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Author Topic: CB400F Unusual Carb problem  (Read 3215 times)

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botheras

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CB400F Unusual Carb problem
« on: July 13, 2006, 01:47:55 AM »
Hi all,

I'm a newbie here and am helping out solve a prob on a CB400F.  The bike is BRAND NEW and never been on the road (77 F2), and is froma long time experienced ex - Honda dealer.   The issue is that the bike starts and idles beautifully, but when you open the throttle, it will bog and run very rich (black smoke) at about 3.5-4k rpm.  The air filter has been replaced, all the carbs stripped, float levels checked and float valves replaced.  The dealer is trying to source (at his cost) a new rack of carbs - but my ivew is that these are rarer than hen's teeth.  ANyone got any ideas, or could point us at a cutaway of the carb body to try to identify any air ways in the carb that could be blocked (lord knows what with)

Larry

Essex UK
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Offline flatblack

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Re: CB400F Unusual Carb problem
« Reply #1 on: July 13, 2006, 02:02:41 AM »
How in hell is there a brand-new 400F laying around? Does he have any more?

 ;D

Anyway, start with the easy/obvious stuff:

1.  Air jets: Are they correct for the carbs? Got springs? How many turns on them?

2.  Air box: Just take out the filter and let it breathe. While you're looking, check to make sure some salaryman's 1977 T-shirt didn't get stuffed in there...

3.  Ignition: Are all the jugs firing at 3.5-4K?

4.  Exhaust: Again, any rags stuffed where they shouldn't be? Any other blockages?

5.  Also, 3.5-4K rpm is right around where the carbs should be transitioning from the slow jets to the mains. If it's *that* rich, those might be some phat mains.

6.  Finally, is the choke linkage rigged properly?

HTH...and let me know about any more of those new 400Fs...

fb



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'76 CB400F
'78 CB750K
'04 CBR600F4i
'76 Yamaha RD400C
'79 Yamaha RD400F Daytona Special
'84 Yamaha RZ350
Dirt bikes?  Sure...

botheras

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Re: CB400F Unusual Carb problem
« Reply #2 on: July 13, 2006, 03:14:28 AM »
Quote from: flatblack on July 13, 2006, 02:02:41 AM
How in hell is there a brand-new 400F laying around? Does he have any more?

 

HTH...and let me know about any more of those new 400Fs...

fb





The bike was for the dealer's brother who died suddenly in 78, and there was a strong emotional attachment.  He was very fussy about who it was going to be sold to... and it was the only one!

The bike is completely stock, and your comments about it being on transition from idle jet to main jet is interesting, because that could be overfuelling at the mains.... 

Larry

LArry
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supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #3 on: July 13, 2006, 03:26:49 AM »
Nice find post some pics  ;)
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Offline GroovieGhoulie

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Re: CB400F Unusual Carb problem
« Reply #4 on: July 13, 2006, 08:16:31 AM »
Yes, the tribunal demands pics!  ;D
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eldar

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Re: CB400F Unusual Carb problem
« Reply #5 on: July 13, 2006, 08:22:06 AM »
It is a 77? Do you know if it has an accelerator pump on it? That may be set incorrectly and causing gas to flood in when you hit the throttle.  Does it run rich above that rpm range?
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supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #6 on: July 13, 2006, 08:24:03 AM »
Quote from: eldar, Master of the K8 Thunder! on July 13, 2006, 08:22:06 AM
It is a 77? Do you know if it has an accelerator pump on it? That may be set incorrectly and causing gas to flood in when you hit the throttle.  Does it run rich above that rpm range?


Have you been drinking  ;D
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Offline JHansen

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Re: CB400F Unusual Carb problem
« Reply #7 on: July 13, 2006, 08:37:07 AM »
I need clarification... is bike for sale now? I might be tempted to sell all my newer bikes for an opportunity to own a "0" mile 400!
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'76 CB400f -cafe'd out
'75 CB400f -future project waiting in wings
'03 Yamaha V-Star Classic
'90 Honda VFR 750

eldar

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Re: CB400F Unusual Carb problem
« Reply #8 on: July 13, 2006, 09:16:15 AM »
nope, I am at work right now.

See, I dont help with the 400s much cause I dont even know if it has an accel pump!

I dont know if UK models have that.
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Offline GroovieGhoulie

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Re: CB400F Unusual Carb problem
« Reply #9 on: July 13, 2006, 09:31:51 AM »
AFAIK, there never was an accel ppump on the 400.
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supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #10 on: July 13, 2006, 09:33:31 AM »
Quote from: eldar, Master of the K8 Thunder! on July 13, 2006, 09:16:15 AM
nope, I am at work right now.

See, I dont help with the 400s much cause I dont even know if it has an accel pump!

I dont know if UK models have that.

