ehenry
join:2007-11-07
Fairbury, IL |  [Help] Setting idle on 1979 Honda Cb750k
I need to set the idle for the bike higher. It idles extremely low to the point the bike dies. With a little throttle it runs great and just needs some adjustment. Is this on the throttle cable itself or does it have screws on the throttle body? |
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3SGTE
ST215W
Premium,MVM
join:2000-11-23
there
clubs: | 3 questions:
-Why is the idle speed low now? (i.e. are the carbs full of junk)
-Are the carbs balanced?
-Why a desire to fix it at this time?
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Striving for Parfection. |
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Its a Secret
Whatever
Premium
join:2008-02-23
U B Funny
1 edit | reply to ehenry
Have you adjusted the idle mixture on all four carbs? As well, 3SGTE  pointed out synced carbs are very important. |
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firephoto
KDE
Premium
join:2003-03-18
 ·Verizon west (ex G..
| reply to ehenry
There should be a single screw adjustment on the carbs that you can turn with your fingers and this will set your idle speed. It could be pointed out towards the side or back or down and might not be in the middle of the carbs but it should be obvious. Probably a black plastic knob but it could be metal too. Also access is most likely on the left side. Most hondas are similar but I'm not familiar hands on with your exact model but a '79 cb400 does have a hand adjustable idle speed so my guess is that your cb750 does too.
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Say no to JAMS! |
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ehenry
join:2007-11-07
Fairbury, IL
| said by firephoto :There should be a single screw adjustment on the carbs that you can turn with your fingers and this will set your idle speed. It could be pointed out towards the side or back or down and might not be in the middle of the carbs but it should be obvious. Probably a black plastic knob but it could be metal too. Also access is most likely on the left side. Most hondas are similar but I'm not familiar hands on with your exact model but a '79 cb400 does have a hand adjustable idle speed so my guess is that your cb750 does too. Thank you. This is the answer i was looking for. |
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ehenry
join:2007-11-07
Fairbury, IL | reply to ehenry
I just got the bike and cleaned the carbs, just needed to set the idle and i am ready to go. |
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Lurch77
Stop looking at me.
Premium
join:2001-11-22
+44.88-87.89
1 edit | I think the other people were just making sure you were fixing a problem and not fixing a symptom. How did you clean the carburetors? The reason I ask is because there are many things that can be done to throw off the synchronization of the four carbs. If you did a real cleaning, involving dis-assembly of the units, you should have them rebalanced. Without the proper tools and knowledge it can be near impossible to get the bike running again at peak efficiency.
We don't know you level of expertise, we are not trying to offend you.
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"On a motorcycle, you're penetrating distance right along with the machine. In a car you're just a spectator; the windshield's like a TV." ~ Kenny "Von Dutch" Howard |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to ehenry
said by ehenry :I just got the bike and cleaned the carbs, just needed to set the idle and i am ready to go. Did you sync up the carbs after cleaning? If not you would need this tool or you'd want to take it to a shop that has the tool and the tech that knows how to setup the carbs with it. 
Carburetor Synchronizer carb sync Gauge balancer CB750
»cgi.ebay.com/ebaymotors/Carburet···Q5fTools
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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Lurch77
Stop looking at me.
