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Offline SurfinBird

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What Happened?
« on: October 28, 2012, 04:24:10 PM »
'78 CB750F SS

After a bad week of dead batteries and broken throttle cables I finally got to putting her back on the road after a couple weeks of sitting. At first look, the throttle feels stiffer than before. The big problem is that she doesn't have the torque she had before the throttle cable swap. The engine is a bit louder and off the line she's slow and labors to reach speed, forget going hard off the line, she stalls. I haven't gotten over 50, and that was down hill. Before the battery died she was quick off the line and ran great, there was no performance change after I put in a new battery. The throttle cable snapped the day after the battery swap. After the throttle cable swap is where I got the difference. Everything appears to be working fine. Am I missing something? If it's not a cable problem what's my first thing to look at?

Thanks
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Offline ekpent

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Re: What Happened?
« Reply #1 on: October 28, 2012, 04:29:09 PM »
Did you have the gas tank and lines off to do the cables. Is it all clean inside. Sounds like maybe a fuel starvation issue possibly among many others.Check all 4 pipes for good heat also,might have a fouled plug if the battery was going bad.
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Offline SurfinBird

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Re: What Happened?
« Reply #2 on: October 28, 2012, 04:32:22 PM »
Fuel starvation could be an issue. I cut a new fuel line and the new one is a bit longer and may have a uphill kink. I'll look at that, that would make sense. All the pipes were hot, 1/4 seemed a  bit cooler. Checked the plugs, looks like I was running rich.
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Offline ekpent

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Re: What Happened?
« Reply #3 on: October 28, 2012, 04:35:17 PM »
As the fuel is gravity fed they can be a little fussy on the routing. Hope its that simple for you.
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Offline SurfinBird

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Re: What Happened?
« Reply #4 on: October 28, 2012, 05:02:32 PM »
That would have been to easy. The line was long for sure and did have an uphill kink, but little change. Is there an adjustment on the cable I should have made? It feels like when it's wide open, there is still more room to open up. I have some room towards the carb side of the adjusting nut. Would adjusting the nut to the bottom of the thread give me more travel on the cable?
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Offline Tintop

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Re: What Happened?
« Reply #5 on: October 28, 2012, 05:26:01 PM »
The cables are adjustable.  1st open to WOT and release the throttle, it should snap closed.  If it's slow to close you have a routing issue, which has to be corrected first.  Then back the adjuster(s) off and make sure the carbs are closed (idle position), then adjust the slack out until there is just a small bit of free play at the throttle.  Then open the throttle to WOT position, hold and check that the carbs are fully opened against the stop. 
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1980 CB750F (project)
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1976 CB400 SS - stock / BOTM 04/11 (SOLD)
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77 CB550 Cafe build
550/750 Filter Thread
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Offline SurfinBird

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Re: What Happened?
« Reply #6 on: December 08, 2012, 11:46:37 AM »
The throttle cable is routed correctly, slides are opening all the way when I open it up and snapping closed, no problem. Any thoughts on what might be making it run sluggish? I replaced the plugs and adjusted the points gap. I thought it might be the clutch cable being off, but it's fine. Where to check now?
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Offline jamesb

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Re: What Happened?
« Reply #7 on: December 08, 2012, 11:55:23 AM »
Have you Checked your airbox boots you may have bumped it while putting on your cables. just a thought.
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Offline SurfinBird

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Re: What Happened?
« Reply #8 on: December 08, 2012, 12:06:06 PM »
I pulled the airbox and made sure to get all the boots on correctly. Could putting a new air filter help? Its really bogging, like 20mph wide open in 1st and gutless
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Offline jamesb

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Re: What Happened?
« Reply #9 on: December 08, 2012, 05:31:42 PM »
check your points wires also you mentioned 1/4 pipes was not as hot they could have come disconnected I have had that happen
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Offline TwoTired

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Re: What Happened?
« Reply #10 on: December 08, 2012, 06:22:20 PM »
Check the head pipes for even heating (...more or less).

Sounds like you have some plugged fuel jets.
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline stickman

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Re: What Happened?
« Reply #11 on: December 09, 2012, 06:10:57 AM »
Check your coil connections.  They are located in the path or near enough for throttle cable routing that you may have moved them enough to disturb the connections on the plug ins.
Could explain why 1 and 4 are not running correctly.  Good luck.
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Ed Jones, Lenoir, NC
1971 CB750, 1994 Kaw police bike KZ1000

Offline Killer Canary

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Re: What Happened?
« Reply #12 on: December 09, 2012, 09:02:39 AM »
Maybe you accidentally engaged the choke?
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Offline SurfinBird

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Re: What Happened?
« Reply #13 on: December 09, 2012, 10:36:44 AM »
I was wondering about the coils. I will check the connections, I'm pretty clueless on the ignition system.
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Offline jamesb

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Re: What Happened?
« Reply #14 on: December 09, 2012, 11:02:34 AM »
Check your points also mine did that on my cb550 it was doing exactly what your is doing. I took the points cover off and found out the little tip on 1/4 that rides on the cam lobe had broken so it wasn't firing on those to very good. But with your pipes running cooler than the others it could be carbs or ignition timing. 
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Offline SurfinBird

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Re: What Happened?
« Reply #15 on: December 09, 2012, 05:06:19 PM »
You guys rule. I would have thought of a million other things before I thought about a loose wire. Yes, black wire w/ white stripe came loose on the 1/4. Runs great, i think I might have honked up the timing messing with the points, but its getting close to a 3000 tune up anyways. Thanks again guys
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