Go Back  RCU Forums > RC Boats > Speed - RC Nitro Boats
Reload this Page >

K&B 3.5 outboard help

Notices
Speed - RC Nitro Boats For all your rc nitro fuel burning boating needs.

K&B 3.5 outboard help

Old 03-06-2005, 10:03 PM
  #1  
DaveG55
Senior Member
Thread Starter
 
DaveG55's Avatar
 
Join Date: Jan 2005
Location: Stockbridge, GA
Posts: 8,275
Likes: 0
Received 0 Likes on 0 Posts
Default K&B 3.5 outboard help

Ok, I'm having a heck of a time getting this motor to run right. Admittedly, this is my first outboard but it really has me stumped. It still needs to be dialed in and that's where I'm having the trouble. It's an old style engine and it starts easily and seems to run well for about 1/4 of a tank. First off, K&B says that the initial needle setting should be 3 - 3.5 turns out. I cannot get this one to run if the needle is past 1.75 turns. At 1.75 turns it still acts and sounds like it needs to be leaner still but feels like it is getting close. At this point, after 1/4 tank, the engine starts to act up. It will not run at full throtle. 7/8's throtle is fine but open it up and it bogs and dies. It does not sound like it gets lean before dying. If I try to run wide open and I let completely off the throtle before it dies I can usually coax it to keep running by slowly feathering the throtle back up. When the boat is running (the 1st 1/4 tank) it gets up on plane quickly and is quite fast and seems to be trimed up pretty close to where it should be. I've already tried replacing all of the fuel line including the exhaust presure line, the pick up line in the tank and the tank stopper and the tank holds preasure. The carb (kind of copper in color) is a real simple affair with just a hs needle to adjust - nothing else. I've verified that the carb is secure and that the base o ring is good. I have not checked engine compression yet - no guage - but will take it to the lhs if need be.
Any suggestions....Please!!!
Old 03-06-2005, 10:37 PM
  #2  
Ron Olson
My Feedback: (1)
 
Ron Olson's Avatar
 
Join Date: May 2002
Location: Kalamazoo, MI
Posts: 18,688
Likes: 0
Received 20 Likes on 17 Posts
Default RE: K&B 3.5 outboard help

Take it richer. What is happening at around 3/4 of a tank is that the motor is building heat, more than it needs to run right. You really shouldn't have to run it leaner than 2-1/2 turns out.
What you have is the Gold carb, a very good one generally. Remove the needle also and check for any blockage in side by spraying some WD-40 or other spray in there.
The piston sleeve could be worn as you may suspect as when it warms up the fit gets looser losing compression. Pull the plug and see if there is a little tightness at TDC when turning it over by hand.
Old 03-06-2005, 10:49 PM
  #3  
piper_chuck
My Feedback: (12)
 
piper_chuck's Avatar
 
Join Date: Jun 2004
Location: Columbia, SC
Posts: 8,044
Likes: 0
Received 0 Likes on 0 Posts
Default RE: K&B 3.5 outboard help

Not sure what you're using for glow plugs. I discovered long ago that mine liked K&B plugs the best.
Old 03-23-2005, 06:28 PM
  #4  
joman2055
Junior Member
 
Join Date: Nov 2004
Location: san jose, CA
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
Default RE: K&B 3.5 outboard help

i have the same engine with a black carb. I have not run it yet. it was my dad's a long time ago now he wants me to get it to run. We were having a very hard time starting it but i will work that out later. When it comes time to replace the plug. which one should i get. would any cold plug meant for a .21 sized engine work?
Old 03-26-2005, 03:47 PM
  #5  
ob nut
My Feedback: (1)
 
ob nut's Avatar
 
Join Date: Mar 2005
Location: Cincinnati, Oh
Posts: 1,350
Likes: 0
Received 0 Likes on 0 Posts
Default RE: K&B 3.5 outboard help

Most .21 motors like high nitro 50%+ and a hot plug. K&B's older motors (black carb's) are either 12mm or 13mm. If it's a 12mm, you'll need to run the short plug. Other option would be to use 2 plug rings for using a long plug. Most people run the MC9's or K&B's HP1L...

Mark...
Old 03-28-2005, 01:09 AM
  #6  
joman2055
Junior Member
 
Join Date: Nov 2004
Location: san jose, CA
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
Default RE: K&B 3.5 outboard help

so if i put an MC-9 in there i need to put two washers on it? Whats the reason? It has clearance. Im JW. Thanks
Old 03-30-2005, 08:37 AM
  #7  
ob nut
My Feedback: (1)
 
ob nut's Avatar
 
Join Date: Mar 2005
Location: Cincinnati, Oh
Posts: 1,350
Likes: 0
Received 0 Likes on 0 Posts
Default RE: K&B 3.5 outboard help

The stock 12mm head was designed for a short plug. If a long plug is used, it "may" come in contact with the piston. Also, the long plug has an effect on compresion ratio. Hence the need for two washers.

I've run 12mm with a aftermarket head, which allows a long plug. When I get home tonight, I'll measure the thinkness of the two.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Manage Preferences - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.