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Discussion Starter · #1 ·
I'm trying to get to the bottom of several issues with my 350K...one of those being that the right cylinder has fouled the plug...all carboned up like it is too rich vs. oily deposits. The right cylinder coughs, sputters, stumbles and sometimes backfires at small throttle openings right off idle or when running in any gear at small openings. Like commonly used following slow traffic or tooling around at 40mph in top gear. If I'm opening it up a bit more, the bike runs like a champ. It will run right up to redline without hesitation or stumbling. The problem is just at those times when the throttle is barely open at any rpm. Last night the right plug fouled. I cleaned it and swapped the plugs between cylinders (left plug is tan like it should be). With the plugs swapped, the left cyl ran fine, right was up to it's same old misbehavings.

I've had the carbs proffessionally sonic cleaned and replaced several o-rings on the jets. The diaphragms, last I checked, were in great shape. I've checked and rechecked the float levels with fuel on the bike...both carbs are the same. I've ajdusted the valves using the running/by ear method several times. I replaced the points and checked and rechecked the timing...also cleaned/checked the advancer. I've fidgeted with the cable settings, flippers, and air mix screws for hours, and think I've got them adjusted to the extent my untrained ears & eyes can get them dialed in. Seems no matter how I adjust the cable pulls, the right cylinder always stumbles off idle. The right carb air screw is set on the lean side...about 3/8 turn open...that's where it seems to idle best. Left cylider is probably about 5/8 turn open. All cables and slides lubed and parts are moving freely without interference. I cleaned the petcock sediment trap and screen. Tank is rust free & clean. Installed new fuel lines and clear filters...they are clean/clear. Drained/flushed the float bowls with the carbs on the bike to clear possible contamination. As for all the above adjustments, I have basic mechanical competence, but certainly no professional. So I've double checked a lot of this stuff and feel relatively positive I did it right, but I do make mistakes.

Things I have not checked...compression test. Plan to get that done soon at a shop. I don't have any tools for that. I have not checked the coil or plug wires, but I'd assume that they are ok since the bike runs sweet other than at small throttle openings. After the compression test, I plan to pull the right carb and reclean it with :?: ...not sure what's best to use to prevent killing the diaphragm.

So any ideas...any specific areas to focus on that right carb or other ideas?

Sorry for the lenghty post...just trying to provide as much information as I can for someone to assess the issue.
 

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Sensei
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First, your air/mixture screws are closed too much... the specs vary from 3/4 to 1 &1/8 turn out (depending on year) so they should be somewhere in that range..... Normal idle speed is around 1100 on the 350's....
A compression test is always a good idea........
 

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Discussion Starter · #5 ·
66Sprint said:
First, your air/mixture screws are closed too much... the specs vary from 3/4 to 1 &1/8 turn out (depending on year) so they should be somewhere in that range..... Normal idle speed is around 1100 on the 350's....
A compression test is always a good idea........
I was thinking that they were set a little lean, but that's where I ended up with the highest idle...thought that was the goal with setting them.
Don't take this the wrong way...not trying to debunk your suggestion, just trying to think it through. Wouldn't the carbon fouled plug possibly indicate that the right cylinder is running too rich rather than too lean?
 

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I didn't take it the wrong way... opening it up for more air leans out the existing over-rich condition......That screw controls how much air does NOT directly draw vacuum across the idle jet (how much by-passes the jet)
 

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Discussion Starter · #7 ·
The good news is that I had the compression checked tonight and all seems well. The left reads 160 and the right (the cyl. that's fouling) has just over 170. So no leaky/tight valves. based on the plug a quick look and listen and a description of the problem, the mechanic thinks I should try going down a size on the pilot jet or slow jet. He also suggested trying to advance the timing slightly on the right cylinder. I tried that with no noticeable difference in performance.

I also tried opening up the mixture screw another 1/2 turn which made it run worse.

I noticed that it runs better when cold...acts worse as it heats up, so seems to confirm the rich theory.

The bike currently has 35 slow jets, which looks like the smallest available from the places I've checked. any ideas where to find a slow jet smaller than 35? I figure I'll pull the carb tomorrow and make sure it is clean, and pull the jet to measure the dimensions to see if there is a smaller jet available.
 

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Sensei
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Try the 3/4 turn out (CCW from gently bottomed) positions on your air mixture screws....This is the minimum factory spec...... the #35 pilot jet is the smallest factory installed size on the 350's....
I'm thinking you have the air-mix screw too closed and have to set the idle screw high (butterfly is too open) to compensate...this allows (too much) fuel to enter as it is now feeding through the primary main jet (#70) and thus runs rich...... Back off the idle screws and re-adjust to about the 1100RPM idle with the air-mix screws....
If this does not work, you may have a defect in the carb itself that allows (extra) fuel past the jet o-rings (especially if they were very corroded before cleaning)...Unfortunately, the test is to try a different carb body on that cylinder.....
ALL this is/may be INVALID if you are not timed correctly beforehand.......Check it with a strobe.....
 

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Discussion Starter · #9 ·
66Sprint said:
I'm thinking you have the air-mix screw too closed and have to set the idle screw high (butterfly is too open) to compensate...this allows (too much) fuel to enter as it is now feeding through the primary main jet (#70) and thus runs rich...... Back off the idle screws and re-adjust to about the 1100RPM idle with the air-mix screws....

