Perfect Century won't work

[rosbullterier]

Learned Gents-I disassembled an LLS (1958), seized for a long time. All components were hardly worn and undamaged. Back together, excellent magneto and timing plate, good spark, good bores,piston and rings; alloy impellor. Sealed the crankcase joint, carburettor appears adjusted and working well, petrol unleaded with 15:1 synthetic two stroke oil. Placed in water just over exhaust. Turned over with rope(until feeling suicidal) then with electric drill, full choke, half choke, full throttle half throttle and every other permutation. It would fire a bit only until I stopped drilling, with an occasional backfire through the exhaust or carburettor. I've studied all I can through forum advice and am thinking of using it as an anchor for my Japanese powered boat. Only fondness for nice old cars with character has prevented this up to now. Professional help is unwilling to become involved

[CatiGull]

I would suspect a compression test might reveal something wrong in the crankcase

I had a hairline fracture in a Featherweight that completely shut it down, on plugging with sealer the engine came to life and ran like a champ.

If the crankcase leaks the mixture will be way off and the engine will not run.

Tucked my Gulls away for winter this weekend..still got sailing in on the Hudson in December in Upstate NY

[charlesp]

Are you absolutely sure that the Woodruff key on the crankshaft taper hasn't slipped out when reassembling? If this has happened then the timing will be wrong - and could lead to exactly the symptoms you describe.

If all else fails I'm sure professional help would be available from John, in the unlikely event he can't assist then pm me. Dorset isn't all that far away from you.

[rosbullterier]

Thank you for your concerned replies. After reading forum advice, I removed and rebuilt he crankcase having trued the mating surfaces - which didn't really need it and sealed with gasket cement. There is now no leakage around the crankcase seam now but no alteration in 'no I won't run by myself'. I did wonder whether the timing could be out, even 180 deg; flywheel and timing plate have been on and off like a yo-yo. The woodruff key is unworn and in place and I have tried leaving the the long grub retaining screw out of the timing plate and twisting it up to an inch either way to alter the timing - no difference so its securely back and the timing plate is a snug tight fit!
The problem is I've started this project with a possibly perverse engine example to be running sweetly for the Lerryn (Cornwall) Seagull race which is now 10 days away! The skiff is finished and works well though . . .

[charlesp]

The only way the timing would be way out is if someone had fitted the wrong crankshaft at some point in the motor's history - very unlikely I think.

May I suggest that you reset the points - with the baseplate in the correct position, ie positioned by the retaining screw. Adjust them carefully, and note the rough timing position by watching a pencil inserted in the plug hole. As the piston approaches the top the points shouldm open.

We've had conversations on this forum before about this type of problem, and doubtless we will again. Actual timing should be about 23 degrees BTDC, but it's far from critical - don't give the exact position too much thought. Far more likely that the gap is wrong.

Given that you have compression, and you're confident about the carburettor (I'm sure you've tried with and without choke, and flooded and unflooded) and you have a spark, the motor should fire.

[RickUK]

Just a couple of thoughts from me - are you sure that fuel is getting through the carb - worth checking the jets again, especially after a rebuild, which may have disturbed some muck, and secondly - did you remove the piston during the rebuild and if so, replace it the right way?
The slope on the piston crown ahould face the exhaust.
I was also goint to suggest timing, but that all seems to have been covered well.
Rick

[RickUK]

Forgot to say - hope you make the Lerryn race - let us know. I'd love to see it, but it's a fair hike from Cambridgeshire and too damn cold for my liking. Good luck!! Rick

[rosbullterier]

Gents, its started on the high speed drill - with huge backfires flames in the exhaust tube and water blasted from the bucket! I've removed timing plate grub screw and turned the timing plate plate anti clockwise about 1/2 inch which allows fairly even fastish running but not a slow idle or acceleration. Could the only starting on fast speed indicate poor magneto output? The mag assembly and points look pristine but 48 yrs old . .Turned the carb needle spring screw 3 turns out to enrich? the mixture with no change. I've retired to change clothes and shoes and ponder about its rare parts value and should I have purchased a working example - 9 days to go.

[CatiGull]

YOu should be able to diagnose a bad magneto by observing the spark whilst you turn the motor with a healthy pull on the starter rope. A nice blue one at the plug of course. An observer can hold the plug against the crankcase whilst you pull. CHoose an observer who doesnt mind possibly getting a small shock.

There isnt more to it than compression, fuel and spark indeed.

[rosbullterier]

Unfortunately I suspect there could be more than just compression, spark and fuel. Is it correct the points should be just opening (tested with thin sliver of paper pulled between them) to allow the HT discharge when the piston has arrived at TDC. As there is only one piston and it's a two stroke I assume it would be the compression stroke. If this is the case, the crankcase location hole for the timing plate grub screw is about 1/2 inch behind the grub screw casting threaded hole when the above events happen. Before I drill another hole, your advice please.

[charlesp]

No the ignition isn't timed at Top Dead Centre. It's at 23 1/2 degrees before Top Dead Centre. But don't get hung up on the exact timing - many earlier models with a very similar ignition had a lever that enabled the user to advance or retard the timing at will.

The possibility of a timing error causing your problem is infinitesimally small. The grub screw and the crankcase will provide the correct position for the ignition timing. Every Seagull in those days was individually tested, and an error would be obvious at the time.

Best advice remains to put the baseplate back in the correct position, and work from there.

You have established by succeeding in running the thing that:

1) The crankshaft isn't the wrong one

2) You have sufficient of a spark to support combustion

3) You have sufficient fuel to run the motor at higher revs - and by extension at lower ones.

You've confirmed you have good compression.


Looking back at your earlier posts I notice that you're running on 15:1, and that you've screwed the needle out three turns to give a richer mixture. Running on 15:1 will make it richer, too. I suggest draining the carb and tank, and refilling with 10:1, also return the needle to its original position.

I then suggest once again cleaning the points, and carefully gapping them (at their widest point).

You'll notice that this advice suggests returning everything - petrol/oil mix, needle adjustment, magneto baseplate, and points, to the way the manufacturers recommended. Modern petrol can respond to closing the points slightly.

Again, I'm assuming that the petrol supply is sufficient, and that the flooding button delivers a decent supply - that way you can be sure that the filters aren't blocked. A glance at the plug if she doesn't fire will show petrol if you use the choke.

Good luck

[CatiGull]

Looking back at your earlier posts I notice that you're running on 15:1, and that you've screwed the needle out three turns to give a richer mixture. Running on 15:1 will make it richer, too. I suggest draining the carb and tank, and refilling with 10:1, also return the needle to its original position.

Charles - I bet that nails it - nice catch. Happy New Year!