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TOPIC: Spark plugs visual check etc.

Spark plugs visual check etc. 3 months 2 weeks ago #24564

  • StanG
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A while back I synchronized the carbs and I used color tune to adjusted the air-fuel screws - all cylinders have a nice bunsen blue color when fired.
The engine is very smooth and seems like gained power. What has also changed is the cold start. My carbs have the vacuum mod introduced by scotch and had been starting beautifully the whole cold winter. Since the recent tune up now, the engine doesn't really like a fully applied choke. We also have summer now, so that's different, but the start up has really changed with adjusting the A/F ratio. So, when starting the bike I pull the choke lever just slightly up. It start beautifully at pressing 'start' and goes smoothly to about 1500 - 2000 rpm's. Depending on much I pull the choke. After 2 - 3 minutes the noises go away and I let it smoothly idle at about 1200 rpm, then a 1000, then just let it run without any help.

This is an interesting change. Perhaps also something to do with summer? This is what the plugs look like. I think it's a bit lean.

What do you think?








1982 Kawasaki KZ1300 A4
1981 Kawasaki KZ1300 A3
assembling engine, chassis & electrical from 79 - 89 parts
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Last edit: by StanG.

Spark plugs visual check etc. 3 months 2 weeks ago #24568

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The outer ring of the plug (Black) which is an indication of Main Jet Mixture is Black.......which is very typical of most CARB model 1300's.
The Centre Electrode in an indication of Pilot Jet and in an ideal world should be a nice Light Brown colour when correct, so I think you are pretty much ok.
I only ever check plug colours after a good long run when the engine has been fuly warmed up and running at every level.

Pete F
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Spark plugs visual check etc. 3 months 2 weeks ago #24574

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Hi Stan, on the third picture, black sooth is loocking a bit wet? or its just the picture making it like this? As for me, like straightsix wrote, middle part of the plug is for pilot jet and the surrounding ring for main jet. I have lambda gauge on the bike and while using various jets I manadge to gain quiet brown electrode by icreasing the size of the pilot jet sygnificantly, but the outer ring almost always remains black, whats more if you engine rpms are low and you go wot, than the engine load is high and mixture becomes rich, as rpm rise and the load on the engine drops than the pilot jet takes over again and the afr start to stabilise and go towards 1 lambda.
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Last edit: by Daro.

Spark plugs visual check etc. 3 months 2 weeks ago #24576

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Daro, to be honest I don't remember if that black soot was wet.. Might had been moist a bit. Possible the engine stopped during intake before next spark plug fire?

Strate6 - yes, the bike had a few short trips after the tuning. And I used some Marvel Mystery 0il as well again, so that really cleaned the plugs.

I like the conservative amount of outer black. But to my true liking I'd like to see the white ceramic a bit more brown.

Do you have notes about the pilot jet sizes you use? Mine are all standard. I might just turn the mixture screws 1/4 turn and see how this affect the spark plugs. I can always go back! The important thing is the bike is not suffering - starts beautifully and runs with gusto.
1982 Kawasaki KZ1300 A4
1981 Kawasaki KZ1300 A3
assembling engine, chassis & electrical from 79 - 89 parts

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Spark plugs visual check etc. 3 months 2 weeks ago #24578

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Daro, to be honest I don't remember if that black soot was wet.. Might had been moist a bit. Possible the engine stopped during intake before next spark plug fire?
Well if it would be the case i thing the fuel would evaporate or better to say the plug will dry out if taken out when hot like in my case i always do, but I'm really not sure. From my experience, when i made some pictures of the spark plugs color to show to my mates, it never justified what they really looked like in true, but if you take the wine cork the one which is little lighter on color not the dark one, that's the color I'm looking for on electrodes. Most difficult part for me was to get all plugs to look at least similar to each other. Now regarding the jets and the needle: On the main jet i use 107,5 it gives me just about 0.8 lambda when i wack the throttle WOT from like 3000-3500 RPM, it may shortly dive little lower but the engine recovers from it properly (still little rich for what i like, but colder on the pistons), but next rebuild I'm going for 105. Idle jet is 42,5 and when riding on just enough throttle to stretch the cable it stays almost perfect on 1 lambda, any speed and light load (speed with in the reason of course) idle screw is at 3 and 1/4 turn out but when i had the 45 in or even 47,5 it was rich but ok, somewhere at about 85 lambda, next time i go for 45 if you ask. Needle is at 3-rd notch, i will lower the needle one notch and fuel level is at 8mm in the chalice or goblet Scotch :evil: and in my opinion that's where i leave it. IMHO the carb are lean on idle and rich on the main, so i try to find the better balance between theme.
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Spark plugs visual check etc. 3 months 2 weeks ago #24579

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I always use a slightly hotter NGK plug in mine , a 5 rather than a 6, and all my 1300s have ran noticeably better in all ways with Iridium Plugs too.

Pete F
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