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rhino69 · 08-08-2010, 09:13 PM

Picked this bike up and was told that the carbs had been gone through. tank and other parts were off the bike. Used a bottle as a temp gas tank changed the fluids and believe it or not the bike started up but had exhaust leak, fixed that and replaced the regulator rectifier and wanted to take it out for a test run. Bike wont rev over 4500 to 5k and seems to fall flat at that rpm, Replaced all carb insulators same problem. I do get an occasional backfire out the pipes and the idle has been rough to set. Need to get some Idea where to start to diagnose the problem. All help is appreciated thanks. If you need more info let me know.

seruzawa · 08-09-2010, 05:26 AM

Is the choke opening up fully?

Could that one of the myriad of hoses in the carb system wasn't re-connected properly. Or that the guy who "went through" the carbs screwed something up.

MOKE1K · 08-10-2010, 05:20 PM

Inspect the needles for wear and also check the airfuel mixture screws. Sounds like it's in the carbs.

The_AirHawk · 08-10-2010, 05:28 PM

Quote:

Originally Posted by MOKE1K

Inspect the needles for wear and also check the airfuel mixture screws. Sounds like it's in the carbs.

Not just the needles - look at the part of the Main Jet that the needles glide-through. Now that Moke jogged my memory, a friend that had a similar problem with a VFR 750 had excessive slide-wear and the needle seats were worn into ovals. IIRC he solved it by buying a "new" set of used carbs off fleabay, slapped 'em in, then he sold the bike - as the work and parts to "fix" the original carbs would be about 3X the bike's value.

On some carbs, the needle-guide is non-servicable; i.e. you throw them away when worn too far. I have no idea if this is such on the CB750.

08-08-2010, 09:13 PM	#1
rhino69 Registered Member Join Date: Aug 2010 Location: Chicago Burbs Posts: 1	81 Honda CB 750 not running right. Picked this bike up and was told that the carbs had been gone through. tank and other parts were off the bike. Used a bottle as a temp gas tank changed the fluids and believe it or not the bike started up but had exhaust leak, fixed that and replaced the regulator rectifier and wanted to take it out for a test run. Bike wont rev over 4500 to 5k and seems to fall flat at that rpm, Replaced all carb insulators same problem. I do get an occasional backfire out the pipes and the idle has been rough to set. Need to get some Idea where to start to diagnose the problem. All help is appreciated thanks. If you need more info let me know.

08-09-2010, 05:26 AM	#2
seruzawa Robby Join Date: Nov 2001 Location: 8501 ft. Posts: 16,803	Is the choke opening up fully? Could that one of the myriad of hoses in the carb system wasn't re-connected properly. Or that the guy who "went through" the carbs screwed something up. __________________ I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tanhauser Gate. All those moments will be lost in time, like tears in the rain.

08-10-2010, 05:20 PM	#3
MOKE1K Registered Member Join Date: Jul 2008 Location: Kalapana, Big Island Posts: 3,956	Inspect the needles for wear and also check the airfuel mixture screws. Sounds like it's in the carbs. __________________ "YOU CAN'T BOLT ON SKILL" "The only thing limiting your bike, is you" We survived Bush you'll survive Obama! "the most fundamental fact about the ideas of the political left is that they do not work. therefore we should not be surprised to find the left concentrated in institutions where ideas do not have to work in order to survive." --thomas sowell

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