Do you have an issue with my comments? I thought it was a bit of light hearted fun, pm if you feel offended and I'll remove it.
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Offline cmorgan47

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Re: CB400F Unusual Carb problem
« Reply #11 on: July 13, 2006, 09:33:56 AM »
no pump.

are you sure the mains are right?
has it been synched?
« Last Edit: July 13, 2006, 09:36:21 AM by cmorgan47 »
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i love babies...
with a nice chianti sauce and a side of fava beans

eldar

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Re: CB400F Unusual Carb problem
« Reply #12 on: July 13, 2006, 09:40:34 AM »
Nope, well not really. See in the US we cant drink at our jobs. Now if I was in ireland, well that would be different! I think it is expected you go to work snookered!

Aside from that, I was just referring to an old post ;)
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supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #13 on: July 13, 2006, 09:46:20 AM »
Quote from: eldar, Master of the K8 Thunder! on July 13, 2006, 09:40:34 AM
Nope, well not really. See in the US we cant drink at our jobs. Now if I was in ireland, well that would be different! I think it is expected you go to work snookered!

Aside from that, I was just referring to an old post ;)

Old posts are just that   old posts    we all must move on and get a smile on our face if we can  ;)
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eldar

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Re: CB400F Unusual Carb problem
« Reply #14 on: July 13, 2006, 09:59:18 AM »
Hey I was just checking! ;D
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supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #15 on: July 13, 2006, 10:10:59 AM »
Quote from: eldar, Master of the K8 Thunder! on July 13, 2006, 09:59:18 AM
Hey I was just checking! ;D

It’s evening here so I’m having a cold beer and the guy’s thread has been hijacked  :o but I hope the confusion is sorted….cheers and I'll have another for you  ;) maybe 2
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eldar

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Re: CB400F Unusual Carb problem
« Reply #16 on: July 13, 2006, 10:46:11 AM »
Well thats mighty english of you! ;D
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botheras

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Re: CB400F Unusual Carb problem
« Reply #17 on: July 13, 2006, 11:09:04 AM »
Well,  you asked for it... Sorry the pics are LARGE but haven't had time to compress
http://www.photobox.co.uk/album/thumbnails.html?c_album=3486858

The new one is the red one... the "old" one is the yellow

Larry
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Offline JHansen

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Re: CB400F Unusual Carb problem
« Reply #18 on: July 13, 2006, 11:16:59 AM »
new one for sale??    ;D
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'76 CB400f -cafe'd out
'75 CB400f -future project waiting in wings
'03 Yamaha V-Star Classic
'90 Honda VFR 750

Offline cmorgan47

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Re: CB400F Unusual Carb problem
« Reply #19 on: July 13, 2006, 11:32:54 AM »
Quote from: _biffta_ on July 13, 2006, 10:10:59 AM
It’s evening here so I’m having a cold beer and the guy’s thread has been hijacked  :o but I hope the confusion is sorted….cheers and I'll have another for you  ;) maybe 2

you suck.
i was going to let it slide when you told me to sell my 400, but now that i know you're drinking, it's on.
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i love babies...
with a nice chianti sauce and a side of fava beans

supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #20 on: July 13, 2006, 12:27:11 PM »
Quote from: cmorgan47 on July 13, 2006, 11:32:54 AM
Quote from: _biffta_ on July 13, 2006, 10:10:59 AM
It’s evening here so I’m having a cold beer and the guy’s thread has been hijacked  :o but I hope the confusion is sorted….cheers and I'll have another for you  ;) maybe 2

you suck.
i was going to let it slide when you told me to sell my 400, but now that i know you're drinking, it's on.


What's on?
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Offline cmorgan47

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Re: CB400F Unusual Carb problem
« Reply #21 on: July 13, 2006, 12:32:12 PM »
Quote from: _biffta_ on July 13, 2006, 12:27:11 PM
What's on?

expect a chain whipping....i could really use a drink right now, so my envy is taking over.
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i love babies...
with a nice chianti sauce and a side of fava beans

supersport_CB400F

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Re: CB400F Unusual Carb problem
« Reply #22 on: July 13, 2006, 12:41:51 PM »
Quote from: cmorgan47 on July 13, 2006, 12:32:12 PM
Quote from: _biffta_ on July 13, 2006, 12:27:11 PM
What's on?

expect a chain whipping....i could really use a drink right now, so my envy is taking over.

Sorry to pi$$ you off CM  I guess I’ll have a beer for you also  for stealing your post.  ;)
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Offline cmorgan47

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Re: CB400F Unusual Carb problem
« Reply #23 on: July 13, 2006, 12:48:59 PM »
Quote from: _biffta_ on July 13, 2006, 12:41:51 PM

Sorry to pi$$ you off CM  I guess I’ll have a beer for you also  for stealing your post.  ;)



AAARRRRRRGGGGGGGGHHHHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!!

i really could use a beer.
and i'm as guilty as you on stealing the thread.

damn i could use a beer.
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i love babies...
with a nice chianti sauce and a side of fava beans
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