nothing... nothing... BANG

[cpasseno03]

Hello HelloIve got me a new (1972..?) Lark 40 and with it I got me a WHOLE new set of problems. When I try ans start her I get nothing for about 10 seconds of cranking, then, BANG! Splash water all over and everything. It seems to big to be just a backfire. Floats might be stuck giving her too much gas. But this sounds like a horrible timing issue, BUT the timing really cannot be "set" as on other motors. I do not know what was done to it last, but the crankcase is different colors, the bolts have all been used, perhaps the lastest mechanic done something bass-ackwards?Thanks in advance, Im open to ALL ideas!Craig
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[The Marine Doctor]

Re: nothing... nothing... BANG

Try swapping the spark plug wires. Then try it.<br /><br />TMD

 

[Joe Reeves]

Re: nothing... nothing... BANG

Craig..... If the other fellow had the flywheel off, it has more than likely been installed without being torqued properly. This would cause the flywheel key to shear, throwing the engine out of time.<br /><br />If this is the case, be sure to clean the tapers thoroughly so that they seat properly, install a new key with its straight edge straight and vertical with the engine (not with the taper), then torque the flywheel nut to exactly 105 foot pounds. Anything less will cause the key to shear.

 

[cpasseno03]

Re: nothing... nothing... BANG

Thankyou, but I shouldve mentioned that this happened after I tried both of those. Switching the wires lead to a less violent ka-pow, but I am sure they were right the first time. The flywheel is not sheared, I had to replace the coils and points to get this far already. Any other ideas?Thanks again!Craig
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[The Marine Doctor]

Re: nothing... nothing... BANG

I believe what Joe is refering to now..is that the flywheel key might be sheared off now. Since the work has been done.<br /><br />TMD

 

[cpasseno03]

Re: nothing... nothing... BANG

I am slightly suspecting that since there was a dribble of gas from the carb, the float could be stuck. Now if that was the case, (i did choke it) would it be possible for the exhaust to fill with some gas and when it finally does fire it FIRES? It seems like an abnormally large fire, each time sending a half gallon of water out of my garbage can, i mean test tank. which normally wouldnt happen. all suspicion points to timing, but I really think it is correct. compression is good, could carburetion cause such phenomenon?
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[JB]

Re: nothing... nothing... BANG

I agree with Joe and TMD, Craig.<br /><br />I think a plug is firing with the exhaust ports open. The most common causes are switched plug wires and sheared flywheel key.<br /><br />Other causes I have run onto, particularly on engines that have been "overhauled" by incompetents or assembled from collected parts are:<br /><br />Incorrectly installed stator or points cam.<br /><br />Incorrect stator, cam or flywheel for that engine, creating a "maverick" spark nearly 180 degrees off.<br /><br />Coils wired to the wrong set of points.<br /><br />Pull the flywheel and spark plugs. Observe the piston and points that match. The points should break as the piston approaches TDC when turned in running direction. Be sure that the lead from that set of points goes to the correct coil.<br /><br />Examine the underside of the flywheel. The magnets should be approximately aligned with the coil for the cylinder that is near TDC.<br /><br />It sound like you bought an engine thrown together from loose parts and never ran. Got one that way once. Took a lot of sweat and every oath known to 30-year Boatswain's Mates, but she ran like a sewing machine when I was done.<br /><br />Good luck.

 

[cpasseno03]

Re: nothing... nothing... BANG

success!!I had already replaced the coils and points and everything, since the whole plate was loose in its mounts. I was positive it was not the ignition. When I did clean out the carb, it fired up and run for about a minute then stopped, it was then that I DID shear the key (I forgot to tighten her up) Anywho, after replacing that I got her running a bit more, But the last person to build this thing up could not have had it running long if even at all. Half the linkages and adjustments are all outta whack. I got my work cut out for me but she has nice compression Thanks for the help!Craig
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