Carbon-fouled plugs during break-in and other related matters

Gentlemen, I have a sooty, carbon-fouled spark plug problem that I believe needs to be solved with adjustments to the carbs and would appreciate some of your insight:
-1975 Z1-B 900 bored out 0.020”, new valves and guides (200 miles on engine since rebuild)
-1976 VM26SS Mikuni carbs with pilot air screw (no pilot fuel screw)
-Kerker 4 to 1 pipes with baffle
-Air box with K&N filter
-Compression – low to mid 120’s (book says it should be 145 psi)
-Spark plugs taped to head with engine cranking – bright, crisp sparks

I checked out the thread titles in the Carburetor forum and investigated approximately 50% of the threads to see if they touched on my problem and got quite an education in the process! I am following the break-in procedure in the Kawasaki Shop Manual – first 500 miles no more than 1/3 throttle and limit engine rpm’s to 4000.

History: Very first ride got 1-1/2 miles down the road when the engine started misfiring – examined plugs and they were all equally covered with soot – lowered the fuel level to spec with clear tube method and was able to get 25 to 30 miles on the odometer before the plugs fouled and engine started misfiring. After each ride all 4 of the spark plugs had to be cleaned. The last ride was 15 miles and the last 5 of those miles the engine misfired as much as it fired. During the six or seven rides I replaced coils, points, condensers and went from the specified plug (NGK B8ES) to the recommended hotter plug for break-in (NGK B7ES). It turned out to be loose bullet connectors between the kill switch and coils that caused the bad misfire on the last ride. One other point – the electrical system connections were meticulously cleaned – there is very little voltage drop between battery and points.

Dad and I completed restoration of a 1959 Triumph TR-3 (English sports car) back in 2004, and since then I have done all of the maintenance and tuning. Working on that car is kind of like going out for a beer with your best friend – not real complicated. Getting the Kaw refurbished to the point of being ready to start the engine was like working on the TR-3. However, getting it ridable is starting to feel like the equipment manager for the high school football team thinking he has a chance of getting a date with the head cheer leader – ain’t gonna happen! I guess what I need from the forum is your thoughts on the following questions.

