Suzuki 2 Strokes

Hi.
My name is Clive and I reside in the U.K. I have been riding bikes since the age of six (49 years ago) and riding on the road since 1982.
I usually run Italain bikes but being a keen 2 stroke fan I recently purchased a 72' T500.
The bike is in very good original condition with only the tank and side panel/oil tank having received paint.
Due to a protracted registration process - the bike was imported from the Isle of Man, I have only just recently started to use the bike on the road and it is having a few issues.

The bike starts first kick - cold or hot, and idles nicely at 11 to 12 hundred rpm with the carb at the factory settings.
When it is first started and used it runs flawlessly, pulls well and sounds and feels crisp.
The problem is when it is thoroughly warm. It starts to surge badly on the over-run and starts to emit a mettalic noise from the left cylinder at around quarter throttle and more curiously when I close the throttle to change cog. If i stop and let the bike cool down it starts first kick and runs great till it gets up to temp.

I have thoroughly cleaned the carb and checked all the jetting is per specs, which it is.
I have also replaced the points, condensor and coils and checked the timing which is set at 2 degrees retarded from the factory setting.
Another thing I ahve noticed is that the left header pipe is blueing.

I have come to the conclusion that the bike is drawing air into the left cylinder from somewhere. There appears to be no blow-by around the head gasket and jiggling the carb at idle produces no change to speed or note. This leaves the left hand outboard crank seal although there is no oily residue around the generator or in the cover.

If it is the seal can it be changed with the motor in the frame?

Thanks
Clive

Clive 2 wrote: ↑Mon Aug 23, 2021 1:00 pm If it is the seal can it be changed with the motor in the frame?

I believe the answer is yes, it looks like it is held in by a snap ring. It can be tricky getting the new seal in, you will need to lube the outside ring to get it in the cases without damage.
I think the 72 T500 has the early style carbs that are not vented to atmosphere, if you have an air leak somewhere, it could affect fuel mixture from carbs. I would think.
Sorry I am not very good with carburetion and especially the early T500 carbs.

With the bike running, squirt carb cleaner around the carb to barrel joints/rubbers and carb to airbox area. If the revs change, that's your air leak.
Plenty of places in the UK that do T/GT500 cranks and seals should the need arise.
Which bit of the UK are you based in?

Hmm my 500 makes the same sort of sounds when hot and surges too but the sound is notably coming from both cylinders the sound is worst at 3k to 5k rpm so I think it may be piston clap due to wear

Hi everyone.
Thanks for the replies. I'm sorry I haven't acknowledged it earlier but work as been manic - I'm self employed and have to take as much as I can.
I've been through the carbs and ignition and all is well. It doesn't use any gearbox oil and idles nicely.
I think it's looking like the top end may need to come off to check piston/bore etc.
By the way Alan H I'm in Dewsbury, West Yorks.
Once again thanks.
Regards

Hope to see you at Squires (near Sherburn in Elmet) on most Thursday afternoons). We park up opposite Sticky Vicky's kiosk usually.
Not too far from you on the back wacks. I live in Wombwell, South Yorks.

Hi Alan.
I sometimes visit Squiers, although I haven't been on the T500.
I got your PM and thanks for the invite. I'm going to delve deeper into the bike to try to get to the bottom of the problem.
If the weather is half decent when I get it sorted I'll be in touch.
I've seen all the 70s' Jap 2 strokes at Squires and there are you really nice ones.
In fact I think they had an effect on me, causing the sudden rush of blood to my bonce resulting in purchase of said T500.
If i go I usually take old faithfull - my 1949 Guzzi Airone.
I'll b' seeing thee.

Reyt cock. Al sithy when a sithy then.