Topic: dohc 1980 engine troubles

[dchoiper4]

ive been lurking on this forum, never really "spoken" up as this forum is geared towards the sohc's. but i think i got a problem that you guys may be able to help me out with.

so i bought an old 1980 cb750k and for the past month ive been slowly trying to get it to run, ive had a slew of carb problems, but everything else had been okay, the engine turned over fine, spark/compression good, but finally when i think i got the dam carbs fixed the engine stops turning over normally, from the crank it turns less then a full turn and stops, i can turn it the same distance clockwise and counter clockwise, previously the engine was turning over fine, its really a mystery to me anyone have the same problem before?

and if this means anything it quits cranking in either rotation when the 2 and 3 pistons are near the top, almost as if the problem is that i dropped something in the cylinder and its keeping the pistons from going up all the way to come back down, im not sure if that last part made sense

[Bill Vaughan]

What happened immediately before this problem occurred?  Was the engine running and then suddenly stalled?

I would hope that it isn't the valves that are preventing the pistons from reaching full stroke.

[MRieck]

 Your cylinders could be full of fuel. Pull the plugs out and see if it spins over. Did you replace the float needles? PS....stand back when spinning the engine with no plugs. If the cylinders are full of fuel it will erupt.

[Bill Vaughan]

dchoiper4,

Hoping that MRieck nailed the problem for you - fuel in cylinders.  What's the verdict?

[mrbreeze]

And make damn sure you disable the ignition when you turn it over.Even with the plugs out,you don't want any juice going through the coils when the gas is exposed outside of the combustion chamber.Last month,I had a Chevy Blazer in the shop that the guy accidently let roll off a small cliff and landed on it's nose and rolled over on it's side.It came in hydro-locked and when I pulled the plugs....had 3 or 4 cylinders full of gas.He had a 454 stuffed in this 74 Blazer and it shot a buttload of gas out when I cranked it over.Not a good scenario for an errant spark for sure!!!