Bogging...

My 79/650B3 has been running great for hundreds of miles, especially after a shim clearance adjustment. Last weekend I went to 2 vintage gear head shows and clocked about 400 road miles. Monday morning I went out to a business meeting and about 20 miles out started to feel a bog, stutter, buck coming from the bike. At first I thought I was getting hit by wind bursts coming off the ocean but soon focused back on the KZ. I throttled and shifted gear and the problem didn't change. About a 1/4 mile later i pulled over, listened, throttled (and snapped the throttle cable). The engine sounded fine. Towed the KZ back home. Replaced the throttle cables, test ride around the block, problem persists.

I'm getting to a wise age of walking away from the KZ a few days and thinking about the issue before getting back in the garage (also helps I own another moto). My bike is all stock, carbs, air box, exhaust with some parts replaced. It starts right up and warms up to idle without problem. Removing the choke the engine revs smoothly to any RPM. I get on the bike and take it to the road. First gear... bogging, second, bogging, around the block and back into the garage.

Obviously many things can be the culprit here. #1 suspect, the timing advancer needs some attention as it's one of the only parts on the bike I have not fully overhauled (still in there as left by the PO). #2 on my list are the ignition coils and weak spark (all plugs were black after the problem started), coils are original with the #2/3 swapped from my other parts bike. #3 carbs, although I did a clean last year, something may have gotten in there. #4 fuel accelerator pump (650B3) may have a diaphragm leak.

From looking at the plugs, they are black and I can smell the engine running rich. Air/mix screws are set at spec 1-5/8 turns out, Points/condensers were replaced last year and timing adjusted, points gap recently adjusted.

I'm not certain what the cause is and I'm asking for advice before further wrenching. What has me puzzled is the fine running engine and the bogging only in gear/motion. Could be drivetrain but my gut is suggesting something not delivering under load; timing, spark, fuel.

Looking forward to your opinions, thank you.

Sounds like a mouse in the air box. :lol:

Since the timing advancer hasn't been cleaned and lubed since you've owned the bike is it also true that the points and condenser haven't been replaced? I'm not saying that is the problem, but if the points are old they probably are pitted and it also is possible the advancer is sticking. When that happens the bike will run poorly under various conditions. Since those maintenance items should be performed regardless, I would clean and lube the advancer and replace the points and condenser if only to eliminate those variables. Ed

Ed, the points and condensers were replaced and timing adjusted, but the Timing Advancer remains untouched. The bog reminded me of a spring and thus I pointed to the Advancer - seems like a good place to start.

daveo wrote: Sounds like a mouse in the air box. :lol:

lol, if he's in there he better be moving that wheel around and help power the air conditioning.

IMHO all of the things you mention need to be looked at.

I suggest that you crack open the tank cap and go for a ride.
Of course, don't try this at home.
Bill

KZQ wrote: I suggest that you crack open the tank cap and go for a ride.
Of course, don't try this at home.
Bill

Actually, did that without any change - and decided to rebuild the cap as good measure (needed the attention). The air hole in the cap was "ok" but nevertheless clear.

Check the fuel tank strainer.

Only happens when the clutch is released in gear. I'm now thinking clutch slip from gas contaminated oil. Bog/hesitation doesn't happen in neutral and at any rev (idle-5000).

Since last fall I had a on/off problem with the number 2 pipe running cold, fouled #2 plug. Turned out the vacuum fed petcock diaphragm was torn and leaking gas into the #2 carb, overfilling, adding more gas to the spark chamber. The problem was fixed a few months ago. I suspect gas leaked down into the cylinder and contaminated the oil (I can smell gas in the oil tank). An oil change may in fact be the solution.

And if so, this goes to show how important to feed these old bikes with "motorcycle oil" and not modern car oils containing detergents and additives for cleaner emissions - that cause clutch slip. Gas will clean oil off metal parts and I think that is what is happening here. I'll report back after the oil change sometime this week. In the meantime I still want to look at other things.

oil change complete - will have to say although there was gas contamination, it was not clutch slip. Went in an looked at the timing adjuster (looks brand new), everything is moving and snapping back correctly, lube, re-install.

Timing - ok here we go. Timing was advanced, I pulled it back to the F mark and took it for a ride - SUCCESS, no more bog. I noticed when checking timing on the #2 wire the mark was shifting, but not on the #3 wire - bad wire or coil lead?

Well the fight to maintain an original points bike is catching up to me, electronic and a new set of coils sounds like a vacation. And from the advice around here there is no going back.