TOPIC:

Bike's been running a little rough lately, and I realized recently it started around the time I changed the air filter foam (Uni brand foam, not sure of the density) and oil (NoToil). If I cup my hand over the intake at the back of the filter box so that it restricts the air flow a little (not a lot), the bike runs like it just rolled out of the factory.

Seems like a good bet that I'm using too coarse of foam and/or too thin of an oil.

So, for those stock air filters, where the foam can be cut out of a sheet and attached to the box, does anyone have a recommendation for type/density of foam and/or oil?

Try double the foam and no oil.


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No eBay APP ID and/or Cert ID defined in Kunena configurationIf it was mine I would just install the stock filter element (part # 11013-1027) and be done. Spending about $12 for a bike air filter is not a bad deal. Ed

I'll keep the partzilla option in mind. Though I'm not clear based on the the eBay listing if it's new foam, or 30 year old NOS foam. Don't get me wrong, OE is always a good option, but foam does break down with time, and then can do more harm than good when that happens. I would prefer an option where I can be reasonably sure that I'm using something that hasn't been sitting on a shelf for a while. And there are a ton of options for foam that is brand new, even if some assembly (or cutting) is required (and a 5 year supply costs about the same as a single OE application).

Rex, I'll try filling the box up with foam and see if that helps.

I got some garage time today. Started out working on this one:



Ended up working on this one:




So far:

• I tried doubling up the foam without bothering to oil, no change
• I tried moving to a finer foam, with oil, very little change. At this point, the foam I've got in there is close enough to stock that I don't think the foam is my problem.
• I gave the carburettors a very detailed cleaning, again, very little change

Here are my symptoms:
When I first start the bike, it runs quite poorly for about 30 seconds, have to play with the choke to get it to fire and to keep it going (I suppose that's probably not all that strange). After some initial warm-up, it'll maintain a low idle with no choke, purrs like a kitten. For the first minute or so, the instant I give it any gas, it'll stall. Another minute or so, and it can take a little gas, but will begin to chug, and quit if I roll on the gas slowly. Once I hit a certain warmup point, if I roll it quickly to WOT, it'll run right up to redline like a champ, but if I wind the grip slowly, it'll stall. As it warms up, I can wind it up more slowly, bit it's basically impossible to stick the needle at 2500 RPM (it'll backfire through the carbs) until the bike is good and warm. After it's good and warm, it runs fairly well, but even well warmed, if I run it under a light load (i.e .up a slight hill) at about 1/4 throttle at around 2200 to 3200 RPM it'll periodically miss and/or backfire through the intake/carbs.
I adjusted valve lash less than 100 miles ago. I did have the head off earlier this year (had another thread on here about low compression), but the symptoms were there prior to pulling the head, so I don't think it's valve timing. I did clean a bit of carbon out of the head and piston top when I had it apart, so I don't think it's running lean. Plugs are unremarkable. About a year ago, I spec'd the coil and it was just barely outside of spec (it was a while ago, so I don't really remember what the resistance came out to), so I convinced myself that it was probably 'fine for now', though I do wonder with the carbon build-up, and 'borderline' spec on coil if I could just have a cold spark, The spark is definitely more yellow than blue with the plugs pulled.

As far as the carb cleaning, I used a set of torch tip cleaning wires to clean every hole of the jets (including the ones through the sides of the tubes), visually inspected for light, blew with compressed air, hit the small hole between the two jets, etc. I do have an in-line filter to catch tank debris.

Compression is, of course, good following the top end rebuild, so no concerns there.

I'm really leaning towards bucking up and replacing the coil. Does anyone have a dissenting opinion/suggestion?

Back firing thru the carbs would indicate a lean condition.
I see you have the later model clutch cover.
You can use any KZ coil. But resistance wise it is best to use the
coil for the ignition system you have, points or electronic.
Mounting the coil on the bike might be an issue.
If I remember right the stock coil for the points ignition is shorter
than the 4 cylinder bikes. I have not worked on the later electronic
ignition models so I know what if anything had been changed.
The system I run is an adapted from a 750/4 that requires some
machine work and welding.


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Also check the carb holders for leaks. Ed

650ed wrote: Also check the carb holders for leaks. Ed

I forgot to mention that the carb holders are only a couple years old. I cinched the carbs pretty good (but not too tight ) and gave them the good old fashioned soak with WD-40 once the bike was warmed up to check for unexpected revs. The boots are fine, and the carbs are firmly in place.

Nebr_Rex wrote: Back firing thru the carbs would indicate a lean condition.
I see you have the later model clutch cover.
You can use any KZ coil. But resistance wise it is best to use the
coil for the ignition system you have, points or electronic.
Mounting the coil on the bike might be an issue.
If I remember right the stock coil for the points ignition is shorter
than the 4 cylinder bikes. I have not worked on the later electronic
ignition models so I know what if anything had been changed.
The system I run is an adapted from a 750/4 that requires some
machine work and welding.
.

There are so many aftermarket options out there it can be a little mindnumbing to pick one. I picked up a coil off of Amazon.com that specifically listed the KZ440 D5 (my model, electronic pickup), coming from a US based supplier (as far as the shipper), so if it's not a straight bolt-on (maybe a little work, but at the very least without having to run to a machine shop). I can just send it back. At least that's how it goes in theory.

I got the coil in and on. My spark does look much better, but it hasn't much changed how it runs when cold, or the 3,000 RPM stutter under light load when warm.
I'm pretty sure that the left cylinder is the one that's sputtering. (i.e. when it is semi-warm and I cup a hand over one exhaust and roll the exhaust back until it sputters then do the same thing on the other side, only the left side seems to miss some strokes).
Since I just did a thorough carb cleaning, I'll spec the valve lash and replace plugs again before pulling the carbs another time. Aside from the pilot hole between the two jet channels, any other spots that folks seem to miss on the Keihin CV Carbs?

For the sake of mentioning it, the diaphragms are only a couple of years old, same for the boots, so I don't think I have a rotten rubber problem.

Please remember that if you have to change shims in order to correct out of spec valve lash, you will also need to recheck carburetor synchronization.

TexasKZ wrote: Please remember that if you have to change shims in order to correct out of spec valve lash, you will also need to recheck carburetor synchronization.

No shims on the 83-440, just an adjuster set screw. Good reminder on the carbs though. When I've checked the carb sync in the past it has always been surprisingly well matched, doesn't mean it is impervious to needing adjustment.