TOPIC:

Hey Gang- Trying to chase down the strangest problem on my 650/810. Need some input as I am at my wit's end:(

I just put the motor back together after changing a slightly bent exhaust valve. The cam chain jumped a couple of teeth on the cams as the cam chain adjuster was acting up possibly due to the cam chain adjuster sprocket's bearing's wear. My mechanic buddy babysat me while I redid the upper end. He double checked my work and gave me an A+ Compression is in the 150-160 range on all cylinders. Clutch was replaced last year.

I put in new battery earlier in the week, new plugs, checked out all plug wires and they were fine even putting on a dab of dialectic grease on the plug wire contact points. I have also done the WG coil upgrade. I am getting excellent spark when checking all plugs outside the enginge. Plugs are BR8ES. There is plenty of new high octane fuel in the tank.

The Mikuni 28 carbs without accelerator pumps are from Wired George so we know they are done correctly. The carbs have only one season -1500 miles of riding Just to be sure, I even gave them a soaking, cleaned out the innards while I had the top end apart. I checked the air screw settings, 1.5 turns, put on a new fuel line and then cleaned the stock 650 petcock.
Needles are 5J9's set on the middle clip. I can with confidence this is not a needle and clipping issue.

The coils are the green Dynas and I have electronic ignition. Cam and ignition timing is dead on.

The bike fired up right away and revved nicely but when when I let out the clutch the motor bogs and dies. I can't get the motor to hold any revs under load. In neutral the motor pulls the rpm like it is brand new. It will idle nicely all day long abut won't let me take it out of the driveway without dying.

Anyone have any idea on what kind of gremlin I should be looking at to get this thing to actually drive again? I gotta think it is electrical as the mechanical side of the engine has been checked and rechecked. Sitting in the garage and sounding sweet revving is not my idea of riding.

Any help would be greatly appreciated.

Cheers-Colin Firth-Ontario Canada
1977 Kz 650 Custom, 810 big-bore

Vacuum lines,Colin?

Just out of curiosity,Bud...does Your bike have a kickstand switch...that might be faulty,and not QUITE doing what it's SUPPOSED to be doing?
When You put the bike in gear and with the clutch in(obviously) how does it rev then?

Petcock...clean and working,to the best of Your knowledge?

Are the wheels turning freely...no caliper sticking?

Are You wearing a helmet?

Probably a long shot but did you sync the carbs when you put them back on ?
Shuld'nt be an issue but perhaps something was disturbed. Like sSandy said maybe vacuum lines.

Thanks guys. The Mikuni 28's have 3 vacuum ports. The two outer ones are to be left open and serve as overflow outlets. The middle one (between carbs 2 and 3) is to be capped off and it is. This is following Wired George's advice and he certainly knows his carbs.
The carb synching wasn't changed and all slider levels are equal by sight. I don't think the synching would be a factor as the engine easily pulls to redline in neutral.

When the bike is put in gear it still revs but not as freely as when in neutral. It seems to struggle. The clutch adjustment is fine. It just seems the load on the engine is killing it.

The petcock is the same one I had on the bike all year long and is not blocked or starving the carbs.

No kickstand switch on this model, the wheels roll freely and I always wear a helmet:)

Gotta think this is an electrical gremlin of some sort:(

Cheers-Colin Firth

would the advance sticking cause anything this major? just a wild shot, but when it starts to bog, turn the choke on (even if its fully warmed up) the cold air could have it lean enough to make it run like this. when I first put my pipe on last yr (before I got to rejet.... wont make that mistake again) it would rev great sitting under no load, under load it needed extra gas to run, and turning the choke on helped....
Scott

77KZ650 wrote:

would the advance sticking cause anything this major? just a wild shot, but when it starts to bog, turn the choke on (even if its fully warmed up) the cold air could have it lean enough to make it run like this. when I first put my pipe on last yr (before I got to rejet.... wont make that mistake again) it would rev great sitting under no load, under load it needed extra gas to run, and turning the choke on helped....
Scott

Hey Scott - I would like to hear more opinions on the mechanical advance suggestion, but I don't think this would be the problem as the motor revs very nicely when it is not under load. If the mechanical advance was the problem I don't think it would rev as well as it does.

For the choke, it doesn't matter where it is set. As soon as I start to roll it dies, choke on or off:(

Cheers-Colin Firth

Then this bike ran fine until you had the cam chain problem and bent 1 exh. valve...correct?

First - check to see if your timing advancer is stuck on retard position.

Airbox or pod filters?

If airbox is in place, check inside it....pull the OEM paper filter right out and see how the bike likes that.

Are there no unusual noises?



Then, If YES...and nothing else was changed.....and I mean nothing at all except for the replaced exh. valve...then the most logical place to look is cam timing.





\reborn650 wrote:

Hey Gang- Trying to chase down the strangest problem on my 650/810. Need some input as I am at my wit's end:(

I just put the motor back together after changing a slightly bent exhaust valve. The cam chain jumped a couple of teeth on the cams as the cam chain adjuster was acting up possibly due to the cam chain adjuster sprocket's bearing's wear. My mechanic buddy babysat me while I redid the upper end. He double checked my work and gave me an A+ Compression is in the 150-160 range on all cylinders. Clutch was replaced last year.

I put in new battery earlier in the week, new plugs, checked out all plug wires and they were fine even putting on a dab of dialectic grease on the plug wire contact points. I have also done the WG coil upgrade. I am getting excellent spark when checking all plugs outside the enginge. Plugs are BR8ES. There is plenty of new high octane fuel in the tank.

The Mikuni 28 carbs without accelerator pumps are from Wired George so we know they are done correctly. The carbs have only one season -1500 miles of riding Just to be sure, I even gave them a soaking, cleaned out the innards while I had the top end apart. I checked the air screw settings, 1.5 turns, put on a new fuel line and then cleaned the stock 650 petcock.
Needles are 5J9's set on the middle clip. I can with confidence this is not a needle and clipping issue.

The coils are the green Dynas and I have electronic ignition. Cam and ignition timing is dead on.

The bike fired up right away and revved nicely but when when I let out the clutch the motor bogs and dies. I can't get the motor to hold any revs under load. In neutral the motor pulls the rpm like it is brand new. It will idle nicely all day long abut won't let me take it out of the driveway without dying.

Anyone have any idea on what kind of gremlin I should be looking at to get this thing to actually drive again? I gotta think it is electrical as the mechanical side of the engine has been checked and rechecked. Sitting in the garage and sounding sweet revving is not my idea of riding.

Any help would be greatly appreciated.

Cheers-Colin Firth-Ontario Canada
1977 Kz 650 Custom, 810 big-bore

hes running stacks, just a thin mesh for a filter

Hmmm...mechanical advance.If it IS sticking,You will still get revs in neutral.You WILL notice a difference under a load...good call.
Colin...have You been in there yet,Bud?

It's running to lean, put pods on it and it will straighten right out.

I had a GPz750 that did exactly the same thing when I tried to run it without the pods on it.

If it was running fine before with the same set up, then you have more than one air leak.

I think it sounds like the float bowl vents or fuel flow restriction.


what you described as a blocked vacuum port sounds like the bowl vents

are your float heights still on the level?

the things will run if the cam timing is 1 or 2 teeth off but you wont notice until you try to ride it.(same as you describe too) doing a sync test will tell you because the vacuum on the gague will be excessively low

there are only a few things left to recheck

trippivot? Where have you been lately? Haven't seen you on this board for ages... hope all is well! wg