Need help - Won't Start

I just rebuilt the carburetors on my 1976 KZ900 something I have done many times, and I do not think this is the problem here.
The bike definitely has fuel to all cylinders, it has spark to all cylinders. The bike ran perfect last year, with a few minor carb problems which should now be fixed.

Now I start it, and it is very hard to start, and its running on only 2 cylinders. The two that are running have correct burn on the spark plugs, which may be hard to tell on two cylinders, but I didn't realize this until after I shut it off, the other 2 are basically like a new plug that is wet with gasoline. It is the 2 middle cylinders which are on the same coil. I only know they don't work because of the plugs and the exhaust pipe is not the least bit warm out of those and its at 120 degrees F on the other two.

I know the timing and points are all good, checked the coils and they test good. Switched the coils around and the same 2 cylinders are not working. Compression is a little on the low side but should still allow the engine to start. Compression is at 100 PSI on all cylinders, that went up and stayed up after I squirted a little oil in each cylinder as my repair manual suggested. It went up to about 150 all the way across after doing this.

I am now considering an engine rebuild but I thought I would ask first to see if anyone can think of anything else as I would sooner rebuild the engine at the end of the season, not the beginning if I can get away with it.

Thanks

Would also check valve clearances (especially #2/3 cyl), as cold compression figures may not obtain at normal operating temperature.

Sometimes a new looking wet plug that fires when under no compression may fail to fire when placed back into service. Probably won't resolve the matter, but would install brand new plugs anyhow just to be sure.

While at it, would check service fuel level in float bowls -- you know, the quick easy clear plastic tube method.

And are #2/3 carb choke plungers going all the way down?

Good Luck!

I would: put in new plugs, if that doesn't get it:

Check out the "electrics" in the front path of that coil which is not firing. The coil swap you did indicates it is not the coil, so it leaves the "igniter" circuitry. Ohm it out and make sure the connectivity to the points is good and opening when it should. Also make sure the +12V feed to that coil is solid.

Easy to trace out if you have a meter: with the key on, the "hot" wire to the coil should read +12V. Key OFF, measure resistance from the negative side of the coil to ground. When the points are closed, you should have a short to ground. Points open should be infinite resistance (open circuit).


Compression is a little on the low side but should still allow the engine to start. Compression is at 100 PSI on all cylinders, that went up and stayed up after I squirted a little oil in each cylinder as my repair manual suggested. It went up to about 150 all the way across after doing this.

That is pretty bad, and out of spec according to my service manual. It shouldn't make the cylinders stop sparking, but it does sound like the rings are pretty hosed.

i agree with Patton. it sounds like #2&3 are flooding.

I also feel it might be something as simple as the connection to the # 2&3 coil from # 2&3's points. I am curious if it is getting proper signal from the ignition.

Ok I know for sure that all the tests I did on the coils and the wiring between the points and the coils all checked out good. Resistance on the coils is within specs. Carb float levels are good for sure. I checked them immediately after the rebuild and checked them again tonight just to be sure. Checked compression again and its at 150-145-160-145 which is all good. Would pouring a little oil in the cylinders actually make compression that good? Did that 3 days ago now.

Also removed carburetors and everything inside appears to be clean, I know it was when I put them back together the first time, but checked again so I can rule out carb problems. As I said before fuel levels are good, all adjustments are roughly correct as per the service manual and fine tuning would be done when engine is at operating temperature. I have done it this way many times without a problem.

I have not yet checked valve clearances, but they were checked right before I put it away last fall and has not run much since, other than trying to get it going lately. Can't see them being out that much in such a short time. But if anyone thinks that actually might be my problem I can pull off the valve cover and check them again and adjust if necessary. Its not that hard, I just figure they should be good. I always set points and timing, and valves, clean up everything before its stored for the winter.

Anything else anyone can think of that might cause this problem?
Don't really want to pull apart the engine unless I have to, but I have sunk so much cash into this lately that I will if I have to because I really want it running well.

Thanks

Compression seems okay.
Valve clearances likely okay (recently checked).
Presuming: good fresh gasoline; unobstructed air supply;
NGKB8ES spark plugs.

Some questions --
Battery up to snuff? Specific gravity test? Load test?
Voltage across battery terminals?
Voltage across coil terminals (ignition turned on)?

