GZ250 Surging & Backfiring

[GreenFamily]

I just bought a 2005 GZ250 with about 16k miles. It was surging at about 3/4 throttle so the dealer flushed the carb for me, it didn't change anything. The mechanic suggested running a tank of fuel with Berrymans B12 or Seafoam to see if it improves. I ran the tank down to about 1/4, put about 6oz of B12 and filled it up with 89. I've put about 85-90 miles on it since then it started backfiring about 15-20 miles ago. Also it died on me twice this morning at about 45mph during my 25 mile drive to work, had to pull over to restart it. It fires up easily and idles great.
Might be work mentioning that I didn't realize I had it in PRI for about the last 100 miles but it's on run now.

[Fawlty]

It is possible that the backfiring is due to the B12 doing its job. More knowledgeable members will be along to advise you.

[gz4me +]

Change oil. ( gas in oil.) Check air cleaner.(could be soaked in gas.) Check spark plug. Does not take long for gas to flow into oil when petcock left in pri.

[GreenFamily]

I'll change the oil, check the air cleaner and spark plug after work today.

[gz4me +]

Alot of us have left the petcock in PRI position at one time or another, so do not feel bad. The only other comment I have is regarding gas. The GZ is designed to run on 87 octane. Do not spend the extra money on any higher than 87. As I mentioned on the PRI postion on the petcock, many have used 89 or higher octane thinking it would be a nice treat for the bike. The GZ runs the best on 87. Jn the near future I suggest you check the valves for proper adjustment. It is not hard to do and will save you alot of money on repairs and hardache if valves are to tight. Enjoy the forum and your GZ.

[GreenFamily]

So I ran out of time last night and got nothing done. I'll let you know what I find when I get a chance to do it. Thanks.

[gz4me +]

I know what you mean by running out of time. I have been trying to get time to work on the GZ and the Yamaha 650. Thought I was going to be able to do some on them today. As luck would have it, one of my blowers took a dump half way thru the lawns I was doing. Wound up doing clean-up with a broom. Took alot longer to get all the lawns done and I still have to work on the blower. Maybe this weekend. I hope!

[GreenFamily]

Ok so the GZ is fixed now. The surging was caused by a bad jet. It was basically running beyond rich and flooding itself. The backfire and die was being caused by a combination of issues. The side stand safety switch was tripping while riding causing the engine to die and the unburnt fuel would cause a backfire right after. After rejetting the carb and cleaning the safety switch she runs like new! This guy is one happy GZ owner.

[gz4me +]

Glad to hear you found the problems. Enjoy the GZ.

[steelerdude99]

Ok so the GZ is fixed now. The surging was caused by a bad jet. It was basically running beyond rich and flooding itself. ...

"GreenFamily", Great that you are up and running. Bad jet? I have never heard of that. How did you make the determination?

chuck

[jonathan180iq]

What size jet did you end up using?

[GreenFamily]

What size jet did you end up using?

Just stock.