Suzuki GT250 two stroke puking out the exhaust! =(

Tdowning

Tdowning

New Member
Just bought this a few weeks ago, she ran like a dream the first two weeks I owned her but it went downhill from there. As the tank got low I heard some junk sliding around in there so I popped the tank off, drained it and took off the petcock to find some rust chips at the bottom. A tiny amount of bad gas must have sat in her for all those years in the barn because the top of the tank is spotless, anyways I got everything out cleaned it, ran gas through it then put it back on and filled her up. She was having trouble idling and would stall out when I took it into first gear but after five minutes of warming up she would run normal, not an excessive amount of smoke(for a 2t) or anything out of the ordinary. I put her away for a week being so busy with work, but the next week I came out to fire her up and she wouldnt even start running. She started dumping gas out of these vent tubes in the right side carb. I left it for another week and just now tried firing her up again. The battery was drained from, trying to start it so much so I took it off and hooked a charger up to the bike, after some pumping on the kickstart she finally, slowly started to rev up, I turn around and a gas/oil mixture is splattering and dripping out of the right hand exhaust. Notice the corrallation between right carb and right pipe? That scared me enough to shut it off, I called out my dad to check it out with me. I went to start it up and first kick it purred to life, no bogging, no idle issues, but the heavy oil mixture was still dripping out of the pipe a little.
Sorry for the novel, if you've read this far I thank you. Now, what do you think it could be? Just a simple misalignment of carbs, or the right one being dirtier than the left one? I've only worked on small 2ts before so I have no experience with dual carbs. Any help or advice would be appreciated, I'd love the reliability of a 4t, but I like her to much to part with it just yet.
 
carbs need to be taken apart and cleaned dude.

It is simple, and if you have never done it before just take your time and take photos while taking them apart so you know how to put it back together again.
 
Well I'm glad it's probably nothing worse than I expected! I don't want to take it into a shop unless I really have to, I shouldn't have to many problems cleaning the carbs. The guy I bought it from said the pistons had some slight rust in them and it was seized up when he got it so he had it professionally bored a size bigger and had new pistons, rings, gaskets, and all that put in so I wouldn't think it would be the rings. I do wonder though, would that mean it could be running a little lean? It was only the next size bigger so it shouldn't be too much of a difference, do you think that would effect the auto oiler set up? What about the carb jetting? I can't tell if the performance is suffering because I've never been on the bike before the modifications, and seeing as it has new pistons I've taken it easy and only gotten it up to about 55-60.
 
just go slow and go through a process of elimination.

the buyer may have been playing a little 'loose with the truth' about what work he actually did with the head.

If it was me, carb cleaning first because of the dirty fuel/tank issue and it seems your problems only started after you got gunked up. Its the logical place to look first. Make sure your fuel lines and filters are clear too of course.

If it is just a 'small' bore as the previous owner claims then my understanding is that factory settings are still acceptable and shouldn't really cause any of the issues you are talking about.
 
Most likely problem is garbage that went from the tank to the carbs. If it were mine, I'd drain the tank and clean it out and remove the fuel tap and clean the screens on that. Then I'd check and clean the carbs
 
Yeah I've got the number to a guy that blasts and reseals tanks, I planned on getting a hold of him this week. The petcock on this thing is messed up too, the prime position acts as on, the on position cuts off fuel, and the reserve position doesn't work either as far as I can tell. I'd like to get a new one but it's different from my vintage moped petcocks, those ones were threaded and screwed right on to the tank, but the Suzukis petcock is held on by two screws and a gasket sealing it to a hole on the underside of the tank. Is that a common petcock for older bikes? I looked on ebay for a petcock from a GT250 but they don't seem to be very common bikes with a large aftermarket of parts. A cheap petcock from a different bike would be excellent.
 
petcocks are pretty simple. When you have it off the tank, if it is in bad shape, measure the distance between those two mounting bolts and find a replacement. Many/most bikes (other than Hondas) used a 2 screw mount for decades.

You can probably clean the tank yourself electrolytically -search on this site for details.
 
Good to know, hopefully it's a common sized petcock. thanks for all the insight man, I know a lot of this stuff is pretty basic knowledge to someone that has been doing this for a while. I've been on sights before where people get really bitchy if you ask a question that has already been asked before. Thanks for the help, I really appreciate it!
 
Thats the awesome thing about DTT! Friendly and helpful.

Its always a good idea to type a question into the search and have a look before you post a question. Many people have the same questions!
 
