Spark plugs fouling on GSX250F

[KingJackaL]

1990 Suzuki GSX250F Across.

Short Version

My spark plugs keep fouling. They take about 1-2 months to go from 'just cleaned' to 'bike doesnt start'. Any ideas why?

Long Version

OK, so I've had this bike since early December, and at the time it didn't start well - you had to warm it up. I suspected the carbs and tappets needed doing. I was riding every week or so for 100-200km, but by January the bike needed a push start to turn the engine over, and you had to keep the revs over 3-5k to stop the bike from stalling (pretty sure sign the spark plugs aren't doing anything I think).

About a month ago I took the bike in, and had the following done:
- new battery
- carbs done
- spark plugs cleaned

So then the bike worked just fine. Started fine, ran fine, etc. I've been riding 2x per week, for a total of between 100 and 300km per week, with a mix of open road, hill and town driving (although mostly open road). Fast forward to this morning, and the bike won't start again.

I eventually got the bike started this morning (by holding the ignition in for around 10 seconds), and it runs - but as soon as the clutch was out and the revs were at all below 5k it just stalled. Even in neutral, you have to hold the gas on for quite a while before the engine picks up past 3k revs (engine idles around 1-1.5k, and very slowly revs up to around 3, then picks up).

So, clearly something is fouling the spark plugs in a repeated fashion.

Could this be because of tappets being very poorly adjusted? (I haven't had the tappets done, and the former owner didn't have a service history, so I assume they need doing)

Any other ideas what could be causing it? Any other info I could give that'd be useful?

[Paul in NZ]

Look around KB threads - you will notice similar threads regarding 250cc and 400cc in line 4's, ie hard to start, fouled plugs, won't idle, won't rev etc. The bike is nearly 20 years old and I'm afraid, these things were waaaay out on the bleeding edge of technology when they were built. The need proper maintenance as per the factory recommendations - they seldom get it!

Unfortunately - with no known history - it's going to be up to someone to baseline service the poor thing and then check out it's mechanical and electrical condition. Trying to diagnose your problem on a forum like this is a waste of time.

Yes - the valve clearances DEFINATELY need checking as do the carbs, the rest of the fuel system, the ignition systems and a leakdown test. You can do this yourself of stump up the cash to get the shop to do it. Be warned - they won't like to accept a job like this though - once you start it rapid gets uneconomic.

Sorry - going fast costs money....