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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 for any help!!

I don't know if this is the problem, but it wouldn't hurt to upgrade the rubber seals in the choke plungers.  We have a member here that offers the service, or you can make the tools and do the work yourself if you are handy with tools.  Another option, is to replace the plungers with new parts.  There are various threads here about these options.

Good luck

Could it be oil fouling as a result of dried out and leaking valve stem seals?

I own a 1977 KZ650-C1 that I bought new way back when, and it is still totally stock.  It has more than 61,000 miles on it.  I do all my own maintenance.  I have found that ND-W22ES-U spark plugs work the best and do not foul at all.   Ed

 

Thank you guys for the ideas!  I'll look into the choke plunger rubbers. Sometimes I can be pretty handy lol. I have looked into new plungers with almost no luck.  I haven't really thought about replacing the rubbers themselves.  The valve seals could be the culprit but the carbon build up is really dry and sooty.  If I can't solve this before the season ends they will get replaced over the winter.  The denso plugs are something I'll try as well. No harm there.  Thanks again, I'll keep you posted on my progress!   

wrote:

I have looked into new plungers with almost no luck.   

Jetsrus.com sells new choke plunger for a reasonable price. They are in my bike now and seem to be OE quality.

jetsrus.com/individual_parts/002-670_su.html

Old / hard valve-stem seals are usually diagnosed by blue smoke on startup, after standing for a couple of hours.

Do carbs ever overflow?
Thinking about what you said... progressively richer and richer. Duff needle and seats struggle to seal reliably  with engine vibration.

H.

wrote:

wrote:

I have looked into new plungers with almost no luck.   

Jetsrus.com sells new choke plunger for a reasonable price. They are in my bike now and seem to be OE quality.

jetsrus.com/individual_parts/002-670_su.html

My money is on valve guide seals. I'd go 200 miles then the plugs would foul. Later the choke plungers made the bike miss at 35-4500 RPM, replaced them the blub blubs went away. The intake manifolds can be soft but at the engine they can be hard and leak causing you to richen the carbs to compensate thus a rich condition. I'd check them first. 

Steve
 

Thanks for the ideas! Definitely not valve seals absolutely  no smoke or even a hint of oil odor on start up even after a week.  Yesterday we did another round of testing, verifying and small adjustments.  It is getting better. We ran it at both idle and at just above idle with no fouling.  We'll see if it gets fouled after a bit of riding.  I also did some deep researching.  Found out that there were 3 variants of the same carb in 1976/77.  First model has the fuel screw located under the manifold side with no air screw, then for the second setup they added a secondary #50 jet under the pilot jet (which are the carbs we have).This was to reduce the amount of fuel in the pilot circuit.  Both of these setups have the screw adjustible pilot port as well as a bypass port located under the slide.   The third setup is the air screw only type which has only one outlet port and a different slide.   With these changes all happening in the first year, it makes me think that they were chasing a rich condition exactly like what we are experiencing.  Since the bike only has 23000kms, I also think that if you weren't on the ball taking care of the ignition and fuel systems you would run into trouble fairly early on.   

Welcome.
One thing I would do is remove those 50 jets.
There was a bullintin about removing them on carbs equipped with them.
I've never seen a set with the extra 50 jets, but others have mentioned them, and it has always been recommended to remove them.
Jet sizes 102.5 main and 15 pilot, with a stock air box and filter.
If the air box has been modified or removed go with a 17.5 pilot jet.
 

Hey I thought I'd finish up this thread.  We picked up a set of unmolested 1977 air screw carbs and rebuilt them.   Wow! What a difference!  This is how it should run!  Kawasaki was right in updating the carbs to improve the low speed characteristics.  We found them easier to tune since the air screws actually make a difference you can hear when adjusting them.  No flat spot or sooting the plugs.   If anybody is having problems with their fuel screw carbs and running a stick air box and filter with a header, try some air screw carbs if you can!  It made a huge difference to our bike!   Thanks for the ideas and I hope this helps out someone!

She looks great.