Author Topic: 400/4 carb problem  (Read 2072 times)

0 Members and 1 Guest are viewing this topic.

84Olsen

  • Guest
400/4 carb problem
« on: August 24, 2008, 01:26:48 PM »
First off all, sorry for my bad spelling.

I recently bought a CB400, and she had some carb problems.
When she was cold with choke, idle was fine and god response, then with warm engine and choke off the idle would rise 2-3000 rpm and terrible response, if I gave her throttle fast she would stop. I really had to rev her high and then hit full throttle to get her going.

Then i bought Keyster carb kits, and did a carb rebuild. I noticed that the original slow jet was size 35, and the new one were size 40.

After a carb sync the idle was perfect :) Then a new problem had appeared, she was now to rich at slow speed. With about 1/8 throttle and 2500-4500 rpm she was now 8 stroking. So i could only drive on the highway  :-[

Then i put the original 35 jets back in, and now the idle is rough. When i give her throttle now she have a dead spot on about 1/8 throttle and she is blubbering when i drive in 20-30 mph. But she is rideable.

I been driving like this for a while now with the air mixture screw 3 rounds out.
The bike have a new airfilter and stock air system.
 
I want to put the size 40 slow jets back in to get the smooth idle again and move the needle clip one notch up to lean out the low throttle?     
Any other suggestions?

I love to ride this bike, bout i want her to behave  :)
   
« Last Edit: August 25, 2008, 07:42:58 AM by 84Olsen »

Offline mattcb350f

  • Hardly a
  • Master
  • *****
  • Posts: 1,625
  • 1974 CB350F
Re: 400/4 carb problem
« Reply #1 on: August 24, 2008, 02:58:02 PM »
Sounds like you may have the choke positions mixed up? Down, or fully clockwise is off, and up is on just to make sure  ;)

I think #40's are stock on the 400 so maybe try them again. Also make sure there aren't any air leaks on the carb boots.

 Matt.
1974 CB350F,  1980 CB125S,  1981 XL80S
Non Honda's: 86 & 87 Husqvarna 400wr's

My CB350F resto: http://forums.sohc4.net/index.php?topic=30467.0
Gallery at:
http://gallery.sohc4.net/main.php?g2_itemId=298318

Offline kghost

  • Really Old Timer ...
  • *******
  • Posts: 6,853
  • www.facebook.com/RetroMecanicaAustralia
Re: 400/4 carb problem
« Reply #2 on: August 24, 2008, 04:06:26 PM »
Did you adjust the air idle screws?
Stranger in a strange land

Offline kslrr

  • There is always a Blaster when there is a
  • Master
  • *****
  • Posts: 1,542
  • Raising her up right!
Re: 400/4 carb problem
« Reply #3 on: August 25, 2008, 05:12:49 AM »
3 turns out on your idle air screws sounds too much.  Should be more in the range of 1-1/2 to 2 if the 400 is like the 350.
Now  1972 CB350FX (experimental v2.0)
        1981 CB650c Custom with '79 engine (wifes)
        1981 CB650 engine
        2004 HD XL883C Custom
        1977 Yamaha XS750D (in progress)
Then 1972 CL175
        1964 Yamaha YGS-1T
No ride is a Bad ride

84Olsen

  • Guest
Re: 400/4 carb problem
« Reply #4 on: August 25, 2008, 07:41:03 AM »
I think i have the choke figured out, and I have tried to adjust the air mixture so that the blubbering would go away, and somewhere between 2,5 to 3 rounds gave me the best result. But now the no.4 cylinder is to lean (the spark plug is dark white) and the other 3 is black.

Its most probably something I am overseeing, but have any others here had similar problems with the keyster kits?

I think 2-2,5 rounds on the air mixture is the factory setup with the 40 low speed jet.
So its strange thats she is still to rich on 3 cylinders when I have put in the 35 slow jet and 3 rounds on the air mixture screws.

I will check the carb-boots soon, will i hear the idle rise if I spray WD 40 on them?, if they are leaking.

The honda dealer here sold me some D7ESL Spark plugs, and told me to use them, because the allowed ricer mixture.

Thanks for fast reply.

Cheers from Norway

84Olsen

  • Guest
Re: 400/4 carb problem
« Reply #5 on: August 25, 2008, 08:25:58 AM »
Some pics are fun :)
Before and after rebuild..