1) I am concerned about an overly rich mixture washing the oil off the cylinder walls and carbon building up on the exhaust valves causing them to leak. Are those valid concerns?
2) What should I expect during break-in in the first 500 miles? I know that 4000 rpm’s is lugging the engine – should I just expect to have to occasionally clean the plugs – every 25 to 30 miles seems excessive?
3) What I learned during my KZR research was that during my rides I was having some of the symptoms that require adjustments to the pilot system – specifically a) pulling away from a red light the engine would bog down and require playing with the throttle and clutch to get going, and b) shutting the throttle at cruising speed would result in cracking and popping sounds coming from the exhaust, and shutting the throttle quickly would cause the cracking and popping sounds to be louder and more frequent. The carbs have the stock jets (115 main, 17.5 pilot) and needle (5DL31).
4) Previously, it was my understanding that cracking and popping in the exhaust was unburned fuel exploding in the exhaust pipes – the mixture being too rich. From my KZR research it seems just the opposite is the case – the pilot system is too lean. Is this true? Why does a lean mixture cause cracking and popping?
5) Regarding the engine bogging down upon cracking the throttle to pull away at a red light – it was my assumption that the rich mixture was causing that, but my KZR research said that if the pilot jets are too small, they won’t provide enough fuel for the instant increase in air flow when the throttle is opened. So where is the excess fuel coming from that is fouling the plugs?
6) I do not think the excess fuel is coming from the starter system – starter system works per the book, and after the engine is started and the starter system shut off, the engine idles nicely. However, regarding idle – the air screws are initially set at 1-1/4 turns out, but there is very little change in idle speed or engine note while adjusting the air screws in and out. Would this condition also indicate the pilot jets are too small?
7) Based on my KZR research I have decided to change out the needle and needle jet. The TR-3 was running rich and changing its needles and needle jets completely cured the problem. The book says to use a block of wood and gently tap the needle jet out the bottom of the carb – can anyone expand on this? Would it be helpful to soak it with WD-40 and/or warm it up with a heat gun before tapping it out?
My bike is basically set up the way I bought it in 1980, and back then it ran nicely and had a strong pull from mid-range up to the redline. Unfortunately, we had someone rebuild the carbs back in 2006 (before the current engine work), and they changed out whatever jets and needles were in the carbs and installed the current stock jets and needles. One thing I didn’t find in my KZR research was discussion on the effect of the 4 to 1 Kerker pipes on the system compared to the stock pipes. Since the Kerker exhaust is the only non-stock item on my bike, I was hoping to find some information on jetting related to the 4 to 1 pipes. What is the usual change to jetting for these pipes?
9) It seemed to idle and run smoothly after mechanically setting throttle slides with a sewing needle – would it help my carbon fouling problem if the carbs were vacuum balanced before riding?
10) Regarding balancing the carbs with a manometer, I have an old Motion Pro carb stick that uses mercury. Does anyone know if the level of mercury in the reservoir should be at the 0 centimeter line? The people at Motion Pro couldn’t help me here. Does anyone know where I can get a small amount of mercury?
11) After the last ride I drained the tank and the float bowls because I knew it was going to be a couple of months before gas was flowing thru the carbs. After a month had passed, I had the carbs off and the small hole in the bottom of the starter pipes and possibly the pilot jets had gummed over. I am using 91 octane no-ethanol gas. Any thoughts – would it be better to add Sta-bil to the gas and leave it in the carbs?
12) And possibly related to Item 11) – I could not find 3/16” ID rubber tubing for the vent and overflow lines on the carbs so I used clear plastic tubing. After each ride clear, oily liquid (maybe a tablespoon or two) would drain out of the overflow lines onto the garage floor. It looked and felt like thin silicone grease. It did not smell like gasoline. Are the gas fumes degrading the plastic lines or is that something evaporating out of the gas in the float bowls? In my KZR research the discussion on using the “chop method” for checking spark plug color, the contributors stated you had to put more miles on the plugs before chopping to get an accurate color due to changes in today’s gas. I’m just wondering if my gumming problem in Item 11) and the weird drainage from the overflow lines are related to the gas I’m using. Any thoughts?
13) Ok, last question, and thanks for your patience for anyone who is still with me. I was intrigued by the guys in the forum that were using the AFR gauges to dial in their jet sizes. Is there some good info on this process to download? For instance, how do set up the gauge to use? Is this a permanent fixture on your bike, etc.?

Any help here would be greatly appreciated!

Brad

You are burning to much gas.
Main jet size ?
Idle jet size ?
Clean filter ?
Do enrichers follow choke lever up and down, no binding ?

1 . Don't baby the engine and don't follow the book for break in.
Don't thrash it but don't lugg it or sit at constant speeds.
Take it up to 6 - 7k rpms and use engine breaking to push the rings into the bores.
This will also help clear the plugs and burn excess fuel and hopefully get the compression up to where it should be if you haven't already glazed the bores.
2. You sound too rich , but shouldn't be the stock jetting.. Could be flooding , float heights too high ?.
Pull them apart and inspect for loose jets and missing or split 'O' rings on the main jets etc Check float heights.
3. With just a Kerker pipe you may have to go up on the main slightly. One size up from stock but not until you cure the over fueling.

I'd double check the cam timing. It's easy to get them one tooth off. How's the valve lash?
Steve

Wow all that writing and not one mention as to float levels, main jet size, pilot jet size and needle position.

baldy110 wrote: Wow all that writing and not one mention as to float levels, main jet size, pilot jet size and needle position.

The jets sizes are given in point 3 about half way down the page and are stated as stock 115 main , 17.5 pilot and 5DL31 needle so shouldn't be the cause of the problem.

Agree on not babying the engine. Ride in an assertive urban style; lots of throttle accelerating up and down the range but avoid high rpm and no lugging.

From a technical standpoint it seems like you have covered a lot of the bases. One question: where are the air screws set? You may want to try opening them more. Also, as mentioned by others, check fuel level. You can make a clear tube gauge by taking common clear vinyl tubing and tapering the end using your grinder and sort of cramping the tapered end into the floatbowl threads and screwing in the tube.