ALL this is/may be INVALID if you are not timed correctly beforehand.......Check it with a strobe.....
What you're saying makes sense. But yesterday, when I turned the mix screw out 3/4 turn, the idle drops and in fact I have to turn the idle up. That's how I arrived at the low setting...it idles highest at the lean setting...it is actually only 3/8 turn out. I'll try your suggestion again just to make sure.

As far as timing, it was spot on using the static method for timing, before i advanced it slightly at the mechanic's suggestion. But worth checking before I go tearing into the carbs. Lucky for me, Dad never threw anything out, so I have a strobe on hand. Problem is it has been so long since I've used one I don't remember how to hook it up, and the manual is no help. Here's a photo of the two leads on the strobe...what gets connected to what? Also, a picture of the old girl, for your enjoyment and so you don't think I'm making all this up to get attention. :lol:
 

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Most 350's I've dealt with get "air screw" settings closer to one turn out - with stock air filters and mufflers.
But 3/4 turn is not out of the ordinary.

If your "air screws" are not dialing near spec, that's an indication (to me) that the carbs aren't really clean, or the air screw itself is buggered, or something.
 

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Discussion Starter · #11 ·
well, I think I got to the bottom of this issue...I removed just the right carb, cleaned it, and that seems to have improved things. At the same time, I rechecked and adjusted the valves with feeler gauges and checked the timing, which was still spot on. There is still a really minor burble off idle, but I didn't do much to dial in the mixture screws, though I did get the cable pulls adjusted fairly precisely. that's much easier to do with the tank off. If I can't get the carbs dialed in better in the next day or so, I'll probably pull the left one to clean it as well. Thanks for everybody's suggestions. Can't count how many old bikes I've had that have given me problems that were solved by recleaning the carbs. I was in denial because I had paid $60 to the local shop...I took the disassembled carbs in to them for sonic cleaning. Seems the $20 bucket of cancer causing chemicals and an air compressor is the tried and true method. Funny thing was, the cleaning solution was hardly changed by the soaking carb, so we're talking miniscule amounts of dirt that caused this issue. Thanks again -
 

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Discussion Starter · #14 ·
Hey, thanks...but don't be fooled mine is a POS in sheep's clothing! Well, not really. It has many mechanical issues as is to be expected with a bike that old. At least it is all stock and all there and not rusty. One dissapointment I found after I brought it home was that someone had spraypainted the frame with just about all the components on it, so there are spots that didn't get repainted and spots of overspray. Wish I knew who that bonehead was! So maybe, just maybe I'll pull it apart this winter and have it powdercoated.

Your bike looks great...it looks like you've put a lot of time and effort into it. I would love for mine to look that way someday, but I get bored/lazy too quickly when it comes to cosmetic resotoration. Don't get me wrong...I can respect what you've done and wish I had the motivation to do the same, but typically if it doesn't make it run better/faster I don't get around to doing it!

I get up to Stamford, CT a few times a year to ride with a buddy...next time I'm there I'll let you know - maybe we can go for a ride.
 

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Discussion Starter · #15 ·
BTW...do you know where that ignition key relocation bracket came from? The one pet peeve I have with the 350 is the dumb location of the stock key. "Hey, I have a great idea! Lets mount the key close to the cylinder and header so it's really easy to burn your hand everytime you come back from a ride! That'll teach them to wear their gloves!"
 

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I'll tell you this, my restoration was very time consumming but it doubled as a stress reliever. As soon as the kids went to bed I went to work. It beat sitting on the couch all winter. As for the ignition relocator thing, it was there went i got the bike. I have seen a few around but haven't seen any for sale.
I'm always looking to go on a nice ride so look me up next time your in the area.

before my restoration I had similar "running" issue that you mentioned. I got a new exhaust, cleaned carbs adn rode it around. I had some puttering, back-fires and funny noises from the exhaust,and fouled plugs. All i did was tune in the fuel mixture screw. One side is one full turn out and the other is one and about 1/8 of a turn out. It runs like a top now.

Matt
 

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NE350 said:
I'll tell you this, my restoration was very time consumming but it doubled as a stress reliever. As soon as the kids went to bed I went to work. It beat sitting on the couch all winter.
That's exactly the situation I have. My wife works evenings so when the kids go to bed (between 8 and 8:30) I have the rest of the evening to myself. Can't watch tv or sit on the couch. Usually in the garage each night for an hour or two. That's the reason I picked up the CB400T, something to keep me busy in the evenings since the KZ was pretty much done.
 

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Discussion Starter · #18 ·
I have no kids...jeez now I really feel lazy for not being more concientious about cleaning her up. Actually been spending enough time trying to get it running right that the wife gets PO'd and need to make room in the garage for it by selling a car.

Herr, what kind of KZ do you have? I am a fan of the KZ650...used to have a '77 B that was in rough shape when that was all I could afford. Finally got sick of getting stranded and had some money so I bought a HawkGT that never let me down, but told myself I'd get a KZ again because I loved it when it ran. I decided on the 350 most recently, but still always combing craigslist for a cheap, but nice KZ. One of the underrated greats in my simple mind...I like CB750s, but the KZ650 would be my choice for a middleweight 4.
 

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You might check the float valve to be sure it shuts completely. If your float valve is letting a small amount of fuel past it all the time, you may in effect be flooding that cylinder at idle. At high speed, your motor may be using fuel faster than the rate of leakage, so the performance of the float in regulating fuel level works normally. If the float valve doesn't shut off the fuel completely, leaving your fuel cock open with the motor not running can result in fuel in your oil, fuel in the intake circuit, wet spot under the bike, and grey smoke from that cylinder's exhaust on startup.
 
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