TOPIC:

hello everyone, new to the forum, my name is Dave. I grabbed an 81 kz440 for cheap and rebuilding to cafe style.

I have 11th hour manifold, inline fuel filter to a vm34 (stock pilot 140 main), brand new plug wires and ngk resistor boots.

12v at coil primary with ign, 2.2ohms cold and hot. secondary I think was 12.7k ohms. sometimes it burns oil on startup when cold, then goes away. figuring valve guides are old as shit and oil pools up on the piston when it sits. with that being said, it should still not die 5 min after a 1/4 mile ride, with brand new B6ES plugs.

- it's getting fuel because I can smell see taste it on the plugs after cranking
- I don't know compression numbers but in that 5 min initial ride I get, the thing hauls ass, and if anything as the motor gets warmer compression increases. I've let too many friends borrow testers and they all disappear, really don't want to buy another.
-just did valve clearances, even though That wouldn't effect it

I come from the high hp drifting world, and have DEF had my share of spark issues, particularly when a coil gets warm. resistance goes up and no spark. I bought a dyna 2.2ohm coil today but it won't be here till Monday


any ideas?

Sounds like the coil,you'll find out for sure when your new one arrives. Try bump starting it when it won't run, if it starts no probs when you bump it, but not off the starter motor then you can be fairly sure its the coil.

I had issues similar to yours, after warm up and a little ride mine would sputter and die. I had some trouble with keeping the timing set properly at first as I brought my 440 back to life, but since I replaced the points and condenser I haven't had that issue any more. Mine smoked on startup for a bit, same deal with seals being old and dry, but i've been riding it like that for a year or two now and it seems to have gotten a little better. Sure replacing those seals is easy but that' can wait until winter

McZed wrote: Sounds like the coil,you'll find out for sure when your new one arrives. Try bump starting it when it won't run, if it starts no probs when you bump it, but not off the starter motor then you can be fairly sure its the coil.

bump start? can you elaborate a little bit? assuming ignition coil is the problem, once it is warm and my issues are occurring, there is another way to make the coil produce a spark? battery voltage is good and fully charged.

I have an electronic ignition, no points.

it's literally after I shut it off it won't restart unless it cools down for a few hours

bump, new dyna 2.2ohm coil and wires, and still has trouble with hot starts.


bike runs fine, just after you shut it off, let it sit for 10 min then it won't start

Nevermind just seen where you posted electronic ignition. For some reason when I looked it up the site showed points for your model.

"I have 11th hour manifold, inline fuel filter to a vm34 (stock pilot 140 main), brand new plug wires and ngk resistor boots. "
How did your plug chops look at idle and WOT. Mine is running a 20 piolet and a 170 main with it he main being just on the lean side if at WOT for extended periods at 5000 ft elevation. Mostly just for my own curiosity, and wondering how hot it might be when failing / how much fuel has condensed inside that manifold after you have stopped. Mine will condense approximately 5-10 ml depending on how hot the aluminum intake is. Maybe large piolet plus excessive fuel inside the manifold is choking it with fuel when hot. Just a thought

might be on to something. never thought of that. it's the stock jet that comes with vm34's. Think it's a 25. came with a 260 main, I swapped for a 160, still too rich. went to a 150, I can floor it without the engine bogging out, but I can tell it's still real rich. I bet 135--145 main jet is right where I should be.

it starts instsantly, no matter how long it's been sitting (cold motor). day, week, it fires up before I can release the button, with no choke at all. Anne Franke's drumset got more use then the choke on this single carb thus far. holds 1300 idle rock solid, rev it to whatever it returns to 1300 instantly. 1/8-1/4-1/2 throttle stamps quick fast and strong. literally bolted this thing on and every aspect of pilot jet tuning in mikuni VM series carbs was checked out.

-maybe try go down a size or 2 on the pilot?
-needle is second from top
-pretty sure I'm at sea level or close to it
-

A few things I can think of as possible culprits if you ruled-out the ignition system:

- vacuum leak at the cylinder head / manifold / carb holders.
I had the exact same condition on my 440 as you describe and this was the cause.
Easy to test - spritz some wd40 at the manifold/head mating surface and listen for engine RPM change.
Fix for me was to cut a gasket for the manifold-to-cylinder head and eventually replace carb holders.

- you mentioned you adjusted the valves recently...
Could they be just a wee bit too close and when engine warms up/expansion a valve is sticking open?

- Vapor lock.
Common problem for many engines where a fuel line / fuel filter may be too close to the hot engine.
Boiling the gas and starving the carbs.

All of these result in - "starts and runs great for 5 minutes then dies and won't restart until cooled down conditions."

I know my vm34 came with a 35 piolet stock, yours could be different but figured it was worth mentioning. I would suggest bumping the piolet down and the main up. I' rechecked my notebook to see what I'm running and its 22.5 piolet, top clip, 170 main at 2 turns air screw. Yours will probably vary as it always does bike to bike but dropping the piolet and raising the main a little should be a safe bet if it starts that easy when warm. I have about 4K miles on that setup and has been very reliable. Figured I would put it out there for a just in case reference. hopefully it's just a vapor lock issue. Easy fix.

okay so I've basically tried everything mentioned.

-no vac leaks

-you were correct, stock pilot was a 35. I tried 27.5 middle clip and 160 main and it was taking a good 7-10 seconds to return to idle after heavy revving. pilot circuit too lean. I have a 30 in at middle clip now and it seems perfect.

-I had 25 miles tacked on with no problems - all of which were 2-3 mile quick rides. but I purposely shut down let it sit get hot and try to restart it 15 min 20 min etc for the past week and it always worked. I finally thought I had it down and today I went for the typical 3 mile ride, then sat for 20 min, then tried again and 5 min into it motor shut down coasted wouldn't restart.

when said problem is happening:
-there is 12v at the coil. with old plugs in and grounding current plugs I have spark. I just put a dyna coil 7mm copper core plug wires and caps in. resistive type ngk b6es (because valve guides are old and she used to smoke on startup and foul plugs. not anymore though 2 weeks or so no smoking.)

- Vapor lock. I purposely routed my fuel line short as possible and all downhill. no spot for an airlock. plus, I have one of them there clear saucer fuel filters with the fine metal screen in the middle. if I flip the petcock from prime to on or res, you can visually see this screen flex and concave with the pressure from the fuel above it. basically it is a way to confirm there is no air lock impeding fuel "vapor lock"

I don't hear a whoosh sound from my gas tank opening as if it were under a vacuum and a vent is clogged. nor does it start after


someone has to have had similars. I found this UK thread that was long as hell I read the whole thing and it was spot on what im dealing with. but no resolution thread died and got old.