Topic: Number 1 cylinder not firing properly.

[jamesb]

1975 cb750 pamco ign stock harley coils drag pipes. Number 1 isn't getting hot like the other pipes the plug is oily and smells like gas. New plugs about 200 miles ago. Could the cool not be hitting on that cylinder like it should. There is unburned fuel coming out  of the pipe. Carbs are good and tuned everything else seems good. Plug wire seems to be in good shape. I'm running 7mm automotive wires I've ran these in the past with out problems. I'm going nuts. Looking for any input please thanks the number 1 pipe gets warm just not hot like the others I ran it for about 1 minute and could not touch the other pipes but can rest my hand on #1

[LesterPiglet]

Swap #1 plug and wire with #4 and see if the problem moves.

#$%* I meant #1 and #4

[Vinhead1957]

If the problem moves then swap the plug cap only

[Black 750K8]

1975 cb750 pamco ign stock harley coils drag pipes. Number 1 isn't getting hot like the other pipes the plug is oily and smells like gas. New plugs about 200 miles ago. Could the cool not be hitting on that cylinder like it should. There is unburned fuel coming out  of the pipe. Carbs are good and tuned everything else seems good. Plug wire seems to be in good shape. I'm running 7mm automotive wires I've ran these in the past with out problems. I'm going nuts. Looking for any input please thanks the number 1 pipe gets warm just not hot like the others I ran it for about 1 minute and could not touch the other pipes but can rest my hand on #1

There is nothing stock about this.

Could the cool?? Want to translate that
What do you mean when you say automotive wires what core do they have?

[jamesb]

Cool one is a typo. I switched 1&3 no difference. I'm going to try and do a compression check if I can find a test kit somewhere. Also could it be getting to much gas in that cylinder.  May e a carb problem???

[mrbreeze]

You have it tracked down to #1 cylinder so I wouldn't blame the coil. Plug wire, cap, and spark plug would be my guess. Make sure the fuel level in #1 bowl is the same as the others or real close. Usually the gas will run out of the overflow hose if the level gets too high but I've heard of plugged overflow hoses (spider webs,etc.). If you are getting too much gas to that cylinder....it could foul out the plug. Do you turn the petcock off when not riding? If not...you should. Usually if there was a coil problem, you would be losing cyl. 4 along with #1. One coil does 1-4....the other #2&3.

[jamesb]

I put a spark tester on it and one and four have the same color and firing pattern I'm going to stop and pick up a  plug on the way home today , switch some plug wires around to see if that makes a difference    Also I will check fuel levels. Thanks for all the info.

[Duanob]

you might check compression too. No compression, no BOOM, no heat. A valve that is too tight might have the same effect.

[iron_worker]

You said the plug is oily ... it's probably fouled.

IW

[Black 750K8]

Over the years I have thrown away a lot of good plugs. If you get a small hand held torch that take those I# cans you can usually burn the crude off the plug. That is what the engine does once you get the RPMs up and the engine hot self cleaning. They get a little dirty during a cold start with the choke.

[LesterPiglet]

I rarely throw plugs away. Set them on the gas cooker, burn them and wire brush after.

[jamesb]

Well I believe I have a defaulty plug. I took them all out cleaned them now number three isn't hitting properly. Number one is getting hot like it should. Now number one pipe is smokey burning all the wasted fuel. Thank you guys for all the help. Now I need to get the other cb750 out and start getting it back into shape and road worthy.

[grcamna2]

If it was me,I'd drain the fuel in all the carbs. and tank and put in fresh.The bowls may have some junk in'em that could have fouled the plugs a little...

[LesterPiglet]

That ^^^^ seems a bit much. Just drain the floatbowls and check for debris if you are concerned.

[jamesb]

I've always had a filter on the carbs tonight I'm going to check the fuel level in the bowls. I did install another plug "used" and it works great now. It does seem to run a little rich though the pipes are very sooty

[grcamna2]

filters can only catch "most" of the stuff,the very small fine micron particles of rust do still get through.I'd be more concerned about what happens to years of old gasoline varnish,the small stuff builds up inside passages.I imagine the problem is most likely spark related.., but I just thought I'd mention the possibility of carb. fouling.