Honda CB-750 '78 running slow

[crossculturesbc]

Working on a Honda CB-750K for a buddy and I'm running into issues I could use some help with.  The carbs have been tuned and synch'd but at full throttle it's going no more than 40/42 mph.  This is unloaded. No glaring issues. I'm open to any suggestions.  So far I've got one who suggested checking exhaust to make sure it's flowing clear and no membrane has deteriorated.  Any help would be appreciated.  I'm trying to get a disabled friend of mine back on the road and this is beyond my knowledge.  Thanks.

[Hellbilly429]

What else have you checked on it and what exactly is it doing when it is running and only going 40mph? And is it stock or modified?

[crossculturesbc]

I'm not good with engine work itself so a local shop cleaned the carbs, synch'd them and put everything back together.  The exhaust smell suggests they're running rich although I'm not sure if that would affect it or not.  We've done nothing else to the engine or drivetrain which is stock, but in good working order.  Regarding what we're doing, once we got all of the parts together and got it all up and running, we took it out for a spin to make sure it shifted well, switches and things worked, etc.  Going through the gears, the bike would only make it up to 40 mph at full throttle (this is post cleaning mind  you).  

That's it.  Some have suggested plugs, some have suggested several carb tuning options.  I'm open to anything, just wondering if this made more sense to those who had more experience.  Thanks for your time.

[Piute]

   There are lots of ?s for this but Give ya this 1 ,can you take the rpm's up to 8-9K setting still,and can ya while on a load on hwy.?

[Hellbilly429]

Have you checked the spark on each plug? All pipes seem warm after running or do you have a cold one? Is it spitting and sputtering? Does it wind up slowly when you hold the throttle open? Does it act like it wants to quit running? Have you checked the plugs to see if the bike is running lean or rich? Is the charging system working correctly? Could literally be anything causing your problem, just need more info is all.

[crossculturesbc]

Thx everyone. We're trying a number of those things now. Plugs are sparking but we're replacing to be on the safe side. Also condesers were bad so we're getting those in soon. Hopefully that'll fix it. Changing timing does not appear to be affect it. I'll post if something fixes it. Thanks for your help

Sent from my iPhone

On Nov 2, 2012, at 7:39 PM, "Hellbilly429 [via Honda CB750'S]" <[hidden email]> wrote:

Have you checked the spark on each plug? All pipes seem warm after running or do you have a cold one? Is it spitting and sputtering? Does it wind up slowly when you hold the throttle open? Does it act like it wants to quit running? Have you checked the plugs to see if the bike is running lean or rich? Is the charging system working correctly? Could literally be anything causing your problem, just need more info is all.

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