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Author Topic: Engine Missing While at Cruising Speed (1981 Honda CB650C)  (Read 37383 times)

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Offline Hush

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #150 on: February 08, 2012, 11:29:10 AM »
Initially I made the same mistake with my 650 accelerator pump spring, had to consult the Clymer manual before I realised my mistake. :)
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline F16Viper68

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #151 on: February 12, 2012, 04:52:07 PM »
Okay, I've bumped up the stock main jets from 120 to 125.  I'm getting entirley too good at taking these carbs on and off.  Removed the seat, tank, carbs, rejetted, check the plugs, installed carbs, installed tank, and seat in about an hour.   8)

I was able to let it warm up and take it for a very quick ride around the block.  I really couldn't notice a difference but I know it was still cold.  Later I'll take it out for a longer ride. 

This is what the plugs look with with the idle mixture screws 2.5 turns out and the main jets at 120.







Click on the photo below for a 30 second clip of the engine post rejetting.  I can't figure out how to embedded a video from SmugMug. 



Dave...
« Last Edit: February 12, 2012, 04:55:34 PM by F16Viper68 »
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72500john

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #152 on: February 12, 2012, 05:42:17 PM »
you have done alot of good work here and had alot of good help. but dont dismiss this suggestion. dump some sea foam in the tank, take er out on the road and ride the p$%S out of it.  put it through it paces.clear everything out so to speak. my bike woke up after alot of carb/ ignition monkeying around after a good run.
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Offline F16Viper68

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #153 on: February 12, 2012, 07:13:16 PM »
Quote from: 72500john on February 12, 2012, 05:42:17 PM
you have done alot of good work here and had alot of good help. but dont dismiss this suggestion. dump some sea foam in the tank, take er out on the road and ride the p$%S out of it.  put it through it paces.clear everything out so to speak. my bike woke up after alot of carb/ ignition monkeying around after a good run.

Well I know the tank and carbs are clean but It certainly wouldn't hurt to run some SeaFoam through the bike.  Thanks for the idea. 

Dave...
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Offline grcamna2

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #154 on: February 12, 2012, 07:54:20 PM »
Listened to the vid...the plugs will tell the story ;) :) :)
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75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
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Offline ThomasD883

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #155 on: March 07, 2012, 10:41:56 AM »
I just had a light bulb go off , those little rubber tubes are the vents for the carbs, supposed to be routed to the air box right? I am having the exact same high load missing after rebuilding my carbs and I removed those tees. My train of thought tells me that the vacuum operated carbs need the vacuum in the bowl as well. I know from experience that the only reason fuel comes out of those is if the bowls are over flowing, 2 leaky float needles gave the lesson. So they have to be there for.a reason right? Any thoughts?
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Offline grcamna2

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #156 on: March 07, 2012, 11:00:39 AM »
ThomasD883,
       I believe those tubes should be Routed over the top of the airbox..rather than connected to it...but I'm not 100% sure about that.....
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75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline Mainerider

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #157 on: March 07, 2012, 11:31:52 AM »
I'm  on my CrackBerry and reading a lot of posts gets tedious so if I'm revisiting this suggestion...I have an '80 in the stable (slide carbs) and a friend has the CV carbed '81. He had similar issues so we eventually pulled the air box cover off and it was like night and day in the upper rpm range. Other CV- carbed 650 owners have had similar results w this freer-breathing set-up. We fabbed up something to keep the air filter secure and all has been good. If you've eliminated fuel and electrical, it may be worth a try on yours. Good luck.
« Last Edit: March 07, 2012, 11:34:17 AM by Mainerider »
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Offline ThomasD883

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #158 on: March 07, 2012, 02:10:22 PM »
I just got back from a road test with the filter out, problem solved. Thanks mainerider!! ;). Does anybody know what causes this, I'm in the market for a reason. While I'm here with the 650 guys, if anybody has a right hand control set you can part with pm me a price, I went down last fall and tore it to 4377
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Offline Mainerider

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #159 on: March 07, 2012, 02:21:26 PM »



Glad to help out.  I believe that the oem airbox construction is too restrictive and not well-designed for proper airflow, a rare Honda misstep.  I think I have a very nice control set downstairs; i will look when I return.
[/quote]
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Offline Hush

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #160 on: March 08, 2012, 11:41:21 PM »
Good for you, I found this was my first major problem on my 79 650, turned out the air filter was about 6 years past it's change date and by running it with the side plate off and two big penny washers holding the filter in it ran a lot better.
From that I learned that even if the air filter looks mint, if I don't know it's history it gets dumped.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline fmctm1sw

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #161 on: March 09, 2012, 06:43:09 AM »
Dave, how did this turn out?
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Quote from: 754
Dude is that a tire ? or an O-ring..??

Quote from: inkscars
This is not a pod thread
This is not a #$%* on my vacuum gauges thread
This is a help or GTFO thread.

1973 CB350F
1973 CB350G
1975 CB550K
1983 GL650I
1973 CB750K3 (http://forums.sohc4.net/index.php?topic=92888.0)
1984 Kawasaki KLT-250 (AKA 3 wheeler of death)
1994 Honda TRX300
1999 Honda TRX250

Offline F16Viper68

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Re: Engine Missing While at Cruising Speed (1981 Honda CB650C)
« Reply #162 on: June 25, 2012, 05:49:49 PM »
Quote from: fmctm1sw on March 09, 2012, 06:43:09 AM
Dave, how did this turn out?

Due to work I haven't had much time to work on this bike.  It still hesistants in 4th and 5th gear around 4k RPM but not so much 1st thru 3rd.  I'm going to wait until the Fall when I strip it down to the frame for powder coating to further explore this issue.  Right now it's tolerable.

Dave.... 
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