Suzuki 2 Strokes

Hi all, so I rushed my bike and now paying the consequences.

I tried to ride it to south of France from London the day I finished building it... on way down it was good, but I started to run into issues with it stalling once into my ride. I tweaked the idle and set it to a fast tick and it was just ok...still stalling occasionally. The big issue was starting it again if it had stalled or if I turned it off, would take about 10 mins of kicking and cursing to bring it back... I also fowled a right plug on in the right cylinder.

This continued when i got off the ferry and just assumed the jets were too big as it was flooding and too much fuel was getting into the engine when it was hot...the normal sign if your pilot is too big...so I sent it back when I finally arrived in Paris.

I got the bike back yesterday and started on jetting. I fitted a smaller pilot, 3.25 (I started with 3.5). I set the idle to 3 turns out and the air screw too, and it was running ok at about 1.5 to 2k rpm...might need to go smaller.

I took it for a ride and it felt ok, but still had some lag in the acceleration and I caught a hint of a dull not when pulling quick throttle, think its the needle position got it at 3, the default....but much better than before.

However after a short while it stalled, the same old thing. Again the right cylinder I had fowled a plug and it was then when I saw the magnetic metal gains mixed with the oil on the plug end. I checked the other plug and found the same metal particles.

So trouble!

I didn't think I was running lean because of the flooding and the setup of my carbs is rich all round, the main jet is 107.5. I did have some air getting into the right cylinder oil lines, but it still pumped oil in and I also started putting two stroke in with my fuel when I was filling up.

Also, when the right cylinder was not firing, it did get a back fire pressure push through the carb as it popped...is that normal for a fowled plug? It was quite loud and the carb would shake when it happened.


I've walked away, and will come back to it next Saturday....need some time off this stressful project.

Can anyone give me some advice as to what they think may have gone wrong?

I've done a complete engine rebuild. The crank has been done as have the con rods. The pistons are original, but new little ends and rings. The crank has new seals and the same big ends.

I'm guessing its rings or bearings as the grains are magnetic so cannot be the pistons.

What kind of things could go wrong here?
Could it be the engine was running too hot?
Must be....or have I done something wrong with the re assembly of the engine?

I've also noticed a rattling sound coming from the head now....so that could mean little ends right?

Oh my, my poor engine!

Sorry to hear about these problems ... unfortunately I think the only thing you can do is lift the head and barrels to see what has gone on. It does sound like a bearing has given up somewhere

Heads off and have a look. Sounds like something rattling about between the piston and head or maybe little ends?
Might be something gone through the carbs into the motor.
Might be something let go inside.

Don't bother buying a lottery ticket this week - looks like the good luck fairy doesn't like you much......

Bad luck - sorry to hear about the probs.

Craig380 wrote:Sorry to hear about these problems ... unfortunately I think the only thing you can do is lift the head and barrels to see what has gone on. It does sound like a bearing has given up somewhere

Thanks Craig. I seem to learn my lessons the hard way....but if it is a bearing issue, then that would mean I was running lean...but my carbs were set to massive jet sizes and the stalling due to flooding?

I did re check my float levels and the right carb was off quite a bit, so maybe they was running lean as there may have been too little fuel in the bowel....but I also fowled a plug.

I put genuine Suzuki parts in this engine...so I don't think they would have been faulty bearings...but what's interesting is that both cylinders have this metal...so either both little ends have packed up...or it's coming from the crank...oh dear!

I might buy another bike as I really loved riding the GT500 felt great even with the rich jetting. going back to my T5 Vespa is horrible...they are such crap bikes! Might buy an 80s BMW R80 to get me by whilst I sort out this issue.

I was also looking at a Suzuki LS650 savage, anyone know if these 4 strokes are any good?

Alan H wrote: Don't bother buying a lottery ticket this week - looks like the good luck fairy doesn't like you much......

Ha ha ha! Thanks I needed to laugh a bit.

So it would make sense as there is a sound coming from the top end now...a rattle. I'll drop it off with my mechanic and ask him to open it up and have a look...maybe I can order more parts from Marcel and fit it on the weekend.

But, if my little ends are gone then I must be running too lean or the parts were put in wrong, or as you say I've got bad luck with this bike. but is it common for both to go like that? I'm hoping its the top end, but wouldn't I need to open the crank and take out the metal? I'm assuming there will be crap floating down there two...

No use speculating Nicholas......get it apart and have a look. 15 minutes and it's all off.
These engines are tough in my experience, and as long as you have oil going in at the right rate, the bottom end should be good. I have done 10s of thousands of miles on these bikes, and on occasions thrashed them mercilessly....the worst result being melted pistons. I've holed a piston in totally stock trim when racing a Gt550 on the motorway at full throttle for 20 miles, and holed one when using chambers without rejetting, other than that...never any issues.

No use speculating Nicholas......get it apart and have a look. 15 minutes and it's all off.
These engines are tough in my experience, and as long as you have oil going in at the right rate, the bottom end should be good. I have done 10s of thousands of miles on these bikes, and on occasions thrashed them mercilessly....the worst result being melted pistons. I've holed a piston in totally stock trim when racing a Gt550 on the motorway at full throttle for 20 miles, and holed one when using chambers without rejetting, other than that...never any issues.

titan performance wrote:No use speculating Nicholas......get it apart and have a look. 15 minutes and it's all off.

Your right, thats what i will do! Next weekend. I must immerse myself back into the real world, I took three weeks off of work to finish this bike for my trip to France.

But thanks for the positive remarks about the engine Paul. Its really great having you guys here! Thanks!

