All 2st Terrible low speed running

[Tzedz]

Ive just done acomplete top and bottom end rebuildto my 360,but the bike is running horendous at the bottom end then goes crazy on the main jet.Ive tried various jetting and needle positions on a tm mukini carb,leaner making it more rideable,but im now on a 32.5 pilot jet and top needle position.Any sugestions

 

[Hurky]

Few things come to my mind:

- Air leak: You should maybe do a leak test, maybe your base gasket or reed case gaskets are sucking air in. (But you say leaner make it better so it's probably not an leak mmmh)
- Ignition timing: Maybe you changed the timing, have a look at the ignition marks, you can check that in the service manual.
- Float bowl height: Did you touch the carburetor bowl / needle ? A too high float level can give rich conditions, you would notice bad running, smoke and fouled plugs.

 

[Tzedz]

Cheers Hurky will try the float bowl height,the ignition timming has not been moved i ve just marked up the stator,could be 0.5 mm difference at most at most.As for an air leak test,i know the jubillee clip on the air boot intake is not best but this would only make it weak.So float bowls it is and ill let you know the results.

 

[robertaccio]

crank seal check also for the air leak trouble shooting.

 

[Tzedz]

I’ve changed both crank seals twice,so I’m sure it not these

 

[Oldscool]

Check reed valves are sealing and powervalve is correctly assembled and operating (not stuck open is it?)

 

[johnnyboy]

Could try turning the fuel off while riding the bike to see if it improves and if so it could point to the needle valve o ring being shot making it rich as it by passes the valve .

 

[Tzedz]

Oldscool power valve is operating as ive taken the cover off and you can see it moving,and i adjusted it at the powervalve cover so it didnt hit the piston,on the power valve drive side ive taken the clutch cover off to have a look,and ive notied that to connect the plastic linkage bar is more troublesome,ie i have to pull up the metal linkage to meet the plastic linkage,sure i just pushed it on before.And when putting the clutch cover on i just turn over the engine until it alines with the water pump gear and drive gear for the power valve so i assume there is no adjustment at that point.

 

[Oldscool]

Cool. Did you remove the valves themselves from the cylinder? Are they fitted correctly? You can check they're fully closed by taking the exhaust off and looking in the exhaust port. Manually operate the external linkage to see their operation.

Have you checked the reed valve petals for fraying, warpage or splits?

 

[Tzedz]

The reeds are not frayed and in good shape.Ive whipped off the exhaust off and the you can see the valves,they protrude about 3mm is this correct,they move up and down with the actuating arm.Theres a lot of oil around the exhaust port,meaning that something is deffinately amiss.Running it on a 2 per cent ratio as per manual(80ml for every 4 litres)

 

[Oldscool]

Looks like you've eliminated most mechanical possibilities, back to the carb and ign suggestions made by others.
Be patient and methodical and you'll find it mate.

 

[lankydoug]

Check the cranking compression.

 

[Tzedz]

Ive got a stator reading off the local bike shop 147ohms pulse coil and 0.9 ohms lighting coil,i told the shop standard figures of 0.7 lighting and 127 pulse and got the informatiion from a previous thread on here,they seem to think that the stators okay .Does any of you know for sure that its in spec,as i want to eliminate it.It has already been rewired twice by west country windings

 

[lankydoug]

Did this problem appear after the top end rebuild or was it present before the rebuild and the reason for the rebuild?

 

[Tzedz]

before the rebuild everything was fine,apart from the gearbox,so i rebuilt the bottom half including crank,then put original top end on,i.e barrel and piston.But it was smoking and oiling,so i then put in a new piston and and replated barrell,acording to my local bike shop the bore was beyond the wear limits.then replaced the seals once more as it was still very oily.Now clounds of white smoke dont come from the bike, but the low speed running is horendous

 

[lankydoug]

before the rebuild everything was fine,apart from the gearbox,so i rebuilt the bottom half including crank,then put original top end on,i.e barrel and piston.But it was smoking and oiling,so i then put in a new piston and and replated barrell,acording to my local bike shop the bore was beyond the wear limits.then replaced the seals once more as it was still very oily.Now clounds of white smoke dont come from the bike, but the low speed running is horendous

It could very well be leaking air and sucking transmission oil from the crankcase seam where the case halves seal together..

 

[Tzedz]

Just done a compression check and after half a dozen hard kicks i got 160psi.im unsure if this is within tolerrence or not.

 

[Tzedz]

also measured the float height at 18 mm which seems correct for a mikuni TM 38

 

[Dirtdame]

Just done a compression check and after half a dozen hard kicks i got 160psi.im unsure if this is within tolerrence or not.

160 is plenty good.

 

[lankydoug]

It might be necessary to do a leak down test on the crankcase. This is done by sealing off intake and exhaust and putting a couple psi pressure on the top/bottom end and see if it holds. The reasoning is you didn't have a problem until the cases were split and erratic running and not being able to tune it is often an air leak. If it tests good you can move on and not 2nd guess an air leak.