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Author Topic: 77 750F Supersport Backfire  (Read 685 times)

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Offline reliv77

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77 750F Supersport Backfire
« on: April 10, 2013, 04:56:08 AM »
When I first start the bike, I get a "Poping / Backfire". Once the engine warms up it goes away. Does this point to anything specific? Points? Plugs? Ect?
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Offline Vinhead1957

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Re: 77 750F Supersport Backfire
« Reply #1 on: April 10, 2013, 06:53:22 AM »
I would look at the plugs.  Look for deposits
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Offline iron_worker

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Re: 77 750F Supersport Backfire
« Reply #2 on: April 10, 2013, 07:43:59 AM »
Conditions that exist when cold and get better as the engine warms up point to a lean condition.

Is your engine hard to start? Take a lot of choke?

IW
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Offline 2wheels

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Re: 77 750F Supersport Backfire
« Reply #3 on: April 10, 2013, 09:34:49 AM »
Are you just bringing the bike out of storage?  How did you deal with the gas over winter?
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1970 CB750 K0 (I can't believe I tossed my duck tail seat in the trash 30 years ago)

Offline reliv77

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Re: 77 750F Supersport Backfire
« Reply #4 on: April 10, 2013, 09:44:30 AM »
Engine is very easy to start. Full Choke till it kicks. 30 seconds later with no choke.
I have been starting the Bike once a week on good gas over the winter. This problem I had late last fall also. Once on the road it runs great.
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Offline lucky

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Re: 77 750F Supersport Backfire
« Reply #5 on: April 11, 2013, 08:09:27 AM »
One of the idle jets may be clogged.

The F model had the smallest idle jets of all the CB750's.


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Offline reliv77

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Re: 77 750F Supersport Backfire
« Reply #6 on: April 11, 2013, 09:39:26 AM »
Lucky, Thanks for the reply. Do you think some Sea Foam might help with the Clog?
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Offline iron_worker

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Re: 77 750F Supersport Backfire
« Reply #7 on: April 11, 2013, 10:22:51 AM »
Just pull the idles out and clean them properly.

IW
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Offline Tugboat

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Re: 77 750F Supersport Backfire
« Reply #8 on: April 11, 2013, 11:19:09 AM »
+1 - the slow jets pull right out. Their passages are tiny, and I've never had any luck with anything but a good soaking & poking. A #9 E guitar string is the perfect fit.
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If it's worth doing, it's worth doing twice.

Offline reliv77

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Re: 77 750F Supersport Backfire
« Reply #9 on: April 15, 2013, 04:01:02 PM »
1) Tried a new set of plugs. Same "Start Up Backfire" till it warms up.
2) Next Try: "Just pull the idles out and clean them properly". I am a novice here. Could someone point to the "Idles"??? Where or what do they look like. Anybody got a Pic?

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Offline Stev-o

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Re: 77 750F Supersport Backfire
« Reply #10 on: April 15, 2013, 07:34:11 PM »
Look here, Lucky posted a good pic....

http://forums.sohc4.net/index.php?topic=106060.0
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'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........
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