Saving Old Seagulls

My (ongoing) problems with my TC-102, and my discoveries arising from a recent strip and reassembly have led me to conclude the following about oil ratios, loss of power and sloppy bearings.

Purchased motor from stranger on eBay who said the correct fuel ratio was 25:1. Couldn't get carbie jet out to confirm so believed him. Ran it for a week or two on that ratio but it had no guts, was a bit "rattley" and would often slow down for no reason. Suspected seizing by others in this forum.

Tried all manner of things to restore power, such as electrical and carb tinkering, all to no avail.

Complete strip of motor found sloppy main bearings, sloppy big end, sloppy little end, and very worn rings.

After re-assembly, on the advice of others, I used 16:1 fuel ratio, and the lack of power was a little less than previous.

Today, I experimented by increasing oil mixtures as I tested it under load. From 16:1 I went back to 10:1 and the increase in power was quite marked. I increased to 9:1 and then 8:1 and (what I think is) full power is now available. .... OK ... OK ... it is a little smokier than desired but I was "experimenting" in the name of science!

Conclusions (and some hard learned lessons)............
The carbie jet had never been changed to a 25:1
Check your carbie jets yourself - Never believe a previous owner!
Irrespective of the carb jet size, the previous owner's usage of 25:1 fuel has worn the motor terribly.
Staying with the factory recommendations for oil mixture (or not lessening it too far because of smoke concerns) is a Very Good Thing to keep power and prevent wear.
I really need all new bearing and rings to come back to a 10:1 or 16:1 running mixture.

I have a sneaky suspicion that the the sloppy bearings and worn may have something to do with 40 years or so since it was manufactured!

What puzzles me is the advise to lower the jet needle when altering the petrol to oil ratio from 10:1 to 25:1. (AMAL carb)

I thought that lowering the jet needle would result in a leaner fuel mixture.
Less two-stroke mixture would mean less oil for lubrication and sealing as well!

So the amount of oil would drop significantly: 1:25 instead of 1:10 AND a leaner carb-setting.

Am I wrong or am I wrong ?


In the seventies I had (a Puch with) a BING carburettor and there was an aftermarket novelty that was every tuners dream: an adjustable jet-nozzle.
This allowed altering the mixture while running the engine.

One could fine-tune the mixture until it reached the point just before the engine would start to " 4-stroke ":
the richest possible setting for a two stroke engine,
offering optimum cooling and lubrication.

Wouldn't this come handy on a Seagull?

[quote="Dr.Lighthouse"]What puzzles me is the advise to lower the jet needle when altering the petrol to oil ratio from 10:1 to 25:1. (AMAL carb)

I thought that lowering the jet needle would result in a leaner fuel mixture.
Less two-stroke mixture would mean less oil for lubrication and sealing as well!

So the amount of oil would drop significantly: 1:25 instead of 1:10 AND a leaner carb-setting.

Am I wrong or am I wrong ?

I think you are wrong indeed. When you use less oil, the mixture will run easier and faster through the jet. Therefore you have to change the jet size to give the same amount of mixture to the engine. So in fact it has to do with the viscosity of the petrol/oil mixture, that is why you have to change your jet. In other words: making the mixture more oily will result in a leaner petrol/oil mixture for the engine when using the same jet size.

Happy Seagulling,

Albert