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Discussion Starter · #1 ·
I hope someone here can brag about giving us a solution!!
We have a 1977 kz650b1 that my son and I have had an awesome time restoring. We picked it up last summer and spent the last year cleaning, replacing and repairing things to get it to a "daily driver" condition. It has 23000kms on it, 700 of which we put on it this season during our test and tuning sessions. The story goes that an older gentleman purchased it brand new in '77 and rode it for a few seasons, parked it and then it sat for quite a while. There was no history of it in the licensing office and there was no stolen reports linked to it. It must have been a very long time between road worthy. It has the correct original carbs with pilot screws and no air screws. We replaced the (sadly) rusted original exhaust with a Delkevic 4 into 1. The original air box with new boots to the carbs have been installed as well as a new air filter. Compression test is 140 psi across all cylinders. We have been chasing a fouling plug problem. They all get carboned up fairly evenly with 2 being the cleanest but far from good.
The rundown of what we have done so far is- throughly cleaned the carbs with ultrasonic cleaner (jets and needles are all stock size) float levels are set to 4.5mm below the carb bowl joint (in an effort to lean it out) and checked with the clear tube method on the bike, the pilot screws are set to 1-1/4 turns out, if we set them below 1 turn out we get the deceleration exhaust popping. It did give a slight sense of highest idle when adjusting them. The intake boots are in great condition no cracks and are quite pliable. We checked and adjusted the valve clearances, all are set to .15mm clearance. The ignition coils, wires(emgo) and non resistor NGK plug caps have all been replaced and the spark looks good, we installed the WG relay mod as we were losing about 1.2 volts to the coils through the cleaned but original wiring and replaced the spark plugs (numerous times now-NGK br8es, br6es, br8eix and br7es) The gas tank is clean (we put an inline filter in as a precaution), with the original petcock which works but will let a very small slow drip through when set to off, found during a bench test of the petcock. The battery is new and settled at 12.8 volts and the charging system is functioning as intended. We replaced the points and condensers, the points were set to .35mm and static set up to the F mark and was double checked with a strobe. The ignition advance starts at 1500rpm and is all in around 3200rpm.
The rich problem happens around the transition between idle and 1700 rpm. If you hold the throttle to maintain 15-1700rpm for a few seconds then raise the rpms it belches black soot and stumbles a bit then accelerates normally. We've had the carbs out numerous times to check double and triple check every setting and passage. The pilot air jets and passages have been cleaned almost every time since that is what the problem seems to be. But the overall operation is pretty good and it cold starts easily with choke and not easily without the choke. It runs through the grars and accelerates well. When it's ridden for a few hours it runs progressively worse until it starts to foul out the spark plugs.

Some thoughts-

We've been running 91 in it as it has no ethanol in it locally, maybe we should try some ethanolated 89?
The installed pilot jets are 15 with the 50 additional jet below it, is it even an option to get a smaller pilot jet even though it seems wrong to do?
We replaced the coils and caps since there is no local availability of b7es or b8es spark plugs, I trust this is the correct way to solve the double resistance issue?
We've replaced most of the items listed even though they didn't really test out as "failed or bad" but as attempt to solve the fouling.
The inital operation was fair and things have become progressively better with each component we replaced, except it continues to foul the plugs.
I hope someone here has (unfortunately) been through this and is willing to help out with some ideas.
We will forever be in your debt!
Thanks if you've read all this!
 

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Mr Wild, I will try to help you out, as best I can, 23k kms is not a lot but the 'rubbers' on the bike get old and are no longer resilient/pliable after 45 years!. First thing that comes into my mind having read your whole story is valve stem seals. You seem to have the carbs well taking care of but maybe not quite there yet. If the bike is fouling plugs just maybe the valve stem oil seals are bad allowing motor oil to foul up the plugs. Just replace them, they are 45 years old!
I suggest keep tweaking the carbs anyway, just in case, but give the bike a valve job with new valve oil seals. Also go by what the service manual says about spark plug type, float levels, jet settings, timing advance etc as the base starting point only after the valves prove good.
Fouled plugs could be caused by: too much fuel, not enough air, bad valve seals, bad rings, wrong heat range plugs, poor quality fuel, or all these to various degrees combined together.
 