Suggestions --
Assure fully charged battery, tight terminal connections, and good solid connection to ground.
Install brand new plugs in #2/3. Regardless of their appearance, the existing #2/3 plugs are imo likely fuel-fouled beyond recovery.

[check-list intended for others]
Petcock on.
Ignition switch on.
Kill switch in run position.
Headlight off.
Choke on.
Throttle fully closed.

Use kickstarter only.
Get off choke asap (use throttle to keep rpm's up).

Can't think of anything else right now.

Good Luck!

Patton wrote:

Compression seems okay.
Valve clearances likely okay (recently checked).
Presuming: good fresh gasoline YES; unobstructed air supply; BRAND NEW POD FILTERS
NGKB8ES spark plugs. NO I USE NGKB7ES Plugs

Some questions --
Battery up to snuff? Specific gravity test? Load test?
Voltage across battery terminals? All battery tests were good, brand new battery, lots of cranking power.
Voltage across coil terminals (ignition turned on)? All coil tests were within specs, have the numbers in the garage.

Suggestions --
Assure fully charged battery, tight terminal connections, and good solid connection to ground. Battery fully charged, just ran new power and ground cables and connections are good.
Install brand new plugs in #2/3. Regardless of their appearance, the existing #2/3 plugs are imo likely fuel-fouled beyond recovery. Have gone through many sets of plugs

[check-list intended for others]
Petcock on. Not using gas tank, I have a gas stand which I built for working on bikes so I do not have the gas tank on the bike, it is always in the way, tank is 2 feet above handlebars, and hoses go straight into carbs, unobstructed. I know there is fuel in the carbs.

Ignition switch on. YES
Kill switch in run position. YES, Engine will not crank if it is off
Headlight off. My bike is headlight ON all the time, no headlight switch, just High/Low
Choke on. YES, and the choke does work
Throttle fully closed. YES

Use kickstarter only. This bike would only ever start with the kickstarter if it was very warm, no matter what, never have I got it to start with the kickstarter when the engine was not warmed up to operating temp.

Get off choke asap (use throttle to keep rpm's up). Always

Can't think of anything else right now.

Good Luck!

I do not personally think anything mentioned above is the problem.
Does the fact that pouring oil in the cylinders made the compression good, show me that there are problems, or is that normal?
Is there a way that the timing could be so far off from the last time it was running? It was checked before being stored and has not really run since. Is there a way to get it close without having the engine running?

make sure the points spring isnt touching the adjustment plate and the condensers are good. And all grounds. Inside of kil switch clean contact. Broken rings can cause fouling plugs too. Open the points with a screwdriver with ig. on and compare the amount of arc for each one, that is a direct relation to the coils output potential.

sean5775 wrote:

Does the fact that pouring oil in the cylinders made the compression good, show me that there are problems, or is that normal?

If you let any bike engine drain down overnight then check the compression cold, and then recheck it with an oil squirt most would show some increase.

The amount of shift tells you about cylinder wear. Mine had 75k miles (and some cylinder wear) and I was getting about a 30psi rise from that shift. After I rebuilt the enging, there is maybe 10psi shift from bone dry cold to fully oiled and fully hot. I think a 30psi shift is too much, more is worse.


sean5775 wrote:

Is there a way that the timing could be so far off from the last time it was running? It was checked before being stored and has not really run since. Is there a way to get it close without having the engine running?

Yes, you can static time it by rotating to TDC and using an OHM meter to detect the points opening (if it has points).

bountyhunter wrote:

Yes, you can static time it by rotating to TDC and using an OHM meter to detect the points opening (if it has points).

Could you elaborate a little more on how this is done. It does still have points however I was planning on putting in a Dyna S ignition. I already have it but wanted to get it running before installing it.

Static timing is basically just making sure that the points are opening at exactly the right time. I did it to mine by connecting one multimeter wire to the timing plate and the other to the spring on the rocker arm. Then you very slowly rotate the engine in the direction it normally turns. You should read some resistance across the points when they are closed and infinite resistance when they are open. So the point of all this is to turn the engine until it reaches infinite resistance and then look at the timing plate to see if its timed properly. Its easiest to do this when the spark plugs are out. This is a pretty general description of how to do it because I have only done it on twin cylinder models and snowmobile engines. Maybe bounty hunter can help me out with the specifics of 4-strokes if they are different.