1980 KZ440B running lean

Im desperately in need of some carb help here. Please, please, please help me out.

The story -
I bought the bike with a stock 2 into 1 exhaust. Didn't ride it much so I can't say if it's always been lean. I put a 2 into 2 on it and once the weather turned I started riding. I noticed very quickly it was very hot. Checked the plugs ane they're white. The stock main size, based on the manual, is 68. I bought 70's and 72's. Put the 70's in and no better. Plugs are still very white and it is running very hot.

I have been over the carbs multiple times (lastime being this morning). I have cleaned them throughly, checked float levels, fuel supply, air box (which is stock, no pods), idle mixture screws are set to 1 1/2 out. Checked and rechecked for air leaks (ala carb cleaner sparyed in the usual suspect areas) Choke is smooth as is the throttle. Bike starts, idles, and runs fine except that it's lean. There is a little back rumble/popping (not backfiring) on decel. but other than that it's just lean.

I know these Keihins have a main, a secondary main, and that the needle is NOT adustable (in the notched sense). I have gone from 68 mains to 70 mains with absolutely no noticeable difference and I can't imagine 72's will make that much difference but I plan to try them tomorrow nonetheless.

PLEASE HELP ME!!!!!

Thanks you in advance.

Mickey356 wrote: ...very hot. Checked the plugs and they're white...checked float levels. Bike starts, idles, and runs fine except that it's lean...just lean....

If "checked float levels" means measured float heights with bowls removed and carbs upside down on the bench, such procedure is inadequate to assure that fuel levels are within specs.

It's the actual fuel level inside the float bowl that matters (regardless of the dry measured float height). This is referred to in some shop manuals as the "service" fuel level.

The correct method to determine fuel level is performing the clear tube test.

A fuel level that's too low will result in lean carb performance, even when the carb and fuel delivery is otherwise perfect.

Besides fuel levels, would also assure the ignition timing is correct.
And that the timing advancer is properly functioning, by using a strobe-type timing light and watching the advancer quickly move forward and backward as rpm is varied by blipping the throttle.

A sticking advancer, due to rust or whatever reason, may be hanging in the idle speed position.
The advancer may require lube, or both cleaning and lube.

Good Fortune!

Thanks Patton.

I will do a clear tube test in the morning (if I can fins some tubing that'll fit the overflow nipple on the bottom of teh bowls. If not, I'll have to do it on monday.

If that's not it than I'll get on the valves and timing.

I appreciate it.

So, it's safe to say that its unlikely that this is a jetting issue? I don't have to keep going up in the main, and/or the seconday main, until I get richer? I hope not because apparently the only jets still available for these Kiehins are the mains and the slow/pilots, all the rest are NLA.
Someone suggested shimming the needle which I know can be done but I think thats odd as these needles aren't notched for adjustment so therefore shouldn't be adjusted unless all else fails. I thought since there were soooo many "other jets" these carbs should be more "tuneable" before going to needle shims, no?

Is there a "common reason" these type of carbs run lean? Is this normal?
I ask because I know some KZ's were sold with 2 into 1 and some with 2 into 2. I literally went from a 2 into 1 to a 2 into 2 and I find it hard to believe it changed things that drastically. I understand if I went to pods AND some funky exhaust but this was a pretty harmelss swap, or so I thought.

Thanks again for you help.

I did the clear tube test this morning and they were within the 3-5mm spec. So they seem to be OK.

I don't have a strobe so I can do the timing but I did check my points (I had a buddy install new ones while it was at his garage) and they were pretty tight. I adjusted them to 3.5mm as the spec calls for between 3-4mm.

Went for a quick spin around the neighborhood and the plugs are still white as the virgin snow. Not even a spec of brown

Ignition timing ---
Would perform static ignition timing check (engine not running).
(1) dress contact surfaces;
(2) set gap;
(3) clean contacts;
(3) adjust timing.


Advancer function ---
Over-heating may result from the timing advancer being stuck in it's idle/retarded position, which could result from water/moisture under the points cover.

If not already done, would lube the timing advancer (especially the weights pivot points), which might be sticking, or maybe both clean and lube.



After removing only the points cover, access to apply lube may be done without further disassembly by going through the inspection window where the timing marks are viewed. Hand rotate the crankshaft by turning it with the 17mm nut (NOT the smaller 13mm bolt head) until each of the two pivot points may be in position to receive a drop or so of oil.










May assure correct operation with a strobe-type timing light, and watch the advancer quickly move back and forth as rpm is varied by blipping the throttle.

The advancer should NOT be rusted as shown in this example:



Good Fortune!

Thanks Patton,
I actually did do everything, mostly, you listed above, except lubing the pivot points on the timing advance. I'll do it tomorrow.