'71 K3 350 Runs Well Under Load, Sputters When Cruising?

songpool5

songpool5

New Member
Joined
Jun 29, 2020
Total Posts
8
Total likes
0
Location
Minneapolis, MN, United States
(Sorry if this isn't the right location for this thread but I'm guessing it's a carb related problem)

Hey All,

I have been working on a K3 350 for the last year and feel like I'm REALLY close to having it in a place where I would feel comfortable driving it around town regularly. (AKA: I've replaced a LOT of parts) There is just one thing thing that is really stumping me right now and I was hoping for some thoughts and opinions!

Basically, it idles great and when I accelerate, go up a hill, into a strong wind etc. both cylinders pull strong and sound like they are running well. However, when I am cruising on flat ground at any speed or RPM (unless I'm going fast enough to use the wind resistance to make it run well ~60 MPH) the left cylinder sounds like it's only firing every other time or sometimes even worse. Does anyone know what could cause one cylinder to behave in this way?

  • Compression: ~180 on both sides warm with an inexpensive gauge
  • Ignition Coils: New
  • Ignition Control: those guys in Houston Collective Shockwave Ignition System
  • Spark Plugs: NKG-B8ES
  • Carb Float: 26MM
  • Main Jet Primary: 70
  • Main Jet Secondary: 105
  • Carb Boots: New
  • Air Cleaner: Stock
  • Battery: Lead Acid, 1 Year, Strong
  • Statically Timed, but Not Dynamically Timed

I've inspected the diaphragm closely and could not find any cracks/tears, but I was wondering if maybe the slide return spring could be out of spec causing too much or too little resistance. Is that even a thing? I'd love to hear any ideas you have and provide any more info that you might need!

Thank you
 
Hey All,

Checking back in with some resolution for my question. First of all, thanks for your advice. I failed to mention it in my original post but I did sync the throttle cable when installing the carbs, but your post gave me an idea. I fired up the bike and went for a ride, while cruising, I reached down and ever so slightly lifted the problem side idle tab to artificially open that side more and it really seemed to make a difference. I went home and changed the cable lengths so that the problem side pulls ever so slightly higher than the other and it seems like it's made a big difference to improving my problem. Does anyone see any issues with this or should I try to fix it in a different way?

Thanks!
 
It's tough to do the cable sync solo because it's all visual and you can't really watch both throttles at the same time. I had my granddaughter hold a finger on each idle screw and tell me which one moved first, took 3-4 adjusts to get it right.
The carbs will work w/o the air filters connected but not correctly. Really have to have those in place to evaluate the carbs.
 
I've heard quite a few bad things about the those guys in Houston ignitions not being ready for commercial use yet. Do you get the same thing happening when you have points?

Also you should do a plug chop while cruising and see if the plugs are wet. Do you have gas in your oil?
 
I've never run into it, but watched a video - where the throttle cable, because it splits from one into two, has an attachment piece, so - when you set the throttle cables that attachment point can be a bugger and mess with the setting. The throttle cables should really start moving at the exact same time, you've got a work around it sounds like, but the root of the problem is still there.

Anyone want to throw out a description of how the carbs are synced at 2,500 RPM? I have no idea how to do that. Currently, I'm just checking the back pressure by feel with my hands at idle, and making sure the cables move at exactly the same time. Not to take over the thread, but it is on topic.
 
I've been syncing the CL350 carbs with a Uni-Syn, Edelbrock #4027.
I use a long screw in the right switch pod, where that short bolt on the bottom is, to lock the throttle at @2500
Then I can adjust the cables to increase/decrease the air flow. Once they are even lock the nuts down,
Before doing this however I have already bent into alignment the mounting brackets so that the cables have direct centered pull and have set the cable slack so there's @10mm of rotational movement of the grip before the cables pull.
 
You must log in or register to reply here.
Back
Top Bottom