TOPIC:

Hi,

I'm on the verge of completing a minor mechanical restoration of a 1980 KZ250 and the major bit that I'm missing is the air filter element box and element (the air box itself and the mesh screen are in place). I can't find these parts anywhere (eBay, Bike Bandit etc).

I've looked into pod filters as a possible substitute, but I'm concerned about having to rejet the carb (realling determining and finding the appropriate jets).

I've also thought about building an airbox with the approximate dimensions and openings as the original and lining it with a Uni-filter element (can be purchased in sheets and cut to size).

Any thoughts?

Thanks, Dave

Dave, Although I am an old man, I can't recall ever seeing a 1980 KZ250. That being the case, I have no idea what type carburetor or carburetors we are talking about. Is this a twin or single?

If the bike were mine, I would install pod(s) until I could locate a proper airbox and whatever parts are needed to use the airbox. Eventually, one will turn up on eBay. If you told me what type carb(s) we are talking about and the stock jetting; that is, pilot/slow jet, primary/secondary main jet (if equipped in that manner) and the jet needle type (and needle jet badge, if you have that info), I bet I could take a guess and get close as far as jetting for pods. It would only be a matter of putting the stock jetting back in when you find the airbox.

I have to tell you that I prefer using an airbox. The reason is that still air to the carbs produces a smoother ride. Some folks who use pods, get used to the turbulance effect and pay no notice to it and you may be one of those folks and find that you don't really need or want to go back to using a stock airbox. Having said that, I suspect you would do well to purchase Emgo (DISPOSABLE/CHEAP) pod(s) for this bike and see how you like them. If they work for you and you get used to the slight surging caused by cross winds and passing vehicles, then you could always switch to a better quality pod, like a K&N (life time warranty/can be cleaned and reoiled).

carb: Keihin CV32
engine: Single 4 stroke

That's the one:
CV32
#68 primary jet
#98 secondary jet
#35 pilot jet
jet needle N425-05A00

I would appreciate any advice regarding rejetting to accommodate a pod filter.

Thanks,

Dave

phonex98 wrote:

carb: Keihin CV32
engine: Single 4 stroke

Post edited by: SIKZ250, at: 2007/07/17 19:21

Bump.

I got the bike running this past weekend, but I'm not sure how to proceed as far as the appropriate jets for a pod filter until I can find the stock parts.

The CV32 is pretty easy to rejet since there are no pilot (slow) jets available. Bump up the size of the main jet to a #70 if you can find them and the secondary main will be about a #125 I am guessing. Once you get the bike running, you will have to check the main jet size... the N425 jet needle you are using isn't familiar to me... The four cylinder KZ750 models use the N100 and N01A jet needles and use two distinct sizes of needle jets to accomodate these jet needles and none of the needle jets have any markings. That being said, the N01A is significantly leaner profile and smaller associated needle jet so uses a much bigger main jet than the other version. Not being able to see your jet needle and compare it, it will be relatively lean or rich compared to the CV versions I have specs for... Give the #125 mains a try. Try and take the bike to redline. If the bike bogs... like running out of gas, pull the choke arm up some and see if this makes the problem better or worse. The choking action makes the mixture relatively richer (don't pull the choke all the way up!) so if the problem with running out of gas seems to be a bit better with the choke up a bit, then the mixture is lean and you need larger pilot jets. Go up two sizes to #130 and retry. I am guessing you will be in the #125 to #130 range. If the problem is worse with the choke partially actuated, then you need a bit smaller main jet... go down to a #120 and retry.

These are the two set ups for the CV34 used on a 750 and the second jetting option will be closer to yours I think based on the size of the main and secondary main jets:

CV34 and jetting

The CV34 comes in two varieties:

CV34 #1

Secondary main #125
Main #62
Jet needle N01A
Needle jet smaller opening (no badge)
Pilot #35 (pilot well plugged)

To rejet for pods/pipes #140 #70


CV34 #2
Secondary main #92
Main #68
Jet needle N100
Needle jet larger opening (no badge)
Pilot #35 (pilot well plugged)

To rejet for pods/pipes #130 - rest stock jets

I removed the airbox and am about the pull the trigger on K&N pod filters and jets. Next issue... There was a crankcase breather hose connected to the stock air box.
Do I plug the short metal tube from the crankcase to which the hose was attached, wrap a screen around it to keep debris from entering or just leave it alone?

Thanks again,

Dave

Remove the tube. Buy a hose and install to the crank breather by retaining with a hose clamp. Run hose over swingarm. You can also use a crankcase breather filter available at your autoparts store. You put it down on the breather and clamp in place same as suggested for the hose. Keep an eye on it because if it gets clogged, your crankcase won't be able to breathe.

Thanks.

Post edited by: SIKZ250, at: 2007/08/03 19:54

Post edited by: SIKZ250, at: 2007/08/05 20:28

Thanks George!

I decided on a Uni pod filter and tried a few
different jets. The bike now runs pretty well with the #130 secondary main.

Post edited by: SIKZ250, at: 2007/08/20 21:38

Any pointers for removing the plug that covers the pilot screw?

The bike starts easily and runs well, but I hear popping during deceleration, which (if I understand things correctly) may be related to a lean mixture in the pilot circuit. The idle is also rough.

I'd like to remove the pilot screw, clean the passages and reinstall/adjust the screw.

The bike has a Uni pod filter and a #130 secondary main, but no other mods.

Thanks,

Dave

If you can find a #70 main jet, that would be worth trying as well... this jet affects off idle to wide open throttle. I use larger main jets to partially make up for the lack of pilot jet choices and this seems to work well... finding the main jet will be the hard part as they are a tad hard to locate.

To get to the pilot mixture screw, the plug has to come off. The CV series carbs have a fairly thin plug making them easy to remove. Some constant velocity carbs, such as the BS30 used on some Yamaha models and the BS32/34 carbs used on GS models have very thick plugs and as a consequence, it seems that Mikuni dripped glue down into the thread of the pilot screw making them hard to remove.

I recommend you buy a small EZ out... probably a #2 and buy the associated correct drill bit. Use a punch to mark the center of the plug. Use the drill bit recommended for the EZ out and slowly drill the plug. It is easy to get through the plug and nick the mixture screw below so go slow and be careful. After you drill through the mixture screw, insert the EZ out and see if the plug will move easily. If it doesn't you might want to use a torch and warm the glue... It is probably best to remove the slide diaphragm because heat will deform it if left in place. Once you remove the plug, take the screw out. There will be a spring in the well as and a small metal washer plus a small rubber washer. It would be wise to replace the rubber washer as this thing is probably old and allowing air to leak and you were having backfiring... this rubber washer is a likely source for the backfiring.