Engine Cutting Out Under Load :(

Hey Gang - Hopefully someone can chime in on this engine gremlin that has me puzzled.

I changed cams last week going with the Gpz750's. Re-shimmed the valves (cold) and all clearances are coming in between 10 and 15 for clearances. The manual says 8-18, so I am within the correct range.

When I put everything back together after putting in the cams, checking the cams, installing the APE cam chain tensioner, putting on the timing light the motor was popping back through the carbs, mostly on #1. The APE tensioner follows along after having gone through two manual adjusters that weren't up to snuff.

Checked all plug wires, put the timing light on the engine and redid #1 plug wire to get a better connection on the coil. Put in new BR8ES NGK plugs and they are all sooty after running for only a few minutes. The bike has Dyna coils and Dyna electronic ignition.

I decided to spray some non-flammable brake cleaner around the carbs when the engine was idling and the motor almost stalled out indicating a probable leak around the boots. I didn't want to use WD-40 because it makes such a mess on the cases.

The carbs are Wiredgeorge Mikuni 29 smoothbores and they have less than one hour running time on them since I put them on the bike, so I know the problem is not carb related. I soaked them overnight just to make sure I didn't have a block in the pilot circuit. The bowls and jets were clean before and after the soaking.

Resealed the carb boots (they are one year old and still soft) with high temp gasket sealant and put everything back together last night with clean plugs.

The bike fired up perfectly with fresh gas and it sounded great without any popping. Thought I had everything nailed down.

Let the bike warm up for about 5 minutes and then took it down the street for a test run. As soon as the bike was running under load it seemed to be running on only two.

Brought the bike back into the garage turned off the engine and checked the pipes for temperature. All 4 pipes were hot. Restarted the bike and started getting some popping back through #3 and#4 carbs. It was around midnight so I packed it in for the night.

The bike's power is showing similar symptoms to when the cam chain jumped a couple of teeth last autumn. I measured 20 links of the cam chain and it was 161.5 mm, the serviceable limit is 162.5 mm.

So my questions is what should I be looking at now and why would it run smooth at idle then under load start misfiring? Everything seems fine on the mechanical side and I gotta think this is an electrical issue which is my weak area for expertise:(

Any help would be appreciated.

Cheers-Colin Firth-Ontario Canada

Post edited by: reborn650, at: 2007/05/29 10:14

Post edited by: reborn650, at: 2007/05/29 14:18

First thoughts --
Is air filter clean? Unobstructed?
Condition of plug wires? Caps?
(Were new Dyna wires also installed--solid copper wire core with caps already built in -- and doesn't hurt to apply a dab of dielectric grease at coil and plug connections).
Battery fully charged?
Full battery voltage to coils?

Hey Patton - I put together my own plug wires and they are all good. No air cleaner as I am running velocity stacks. The carbs were set up for these by WG.

I fired it up after work-starts first crank of the starter and it started popping again. The pipes all got hot together. I've got a couple fellow kzr members over tonight and I suspect that I will be pulling the cam cover to see if this thing jumped a tooth from a chain that might be beyond the limit of us.

Cheers-Colin Firth-Ontario Canada

I'm not sure nut my guess would be the timing in some form a or another. If it's in correct time with a light, most likely the cam is off a tooth.

dont think you have a tooth off, my feeling is timing / vacum leak still, look for the simple stuff first, always bites me in the ass

While using the timing light, was the ignition advancer unit operating properly (not sticking in closed position)?

Hey Gang - So I had a couple of fellow Kz'ers over tonight.

Checked the compression in all cylinders and they were down under 100. This told me that a valve might be hanging open at TDC due to cam chain timing issues.

Pulled off the valve cover and found my suspicions were correct.

Reset the cams (off one tooth) and pointed my finger at a sloppy cam chain tension. I didn't tighten the manual adjuster after taking turning the motor and taking up the slack. Did it this time.

Buttoned her back up, checked the ignition timing and it sounded not too bad so I took it out for a short squirt on my street but it didn't seem like it was firing properly.

Came back in, had my son (thekawasakikid) pull the plugs which were showing a serious rich condition. One of my buddies, a seasoned Kz veteran asked for a small screwdriver and adjusted the air screws on the carb. Lit 'er up and it sounded wayyyyyyy better.

It was too late to take it out for a test so I have to wait until tomorrow.

Just might be getting off work tomorrow a little earlier to see if the cam, ignition timing and air screw setting is nailed. Luckily I have a good boss who understands my Kz project:)

Thanks for everyone's suggestions. I will post results tomorrow for anyone interested in finding out if I caught this gremlin.

Cheers-Colin Firth-Ontario Canada

way cool, I didnt think about both cams being off by a tooth, guess that would cause a lot of problems, good to see you gotit under control