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Suzuki 1987 DT40 2 stroke only running on 1 cylinder

ronster66

New member
Last year I bought a 1987 DT40 2 stroke that turned out to be running only on 1 cylinder. (I took it in for a service and found this out.)

They couldn't find the problem, fuel was getting to the carb and to the manifold, but not reaching the lower cylinder. Compression was good on both cylinders, sparks good on both(swapped around, no change to lower cyl) fuel is getting to the reed plate but not into the cyclinder.
Was advised it may be the reed valves or lower crank seal. (cost £400 to diagnose this!) The reeds and plate looked ok, So i stripped the engine and changed the seal. No difference. I then revisited the reed plate and swapped some reed valves around, one seemed like it wasn't fully sealing, as i could suck a little air through it.
This got the lower cylinder running somewhat, i could start it up on the lower cylinder only.

It ran ok for a few short trips on the river seemed heavy on fuel and 2nd cyl was running rough .
So i fitted a new reed plate, but now it is back to running on 1 cylinder. I tried refitting the old one, but it still ran on 1 cylinder.
I'm wondering if there could be a problem with the casing not sealing with the reedplate/manifold? something that is preventing the vacuum needed to suck the fuel into the chamber?

Its a nice engine, apart from the main issue, everything else is running well, remote is good, power tilt is working fine. and i'd really like to get it working again if possible.

The engineers couldn't help any further, so i'd really appreciate any advice on what to try next.
 
I'll check it anyway, but it goes to a single carb, which the engineers serviced and said was setup correctly(changed the float \needle?)
cylinder 1 fires and runs well, could it be timing related?
 
A ruptured diaphragm would likely flood just the one cylinder !!------------The fuel would go into the crankcase without even going to the carburetor.----Cheap and easy to check too !!
 
The fuel pump is operated by fluctuating crankcase pressure in the lower section. If the diaphragm is leaking fuel into the crankcase it would make this cylinder too rich to run. Is the lower sparkplug wet with fuel or fouled by too much fuel? The pump is simple to remove and inspect.
 
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