Premium
join:2001-11-22
+44.88-87.89 | After trying a while I finally bit the bullet and paid a mechanic a reasonable fee to do my Suzuki's carb balance. The bike never ran so good. |
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Its a Secret
Whatever
Premium
join:2008-02-23
U B Funny
 ·Shaw
1 edit | I always do my own on my '84 900 Ninja; but then again, I do all my own mech on my bike. *heart thumps!* 
I run the 1000's 36mm carbs instead of the stock 34's. Jets at 157.5; needles 3 shims up from stock. 270 KPH's @11,000 dead on. |
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ehenry
join:2007-11-07
Fairbury, IL
| reply to Lurch77
said by Lurch77 :I think the other people were just making sure you were fixing a problem and not fixing a symptom. How did you clean the carburetors? The reason I ask is because there are many things that can be done to throw off the synchronization of the four carbs. If you did a real cleaning, involving dis-assembly of the units, you should have them rebalanced. Without the proper tools and knowledge it can be near impossible to get the bike running again at peak efficiency. We don't know you level of expertise, we are not trying to offend you. I'm definitely not an expert. I did dis assemble the units (using a Hayne's manual for the bike). I did pay the local Honda dealer to make sure everything was up to par. The bike didn't run at all before I started so I'm not sure how the idle was before hand. |
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ehenry
join:2007-11-07
Fairbury, IL
| reply to ehenry
I adjusted the idle using the black knob screw in the middle of the carbs. It idles at a nice 1200RPMs. The motor sounds pretty good and the bike runs great. Is there a way I can test the performance from a novice stand point? I don't really have access to the high tech tools for this project. |
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Its a Secret
Whatever
Premium
join:2008-02-23
U B Funny | The bike should idle at 800 rpm or so... |
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Doctor Olds
I Need A Remedy For What's Ailing Me.
Premium,VIP
join:2001-04-19
1970 442 W30
clubs:
| reply to ehenry
said by ehenry :I adjusted the idle using the black knob screw in the middle of the carbs. It idles at a nice 1200RPMs. The motor sounds pretty good and the bike runs great. Is there a way I can test the performance from a novice stand point? I don't really have access to the high tech tools for this project. If you don't have the basic tool to work with syncing the carbs, I'd highly suggest taking it to Honda and pay them to properly sync the carbs. It just won't be right until that is done.
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What’s the point of owning a supercar if you can’t scare yourself stupid from time to time? |
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ehenry
join:2007-11-07
Fairbury, IL
| reply to Its a Secret
said by Its a Secret :The bike should idle at 800 rpm or so... Does it run better at 800rpm....the manual i have says to idle at 1250RPM but i couldn't accurately hit 1250. I should be able to adjust to 800rpms with no problem.
Also for Dr. Olds, what is a usual price for syncing the carbs. The dealer charged me $100 to check to see if a cleaned the carbs ok and see if everything is ok. I will call to see if this test was performed at that time. If not i will make sure i will get it in this weekend. I'm in Illinois and just want to make sure i'm not going to over pay for this service. |
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Its a Secret
Whatever
Premium
join:2008-02-23
U B Funny | 1250 rpm seems a bit high to me, but you can play with it. As for running better, I would idle it as low as I could while still running smoothly. |
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neonhomer
Honoray Mythbuster
Premium
join:2004-01-27
Edgewater, FL
clubs: | reply to ehenry
Look on the swingarm, there should be a label detailing what the idle spec is.
Low idle can cause oil pressure problems, and low charge. (Though most bikes don't charge, or charge very little at idle.) |
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Lurch77
Stop looking at me.
Premium
join:2001-11-22
+44.88-87.89
| reply to Its a Secret
It depends on the bike. My '93 Gixxer idles at 1200-1500 as per the factory service manual. I cannot for the life of me remember what the old 750's idle at, but 1200 sounds in the ball park for these decent revving 4 cylinder engines. My father has one that will be added to my bike collection when he is done riding. I have worked on it over the years for him. It's a '76 model.
ehenry, check out this site for a bunch of technical info and more. All dedicated to these old bikes. »www.sohc4.net/
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"On a motorcycle, you're penetrating distance right along with the machine. In a car you're just a spectator; the windshield's like a TV." ~ Kenny "Von Dutch" Howard |
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Its a Secret
Whatever
Premium
join:2008-02-23
U B Funny | Thanks for that info. |
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ehenry
join:2007-11-07
Fairbury, IL
| reply to Lurch77
said by Lurch77 :It depends on the bike. My '93 Gixxer idles at 1200-1500 as per the factory service manual. I cannot for the life of me remember what the old 750's idle at, but 1200 sounds in the ball park for these decent revving 4 cylinder engines. My father has one that will be added to my bike collection when he is done riding. I have worked on it over the years for him. It's a '76 model. ehenry, check out this site for a bunch of technical info and more. All dedicated to these old bikes. » www.sohc4.net/ Thanks for the website, this should help out alot. |
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