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Hi, I am Ötzi from Belgium. I have since several months a Suzuki T20 250cc twin from 1969. The bike is very beautifull and in a general good order. But there's one big problem I cannot solve till now.With the bike stil standing you can let go the engine easy till 8000 revs and more. While riding the engine starts to sputter by more than half gas, it's smoking also to much. Sometimes, especially when cold, it will go well for some seconds, than it's sputtering again. The maximum speed I sometimes can reach is 100km/h.What I did already: clean the carbs, put the needles at lowest, control and adjust the ignition, slack the cable from the oil pump a few mm., clean the petrol tank, renew te spark plugs. The jets are 85, the spark plugs are NGK 7. What can I do more to solve the problem?Thank you! regards, Ötzi
 

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Oops! Sorry the jets are 95 and that's original. Now I placed the needles at the lowest possebility and the behaeve of the bike is already a bit better.
But, unfotunally, not good!
Regards, Ötzi
 

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Ötzi, don't I know you from a glacier in the Swiss Alps? :) Welcome, I am new here myself. I lived in Brussels for 6 months many years ago and loved my time there. I can't help you with the bike. Just wanted to say hello.
 

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Hi Blackadder! Yes it was me on the Alps in Austria during the Moped-Marathon 2016.
Gr. Ötzi
 

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Otzi is this bike a two stoke? Lowering the needles causes the fuel mix to become leaner which may be why the motor seems to run a bit better. A two stroke is very suseptable to fuel mix changes. As the fuel mix is compressed in the crankcase and relies on this compression to transfer it to the combustion chamber it follows the carnk seals need to be in good condition. You may also need to check any reed valves...usually under the carb.

If its a four stoke a compression test is a good way to check the general condition of the bores/pistons/rings and valves. You will need to crank the engine with the throttle open. Without oil in the bores checks the valves add oil andif the compression increases its an indication the bores or rings are worn.

These are just a few start points I may be way off and your motor just needs a new air filter and a tune up...maybe run some fuel system cleaner through check the fuel filters and tank vent...on such an old machine you might have a build up of gunk in the tank, fuel lines and filters

good luck
 

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Thank for your reaction. I am in bikes already 60 years. This bike is a 2 cil. 2 stroke with normal piston controlled inlets. it has separate 'Posi Force' lubricating, only the middle crankbearing is oiled via the gearbox. All the parts of the fueling, carburettors, airfilter and so on are controlled and carefully cleaned. I now ordered 90 jets, carb.revision sets and one new float. We'll see what happen with these new parts. I do not know the amount of oil in the gearbox, one book says 1,2 ltr. another book says 2,11 ltr. Who knows what's good and what's wrong?
Gr. Ötzi
 

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Two stokes can be very temperamental. If the motor is bogging down under load and smoking a lot then the oil fuel ratio coud be over oily...alternatives could be the auto oiler setting or worn parts. You may want to check the exhaust and exhaust port for carbon build up...the port can be cleaned with a soft scaper...aluminium is good and the exhaust typically will have a removable baffle that can be heated with a blow torch to fid it of any carbon build up.

On many two stoke oil pumps there is a setting that needs to be lined up with a mark on the case at full throttle. adjusted by tigtening the cable. This sets the oil delivery correct across all throttle openings. If the engine revs freely without hesitation the mix is usually OK If it hesitaes then the mix is lekely to be lean...bogging down typicall is from an over rich mix...this can be either too much oil or too much fuel.

Do not run the engine too lean as two strokes are renown for holing their pistons.

As for the gearbox oil I would err on the side of safety and see what happens with 1.5l in it...dont run it too long...the gears shouls shift smoothly with no excess clunking. Alternative would be to find a specific forum where you can ask questions specific to your machine.


Good luck
 
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