Carburettion setup for KLE/GPZ. *updated*

[stinkwheel]

Ok, the bike is a KLE500.

It has a GPZ500s engine in it complete with the CDI that goes with that engine.

It has a 'wide open' sports exhaust system designed for a KLE500. Basically a 2-1 with an unbaffled end can, made by laser pro-duro.

When I first fitted the engine I used the carbs that went with the engine (the GPZ ones). With these fitted the engine was totally dead over 6,000rpm. No power, cutting out, as if the throttle had reached a 'stop'. I tried removing the airbox, this made it even worse.

So, I fitted the carbs off the KLE (same choke diameter). It runs ok with these and will rev to the redline (eventually). It has increased midrange but nothing like the top-end you get from a GPZ500, no howl of acceleration, just a steady and rather slow climb. Nothing to be gained by pushing it over 8,000rpm.

The bike is currently perfectly rideable and somewhat better than in standard KLE guise, I just know it could be so much better

The KLE airbox is half the size of the GPZ one.

So, my thoughts revolve around the airbox/carb combo not matching the engine setup.

The way I see it I have three options:

1) Fit a dynojet kit and free-flowing air filter designed for a KLE500 which would retain the airbox, something I have always thought of as desirable. Given the GPZ engine is essentially a 'tuned' KLE lump, this should work.

2) Go the whole hog and fit a stage 3 kit and pod filters designed for the GPZ motor. Do away with the airbox and learn to live with any problems assosciated with this.

3) But a selection of main jets and have a fanny about myself.

Of course, taking the bike to a dyno centre would be the best course of action. There isn't one I am aware of that I'd entrust my bike to less than two and a half hours away from where I am in North Cumbria (ie, there's one in Edinburgh).

Any comments would be welcome, especially with experience of using a stage 3 setup on a road bike which does reasonably high mileages.

[Kickstart]

Hi

I would suspect the most important part is the lengths of the intakes going into the airbox.

Beyond that I would think it really does need to be set up on a dyno. CV carbs are a law unto themselves.

All the best

Keith
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[stinkwheel]

[sickpup]

SOunds like the restriction is the air box. I would look at swopping in the KLE cams and CDI then changing one item at a time.

[Kickstart]

[hmmmnz]

id put the original carbs and airbox back in, checking that the carbs havnt been restricted, (extra hole in the slides or smaller jets)
but possibly the carbs and airbox you have in now could be tuned to the new engine with out too much trouble.
i wouldn't go the pod filter route, i havn't managed to get my set up perfect yet even after 6 rejets and numorus tweaks it seems to play one area off another,
check that all the rubbers from air box to carbs and carbs to engine havn't got any leaks,
check the jet needle is set to the right clip position and the float needle valve isn't worn,
my guess is you are running lean, and bigger mains are in order,
all just speculation on my behalf with out riding it i'd never know
what colour are your plugs??
good luck
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[stinkwheel]

Just to clarify. The engine complete with carbs and CDI was lifted directly across from my old GPZ that I know was working when I broke it. So, the only things that were different from the original, working GPZ were the exhaust and the airbox.

For some reason, this meant the bike would not rev over 6k. I bunged the KLE carbs on as an experiment and found this worked, not quite as well as expected, but passably well. The bike has done about 15,000 miles in its this setup and hasn't missed a beat.

I even fitted the GPZ carbs to my other GPZ to make sure there was nothing wrong with them. Runs fine.

I've got the GPZ airbox rubbers. I suppose that would be something cheap and easy to try. I'll give it a whirl at the weekend.

Otherwise, I suppose I'll have to try and make time to get the bike up to Edinburgh and on a dyno (with someone who knows what they are doing).

[hmmmnz]

right well the exhaust really wont make to much difference to a 500 (mabee a teeny tiny bit leaner nothing worth worrieing about)
but the air box, thats a whole different kettle of fish,
if you can fit the original airbox in there i'd do that, other wise you'll have to figure if the smaller air box is sucking more, or less air through.
if there is a leak between the carbs you have on there now and the airbox you will be running lean, get those rubbers on there if you arnt going to put the orinal box back in
good luck

____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[Kickstart]

[hmmmnz]

hmmm is that how it works kickstart(always good to know these things), but compared to the airbox and jetting its a small thing, i changed my exhaust over(also a 500) to a free flowing one no baffles, and it didn't make any difference at all (a hell of alot noiser for the most part). i dare say the system he has in there isn't much different in lenth to the orignal any way.
just my opinion of course
____________________
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Wiring Diagrams BIDNIP it bitches

[Kickstart]

Hi

Silencer isn't that important compared to the downpipes and how they join up.