I am curious though, and will look for myself....but can this happen if the bike is rich? It must have been lean.

Things to mention:
When I was doing the jets, I double checked the crabs and found the right float was off by about -.5mm, so it was way off! So it could have been lean, but it fowled two plugs!?

The right oil line, was letting air in so it wasn't pushing the 'right' amount of two stroke oil, but I countered by putting it in the tank.

And the pop backfire through the carb, is this normal for a fowled plug? It was quite aggressive and shook the carb as it happened...concerning?

Paul, I'd like to pick your brain about the jets too...I fitted jemco expansion pipes and was advised increasing all jets by about 3 sizes, especially because i had ram air filters.

i started at 3.5 pilot with 107.5 main, main could be OK. 3.5 was flooding when the bike warmed up, so yesterday i tried 3.25 and i think it was OK, but I'm not sure i could find the sweet spot with the airscrew and it flooded again when the right plug fowled....Or is that what happens with two strokes, if a cylinder is out you just cannot start it?

But I'm thinking this needs to be sock, and maybe jemco was wrong about the pilot...what have you increased when fitting custom expansions? main jet and needle position? have you changed the needle type?

having followed your build on here Nick, I commiserate, BUT wonder perhaps that you should have listened to my advice at the begining of your project when you contacted me!!!

Pete O'Dell wrote:having followed your build on here Nick, I commiserate, BUT wonder perhaps that you should have listened to my advice at the begining of your project when you contacted me!!!

Well Pete, hindsight is a marvellous thing....but I'm not sure I would have learned as much if i haddnet done it this way.

But I'm hopeful it will be okay, I'll have to take account of what has actually happened and then work out the appropriate course of action. I am where I am and just want to see this through, clearly something is afoot, either sheer badluck or I've done something wrong...I'm sure the latter!

The good news is nothing has seized, but there is an unhealthy rattle at the top end and my carbs are a mess...but I guess it can only get better, right?

+1 on the melted/holed piston theory who ever mentioned it earlier?
That's the only way you're going to get metal on the end of a plug!!! Little end/big end failing would be very noisy & let you know something was amiss straight away,pretty sure once you lift the head you'll see damage to the top of piston/s.....sorry to hear about the problem.I take it you were taking things a bit easy with new rings,little ends & not sitting on motorway speeds!? PS if its done a little end bearing (circlips may have come out) you may have damage to the bore,not to mention where broken bits & pieces have ended up inside the motor, ouch!!
Regards,
GT750Battleship.

Obviously I cant comment on the requirements of a motor being run on Jemco pipes, as I have never even owned any. But running a little rich is unlikely to do much damage, whereas lean will get the motor hot, particularly when used hard. In my opinion..and it is only my opinion, I would have used less pilot and more main than what you were told, and would leave the needle in the centre notch. There are many pods about, and I hear some flow no more air than the stock airbox, which is hard to believe, but I would have increased the pilot jet by one size, and the mains to 115 as a starting point. You may be able to run more lean than this after the motor had bedded in, but erring on the cautious side is better. Jets are cheaper than engine parts, so start rich and work down if you don't have any trusted settings.
If the motor is reluctant low down, then go up one size on the pilot, and perform a plug chop to get some idea how hot you are at full bore.

titan performance wrote:Obviously I cant comment on the requirements of a motor being run on Jemco pipes, as I have never even owned any. But running a little rich is unlikely to do much damage, whereas lean will get the motor hot, particularly when used hard. In my opinion..and it is only my opinion, I would have used less pilot and more main than what you were told, and would leave the needle in the centre notch. There are many pods about, and I hear some flow no more air than the stock airbox, which is hard to believe, but I would have increased the pilot jet by one size, and the mains to 115 as a starting point. You may be able to run more lean than this after the motor had bedded in, but erring on the cautious side is better. Jets are cheaper than engine parts, so start rich and work down if you don't have any trusted settings.
If the motor is reluctant low down, then go up one size on the pilot, and perform a plug chop to get some idea how hot you are at full bore.

Thanks Paul, so I might need to enrich the main jet, but need to get over the pilot. So right now I have the pilot on 3.25 which is one up from stock. I started with 3.5 and I think this was too rich, I will order 3.0 tomorrow and give that a shot too. But thanks for the advice.

Ok, so I took of the head today and found:
1) Small end bearings were perfect, con rod holes great.
2) Rings looked good and piston heads no problem. But they had a strange and hard to clean carbon, I think it had metal in it.
3) Sides of pistons and barrels heavily scored
4) Did not open crank case, but big end felt right and looked well oiled.

So some of the carbon was magnetic and something has come undone...I am not sure if it is piston ring wear or something else....maybe the crank? or when I first started the engine it was not oiled and the metal is from the cylinder?

I'll need to re-bore the barrels and get new pistons and rings...but think I might as well put it all back together and try to get the carbs right. If I can do that then I can come back and fix the head, but it should be OK...do people agree?

The mystery is where did it come from? It is strange that it was in both cylinders...could it be the crank?

I spoke with someone today and I am not sure if they understand the Suzuki engine but he said that if a two stroke stalls when warm it most likely a compression issue with the crank and it isn't seated right....but the GT500 has dowels and I am sure I put it in right...the top half wouldn't have closed...anyway does that make sense? I thought the stalling was because the fuel circuit was too rich, the pilot jet?

Anyway I the following are some pictures. I tried to clean up the pistons and barrels, but unfortunately they are for the bin once I have sorted out my carb jetting....interesting how parts of the piston were not covered in the carbon...it was really thick stuff.

And to think I did this to my poor pistons before putting them in....