Suzuki DT4 (2-stroke) strange noise.

[Douglas C]

OK...how do I describe a strange noise??

Engine starts and runs fine, but if opened up past about 1/3 throttle, it starts making a horrible noise/vibration. Goes away when throttle closed.
A number of knowlegeable people have listened, and declared that it was most likely a problem with the main bearings.
I dismantled the engine, replaced the bearings and started it this morning.

Same noise...

I now get the impression that it could possibly be coming be from the lower leg, and suspected it was coming from a partially engaged gear. (It's that sort of noise....like in a car when you try and engage gear with the clutch not fully depressed)
Checked the rod adjustment, and tried the gearshift in various positions...no change.
Set it up in a big water tank, and tried it in gear. Prop turning fine, and same noise.

Has anyone experienced anything like this?

[Downhilldai]

Could be a knackered (tech term ) bearing on the bottom of the driveshaft, or on the propeller shaft.

[Douglas C]

Originally Posted by Downhilldai

Could be a knackered (tech term ) bearing on the bottom of the driveshaft, or on the propeller shaft.

Bottom unit coming off tonight.
Driveshaft more likely than the propellor one, as it makes the noise in neutral.

[Downhilldai]

If the lower unit is at fault, this may be of interest to you:

http://cgi.ebay.co.uk/SUZUKI-4HP-GEA...A3%7C294%3A100

[Douglas C]

Ok,
Think i've diagnosed the cause.
Discovered that a rubber bushing about half way up the driveshaft had dropped down. The driveshaft had a mark where it had rubbed against the lower leg casting where it passes through the hole where the bushing should be.
I can only assume that the driveshaft starts vibrating and flexing at a certain engine speed, causing the horrendous noise.
Stuck the bushing back with silicone to see what happened....no noise.
Will get a new one soon. :-)

Douglas