Given that he has an exhaust designed for use on a KLE engine it is probably designed for power lower down, probably peaking not long after a GPZ would want to take off. If you used that along with single filters with no ram tube them that might try and move peak power further up the rev range. Then the GPZ cams. Result is you have an engine that is trying to peak at (rough example) 8000rpm (exhaust), 10000rpm (cams, ignition, etc) and 12000rpm (carbs). Results in no real top end performance. Say each of those is worth 5hp at their peak, then on a bike making 60hp at peak, 15hp is down to those items all peaking at the same moment. Move them out a bit and at that same peak you now only have 50hp (all VERY rough figures).

All the best

Keith
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[hmmmnz]

arhh ok well that kind of makes sence, i have never put to much thought into 4stroke exhaust systems i think ill have to look into it
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[stinkwheel]

I've been tinkering this weekend.

The exhausts are exactly the same diameter on both bikes, roughly the same length although there are sharper bends on the KLE ones. The airbox rubbers are identical. The inlet stubs are the same length.

I was going to try the GPZ needles in the KLE carbs. Bloody flange snapped on the carb casting as I was undoing the top of the carb so I've only got the GPZ carb bodies to play with now.

Gave them a good clean in the ultrasonic bath at work (they've done 65k miles and looked it) and washed all the jets in benzene followed by ether. (whoo. head rush!) so there is categorically no crap in there.

So, what now? Well, I had another fiddle, tried the GPZ main jet (112->130) with the KLE needle. Didn't like that, filled the airbox with petrol.

Tried the GPZ needle with the smaller jet. Ran, but with the same 'brick wall' in the rev range, although now moved closer to 8k.

Tried the KLE needle and jet in the GPZ carbs. Runs pretty well, more top-endy. Still not as much as the GPZ but better. I can only put this down to the 'power jets' being different between the two sets of carbs because the choke is the same diameter.

So, what I've learned from this.

1) Definately the airbox causing the problems.
2) The needle and jet need to match the airbox, not the engine.

This means if I get a performance jet kit and filter designed to work with the KLE airbox, I should get results.

Also noticed some differences between the two sets of carbs. There is a balance pipe on the KLE ones which is not present on the GPZ ones.

There is also a 'bit' bolted on the side of the right hand carb of the KLE carbs. I don't know what it is and does? I see from the manual it is called a "coaster enricher". I presume this is what makes it 'pop-pop-pop' as you're going down hills on a closed throttle. What would the implications be of not having this? Would I need to blip the throttle periodically like you do on a 2-stroke? (picture attached)

[0ddball]

An addition to this circuit is found on later Hitachi and all Mikuni carbs. This is the "coasting enricher". A typical problem in earlier carbs was the fact that when you chopped the throttle (closed the butterfly) on deceleration, there would not be enough fuel in the mixture at the (at that moment) high revs to allow the engine to fire consistently. You would then get a "lean misfire". That is, the engine would fail to fire, and the unburned mixture (lean though it was) would enter the exhaust header. Then when the engine next fired, you'd get a backfire. (So backfiring on decel is typically a lean condition, and not "loading up" as some people think.) The solution they came up with was to reduce the amount of air in the "airbleed" circuit by about half, meaning the fuel content hitting the bore from the pilot oulet was much higher than the normal idle fuel mixture you get on closed throttle. Once the revs came down, the full air bleed would be restored for proper idling. The "coaster enricher" is activated by the strong vacuum created in the carburetor holder (intake stub) by high revs when the butterfly is closed on deceleration.


HTH

[stinkwheel]

That'll explain why it sounds like a rally car now. Thanks.

[finpos]

Also well known for the diaphagm splitting when they get older, letting MORE air into the carb and making the decelleration popping problem much worse . Present on plently of big-cylinder bikes from the 80s.

By the way, that lumiweld stuff works like magic on bits of snapped off carbs.

finpos.

[stinkwheel]

That's what I considered too, but it has snapped through the corner of the flange that holds the plastic lid on the venturi chamber. Right through the groove that the diaphragm seals into.

I suppose I could fix it with lumiweld but it would mean building up a big chunk of alloy underneath the break, re-drilling and tapping the M4 hole and burring out a new groove.

On consideration, it would be easier done with JB weld (much easier to drill/machine than lumiweld) but I have none at the moment and as the bike seems to be running somewhat better on the carbs that are on it, I'll put them in the box with the knackered KLE engine for just now

[tsmith]

some good info on the GPZ's carb here:

https://members.aol.com/roundr1/CVK40.html