Topic: #4 not firing.. could it be a timing issue?

[lowbrowcustoms]

This is in regards to my '74 cb750k4 with new dyna 3 ohm coils, hondaman resistor pack, new dyna-s ignition, new plugs, new wires...

I statically set my dyna-S ignition, bike fired right up, but white running I noticed the #4 pipe was lukewarm at best, while the others were real hot. I charged my battery, put it back in, fired it up, same issue. Swapped the wires for #1 and #4, still no fire on #4. I switched the wires back and swapped the plugs, still no fire on #4. I checked and the float bowl on my totally cleaned and rebuilt carb had fuel in it.

I am wondering if it could be a timing issue. I statically timed the 1-4 and 2-3 on the dyna-s as stated in the directions with a test light, but I didn't manually advance it because I don't see how you can with the dyna-s pickup mounted in place. I statically aligned the F marks for side as soon as the test light kicked on. Then I hooked up my timing light to the #1 plug, it is the type where it plugs into the wire and onto the plug in a series. The light was flashing really fast, and with the bike running at a fast idle and at higher RPMs I couldn't see any marks as it was spinning, just a blur...

So I guess my no fire on #4 could be a problem with some crud in my idle jet of my #4 carb or something, but because of not being able to time with a light I think that it probably isn't a fuel problem.. Can anyone shed any light on this?? It's driving me crazy!

Thanks!
Tyler

[TwoTired]

Remove the spark plug and lay it against the engine, and look for spark.

Swap the spark plug with another, to see if it works in another cylinder.

I you have a good plug and can see spark, then look toward the carbs.

[Cvillechopper]

Also, when was the last time you had the bike running?  Have you recently adjusted the Tappets?  there have been several posts recently where incorrectly adjusted tappets were keeping the cylinder from pulling in fuel/air or pushing out exhaust.  Once you know that you have spark, I'd look to the tappets to rule them out.

[Hope]

I think if it was timing, it would be 1&4 instead of just 4.  I had a similar problem, but it turned out to be the carbs...  but first I ruled out the spark plug, the spark plug cap (yes, those go bad)... I see that you already checked your spark plug wire.

After cleaning the slow jets, #3 is hitting fine along with the others...  you may want to look into doing the same... SOUNDS A LOT LIKE THE ISSUE I HAD.

[hymodyne]

My #4 pipe was luke warm and it was a blockage in the low speed jet in that carb.

hym

[lowbrowcustoms]

OK, I think it may be the idle jet on #4 carb.. The carbs are freshly rebuilt but the passage for the idle jet in the #4 carb looked a bit messed up, I blew it out with compressed air and thought it was fine but maybe it isn't...

I just adjusted the tappets (and re-checked them all right after) a week or two ago, I had never had this bike running before, I just got it up and running on Sunday evening. The PO said he hadn't ridden it in a year..

So what about the timing issue? Not being able to see the timing marks with the strobe on it? It seems to run good, and statically the timing is set right on, so why can't I see anything with the light?

Thanks
Tyler

[Hope]

I think that if it was timing it would be 1&4

[lowbrowcustoms]

It is the idle jet passageway on my carb #4. I sprayed a bit of ether in carb 4 while the bike is running and it revs up. I ran it at higher RPMs for a minute and pipe 4 got hot. I took it apart, the passageway for the idle jet is damaged, I sprayed it out with carb cleaner and compressed air, got a speck or two of brass flakes out, put em back together but I still have the same problem. Must have more serious blockage inside. Looks like jet was snapped off in there at one point and maybe a piece of it is lodged in there somewhere. I am looking for a good carb body to swap my over to, if anyone has one let me know!!
Thanks
Tyler