Trouble shooting engine start up

I just spent sunday doing them. First time to do this, but it went very well and I had all the correct shims swapping from another motor. All clearances were within specs. If, say, clearance was off, wouldn't I get leaking when I do a compression test? It seems like the rings are a bit dirty an perhaps a bit worn, not outside what it might be at it's miles driven. Bike has 18K on speedo. A little oil in the spark plug hole will get compression up to 175psi, so I think the valves are relatively tight. I just checked Secondary coil resistence to be 14.4K ohms. This means coil is ok. Compression is around 125, not great but matches or exceeds the other three cyls. I'm checking breaker points again now, gap and setting for timing without a timing light. Would a timing light help here? It seems like if it were timing then both #1 and #4 would be affected together, I'm pretty inexperienced on timing, just following manuals and post searches.

Without changing plugs, have you tried swapping the 1 and 4 plug wires at the plugs?
Since #1 works, everything attached to #1 works. So just switch the wires and see if the problem moves from 4 to 1.
If #4 starts working, and #1 stumbles, then it's in the coil, plug wire, or plug cap that goes to #4.

If #4 continues to stumble, then it's #4 cylinder compression, or #4 carb.

mountain wrote:

...All clearances were within specs. If, say, clearance was off, wouldn't I get leaking when I do a compression test?....

Not necessarily, as minimal clearance when cold may not leak compression. But lose clearance as the engine warms causing loss of compression.

Interpreted original post to say compression readings dropped a lot when the engine was hot. Thought too tight valve clearance might be the reason.

Good to hear the clearances are okay.

I went through the timing and breaker points, set points break with ohmeter. Same thing happens. Swapped 1&4 coil wires (1 onto 4, vice versa) and still the same #4 not firing. I'm beggining to think perhaps I should take the valve cover off and make sure clearance is right. After all, it was my first time doing a valve clearance adjust. #4 cyl is reading 125psi hot or cold, but maybe it is not compressed exactly when it should be at spark moment, which could mean leaky valve, am I correct in my analysis? Gees, I'll be doing a jig if I can figure this one out. Please feel free to critique how I'm doing on this, it's the only way I'll learn. Thanks, too!
Ben

mountain wrote:

I went through the timing and breaker points, set points break with ohmeter. Same thing happens. Swapped 1&4 coil wires (1 onto 4, vice versa) and still the same #4 not firing. I'm beggining to think perhaps I should take the valve cover off and make sure clearance is right. After all, it was my first time doing a valve clearance adjust. #4 cyl is reading 125psi hot or cold, but maybe it is not compressed exactly when it should be at spark moment, which could mean leaky valve, am I correct in my analysis? Gees, I'll be doing a jig if I can figure this one out. Please feel free to critique how I'm doing on this, it's the only way I'll learn. Thanks, too!
Ben

Compression on #4 seems okay hot or cold, so believe valve clearance is not the culprit.

Question, please --- what does the tip of #4 spark plug look like when removed from hot engine after the engine has run for a few moments on #1, #2 and #3? (Might use a short length of hose to grip and unscrew plug from hot engine). Is the tip dry or wet with gas? Dry would indicate your suspicion of fuel blockage. If wet, would suspect a too high service fuel level in the float bowl, causing an excessively rich mixture which could be flooding out the plug. Has the service fuel level in #4 float bowl been checked? (You know -- the world-famous quick easy clear plastic tube method )

Post edited by: Patton, at: 2007/03/28 16:15

So the valve cover is off and It looks like the clearance is where I left it when I adjusted Sunday, a bit tighter by a few thousandths becase it's a little warmer right now. They're all pretty close to .150 and none are less than .100, just had to get them as close to .150 with the shims on hand. So I guess I'm going to pull my carbs off again and take them apart further. The float bowl is filling with gas alight, and I cleaned everything out in the #4 bowl this morning, jets pilot screw, all the little brass parts, and carb passages with compressed air. The carbs are really clean from soaking and rebuilding them not long ago. I'll take it apart far enough to get to the float plunger and pull out the throttle valve and blow more air. Could I be blowing that much copression by the rings? If not it has to be fuel dilivery.

Patton, I like it, I like it. I have NOT set or checked the float level. It seems very difficult to do this, I don't have the little screw in clear hose level tool. Perhaps this is a good next step. YES, the spark is wet when pulled. I may try just tweeking the tang a bit to see if that does anything without going through the float bowl level setting process. I'll try that before I take the carbs out again today. I'm getting frustrated.

you can put the timing light on on number 4 while it is runing, you can check the timing that way also, I have seen a bad plug that will not fire under the cyl compression, but would fire in the open air.

then more this gets kicked around, it sounds more like a carb issue.

Just set your float on your bad carb the same as a working carb when looking at them dissassembled. Using that clear hose to set fuel level is a major pain and not worth the effort. Float level is not critical to running. Of course you need ample fuel, but too low a float will not cause the cylinder to not run and too high a level will cause gas overflow through the overflow tube. Either way if you have gas in the carb bowl it should run. The reason I say this is that once I stupidly assembled a carb with the needle upside down:lol: and although the float would never shut off 100%, when the engine was running the motorcycle used more gas than what gas was leaking past the needle/seat by my error, so I rode it like this for quite a few days thinking I just had dirt or something stuck in the needle. It ran just fine. Also if you've ever run out of gas you'll find the motorcycle still runs just fine as your bowls are being drank dry, until they are near empty.

I guess I need to figure how to check timing with a light sometime. As far as the spark, I got new ones and swapped #1 plug and coil wire with #4 plug and coil wire and got similar results. No go on #4 firing. I'll try reducing the float level in #4 carb by tweeking the tang. Patton has something there. Maybe it's flooded from that carb. I'm hoping so.

I hear you Ron, but I'm running out of next steps to try. You wouldn't think that a little too high fuel level in the bowl would massively flood. Visually, by measurement, when the carbs were on the bench the floats all seemed to ride to the same hieght, pushed out by the little valve needle spring. #4 carb is not overflowing either. Same amount of fuel comes out of it as the others when I drain them.

mountain wrote:

...have NOT set or checked the float level. It seems very difficult to do this, I don't have the little screw in clear hose level tool. Perhaps this is a good next step. YES, the spark is wet when pulled. I may try just tweeking the tang a bit to see if that does anything without going through the float bowl level setting process. I'll try that before I take the carbs out again today. I'm getting frustrated.

Quick and easy as pie to check, with bike fully assembled.

Don't need the special tool.

Only need a short length of clear plastic tubing to squeeze-thread into the carb drain screw hole.

If adjustment is needed, then the float must be removed to access and bend the tab which pushes the float needle into the seat.

Don't rely on the upside-down bench measurement and adjustment, as that often fails to result in the actual operational fuel level desired.

Now, please go up to the search forum box and type in clear plastic tube. This will reveal several informative articles you will likely enjoy.

Let us know if further reference is needed for the prior articles.

And BTW, when cleaning the carbs, surely you were very careful to keep the float needles together with the same seats, as these are paired units. If needle is used with the "wrong" seat, it will likely leak, regardless of how clean they are.

FYI -- Trouble Shooting Guide in the KHI Service Manual includes "fuel level too high or too low" as one of the causes for "Fuel/air mixture incorrect" under low speed and/or high speed conditions.

And not to disparage the prior cleaning operation, it might yet wind up being a clogged pilot air passage or starter plunger stuck open. (Am assuming the pilot mixture screw is already properly set equal to the those in the other carbs.)

Keep the faith!