Hi All,

I have done my first trial now and have a few issues with my 1978 Cota 247.

It smokes a LOT.

It dies at low revs.

It feels all choked up.

The person I bought it from said to use a ratio of 25:1 and it is a mineral oil

Is this the best oil to use or go to a synthetic?

Is the ratio correct?

I will go and pull the plug soon to see what it looks like.

Is it worth pulling the exhaust off and clean it out?

Is the gasket on the exhaust re-usable or will I need a new one?

Sorry about all of the questions, but you guys look a friendly bunch.

I run my beamish on 40:1 on modern synthetic oil and its pretty much smoke free

It could also be the crank seals causing the smoke

Uh oh, that doesn't sound too good. Is there a way of checking the crank seals or is it a strip down job?

With fully synthetic you can go a lot leaner, 40:1 60:1 and even 80:1

What oil are you using now?

Try going leaner than you are now, as 25:1 is too rich (that's ok for a chain saw! Lol)

Get some good quality oil, then try out different ratios, until you find what works for you.

Just mix a litre each time, then you won't be wasting so much fuel.

Cheers

I wouldn’t go any leaner than 40:1 on an air cooled!

Try it on some synth oil, if it doesn’t clear up then it my be the crank seals.

I’ve not had a Montesa for a few years but if I remember correctly they are quite easy to change. (you don’t need to pull the engine apart to change them)

Agree with previous post do not go lean on an old air cooled motor. I never had any problem on my monts at 24:1. Try Smith and Allan fully synthetic at 33:1 (that is what I now use) and I get virtually no carbon build up and virtually no engine wear.

Main thing is to get your carburation right.

Thanks for all the responses.

The oil I am currently using is Central No Smoke Oil !!!! Again this is what the previous owner used.

My plan now is:-

Change the oil in the clutch and gearbox so I know exactly how much there is. Then I can monitor if I am losing any through the seals.

Drain the petrol tank and then use some fully synthetic oil, but not going too lean.

Strip the carb and clean it.

I have found a number of manuals for the Cota 247 but they all stop around 1975, is there one for the 1978, it is a 21m26000. Just want to be armed with the correct information before I go diving in.

Stripping the bike down today. Removed the carb and I am getting more blowing than sucking on the inlet. This doesn't sound good. Are there reed valves on this engine? They are not between the carb and the block. Could thus be really bad crank seal leaks?

Lots of oil in the exhaust system too!!!

So done a bit more research and have stopped look for the reed valves.

Still a bit unsure why there is so much pressure coming back through the inlet even with the exhaust off and plug out!!!

Looking at the manual I found there should be 200cc of oil in the clutch and 300cc in the crankcase. There was nowhere near enough oil in either!!

Again the manual says SAE20 for the clutch and SAE90 for the crankcase. Does anyone know the modern day equivalents or recommend an oil that I should use?

There was also loads of oil in the exhaust which could explain why I looked like one of the red arrows during the trial.

Did manage to break the inlet spacer between the carb and the block during reassembly, not happy, but as it wasn't flat on both faces there could well have been an air leak there.

Not sure on the grades, but I use silkolene light gear oil in my beamish and it seems to work well.

It might be worth changing the seals anyway as its only an 1 hours spanner work at the most

Edited April 4, 201511 yr by suzuki250