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I had the same thoughts as Olmo. Are you certain that the fouling is caused by running rich, or as Olmo suggested, is it oil fouling? That would be the first thing to look at.

I will assume for the moment, that you have carb issues.

You state (in your very thorough write-up) that "The pilot air jets and passages have been cleaned almost every time since that is what the problem seems to be" but you don't mention if dirt was found in the jets.

So, a couple of points:
1) Have you replaced all fuel lines? Rubber degrades and will start to shed tiny bits of rubber that will constantly clog your jets. You installed an inline filter, but the rubber hose downstream may still be shedding rubber bits.
2) Is your inline filter made for gravity feed?

There may be a chance that the throttle hesitation is not rich-related but could be lean-related because your plugs may be rich fouling from a needle or main jet setting. Thus it would be wise to check the above 2 points.
 

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Discussion Starter · #4 ·
Thanks for the replies! The fouling is definitely carbon. Very light dry fluffy soot. It appears fairly quickly and there's no oil odour whatsoever on startup. We'll get into the valve seals as a off season project since they will need to be replaced sooner than later. I didn't find dirt in the pilot circuits every time but there was some the first couple of times. Then when it still fouled plugs I assumed that we didn't clean the air side of the pilot circuit well enough. It seems that at idle it runs good and when you lift the slide up a bit which uncovers the unregulated portion of the pilot circuit is when the issue happens. The fuel filter is a gravity feed type and all the hoses were replaced with a semi transparent type of hose. We did find that black hoses we used were deteriorating and causing blockages earlier on. This has been corrected now and we haven't found any dirt in any circuit since. I'm thinking now to put some fresh hotter plugs in it and give it a good flogging and see what happens. We haven't been very aggressive in the test rides we have been on. The other possibility that has been brought up on kz rider (and follows Olmo's idea) was to replace the choke plunger seals, I will definitely check this out. Thanks again, I will keep you posted on our progress. I'll also post some pics of this great looking bike!
 

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In box stock condition your bike came with Mikuni VM24SS carbs in the following config:

Main jet 102.5R
Needle O-8
Needle Jet 5DL31-4
Pilot Jet 15
Air screw two turns out from lightly seated
Fuel Service Level 2-4mm
Slide cutaway 1.5

Hope this may help. If everything is to spec and still no joy, you may want to try a smaller needle jet or larger cutaway.
 

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Discussion Starter · #6 ·
The carbs are original and have pilot mixture screws and no air screws. The current set up is:
Main jet 102.5
Needle 5DL31-4 clip at the 4th from the top
Pilot Jet 15
Pilot Screw 1-1/4 turns out
Fuel level 4.5mm

Seems to be one year carbs only and even at that possibly limited to the b1 models as well.
We have an original Kawasaki FSM that has the supplements for the newer carbs and other updates. We're going to readjust the mixture screws, resync and take her out for a plug chop session to make absolutely certain where the sooting is happening. Thanks for your interest WFO.

Edit- there are #50 jets installed below the #15 pilot jets that are not shown in the manual. Doesn't make sense to remove them to reduce fuel but I'm not a fluid dynamics engineer either! Lol!
 

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Don't worry about the terminology of air screw vs fuel screw. Kawi makes no distinction on this and they still refer to a "choke" when it is an enrichment circuit. When it comes to carbs I guess they like to stick to one common word as opposed to being precise with terminology.

Are you saying you have #36 on the diagram below in addition to another pilot jet? That seems very odd indeed.
Do you have the rest of the gear shown in the diagram below? If so I think that would mean those carbs are for a B2A model.

