82 cb 750sc idiling problem

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82 cb 750sc idiling problem

killswitch750
I just bought a 82 750 and when I'm riding and pull the clutch and shift down to stop it wants to shut off it has new plugs and wires when I got the bike it had those pod filters on witch made it run like shit. So I got the original air box and it definetly runs better but it still wants to shut off any ideas?
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Re: 82 cb 750sc idiling problem

motogrady

there's a small knob, under the carbs, it's hard to get to.
try turning it in, a little at a time, between stops.
yes, it's hot, but it controls how far the throttle position on all 4 goes before it stops
when backing off.

the 4 airscrews under there, 2, maybe 3 turns out from seat on all 4, keep them the same.

that don't work carbs are clogged, they need a good cleaning.
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Re: 82 cb 750sc idiling problem

killswitch750
Are you talking about the black knob? I tried turning that and nothing happened but I was not moving it was just sitting. But what screws are you talking about on the carbs? Could you send me a pic. The kid I got it from said he took the carb off and cleaned it but he could have been just saying that. But I dumped a whole bottle of sea foam in the gas tank and filled the tank with the highest test gas I think it was 94 and ran the hell out of it. But its shooting out a little white smoke out of the muffler doyou know what that is? I was thinking the sea foam but iI'm not sure.
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Re: 82 cb 750sc idiling problem

killswitch750
In reply to this post by motogrady
The 4 screws your talking about on each carb if your on the left side of the bike are they the ones that are on the bottom right corner of the carbs?
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Re: 82 cb 750sc idiling problem

motogrady

yes, little brass screws.
one for each carb.
only ones you can get to without dropping the bowls (bottom half of the carbs)

thing is, the passageways from those screws to where the gas actually dumps into the airstream are real small.  they get clogged or gunked up, or heaven forbid something crystalizes in there,
it won't matter what you set the air screws to.  fuel won't get past the clog.

as far as the knob adjustment, something is off there.
screwing the knob in should be just like turnining the throttle a small bit.
if the rpms increase with the throttle, the knob should do it also.

I recommend cleaning them as per Tools thread on the subject, he has it on a sticky, carb cleaning for dummies I think.  One of the best procedures I've ever come across on the subject.
The kid that had it prob just glossed over them.

if it pulls good all thru the rpm range, but just won't idle, study that knob, how it's supposed to work
and how it actually works.  Some little tit or stop might be bent or missing.

good luck guy, keep the faith, and us updated too.
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Re: 82 cb 750sc idiling problem

motogrady

not to be a pain, but if you're adjusting these in the garage with it running,
put a house fan in front of the motor to keep it from overheating.
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Re: 82 cb 750sc idiling problem

killswitch750
OK I did adjust the black knob when I come to a stop now it idles good at about 2 I know that's a little high but still it will idle like that for about a min and start dropping and it drops fast. I love this bike I'm gonna keep the faith and the bike lol I've wanted a nighthawk for a long time. Well since we are talking my name is Paul I really appreciate all your advice next step I'm gonna find those screws on the carb if that don't work I'll be buying the carb kit with the new jets and gaskets
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Re: 82 cb 750sc idiling problem

motogrady
In reply to this post by killswitch750


Nice to meet ya Paul, Grado here.

Being a nighthawk, I'm not really sure on the carbs you have.
If they are CV, that is the slides are drawn upwards and open with the vacume (sp?)
they should work the same as mine.

You may be on the right track, yours are acting just like mine did.

Carbs..........remember, the airscrew and small jet inside the carb feed the bike
for idle and the first 1/4 turn or so of throttle, after that the needle in the slide and the main jet
feed it the rest of the way to wide open.  The knob just acts like you are keeping tension
on the throttle cable with your hand.

Coming off pods, who knows what size jets he has in there, when you knock them down you can check them, they're stamped with size.  They should be bigger than you need, airbox kinda chokes it.
If the PO knew what was up bigger jets went in with pods, and bigger still with 4x1 exhaust.
More air moving thru the motor, you needed to mix more fuel.
Too big, you run rich, black tip sparkplug.  Too lean, white tip plug.

I think I'm running 68s and 110s, on a bike with a 4x1 exhaust and a super secret modified air box.

good luck dude........grado
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Re: 82 cb 750sc idiling problem

killswitch750
Hey thanks grado can you send me a pic of the screws you are talking about on each of the carbs I think I know what ones your talking about but I wanna be sure.
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Re: 82 cb 750sc idiling problem

killswitch750



Is this the screw your talking about?
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Re: 82 cb 750sc idiling problem

motogrady
In reply to this post by killswitch750
I think thats just a drain screw, but like I said, you're on a nighthawk.

Pilot screws..........  http://honda-cb750-s.456789.n3.nabble.com/3-turns-out-td4038339.html#a4038342

Maybe take the time to download the manuel for your year, if it's here, if not it's out there somewhere for free.
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Re: 82 cb 750sc idiling problem

killswitch750
I think I see were the pilot screw is but it looks like I have to take the bowls off cause they can only go so far before they hit this thing that sticks out I'll take another pic and you tell me
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Re: 82 cb 750sc idiling problem

killswitch750
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Re: 82 cb 750sc idiling problem

motogrady

No, they shouldn't hit anything.
In the link to the other thread, they show 'em.
To adjust them the bowls stay on.

Heck 2 turns out and the pilot screw will only stick out from the bowl maybe 1/16th of an inch, if at all.
I just did it on a C model, it's tight in there for sure.
Study that link to the other thread, heck, it took a flashlight and me laying on my back
with a super small screwdriver.    It ain't easy guy, but it is possible.
It messes with you let us know, I give you guys a lot of credit, these are pretty complex machines,
heck, half the mechanics I know won't even touch them.