KZ440 with pods, wide open throttle stuttering

I've been working on an '81 KZ440 that has been sitting for quite a while. I have it up and running now with pod filters since the original air box was long gone when I got to the bike. I was having some problems with a flat spot at around 4k rpm which I recently fixed by shimming the needles up some. Now that is gone and the bike is running much better, however I've noticed that at wide open throttle, regardless of gear, the bike begins to stutter and stumble. In 5th and 6th gear, this occurs at somewhere between 5.5k and 6k rpm. I have NOT been able to get the bike to go past this point, it just stutters around at 5-6k until I let off slightly and then it's perfectly happy with running at the same rpm's.

A couple of notes, the bike runs perfectly every where else in the rpm range and has no problem revving up to redline when in neutral (albeit I don't need wide open throttle to get there). I have NOT yet rejetted to accommodate the pods. Also, the carb boots between the carbs and the engine are split and I have some new ones on the way.

I am just wondering what you think is the issue with wide open throttle? Is it likely the carb boots are sucking air, but only when wide open? Or are my primary or secondary main jets just not large enough to flow enough fuel when the throttle is wide open.

I'm close to getting the bike sorted out and it's still fun to ride, but this problem is really bugging me and I don't know which way to go next.

it sounds to me that the engine is very lean i'd go up 3-4 sizes on the main jet's see if your problem get's better

Ok, I'll probably pick up some new main jets, then. I may hold off until I put the new carb boots on just to see if they make any difference. By the way, which mains should I go up in sizes? Primary? Secondary? Both? Sorry for all the questions, but I'm kinda new to this whole carb tuning thing. This is my very first bike.

This may not be any help.... A number of knowledgeable folks have stated that the KZ440 w stock carbs is difficult to tune w pod filters. That may be where you are now.

Also, the carb boots between the carbs and the engine are split and I have some new ones on the way.

I am just wondering what you think is the issue with wide open throttle?

First thing first, get the new boots on for you may find that due to crap boots, previous owner jetted/tweaked around this fact so don't do anything until boots is accomplished, then go from there....

Don't even tweak pilot screws or sync.... initially if possible...

Take her for a ride and see where she lies in performance, accelerations, WOT & release the throttle, see if she back fires, pops, stumbles etc....

Then go after sync, adjustments possible jetting requirements....

OMR

I'd fix the boots before anything else. Even if you get it to run decent with the boots you'll never get it right.

I know the jets are stock because I got a set of replacement carbs for it and compared the sizes to the factory service manual.

I've been riding the bike for a week or so now and it runs great everywhere except wide open, no stumbling or backfiring at all (pops a little at low rpm when cold, but is fine once it warms up). I let my brother listen to what it does at wide open in 4th gear and he says it sounds like it's bogging down just like it did around 4k before I shimmed up the needles.

The bike has no problem cruising at 60-70 mph I just can't go to wide open throttle in order to pass someone. When I do it starts to bog down some and will only continue to pull once I release the throttle back down to where I was cruising.

I plan to see what the boots do and then decide whether I need bigger main jets. By the way, which main jets would I need, to affect wide open throttle? Secondary or primary?

All in all, I think the bike is running pretty well after spending the last 14 years in a shed!

Thanks for all the help.

An update on my carb situation:

I got the carb boots put on this evening and to the bike for a test ride. The bike seemed to run better overall, but my full throttle problems continue.

While I was out, I decided to test the issue by giving the carbs about 1/4 to 1/3 choke and pinning the trottle open. The bike pulls easily all the way up to the red line(9k rpm)! When I took the choke off, I couldn't get beyond ~6k.This tells me that the bike definately isn't getting enough fuel at full throttle.

So I guess this means I need to go up a few sizes on my main jet? If I understand the theory correctly, isn't it the primary main that would make the most difference in this case?

As I under stand it, the idle mixture screw and pilot jet size affects small throttle openings, the secondary main jet size and needle position affects the midrange and the primary main jet size affects wide open throttle.

The jet sizes currently on the bike's Keihin CV36 carbs (stock sizes) are 35 pilots, 88 secondary mains, and 65 primary mains. Should I go to 68 or 70 on the primary main and see what happens?

Ok, I ordered some larger secondary main jets after re-reading the carb jet section of the factory service manual. I am currently running 100's instead of the 88's that were in it before and it sounds and feels like it is running much better.

However, it still has problems with a flat spot at ~6k. In any gear up to 4th it will now jump the flat spot and go all the way to red line all at once. In 5th or 6th it still doesn't seem to have the power to do that and just stops at ~6k. I spoke to the PO and he says that it never did have the power to come close to red line in 6th. Remember, it is just a 440.

I have jets sizes up to 105's and plan on trying those out this weekend. I haven't had a chance to see about the top speed with the 100's, but with 95's it still would not go faster that about 75mph (close to the top speed with the stock 88's). Also talked to the PO about that too and he said he's had the speedo pegged (85 mph) in 5th gear at redline back when he was running the air box many years ago.

I read somewhere on here that the stock air box on the 440 was restrictive on purpose in order to create enough vacuum so that the vacuum diaphragms on the needles could lift all the way (which happens at wide open throttle). I've read that this is why pods are hard-to-impossible to tune for on this bike. Is there some truth to this or would still bigger jets make up the difference?

The bike is running very well and will cruise all day up to about 70 so I'll definitely keep riding it even if it's only in town or on the back roads (and honestly, interstates are boring). Thanks.

Here's a pic of my project soon after it was resurrected this summer. Pictures here with the ORIGINAL tires!:ohmy: (They were replaced very soon after, well before it was put on the road.)

Looks like a really nice complete bike. Someone stole the air box out of that huh? I guess you know why now.

Yeah, wasn't so much stolen as "lost" by the PO. Said he was sick of having to fight it every time he had to pull the carbs, which was often since he said he had to clean them every year after he put the bike up with gas still in the carbs.