Carb Setup on Dyno | Page 2 | GTAMotorcycle.com

Carb Setup on Dyno

Regarding your final numbers that isn't a little rich at all, depending on where you mean. At WOT you actually want to be richer (around 12.5-13) for the most power. You don't always want 14.7.

Ah OK. Thanks Johnnnw.

I'm at around 13.8 at WOT. I'll go up a jet size and try it again. I can also try to drop the clip one notch as its also around 13.8 between 1/2 and 3/4 throttle and see if that makes a difference. Its 14.2 on idle but I can't be bothered taking the carbs off to change the slow jets.

Its actually been a good learning experience as I basically got to feel what it was like when it was out of whack and how the motor changed when it got closer to proper jetting.I think that would be hard to experience without the gauge.

Still its 100% better than what I started with
 
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BTW. A big shout out to Winners Circle. They had all the Jets in stock and were very helpful
 
Question for ya. You've said "GPZ" but haven't said which model.

Sometime in the early 1980s, maybe even late 70's, Kawasaki started using something called the "Clean Air System" which is a little gizmo that draws a bit of extra air into the exhaust ports to allow combustion to finish in the exhaust header pipes. (They still use this system to this day - and the other manufacturers all use something similar.) The good thing is that this reduces pollution by helping the unburned stuff finish burning. The bad thing is that if you do exhaust analysis on the engine, you are not actually seeing what the engine is getting ... you are getting a false reading which is slightly leaner than what the engine is seeing because of the extra air that this system draws in.

On top of the valve cover, there will be a couple of hoses connecting to a little contraption sitting directly above the valve cover which in turn has another hose leading to the airbox and a little hose leading to a vacuum port somewhere at the carbs. That contraption is the valve that makes this system work. To get a proper reading on your air/fuel gauge of what the engine itself is seeing, you need to plug the hose from the airbox that leads into this gizmocontraption.

You can install fancy looking block-off plates to eliminate the gizmocontraption completely, but for testing purposes there's no need. Just pull the hose off the airbox and jam some suitable object into the end of it to plug it (in a way that you can get it out again afterward) then stick the now-plugged hose back on the airbox so that you don't have an air leak at the airbox. You can put the plug into the other end (at the valve in question) if it's easier to get to, makes no difference.

14.2 at idle is good. 13.8 under moderate acceleration is also good. 13.8 at full load IF KCAS is plugged or blocked off is a bit lean. If KCAS is still connected and working you may end up finding that it's actually a bit richer than that once you disable it to see what the engine itself is doing. Air cooled engines don't like being lean under load. It should be mid 12s at full load acceleration with KCAS plugged. (and if it runs happily right now, you might find that it's already there once KCAS is plugged)

Needles should normally be set to the leanest setting that gives smooth operation. If you can get it to be 15:1 at steady cruise (with KCAS plugged) you'll be happy with the gas mileage and range, and you'll get less fuel dilution in the oil.
 
So I took GreyGhost's advice and bought a Wideband 02 sensor and gauge. I ended up with a AEM 30-4110 based on the reviews it got. I also bit the bullet and had a bung welded into the exhaust right at the collector.

It definitely simplifies things a great deal and the initial settings were all over the place. At idle it was about 10:1, midrange (1/4 - 3/4) was about 12:1 and up top it dropped to about 16:1.

It took me about an hour. The nice thing with the CR's is that you can take out the jets (with the exception of the pilots) and the needles without taking the carbs of the bike

Its now running between 13.8-14.2 across the range and its a pleasure to ride. Still a little rich and I guess I could try to get the curve a little flatter but I'm pleased with it for now.

I also bought a plug for the bung so I'll leave it on for a few weeks and if everything still looks good I'll probably remove it and just stick the plug in.

Thanks GreyGhost. I owe you a pint.

Glad it worked out for you. An added bonus is your money has been used to make you a more competent mechanic instead of just disappearing with little knowledge gained.
 
Question for ya. You've said "GPZ" but haven't said which model.

Sometime in the early 1980s, maybe even late 70's, Kawasaki started using something called the "Clean Air System" which is a little gizmo that draws a bit of extra air into the exhaust ports to allow combustion to finish in the exhaust header pipes. (They still use this system to this day - and the other manufacturers all use something similar.) The good thing is that this reduces pollution by helping the unburned stuff finish burning. The bad thing is that if you do exhaust analysis on the engine, you are not actually seeing what the engine is getting ... you are getting a false reading which is slightly leaner than what the engine is seeing because of the extra air that this system draws in.

On top of the valve cover, there will be a couple of hoses connecting to a little contraption sitting directly above the valve cover which in turn has another hose leading to the airbox and a little hose leading to a vacuum port somewhere at the carbs. That contraption is the valve that makes this system work. To get a proper reading on your air/fuel gauge of what the engine itself is seeing, you need to plug the hose from the airbox that leads into this gizmocontraption.

You can install fancy looking block-off plates to eliminate the gizmocontraption completely, but for testing purposes there's no need. Just pull the hose off the airbox and jam some suitable object into the end of it to plug it (in a way that you can get it out again afterward) then stick the now-plugged hose back on the airbox so that you don't have an air leak at the airbox. You can put the plug into the other end (at the valve in question) if it's easier to get to, makes no difference.

14.2 at idle is good. 13.8 under moderate acceleration is also good. 13.8 at full load IF KCAS is plugged or blocked off is a bit lean. If KCAS is still connected and working you may end up finding that it's actually a bit richer than that once you disable it to see what the engine itself is doing. Air cooled engines don't like being lean under load. It should be mid 12s at full load acceleration with KCAS plugged. (and if it runs happily right now, you might find that it's already there once KCAS is plugged)

Needles should normally be set to the leanest setting that gives smooth operation. If you can get it to be 15:1 at steady cruise (with KCAS plugged) you'll be happy with the gas mileage and range, and you'll get less fuel dilution in the oil.

Brian. This one is a GPZ550 D1. It’s the 1981 twin shock. They only made them for 1 year and they didn’t have the CAS.

I am running the head from a 1983 as I need the bigger carb boots and inlets for the 26mm carbs - the 81 only had little TK22’s - but the 81 valve cover has a casting that blocks those ports off. It’s hard to explain
 
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OK. Went up a jet size and its around 12.7 under WOT.

I don't thing it made a big difference on the Seat of the Pants Dyno but its close to your recommendations. Thanks for the input
 
That's good. What's it do at steady cruise on level ground at (say) 90 km/h?

Even as it stands ... You would have never gotten this close this quickly without that gauge. Nice work.
 
That's good. What's it do at steady cruise on level ground at (say) 90 km/h?

Even as it stands ... You would have never gotten this close this quickly without that gauge. Nice work.

Its about 13.9 @100k mph

Agreed on the gauge. It made everything so simple
 
My son is building a CB350 and has a 2:1 with a bung already welded in. I might keep it until he is done, but its definitely something worth while having
 
Its about 13.9 @100k mph

Agreed on the gauge. It made everything so simple

While riding around at various steady cruising speeds, particularly low speeds just off idle, if it's always rich of stoich, you could try dropping (leaning) the needles the slightest little bit - maybe one washer-thickness. (If necessary, move the clip one groove towards the top of the needle and put a washer about half the thickness of that move underneath the clip.) Light-load cruise slightly lean (15.something) will help gas mileage and range, reduce fuel dilution in the oil, and help minimize carbon build-up on the spark plugs, pistons, and combustion chambers.

It is possible that you will encounter a lean stumble just off idle when pulling away from a stop, if you go too far.
 

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