Suzuki 2 Strokes

I have owned this '73 GT 380 J for 5 years now and it was been running well and making a consistent and great sound, both from the pipes and engine. Just the other day I took it out and the sound was very different, as was the smell. It is hard to describe the new sound but it is consistent with the engine revs and has a higher pitch to it.

The engine still pulls well and performance wise I have not noticed a change. At idle the bike sounds fine, however when it is revved in neutral or in gear it make this noise.

Any insight to this would be much appreciated. Great forum!

Hi and welcome. Are there any leaks from where the exhaust headers mount on the cylinders? Any leaks / holes in the pipes, along the seams or around the joins / mounts? Are any of the spark plugs loose? Any obvious oily smears visible around the head gasket or base gasket joints?

Thank you...good to be here.

There is a small hole in the right side expansion chamber that has been there for a while. No leaks around gaskets. No other leaks either. Will make sure plugs are tight. I pulled them and they look pretty normal.

Really hope it is something simple!

Funny coincidence this, I also own a 78 GT380B and recently noticed the 'general' sound was different.
Thought it was my imagination but a work colleague also commented on it. I first put it down to the unusual warm weather we've had in the UK recently.
I did all the checks Craig suggested and nothing obvious came to light. Next plan was to get some exhaust wadding and some stainless steel locking wire to wrap the baffles.
Armed with the required bits I started to remove the baffles, top two came out no problems, lower left no problems then to the lower right it came out about 75mm and would not come out any more.
A bit of jiggling and out it came. What was holding it was the internal baffle plates that have completely broken up.
Now I know it wasn't like this 750 miles ago when I had the pipes rechromed.
So I suggest remove the baffles and have a look.

Hi,GT-Keith,I was going to suggest the baffle plates also...then I re read the post..he's running expansion chambers...!! Sounds like an air leak of some sort or something clutch related...maybe..?

Cheers,
GT750Battleship.

I dont think it is the exhaust. (I have stock pipes on it now.) Sounds like an internal engine issue. I am going to go over it well today and report back. Canada here btw.

If your gearbox oil is low, you will maintain power, no engine hickups happen...but your clutch plates will get hot and "sing" to you.

Thanks snapper33. That "singing" sounds like a good description. I will change my oil. What do you recommend I use for oil, and if this is the issue will it stop singing or do you think there will be clutch plate damage?

I realize that oil questions are Pandora's box. However, I highly recommend Motul 10W-30 motor cycle gearbox oil. It takes a lot to smoke clutch plates, so change your oil, and if it runs fine with no slippage, you are good to go.

+1 on the Motul oil.

Motul transoil 10w-30 I believe its called. I had slight clutch slip before I used this, no problems now.

Thanks everyone! I will add today and report my findings.

+3 on the Motul gear oil,have used this & the Castrol equivalent,MTX 80 grade two stroke gear oil,both offer smooth & efficient operation.
Cheers,
GT750Battleship.

Common problems on bikes this age are often the intake rubbers. If they leak you can get a singing noise too. You won't feel the leak as it will be a vacuum leak and not a pressure leak (it sucks air in, NOT blows it out). Check by spraying "easy start"/"cold start"/"start-it" or similar around them while the engine is idling. If the revs alter when you spray then you have an inlet leak. DO NOT use damp start or wet start, they are not the same stuff and will not help you at all.
I plan on replacing all of my intake rubbers as the rubber gets rigid with age and doesn't clamp or seal tightly even if it doesn't have any cracks from perishing. This is a very common fault on older cars and motorcycles that often goes undetected but can lead to the engine running too lean a mixture, which on a stroker can be devastating! Lean burning can burn hotter and lead to seizure and/or a piston damage. I would advise that you do not ignore the problem, you'll only end up paying for it in the long run if you do. Good luck
Tom

Sorry had to go on the summer holiday....

Anyway, changed the oil to Motol 10 30, but still getting the loud signing noise. Everything external checks out fine. Starts first kick, idles smoothly and runs well. Although with the noise I am reluctant to ride it at all.

I dont want to take it in to the shop yet...I want to ride the thing before it snows here.


Is it possible the plates are smoked, after all they could be 40 years old? Anything else I should look for?

Cheers everyone and thanks in advance.

p

Did you eliminate final drive noise? I hada singing noise on my 750A which turned out to be slightly misaligned and tight chain - all sorted once I thought of adjusting it!
Mike