over perfect but when revved misses and backfires...I hope a quick run will sort it out

Mr Gazza · 02-05-2022, 07:12 PM

A little two-stroke in the petrol shouldn't do much harm. If it is that you should be able to smell it in the exhaust. Sloshing the tank about and mixing it up might reduce the effect, but the first thing I would check would be the spark plugs. Changing them is never a bad thing. I give mine 6000 miles and put new ones in. I sometimes notice them going off at slow speed running towards 6000 miles.
You might see some evidence of oil on the old ones or maybe even a wet plug?
An Italian tune up might be the simple answer at the end of the day.

Jam911 · 02-05-2022, 09:04 PM

Thanks. The plugs have only done a few hundred miles so I would expect them to be ok.

I will try the Italian tune up ...

Darren69 · 03-05-2022, 02:12 AM

It's probably gummed up carbs. I run injector/fuel line cleaner periodically in my fuel. It may help or you may have to clean the jets manually if it doesn't clear itself.

Jam911 · 07-05-2022, 11:17 AM

So quick Italian tune up and normal service resumed.
Great

02-05-2022, 02:10 PM	#1
Jam911 Registered User Join Date: Jun 2021 Location: Stratford Upon Avon Bike: Multiple Monsters Posts: 288	M900 Misfire I fired up my M900 this morning...took a bit to start but fired up ok... ..after a few minutes, when warmed up a bit, it misfires / backfires when revved. ...now it had not been run for 8 months and during storage I was advised to coat the inside of the tank with a mixture of petrol and two stroke oil... ...I drained the tank and then filled up with super unleaded before starting... ....would the residual two stroke oil be causing the missfire? Thanks

02-05-2022, 04:48 PM	#2
Flip Registered User Join Date: Mar 2010 Location: Beachtown Bike: M900 Posts: 2,188	It is possible the oil may be giving you a bit of trouble but I would of thought it would blow through relatively quickly as it's so soluble in petrol -did you not flush the tank out before filling it with fresh? More likely in my opinion though is residue from the old fuel which dried out in the carbs over the time the bike was laid up has gummed up the jets. These old carburetted bikes were never a fan of long periods of inactivity but that is magnified further as modern fuel has got worse over the years. __________________ You're perfect, yes, it's true- But without me you're only you!

02-05-2022, 07:12 PM	#5
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,983	A little two-stroke in the petrol shouldn't do much harm. If it is that you should be able to smell it in the exhaust. Sloshing the tank about and mixing it up might reduce the effect, but the first thing I would check would be the spark plugs. Changing them is never a bad thing. I give mine 6000 miles and put new ones in. I sometimes notice them going off at slow speed running towards 6000 miles. You might see some evidence of oil on the old ones or maybe even a wet plug? An Italian tune up might be the simple answer at the end of the day. __________________

03-05-2022, 02:12 AM	#7
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,095	It's probably gummed up carbs. I run injector/fuel line cleaner periodically in my fuel. It may help or you may have to clean the jets manually if it doesn't clear itself. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

02-05-2022, 06:23 PM	#3
Jam911 Registered User Join Date: Jun 2021 Location: Stratford Upon Avon Bike: Multiple Monsters Posts: 288	No in my haste to get it running I forgot to flush the tank...

02-05-2022, 06:24 PM	#4
Jam911 Registered User Join Date: Jun 2021 Location: Stratford Upon Avon Bike: Multiple Monsters Posts: 288	It ticks over perfect but when revved misses and backfires...I hope a quick run will sort it out

02-05-2022, 09:04 PM	#6
Jam911 Registered User Join Date: Jun 2021 Location: Stratford Upon Avon Bike: Multiple Monsters Posts: 288	Thanks. The plugs have only done a few hundred miles so I would expect them to be ok. I will try the Italian tune up ...

07-05-2022, 11:17 AM	#8
Jam911 Registered User Join Date: Jun 2021 Location: Stratford Upon Avon Bike: Multiple Monsters Posts: 288	So quick Italian tune up and normal service resumed. Great