Carb mixture screw settings? Update!

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Shedman
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Joined: 06 Dec 2017, 07:31
Location: Swindon UK

Carb mixture screw settings? Update!

Post by Shedman »

Hi guys, according to the Haynes manual my Zephyr 750 mixture screws (says UK model) should be set at 1 and 5/8 turns out, does this seem right? Does turning the screw in make the mixture richer and out to make it leaner or is it the other way around? The reason I ask is that my plugs are really sooty and whichever way I try to adjust them the plugs are still sooty. The thing is I have recently added some Wynn's Dry Fuel stabilizer to my tank, could this actually be causing the soot? The choke isn't stuck on cos I've checked that :lol:
Last edited by Shedman on 06 Apr 2018, 14:54, edited 1 time in total.
Freddy
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Location: Sydney Australia

Re: Carb mixture screw settings?

Post by Freddy »

Screwing it out makes it richer, in leaner.

I'd set my D model to 2 1/4 which is what the genuine Kawasaki service manual says it should be for a C model. Actually I use 2 1/4 on the outside carbies, and 2 1/2 on the inside ones. As all models use the same #35 pilot jet I reckon the differences in settings for countries and models is just environmental compliance related and nothing to do with performance. Hence why I use the 2 1/4 turns.

My opinion, if the plugs look 'sooty' probably something else as these bikes run lean at the best of times.
Shedman
Posts: 212
Joined: 06 Dec 2017, 07:31
Location: Swindon UK

Re: Carb mixture screw settings?

Post by Shedman »

Thanks Freddy, when I first stripped the carbs, two of the mixture screws were all of the way in and the other two were both less than one turn out but the plugs looked ok when I checked them at the time. Do you think it is possible that for the carbs to have been set like this would indicate that the jets aren't standard for the bike? I never checked them when I stripped them.
andye
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Joined: 11 Sep 2017, 10:03
Location: Merseyside

Re: Carb mixture screw settings?

Post by andye »

Hi Shedman

I've used Wynns the last two winters & as far as I can tell it makes no difference to the mixture.

Does it Run OK, & what happens when you rev it & release the throttle. Does it hang up or bog down.

Slightly rich is OK on an air cooled motor, but not too rich.
Shedman
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Joined: 06 Dec 2017, 07:31
Location: Swindon UK

Re: Carb mixture screw settings?

Post by Shedman »

Hi andye and thanks for the input, it doesn't seem to hang or bog at any rev range. I just had a Doh! moment while staring at the bike before I covered it up for the night. When I bought the bike it had a Nexus 4 into 1 exhaust on it, it ran ok ish?, valves needed shimming, air filter, oil change/filter, etc... But I put a standard replacement exhaust on it :? I never used the bike a lot after fitting the standard exhaust but when I did I noticed it was getting harder to start, is it possible that the PO changed the jets to better suit the 4/1 exhaust? The bike is more than a little rich, there is an unburnt fuel smell coming out of the exhaust and fuel is dripping out of the right hand silencer drain hole. The bike is showing 28k on the clock.
Freddy
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Location: Sydney Australia

Re: Carb mixture screw settings?

Post by Freddy »

Shedman wrote:Hi andye and thanks for the input, it doesn't seem to hang or bog at any rev range. I just had a Doh! moment while staring at the bike before I covered it up for the night. When I bought the bike it had a Nexus 4 into 1 exhaust on it, it ran ok ish?, valves needed shimming, air filter, oil change/filter, etc... But I put a standard replacement exhaust on it :? I never used the bike a lot after fitting the standard exhaust but when I did I noticed it was getting harder to start, is it possible that the PO changed the jets to better suit the 4/1 exhaust? The bike is more than a little rich, there is an unburnt fuel smell coming out of the exhaust and fuel is dripping out of the right hand silencer drain hole. The bike is showing 28k on the clock.
Based upon what you've said regarding the aftermarket exhaust , pilot screw settings, plugs, and smell of fuel .......... you'd have to conclude there is a good possibility the previous owner has changed things in the carbies e.g. fitted an aftermarket kit. Me, I'be be pulling them apart and checking.

The good news if you do find something non standard, the original OEM size pilot and main jets are readily available (not from Kawasaki). The bad news, the emulsion tubes, needles, and needle jets are not. BUT, you can get Keyster (made in Japanese) kits that have the lot. How accurate they are to the originals I have no idea. If I had to use one I's still probably swap in the genuine jets that are available (they are only $6 each).

Image

It's easy to check the jets and needles are original but you need one of those magnifying lights to be able to read the marked sizes (and most importantly the symbol like a Star of David before the jet number which tells you if it's a genuine Keihin jet). Maybe someone with perfect eyesight might be able to read em with the naked eye, but I certainly can't.

The jet and needle sizes indicated in your Haynes manual for the various models/countries are I believe correct. Pilots should be #35, that are for all models, and just about any every bike this motor has been used in.
Shedman
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Joined: 06 Dec 2017, 07:31
Location: Swindon UK

Re: Carb mixture screw settings?

Post by Shedman »

Hi Freddy, all of the genuine carb parts are still available in the UK but the prices are enough to make your eyes water :cry: I had a few minutes this morning so I checked the carb fuel level with a clear tube and they are all ok, so the carbs will be coming off and the jet sizes will be checked.
Freddy
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Location: Sydney Australia

Re: Carb mixture screw settings?

Post by Freddy »

Shedman wrote:Hi Freddy, all of the genuine carb parts are still available in the UK but the prices are enough to make your eyes water :cry: I had a few minutes this morning so I checked the carb fuel level with a clear tube and they are all ok, so the carbs will be coming off and the jet sizes will be checked.
Your correct that the CMS web site are showing all the C models parts available, I was thinking it was similar to the D model where the needles and needle jets are definitely no longer available.
Shedman
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Joined: 06 Dec 2017, 07:31
Location: Swindon UK

Re: Carb mixture screw settings? Update!

Post by Shedman »

Well I finally got the time to take the carbs apart, I checked the main jets and they were 90's on carbs 1+4 and 95's on 2+3 but that wasn't the only problem to cause the richness.
When I put the carbs in the ultrasonic cleaner I never bothered removing the pilot jets as before I started working on the bike it idled pretty smoothly. After reassembly it was running so rich that the cylinder's 3+4 was dripping fuel out of the silencer drain hole but there was also thick blue smoke from both silencers and no amount of playing with the air screws would alter it.
When I poked around in the carbs today the #4 carb pilot screw was missing, like gone, just a hole :o I looked in the float bowl, on the floor, under the cat, nothing, no sign of it. I started thinking then :idea: I got my ultrasonic tank out of the shed, carefully tipped the contents through a sieve and found half of the pilot jet (see picture below :? ).
Well I figured that if this one had broken then I'd better remove the other three and inspect them (keep looking at the picture :shock: ) the pilot jet from #1 carb looked like it had gotten woodworm, two of the holes had joined up so it was more of a slot than two seperate holes and there is a crack and damage to the threads. Now I know why it was running so bloody rich!
New pilots and mains on order.
the head and the jets 008.JPG
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Richard
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Re: Carb mixture screw settings? Update!

Post by Richard »

:shock: :o :?: :!:
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