bad spark plugs?

[zed]

I'm busy looking for the cause of a mis-fire on my L18. It's only on one cylinder, and only when the engine is cold.

Anyway, I checked the resistance of the distributor cap and plug wires with an ohm meter. The wires measure '0' - zero ohms resistance, but by elimination I found all the spark plugs have resistance between 350 to 1800ohms - strange? I'm running solid copper core wires and NGK BP5EY plugs - these are NON-RESISTANCE plugs. They have around 2500miles on them. For comparison I checked some new plugs I have - they also show resistance around 100ohms. Would 1800ohms resistance cause the mis-fire? I'm running a Pertronix with 40kV coil. Any ideas about the plugs, or where else to look for the mis-fire? thanks

[Skib]

have you pulled your plugs and looked at them yet?

[datsunfish]

Are you sure its a misfire issue? How do you know its only one cylinder? Have you pulled off wires while its running? Ive had similar issues that turned out being vacuum leaks or faulty carb.

[zed]

First thing I did was pull the plugs - they look good - dry, light grey. I replaced the 'high resistance' plug with a new one. I've tried pulling the plug wires off one at a time while it's running - when it's cold it just dies. After it's warmed up some the mis-fire seems to go away at idle - but it will stumble or hesitate as I pull off from standing. Above about 40mph it seems to run perfectly. But that may be because it's hot by then. Tonight I'll check the fuel pump and filters. I'm running a Nikki carb - OEM on my truck. It has an accelerator pump - could it be that? What about valve clearances? thanks for the ideas so far

[ariascarlos1990]

Whats your timing set at?

[zed]

timing is 8 btdc

[datzenmike]

Try a set of resistor plugs and wires.

 

Here's wht NGK says about non resister plugs....

 

NGK (faq)

[zed]

will get resistor plugs in the town next week - no shops in my village. Blew out filters, fuel pump fills a litre bottle in about 10 seconds - should be ok. Im busy setting valve lash - but doubt its the problem.

[banzai510(hainz)]

anytime uyou loose one cylinder alsways ck the valve lash.

buy NGK wire sets I have had mine minumum of 6 years on a motor if not longer

[zed]

Well, I re-set the valve clearances real careful to spec - and the problem is gone! Some of the valves were quite far out - like .015" instead of .008". But I can't believe this would cause such a strong mis-fire? How can so much compression escape through a gap .008" wide? Doesn't really seem logical. Anyway, thanks for the advice

[banzai510(hainz)]

of caose I ck the plus but I also do the wiggle test on the rockers. if its loose when the cam lobe is up the the valve is closed and should have compression unless valve or piston is cracked.