Possibly ignition related. Poor spark from weak coils, bad wires and/or plug caps, excessive resistance...
High octane gas with low engine compression. My plugs sooted whenever I ran premium pump gas, and clean up with E10 regular.

Gentlemen, very appreciative here!
Here's my battle plan so I will be ready to ride next time we get some halfway decent weather.

I have double checked cam timing and valve clearances - so pretty confident about that as I am about the electrical (spent the last month cleaning all connectors and verifying circuiting) plus I have all new ignition components (coils, points, condensers and plugs) and getting good spark when plugs are taped to the head.

Carburetors are currently disassembled and will be rebuilt with all new jets, needles, etc. with Keyster brand components. The Keyster kit was chosen because it includes the needle jet. Yesterday I removed one of the needle jets (it was easier to remove than I expected) and compared the fit between needle and old needle jet to the fit between needle and new needle jet - there was a noticeable difference. So, I am hopeful the new needle jets will solve a big part of my carbon-fouling problem. I do not think the needle jets have ever been replaced. The last time the float level was set I used the clear-tube method eyeballing 1/8" - book says 3 mm +/- 1 mm - so I will check the float level and be sure it's no higher than 3 mm. Baseline for carb set-up will be stock - 115 main, 17.5 pilot 5DL31 needle in 3rd position and air screw 1-1/4 turns out.

daveo - that's interesting about the gas - believe I will go that route for the next ride - assume you are talking 87 octane E10?

Nessism and zed1015 - thanks for break-in info! It was really bugging me not revving more than 4000!

I will look forward to the next ride and share what happens - thanks again.

Brad

My apologies I stand corrected. Stick with mikuni jets. With the current jetting it should not be running rjch. What is the voltage at the coils. Should be 11 volts or higher.

I really like the Keyster kits but I don't use their choke plunger because it doesn't have the point on the bottom. I'm also a believer in replacing needle jets because as you pointed out...they wear. This means more fuel flow and also less emulsification.

Saturday, March 21, 2020

Just want to check in with an update. Since changing out the needle jets and running the engine at higher rpm's during the rides, I have not had to clean soot off the plugs! So that is progress. Since the engine rebuild, the odo has 527 miles on it, so for the last 300 plus miles I have noticed the engine getting stronger as it gets broken in. During the rides I kept the rpm range between 5000 and 6500 with lots of engine braking, and for the last 50 miles let the rpms creep up between 7000 and 7500 - all of this without any misfiring. Big thanks to zed1015 and Nessism for encouraging me to disregard the book’s break-in procedure!

I have been online researching how to read spark plugs for tuning and found a website that is very informative (in my very inexperienced opinion), and I believe the plugs show that I still have a rich mixture – just not sure at which rpm range(s). Since I’m not cleaning spark plugs, the plan is to get 1000 miles on the engine before analyzing the running characteristics. At that time, I will feel confident at running the engine between ¾’s and wide-open throttle.

FYI, I experimented with my old Motion Pro manometer and found that the 1 teaspoon of mercury that I had on hand was more than enough so, I did a manometer sync on the carbs and think that may have helped reduce a vibration problem around 6000 rpm, but, again, that’s a very inexperienced opinion. I changed out the plastic overflow lines coming off the bottom of the carbs to rubber fuel line, and the clear slick drainage from the lines has stopped. Also, the cracking and popping from the exhaust during deceleration has been drastically reduced so I’m giving credit for that to the new needle jets not letting excess fuel come through.

My biggest concern during the past 300 miles is the hesitation or stumble in engine rpm’s when the throttle is blipped at idle to get the rpm’s up when starting to go after being stopped. When the engine is still warming up blipping the throttle gets almost instant response in increased rpm’s. However, after the engine is warm, blipping the throttle causes the rpm’s to hesitate or even reduce somewhat before revving enough so the clutch can be engaged. CV carbs take care of this problem with a vacuum-controlled throttle slide or another solution is an accelerator pump, but it appears the only option for my carbs (1976 Mikuni VM26SS) may be the size of the pilot jet. My research on the KZR forum has left me confused so I’m hoping to get further opinions from the forum on this matter.

I will close for now, and report back after the 1000 mile mark.