Font Parallel Rectangle Circle Pattern
 

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Discussion Starter · #8 ·
Schematic Font Rectangle Material property Parallel
That pic is the pilot mixture screw. It only controls some of the total pilot mixture. Manual says 1-1/8 +- 1/8 turns out.
This mysterious #50 jet is screwed in below #2 pilot jet in this pic. As you can see, there are two pilot ports in the carb bore. One controlled by the screw and another one (bypass outlet) is below the slide which shouldn't see any flow when the slide is closed (at idle). It comes into play once the slide is lifted even a small amount. This is where we're getting fouled. We rechecked all the settings this morning with new plugs and it seems to be a bit better again, less fouling so far. Only a slight sync adjustment, but we've only put 150kms on it. Maybe the cutaway is not correct but I'd really be surprised that they were replaced in the first 23k. Maybe this is why it only has 23k! Lol!
 

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Discussion Starter · #9 ·
I just found this over at KZ Rider, posted by Wired George. Unrelated to me but may be good info!

"Your #50 "pilot" VM24s don't have #102.5 mains stock... they are much smaller; probably #90.5 or something like that. I doubt using a #110 main will hurt anything so give it a try regardless of what mains you find in there or a #105 main; either will work.

Your pilot jets are #15 on both sets. The one with the #50 barrel jets OVER the top of the pilot jets was made a bit later and they used the extra set of jets to restrict gas flow to the pilot jets. Either set will do well with #17.5 pilot jets. "


My carbs had 102.5s in there so my bad for not researching more. This hopefully will help.
 

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Discussion Starter · #10 ·
New info again! I haven't really been surfing for answers until recently. There are two carbs for 1977. They superseded the fuel mixture screw type with an air screw type. I wonder if the change was partially caused by the issue we're having? I know that later years had both screws but I didn't know that there were two different types in 1977.
Font Gas Machine Auto part Metal
 

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floats. you sound smart . just remember that's it's like tin metal and hot and cold, expansion and contracting and float bowl sloosh all directions. my 78 650 had issue with number 2 leaking after like 30 min of riding. so I changed them. didn't fix it. went back and pulled out the straight edge and all 4 floats metal arms were just a little bit off. seriously not by much. so being a marine, went OCD on all 4 float arms the metal parts and sure enough it rana the the wind blew in. hope this might help someone. GOD SPEED.
 

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Discussion Starter · #13 ·
Thanks Maddison. My brother was by yesterday and after a couple of minutes he said maybe the choke shaft is a bit twisted since the lever is on one side. Like your floats I think this shaft may be twisted. Seems like the right hand carb (#4) choke doesn't close as tight as the left hand one(#1)
 

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Discussion Starter · #14 · (Edited)
Apparently the early carbs can be troublesome to tune. I'm sure that we are completely capable and I really doubt that they are able to run without fouling the plugs. At least with original air box and filter set up with 4-1 delkevic exhaust. We've found a decent set of '77 air screw carbs. Going through them this weekend and see what happens. I'll keep the thread posted. Going by the chart above, the carbs we got on the bike are the '77 272's ( which are came on the early bikes like up to around 16000 serial number) and the new ones are the 1020's ( which were supplied after 16000) So as close to original equipment that you can get. Our bike is 12518.
 

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Discussion Starter · #16 ·
So we've cleaned the "new" air screw carbs and replaced the jets as required. Put them on and tuned 'em up. No other tuning or ignition changes were done. The results were dramatic! Idle is stronger and overall operation is way better. No flat spot just above idle and the plugs aren't getting fouled so far! We have them set to 11/2 turns out on the air screws, #15 pilot jets, 102.5 mains, standard needle set to the 4th position. Ignition timing is set to standard .35mm gap, firing at the f mark. Quite pleased with the outcome. I'm not sure if this problem was due to running the Delkevic 4-1 with air box and filters but using the air screw carbs certainly was the solution. At no point did the fuel screw carbs operate as well as the air screw ones are. I hope this helps someone looking for a solution for a similar problem!
 
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