Odd "miss and hit" during acceleration

[Bobcat]

To elaborate a little on what Dean said about the power valve .... if it fails , the engine will run really rich . Where it will be the most noticeable is at idle with the engine running really rich and rough . If you take the metering block off and find fuel in the well behind the PV , it`s bad .
Another thing I`ve had happen is the gasket under the pv is a two piece gasket that is cemented ( ? ) together . If you tighten the pv too much , the gasket will separate and give the fuel a sneak path to screw you up . When you take the pv off , the gasket will actually be in two pieces .

[Argess]

Well....it does seem to be a bit rich at idle and lower speeds and when accelerating seems to clear itself. But not rich enough to cause black smoke. Good tips on the PV though. Thank-you.

Last night, in the dark, I started it up. No arcing or anything. I then hooked by spark tester (just an adjustable gap device with a sparkplug tip on one end and an alligator clip on the other). I set the gap for just over 1/2 inch and connected the HV wire form the coil to it. Cranking the engine over I had a nice blue spark. It was hard to tell, but it seemed that every so often I'd miss a spark during cranking. This seems to match up when I used a timing light and every so often it misses a flash. Previously I blamed it on the light. Now I'm not so sure.

Anyway, I took it for a drive after my testing and except for some light bogging just off idle, it seemed fine. Seems the problem gets worse when the engine is very hot and complimented by driving during very hot/humid weather.

More testing today........

[patrickt]

Originally Posted by Argess

Cranking the engine over I had a nice blue spark. It was hard to tell, but it seemed that every so often I'd miss a spark during cranking. This seems to match up when I used a timing light and every so often it misses a flash. Previously I blamed it on the light. Now I'm not so sure. ... Seems the problem gets worse when the engine is very hot and complimented by driving during very hot/humid weather.

Remember that occasionally a horizontally mounted oil-filled coil will have an internal intermittent fault that can be very hard to diagnose. A vertically mounted coil can also go bad as well -- before you moved on to any serious disassembly/exploration I might just go ahead and change out the coil if you have any suspicions at all about it.

[Argess]

That's my next step. Being cheap, I'm looking around at what I have on hand, and if I can get improvement, then I can select and purchase a good new brand name coil.

Notes on coils:

I have a brand new Jacob's variable permeability coil (which I never understood as I always thought permeability was constant for a specific material). I am not going to use that because the engine would barely run with it when I tried it years ago. Plus it got very hot, very quickly. Jacob's help line was of "no help". I am not impressed with Jacob's stuff based on that experience.....$60 wasted.

I do have a Mercruiser coil which worked fine when I swapped it out. It had a bit of arcing at the tower, but that was bad wires. I changed both wires and coil as a failure in open ocean is not an enchanting experience. I just need to check to see if a ballast resistor is required for it before I hook it up.

You know, when you look up coils on Summit's web site, they often check the box that says the ballast resistor is "not included", however I suspect many of them don't actually use one, so it should say "not applicable". Some of the manufacturer's web sites are not clear on this point either. Some things still need a phone call to sort things out properly.