Everyone is suggesting carbs and i will too, sounds like the fuel inlet needle is leaking causing the leaking vent line, this can also let fuel into the throat of the carburetor from there it will leak into the engine through the intake and reed valves and pool in the crank case. Then when you go to start it that cyl will instantly foul on the excessive gas and puke out the exhaust. If the carbs condition is questionable, i would spend the $40 and get two rebuild kits, install them along with your cleaning, set your float heights and everything should be good now!

one thing is to turn off the petcock always when not in use. To fix the bad cylinder take the plugs out, keep the plug caps out of the way and kick the engine over to clear all the excessive fuel, now use a torch or lighter to burn all the excessive fuel off the plugs, after its burned off, put the plugs back in hott and it should start fairly easy.
 
Thanks for the info, it seems the general consensus is that the carbs are just gunked up or bad. I'm gonna tear into them tomorrow, hopefully they won't both need rebuild kits! I planned on getting fresh fluids and plugs for it anyways so I can just swap them out instead of burning the extra fuel off the other plugs. It probably wouldn't hurt for me to do a couple plug chops either to make sure everything is running right, not to lean or rich. You learn fast on old mopeds to turn the petcock off when you are done riding, forgetting that is the easiest way to foul plugs hah!
Also, I was doing a little searching on the forums for more info on the GT250 and I stumbled across a diagram on how to build your own expansion chambers that will work specifically with the GT250. It said that you would gain a huge amount of top end power but all of your low end torque would virtually disappear. That sounds good for a racetrack situation, but around town that wouldn't be good. Now I know with the little 50-80cc engines on old mopeds you could get different performance expansion chambers to increase low end, mid range, or high end power. A lot of the low end/mid range pipes were called "circuit pipes" and would coil around under the engine in almost a kidney shape rather than just sticking out the sides. Is it possible to construct pipes like this for bigger CC two strokes? or would the stock pipes be my best bet for good low end? I know that in the case of a moped, any expansion chamber was better than stock and increased all around performance greatly, but certain pipes gave you even better performance at different RPM ranges as I said before. Anyone know anything about this kind of stuff?
 
Forget about "kits" for now. There's a 99% probability that the crabs can be cleaned and if something needs to be replaced, it may not be in the kit anyway, so spend the time getting them spotless.

It is possible in theory to make a pipe that would work better at low revs than a stock pipe. Armed with all the stock engine dimensions it's quite possible to shape ports and pipes to change the powerband completely, but it isn't a 30 second job. Stock pipes are pretty good for the street.

You could always bore it out, port it, fit reed valves, programmable ignition, flat slide carbs and a modified crank but the return on investment is not good. ;-)

Get it running and have some fun first and worry about spending money later.
 
Right on, any modification to performance would be way later, maybe over the winter months or something. Getting it running perfect right now is my main concern. Thats what I've heard is the stock pipes are pretty much your best choice for around town street riding (probably why they came stock) ;p I've got a buddy that welds though, and it would be fun to play around with different expansion chambers eventually! I hear ya on the cash vs. performance increase though. With all the money you could put into one of these two smokers you are better off just buying a fancy newer bigger four stroke ya know? There is something charming about the way a two smoker sounds, preforms, and all the different tweaks you can do to it, something a four stroke just lacks, I can see why people get hooked on these little devils!
I cleaned out the mesh screen on the petcock today, fired right up so I took it for just a little test drive, ended up dumping it on a hairpin turn ='( there were trees and bushes blocking my view of the other side of the turn so I didn't see the inconvenient pile of gravel laying there. it wasn't even my back tire that slid as I wasn't accelerating (just coasting at a smooth 20mph) My front tire dipped and I went over the side of the bike. Dislocated wrist and of course it was the ONE TIME I didn't wear my jacket, but only minor road rash and and bruises besides the dislocation which popped in when I got on my feet. Only damage to the bike were the two right blinkers slightly bent and the foot peg bent pretty far back. I managed to ride home and fix the blinkers like new but I haven't messed with the foot peg yet =X Woo for walking away from my first lay down, and managing not to scratch the paint up at all!
 
I haven't read all posts, but, is transmission oil level down?
It's a TWO STROKE worn rings will mean compression is down, not that it will burn more oil ::)
More likely, flooding carb has damaged seal behind primary drive gear, particularly if you have E10?
Check transmission oil, there should be a level screw on clutch cover (10mm head with fiber washer under it, either just in front of kickstart or just ahead of clutch 'bulge' (it's at least 25 yrs since I've done one)
 
Transmission fluid level looked to be pretty good, but I have NO idea how old it is. I should probably change that out pretty soon here. What is recommended to use with these two strokes? I try to buy high grade everything for my motorbikes, so whats the best stuff to get?
 
Oh No. The dreaded "which oil is best" question. LOL

I use Honda 2 stroke transmission oil in most of my 2 strokes. On our high stressed racers we have used Silkolene Pro SRG 2 stroke trans oils with zero wear.

Call MotoLiberty (silkolenestore.com) in TX and get the good stuff. This should be fine
http://silkolenestore.com/more.asp?ProdID=154
 
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