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Author Topic: Another Carb Observation CB750  (Read 815 times)

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Offline ekpent

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Another Carb Observation CB750
« on: August 25, 2011, 06:12:50 AM »
Tlbranth put one on, here is another that may help someone.
So yesterday I pulled a 75 750F out of storage to prep for sale.Had it running last summer. Hooked up my slave tank,turned on the valve and gas ran into the float bowls and promply started to squirt profusely out of the little brass ports at the carb mouth. on carbs 1 and 2. HHMM what the He&*.  Dropped the bowl all looked good. Pulled the 2 rubber overflow tubes off the bottom of the bowls and blew into them and they seemed clogged.Turned on the gas again and all was good with them off.
   The lesson here should be to not underestimate the importance of the carbs being able to vent and breathe.Check those tubes and the brass overflows inside the bowls to make sure all is clear and good.OK ,carry on folks  :P
« Last Edit: August 25, 2011, 06:14:37 AM by ekpent »
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Offline Magpie

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Re: Another Carb Observation CB750
« Reply #1 on: August 25, 2011, 07:32:30 AM »
Eric, also check that the overflow tubes are routed so they don't get pinched at the swingarm. The bike will run nice at idle but at speed will not. Cliff.
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Offline ekpent

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Re: Another Carb Observation CB750
« Reply #2 on: August 25, 2011, 07:40:19 AM »
Was that you or Johnie that posted that observation sometime ago when there were running issues associated with that.  Could be the cause of a few problems out there for the folks,I think we take the overflow tubes for granted.
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Offline Magpie

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Re: Another Carb Observation CB750
« Reply #3 on: August 25, 2011, 07:59:02 AM »
I can't remember Eric but I did just that, pinched the tubes, and it would run fine at low rpm's but be starved at faster engine speeds. it took some time to figure that one out. Sometimes learn things the hard way. Cliff.
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Offline Terry in Australia

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Re: Another Carb Observation CB750
« Reply #4 on: August 25, 2011, 07:15:51 PM »
Yep, good info men, and I've had the same issue, particularly with bikes that have sat for several years. First time it happened to me I couldn't work out why there was gas running out of the airbox, but once I took the float bowls off and blew the overflow tubes out with compressed air, it was all good! Cheers, Terry.  ;D
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Offline Spanner 1

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Re: Another Carb Observation CB750
« Reply #5 on: August 25, 2011, 07:59:37 PM »
One word; " Dirtdaubers'..... I'll have to explain that to our oversees readers ( and to our North of the Mason-Dixon line folks  too !)
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If your sure it's a carb problem; it's ignition,
If your sure it's an ignition problem; it's carbs....

Offline robvangulik

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Re: Another Carb Observation CB750
« Reply #6 on: August 26, 2011, 03:08:39 PM »
Quote from: Spanner 1 on August 25, 2011, 07:59:37 PM
One word; " Dirtdaubers'..... I'll have to explain that to our oversees readers ( and to our North of the Mason-Dixon line folks  too !)
Not really, we have Wikipedia too ;)
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Offline Deacon Thunder

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Re: Another Carb Observation CB750
« Reply #7 on: August 26, 2011, 05:15:40 PM »
That's an amazing tale. I have one recent experience that is probably related. While removing a whole raft of stuff from the 1977 CB750F in preparation of pulling the engine from the bike I removed the carbs. The jossling they got during remove left a large slimmey mess under the bike that came from the vent tubes. That alone might have cured some of my carb problems. Now I won't ever really know because it will all get rebuilt before it turns over again.
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