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[long story]
Well, my GZ250 died on the side of the road a couple of weeks ago . Had some experienced friends over the other day to help me tear the carb apart, as the bike had sat for 2 years before I got it, and we thought that was the most likely suspect. The jets were a little clogged, but we got that taken care of.

After putting it all back together the bike is still having the same problem; sputtering, backfiring, and eventually dying out, and only when it's in gear. In neutral it runs much better .

The strange thing is the bike ran fine for ~200 miles. I put a tank of high-grade in it, rode it about 50 miles, and then suddenly had this problem. My dad thinks the higher grade loosened some junk off of the inside of the tank which is now clogging the fuel filter.

[short story]
So I want to clean the tank out to remove any rust/varnish. My question is what is the best way to do this?

What I am planning on doing is adding a box of BB's and a half gallon of diesel and shaking it up, then cleaning the diesel out with some unleaded, then putting the unleaded back in and adding some carb cleaner for good measure. We found this method online and it sounds good.

Has anyone tried this, or another method that works well?

I like the POR-15 cleaning and sealing kit myself. Only need to clean it once and doesn't flake off like Kreem.

That said, if the filter was clogged, what happened when you replaced it with a new one? Did it go back to working the way it was before? Or are you referring to the screen in the petcock and not an inline fuel filter?

If so, get an inline fuel filter and break down those carbs again- things slip past the petcock screens enough that I don't ever trust them.

I haven't taken the fuel filter off yet. All we've done is checked the carb. I'm going to try to tackle the fuel filter when I remove the tank either Saturday or Monday.

This is what the service manual shows the fuel filter looking like, FWIW.

That looks like the petcock to me. Your bike might not have a fuel filter, but it's worth adding one at some point. The fuel filter is usually some form of gadget in the middle of the rubber tube which goes from the fuel tank to the carbs.

If the petcock is blocked you can easily test by switching to reserve (it'll use the other pipe in the petcock). However I think this one is probably the spark.

If it's been backfiring a lot, its probably either been caused by fouled up sparkplugs, or you can pretty much guarrantee they'll be fouled now, by the inconsistant firing of the cylinders. You should really clean them back up before playing with everything else trying to get it going.

Just pull the plugs, and scrape off all the carbon deposits with a wire brush (making sure you don't leave any metal bristles in the spark gap when you're done). Then give it another go.


I'm not familliar with the GZ250, is it an old bike? If so, its probably designed to run with a much lower octane rating than premium fuels. This might cause it not burn the fuel properly without a decent spark to set it off. Annnnnd ofcourse unburnt fuel adds carbon deposits onto the plugs and makes the next spark even worse, etc.

When you say it runs fine in neutral, do you mean that its dependant as to if its in gear? Or might it be related to being on idle revs for most of the time when in neutral?

Also does it splutter from the moment it's started (sparkplugs)? Or does it take a few minutes to get like that (fueling - either blockage or vacuum in the tank)?

Nibblet99 wrote:If the petcock is blocked you can easily test by switching to reserve (it'll use the other pipe in the petcock).

It runs the same when switched to reserve

Nibblet99 wrote:However I think this one is probably the spark.

If it's been backfiring a lot, its probably either been caused by fouled up sparkplugs, or you can pretty much guarrantee they'll be fouled now, by the inconsistant firing of the cylinders. You should really clean them back up before playing with everything else trying to get it going.

Just pull the plugs, and scrape off all the carbon deposits with a wire brush (making sure you don't leave any metal bristles in the spark gap when you're done). Then give it another go.

We pulled the plug and thumbed the starter. The plug is firing fine

Nibblet99 wrote:I'm not familliar with the GZ250, is it an old bike?

It's an '01. Suzuki still makes them. They're a MSF standard .

Nibblet99 wrote:When you say it runs fine in neutral, do you mean that its dependant as to if its in gear? Or might it be related to being on idle revs for most of the time when in neutral?

In neutral it seems absolutely fine, even if it's running at it's worse (backfiring, etc.), if I switch it into neutral it idles and revs fine, with the exception of not having as much at the top end. I mean the revs die off a little early.

Nibblet99 wrote:Also does it splutter from the moment it's started (sparkplugs)? Or does it take a few minutes to get like that (fueling - either blockage or vacuum in the tank)?

It takes it a little while to foul up. Well, at least when I rode it home from work (the first time it did this) it started fine, and then a few days ago it seemed to be fine and I rode it around the block once or so before it started doing it again. The other day when my friends showed up it started like that off the bat and got progressively worse as it ran.

Does anyone have any thoughts/suggestions?

Well, I cleaned the tank today. What a mess! I'd better not be around an open flame for a few days .

I couldn't really see any rust in the tank. It didn't really look like there was a filter. Just 2 rubber tubes attached inside the petcock, a short one and a long one (on and reserve?). I couldn't see any holes in the tubes, but gas did come out of them. Small holes I guess.

After everything was re-assembled and washed I put some carb cleaner in the tank and started it up. It's much better. It still backfires one time or so every time it's de-accelerating, but at least it's running, and much more smoothly.

I will go ahead and replace the spark plug. The engine idles a little funny. It's like "ba-ba-ba-ba-ba-baba-ba-ba-ba-bababa-ba-ba-ba" (it's a thumper, btw. If there's a better way to type engine speak, please let me know.) I'm told it sounds like a timing issue, but a spark plug may help. Past that I'm a little lost for ideas.

Well, I've replaced the sparkplug, and now it's back to running like garbage. Stalling, sputtering, backfiring. If I roll the throttle back all the way the engine won't rev much at all before it starts coughing.

I'm getting some help on the GZ250 forum. Most people there are thinking carbs. Looks like I'll be giving them a thorough cleaning ASAP.

Getting anxious... want to ride!

Open the tank, like leave the gascap off. How does it run ?