Won't start after rebuild

Greetings. I'm looking for some help after having my 1982 KZ750N1 Spectre engine rebuilts by a member of this site (who won't return my calls or emails but nevertheless will remain as yet unnamed).

The bike developed a condition in which the plugs would foul quickly. At first it was about once a week, then every day, and soon I couldn't even keep it running at all. I checked the compression - 70 to 100 psi. So, rebuild.

Took the engine out and gave it to the unnamed member. HE called and said it was done after a week or two. I paid him and brought the engine back, and installed it. Found that he'd failed to mention stripping one of the cam chain tensioner bolts. Fixed that. Put it al back together and tried to start it. Ran badly for a minute then nothing.

I have tested the compression - it's low but still 90-120 psi. I have tested and/or replaced the pickup coils, IC Igniter, ignition coils, and ignition wires. I have cleaned and rebuilt the carbuetors. I have verified the cam timing and the speark timing.

The engine will crank for a while and eventually start to backfire intermittently. Starting fluid doesn't help.

The bike gets air, fuel, and spark. There is sufficient compression. Why, oh, why, will this bike not run?

Any help you (all but one of you, that is; you know who you are and you've done quite enough) can offer will be most appreciated.

Thanks,

Frankenchopper

If the engine has fuel, air, and spark, in the proper amounts at the proper time, with compression, then it will start and run. Since yours isn't running it's missing one of those.

Chances are you missed something, happens to everyone at least once, even I have been known to put a timing advancer in 180 degrees out (but it took me like 15 seconds to figure out why it wouldn't start).

Go back over everything, one system at a time, and start at the basics, the answer is there, you are just overlooking it or taking something for granted.

Do you have a good ground connection from the battery to the motor?

Check plug wires. See that they are connected in proper firing order.

frankenchopper wrote:

... The bike developed a condition in which the plugs would foul quickly. At first it was about once a week, then every day, and soon I couldn't even keep it running at all. I checked the compression - 70 to 100 psi. So, rebuild... Ran badly for a minute then nothing. I have tested the compression - it's low but still 90-120 psi... I have cleaned and rebuilt the carbuetors... The engine will crank for a while and eventually start to backfire intermittently. Starting fluid doesn't help....

Concur that all ignition components should first be assured to specs.
Will shotgun a little --
Were new plugs installed? What do plugs look like now? Did they again foul quickly as before the rebuild? Are air filters clear? Is fuel from tank clean and fresh? Are carb float levels correct?

Good Luck!

frankenchopper wrote:

... The engine will crank for a while and eventually start to backfire intermittently. Starting fluid doesn't help....

On re-reading, am interpreting to mean the engine just spins over without any firing until eventually only sporatic backfiring. In other words, the engine does not momentarily crank up and run before the backfiring begins, so new plugs would not have time to foul.

Where plugs have spark, but only some engine backfiring, and starting fluid doesn't help, am liking hwms' suggestion to assure plug wires being properly connected.

Post edited by: Patton, at: 2007/12/08 21:39

same thing happened to me a couple mos. ago. the engine would crank and crank, then it backfired like a shotgun blast. had the coil wires switched up, i just reversed them, cleaned the gas off the plugs and she fired right up!

make sure you brake them rings in on dino oil, and since everything else (i assume) is alreadsy broken in, break that baby in hard!!!

one condition that seems to be the same is the fouling of plugs,

put a timing light on the bike to see if the plugs are firing or not, and check the carbs real close to see if something is causing them to flood.

work it as a process of elimination, figure out what is right and go to the next item until you find something wrong

Thanks for all the advice. The engine does indeed just crank with no real attempt at running. The sparkplugs are new NGKs as recommended by the Kaw service manual. I have checked the sparkplugs and the wires with a DMM and with a timing light - everything seems to work fine including the firing of the 1 and 4 plugs at the F mark on the timing indicator. I will look at the timing advancer to make sure it's oriented properly.

Any other ideas? If I didn't have my '85 GPz running at last, I'd be going insane here. Ferris Buehler had it right, but he meant motorcycle.

On larger fours, left coil fires outside plugs and right coil fires inside plugs. Uncertain whether 750 is the same left coil to #1/4 and right coil to #2/3, but am reasonably certain 750 left coil is supposed to fire either #1/4 or #2/3, and right coil fires the other pair.

Just assure that neither coil is attempting to fire #1/2 or #3/4.

Under points cover on large fours, left side wire from ignition triggers left coil (1-4 F mark), and right side wire from ignition coil triggers right coil (2-3 F mark). 750 may be the same.



Post edited by: Patton, at: 2007/12/09 10:12

Post edited by: Patton, at: 2007/12/09 10:17

Greetings again.

Verified right coil 1/4 and left coil 2/3. Tried swapping sides on the primary leads (effectively the same as swapping plug wires) and it puffed through the carbs, so I put it back the way it was.

A thought: If the supply voltage/current to the IC Igniter is low or the pulse voltage from the pickup coils is low, won't that reduce the output voltage to the primary side of the ignition coils, and thus make a reduced energy soark that may still have enough of a pulse to fire the timing light? Any ideas how to measure the voltage pulses?

i'm thinking his cam timing is off.