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Author Topic: 1978 CB 750f Fires but only a few times then quits  (Read 7866 times)

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Offline apetersonboy

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #25 on: February 15, 2014, 08:19:42 AM »
Quote from: Stev-o on February 14, 2014, 03:05:12 PM
Dont need no stinkin speedo. Is the bike running now??

It isn't running no. I hooked up the solenoid the correct way but it still just does the one solid click when I hit start. Doesn't the bike have to be in neutral to start? The neutral light never came on before the big FRY of the speedo, so maybe my neutral switch is bad?
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Offline LesterPiglet

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #26 on: February 15, 2014, 11:13:11 AM »
Try bridging the solenoid now.
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Offline MoMo

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #27 on: February 15, 2014, 11:44:34 AM »
I forget but does the motor turn over with the kick start?
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Offline Stev-o

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #28 on: February 15, 2014, 12:42:14 PM »
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline apetersonboy

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #29 on: February 15, 2014, 11:02:58 PM »
Quote from: MoMo on February 15, 2014, 11:44:34 AM
I forget but does the motor turn over with the kick start?

It does kick over yes. I'll try bridging it tomorrow.
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Offline apetersonboy

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #30 on: February 16, 2014, 01:06:05 PM »
Engine is turning over now with the button! I just need fuel line now and I can try to start it ;D ;D ;D
If it does start it will be the first time I've ever heard it run on something other than starting fluid in 2 years since starting my project! What size fuel line do I need? It looks like 3/8 and 1/4 but I don't know for sure. Anyone know off the top of their heads?
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #31 on: February 16, 2014, 04:06:27 PM »
Honda size from your Honda dealer.

Good luck!
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline apetersonboy

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Re: 1978 CB 750f Solenoid click but engine won't turn over.
« Reply #32 on: February 16, 2014, 05:09:11 PM »
Been cranking it over! It will fire for two or three hits and then quit trying. I don't know what else to do other than keep turning it over :P I will post a video so you guys can see.
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Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #33 on: February 16, 2014, 05:50:50 PM »
Also, my speedo is fully functional again  ??? .  I'm guessing it just wasn't getting enough juice! Does any one have any suggestions to get my bike to actually run? It just fires a couple times, sometimes three or 4 times but then it won't fire for a few more seconds. Fuel starvation maybe? The line I'm using is not from a Honda dealer and is just what I could borrow from a neighbor. It is a bit tight, but I figured fuel line needs to be tight on the fitting anyway to keep it on there. Any help would be appreciated Thank you
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #34 on: February 16, 2014, 06:38:36 PM »
Did you check your carb bowls with the drain screw to see if they have fuel? Sounds like fuel issue to me. Is your choke working properly? Might take a peak at your plugs and look for spark.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline MoMo

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #35 on: February 16, 2014, 06:50:44 PM »
On the line you borrowed from a neighbor-if it is not fuel line, get it off  and replace it with fuel line as gas will melt the plastic and block the jets.  Know that one from experience-the only time a Honda ever broke down on me was caused by gas eating the line the owner had put on...Larry
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Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #36 on: February 16, 2014, 08:25:14 PM »
I checked for spark using the arcing method. All plug caps gave me good spark. And no I have not tried checking the bowls for fuel, I will try that tomorrow. The line I have is indeed fuel line, I think it's just a little small.
I agree with you that it is probably a fuel problem. I'll report back tomorrow with progress!
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Offline Stev-o

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #37 on: February 16, 2014, 08:35:40 PM »
Have fresh fuel in tank?
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #38 on: February 16, 2014, 08:54:49 PM »
Yes, using an auxiliary tank filled with fresh gas.
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Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #39 on: February 16, 2014, 08:56:17 PM »
Here's the link to a video: https://www.youtube.com/watch?v=Cm30n7XMT2M&feature=youtu.be

I apologize for the terrible quality. Used my phone and its kind of a piece.
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Offline Stev-o

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #40 on: February 16, 2014, 08:59:30 PM »
Confirm the choke is closing all the way. Don't give it throttle til you hear it fire. 
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline apetersonboy

  • 1978 CB 750F SS
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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #41 on: February 17, 2014, 03:13:18 PM »
I got 1/4 inch fuel line today to see if that would help but it's too big and its too cramped to get a clamp in there so I'm back to using my 4.8 mm fuel line. I still think that is the problem.

I checked to see if all the carbs are getting gas and they indeed are.

I'm fairly certain choke is functioning as it should. The bike is having better fires with no choke at all.

Any thoughts?
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Offline Stev-o

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #42 on: February 17, 2014, 03:20:26 PM »
Quote from: apetersonboy on February 17, 2014, 03:13:18 PM
I got 1/4 inch fuel line today to see if that would help but it's too big and its too cramped to get a clamp in there so I'm back to using my 4.8 mm fuel line. I still think that is the problem.

I checked to see if all the carbs are getting gas and they indeed are.

I'm fairly certain choke is functioning as it should. The bike is having better fires with no choke at all.

Any thoughts?

Doubt fuel line is an issue but why buy inch size line for a metric bike??

I'd be checking my carbs......
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline apetersonboy

  • 1978 CB 750F SS
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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #43 on: February 17, 2014, 03:24:26 PM »
It was the closest thing I could find to what I've read is the normal size. No place that I went had metric sized. I'm just going to order the correct size tonight. Digger rebuilt my carbs so they should be all good to go I think!

One other thing is that I am not sure my boots from the airbox to the carbs sealed perfectly. They are old and deformed. But shouldn't it still be able to at least start and idle even without a perfect seal? I've heard of guys starting these engines without airboxes on at all just for trial and error purposes.
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Offline seanbarney41

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #44 on: February 17, 2014, 03:29:31 PM »
Are you giving it some throttle when it starts to catch?
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Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #45 on: February 17, 2014, 03:33:31 PM »
None at all.
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Offline seanbarney41

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #46 on: February 17, 2014, 03:35:55 PM »
Try givin' it some right when it starts to catch.
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If it works good, it looks good...

Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #47 on: February 17, 2014, 03:38:24 PM »
Will do, be back in a few.
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Offline apetersonboy

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #48 on: February 17, 2014, 03:38:44 PM »
Rhyme unintended.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 1978 CB 750f Fires but only a few times then quits
« Reply #49 on: February 17, 2014, 03:38:51 PM »
Hold the start button a little longer and give it a little throttle as it starts to fire. Adjust your choke too.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)
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