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Author Topic: 78 750F Won't run for more than a couple seconds at best.  (Read 1266 times)

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Offline apetersonboy

  • 1978 CB 750F SS
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78 750F Won't run for more than a couple seconds at best.
« on: February 18, 2014, 03:49:17 PM »
Hi, I just got my bike to the point of starting recently and am having troubles.

My carburetors are rebuilt and are jetted appropriately for open exhaust and the stock air filter. I am using clean new gas. When it cranks over it will run (at best) for about two seconds or sometimes longer than that. But other times it will only fire two or three times. When it does have it's good runs, it instantly dies when I give it any throttle at all. When I don't give it throttle, it still eventually dies. I am not using any choke, this has been getting me the best results. I have been trying different settings on the air idle screw, with varying results. Any help would be greatly appreciated.


Video:  https://www.youtube.com/watch?v=c1x_iMNw4go
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Offline apetersonboy

  • 1978 CB 750F SS
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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #1 on: February 18, 2014, 03:51:53 PM »
And yes this is the same post that's been going on in the Project Shop Forum, but I felt like it belonged here more so than there.
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Offline harisuluv

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #2 on: February 18, 2014, 04:09:01 PM »
Hi, sorry to hear about your troubles. 

I remember you contacting me about a partial rebuild, this is the kind of thing that is scary cause if I would have been the "tune upper" the end product is I would have handed you back a set of carbs that didn't work (possibly).  It would have been no fault of my own, but that's why I don't generally do that.

Can you give us some details on what the person did to the carbs first?  And what was decided was "appropriate jetting" etc.  Not saying for sure it's the carbs, but I would be lying if I said it wasn't something I would suspect at the top of the list.  Idle jets would be the first thing I checked.
« Last Edit: February 18, 2014, 04:24:52 PM by harisuluv »
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Offline Xxthegonzxx

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #3 on: February 18, 2014, 08:28:51 PM »
What's up broski! I also have a '78 cb750F ss. Just finishing my rebuild and all is well so far. Starts up pretty well but needs some final tweaking. Anyway, you need to do some more troubleshooting…The age old saying goes "Fuel, Air, Spark". It looks like you're getting fuel possibly but are you spark across all 4 cylinders? I would double check that just in case, but it sounds like you are. Check for any air leaks as well. I would triple check your carbs again though. Could be a fuel issue…maybe spray some starting fluid to help with the start then give a little throttle to help.
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Offline 750cafe

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #4 on: February 18, 2014, 08:33:31 PM »
Pilot jets and the circuits that feeds them CLEAN?

Eric
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Is there anything more fun than riding? They are between your legs and are quiet when you turn them off.

Offline nccb

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #5 on: February 19, 2014, 07:04:58 AM »
maybe fuel line is kinked?
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Offline apetersonboy

  • 1978 CB 750F SS
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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #6 on: February 19, 2014, 10:10:08 AM »
Got it going! Just a matter of messing with choke and air screw.
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Offline lucky

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #7 on: February 21, 2014, 10:43:39 AM »
Quote from: apetersonboy on February 18, 2014, 03:49:17 PM
Hi, I just got my bike to the point of starting recently and am having troubles.

My carburetors are rebuilt and are jetted appropriately for open exhaust and the stock air filter. I am using clean new gas. When it cranks over it will run (at best) for about two seconds or sometimes longer than that. But other times it will only fire two or three times. When it does have it's good runs, it instantly dies when I give it any throttle at all. When I don't give it throttle, it still eventually dies. I am not using any choke, this has been getting me the best results. I have been trying different settings on the air idle screw, with varying results. Any help would be greatly appreciated.


Video:  https://www.youtube.com/watch?v=c1x_iMNw4go

You will need to tell us what the jetting is.
Main jet.
Idle jet.
Slide needle position.
Does it have the accelerator pumps system?
Type of intake.
Type of exhaust.
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Offline strynboen

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #8 on: February 21, 2014, 12:00:14 PM »
have you taken pover to the coils from soloniode?..so it only gets ignision when starter runs.

..it must have power on coils vhen key are turned/and lights are on in oil and kontroll lamps


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Offline apetersonboy

  • 1978 CB 750F SS
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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #9 on: February 21, 2014, 02:24:54 PM »
You guys will probably laugh and call me an idiot but I probably deserve it. I called over a neighbor and he had in running within a minute of toying with the choke and air screw. Nothing wrong with the bike, the problem was the inexperienced owner. Thanks for the input any way!
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Offline LesterPiglet

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #10 on: February 21, 2014, 02:37:43 PM »
It seemed like that from your video.   :) Have fun with your bike.
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'Then' and 'than' are completely different words and have completely different meanings. Same with 'of' and 'have'. Set and sit. There, their and they're. Draw and drawer. Could care less/couldn't care less. Bought/brought FFS.


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Offline 750cafe

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Re: 78 750F Won't run for more than a couple seconds at best.
« Reply #11 on: February 21, 2014, 06:40:53 PM »
Quote from: apetersonboy on February 21, 2014, 02:24:54 PM
You guys will probably laugh and call me an idiot but I probably deserve it. I called over a neighbor and he had in running within a minute of toying with the choke and air screw. Nothing wrong with the bike, the problem was the inexperienced owner. Thanks for the input any way!

Good to have good neighbors. Especially if they are into bikes.  ;)   8)

Eric
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Is there anything more fun than riding? They are between your legs and are quiet when you turn them off.
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