Misfiring after rain.. but fine after sunshine!

Squeaky back brake? Hard to control at 30mph/40kph?
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AkasakaSMT
125cc
125cc
Posts: 9
Joined: Mon Jul 04, 2016 1:53 am
Country: Japan
City: Minato-ku
Year: 2012
Model: SMT

Misfiring after rain.. but fine after sunshine!

Post by AkasakaSMT » Fri Jun 26, 2020 10:05 am

Again the SMT is playing up.
After fixing an issue caused by dodgy fuel I know have a different issues.

Riding the bike the other day in the rain, (heavy rain) it began to bog down, misfiring, back firing and generally not doing great.
There was a big drop is power due to these issues and the bike eventually coughed and died.
At the side of the road, the bike would start up - eventually - and rev freely.
Once I started moving again, the misfiring, banging and popping would start again resulting in lack of power again. It sounds like the backfires are coming from one of the air intake ports.

As it was getting dangerous to drive, I parked it up and left it for a few days - during which the weather changed and there was sunshine. The bike was all nice and dry now and operated without any issues.

I've checked resistance of ignition coils and although these seemed ok replaced them both.I've gone through every connection, checking for water, cleaned each and reassembled.

Bike worked fine until it rained again and the symptoms returned... :(
Anyone have ideas or suggestions on what could be the cause.

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limeyduffa
900cc
900cc
Posts: 429
Joined: Tue Mar 15, 2011 9:22 am
Country: Australia
City: Adelaide
Year: 2012
Colour: Black
Model: SMT

Re: Misfiring after rain.. but fine after sunshine!

Post by limeyduffa » Sun Jun 28, 2020 11:44 am

If the rain is monsoonal, and your tank cap seal has perished, it could be possible that water is in your fuel tank. Water is heavier than fuel, so it will float down to the bottom of the tank and get sucked in by the fuel pump. I'm guessing that the fuel pump filters would not be happy with water. Pump may not be getting enough fuel through when wet with water ?

Do this test: close off the fuel tank equaliser taps. Remove the equaliser fuel line from left side tap. Pour some fuel into a glass using left tap. See if there is any water at the bottom of the glass. If so - there's your problem.

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