Spitfire firing on clutch side cylinder only

[tullybrewing]

I just picked up an original owner 1979 Spitfire. Last registered in 2002 with 1800 miles on the odometer. I just did a complete fuel system overhaul (cleaned tank, pump & butterfly Mikuni), new fuel lines, filter and added a petcock. The sled is now back together and it started right up on the 2nd pull and seems to idle well, but only on the clutch-side cylinder. I have the exhaust manifold off to notice the pop and heat from this cylinder, but just a blast of non-combusted fuel coming from the magneto-side. I know I've got fuel going, however nothing happens when I open the carburetor up while it's running. In checking spark, I seem to have good spark at both plugs when pulled. I've haven't metered compression yet, but in covering the hole with my thumb on each cylinder, it seems to feel that the compression is equal between both sides. The only thing I haven't tried yet is reversing the yellow wires at their connections coming out of the motor, as I may have reversed these when I put the Kohler back in. Aside from this, is possible that I may have a bad CDI that's allowing for the magneto-side plug to show spark when outside the head, but then under compression I'm losing spark? Is it possible that by having the exhaust off that I'm not allowing this cylinder enough back-pressure needed to run? Any guidance someone could offer would be greatly appreciated.

[robtan88]

First thing I would do is crank seals. Machine that old with low miles and no use is prime candidate!! Air leaks will do this as you described...Rob.

[Matt]

Yes it's possible the spark is failing when the cylinder is under compression, however I would borrow a compression gauge and make sure the numbers are OK before buying a CDI. As robtan said always replace crank seals on these engines too, also much cheaper then a CDI.

[sledhead16]

You need to know 3 things, what's your compression numbers, does it have spark, is it getting fuel. After that is all known, then you can start pecking away. I'd always have that muffler on if your running it. You could have low compression on the mag side.

[tullybrewing]

I borrowed a compression tester from a friend to check this weekend and I'll share the readings. I have spark and gas.


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[tullybrewing]

I borrowed a compression tester from a friend to check this weekend and I'll share the readings. I have spark and gas.


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Compression test today 10.20.16
Mag side = 100PSI, Clutch side = 100PSI.

Will order crank seals and gasket kit today. Cylinders don't appear scored and will inspect rings during tear down.

What should I expect the compression to PSI to be?


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[sledhead16]

100 is really the minimum you'd wanna see, 120+ is ideal

[tullybrewing]

Minor ID10T error on my part in figuring why the machine will only fire on one cylinder today. The previous owner replaced the ignition coil and had the plug wires on reversed. I assumed they were right and never checked them. As soon as I swapped them around the sled runs as it should. I ordered crank seals and gaskets for the motor and while I have it apart will replace the rings. Still only 100PSI cold and 90PSI warm now that it runs. Would like to see what I can do to get the compression up.


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[TASKY]

Try another compression gauge.

I have two of them and they both read different every time.

The information that I look for from the gauge is the relationship between the 2 cylinders.

[tullybrewing]

My pressure readings are consistent between both cylinders. The gauge is from Harbor Freight, so I wouldn't be surprised if its reading lower than what the Kohler is actually generating, plus it's running well. I have a tire filler/gauge from there that is no where close to 3 others in my tool box.


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