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Discussion Starter · #1 ·
Having a problem with an idle so low that the bike won't keep running. Using the idle speed knob on the left side of the bike either gives an idle too high or too low even with making small adjustments. Using the choke will keep the bike running but that doesn't solve the problem. I assume an adjustment needs to be made, but what?
 

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Pilot jet sounds about right. It likely won’t idle because it’s only idling on one carb, until you crank the idle high enough that it’s running on the needle
 

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Discussion Starter · #5 ·
Thanks to every who responded. What about the Pilot Air Screws? What affect do they have? Could they be turned in too much or out too much?
 

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If the lead caps have been removed then they certainly could be out of adjustment. They’re covered up from the factory. If they’re not covered then turn then all the way in (gently) and then back them out 2 1/2 turns out. The default factory setting is intentionally a little lean.
 

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Discussion Starter · #10 ·
The covers (plugs) on the screws are long gone. I bought the bike used and they were gone when I got it.
 

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Discussion Starter · #11 ·
Concerning how many turns out on the screws: The manual says 1 5/8 (I saw the comment about lean from the factory, I'm guessing that's true). I've also seen 2 and now 2 1/2. Any consensus on the best number?
 

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Discussion Starter · #12 ·
Also, I've seen replacement screws for the Keihin carbs on other bikes which have knobs on the ends to make adjustment easy. Are these available for the VN750?
 

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2.5 has been standard on most carbs, kawi just went for lean. I'd try 2.5.

I think those knob screws were available, but it's not an adjustment that needs done very often.

Count the turns as you tighten, so you'll know where it was.
 

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Concerning how many turns out on the screws: The manual says 1 5/8 (I saw the comment about lean from the factory, I'm guessing that's true). I've also seen 2 and now 2 1/2. Any consensus on the best number?
I also noticed that 1 5/8 turns in the manual when doing my rebuild. But even tho my pilot screw covers were missing, everything on my bike seemed bone stock, and the carb gaskets looked like they had never been opened when I took them apart.

Just to let you know, my pilot screws were set at 2 3/8 turns, and I used that on the rebuild, and it idles perfectly. My idle screw stock setting was two-threads thru the bracket, and it only needs to be moved a fraction to get any effect, so I am very pleased with these settings.

So yeah, you likely need to follow Spockster's advice. He thinks a lot just like the real Spock, and because your fueling is ok at mid-range and high-throttle, then he surmised that your other jets and the jet passages are not clogged, so he recommends going after the pilot jet circuit first.

I have all the detailed and labelled photos from my rebuild if you are curious about anything in the process.

Another FYI: My bike had sat for 7+ years so it was clogged solid with black gunk, some was even hardened. I pulled out my rear carb pilot jet and it was so bad that even using a thin wire would not push out the hardened gunk, so I replaced the jet. Not saying this will happen to you, just my experience.
 

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Also, I've seen replacement screws for the Keihin carbs on other bikes which have knobs on the ends to make adjustment easy. Are these available for the VN750?
I was lusting after those thumb-adjustable pilot screws too on my initial rebuild. It is not easy getting a flat-blade up in there. But like Spockster says, once you get the pilot screws set, then you rarely/never have to touch them afterwards. But yeah I think that is a cool thing to have, I researched them and found them but didn't try them.

Most importantly: You can pull the jet chamber cover off the bottom of the carbs without removing them from the bike (7mm hex screws). Then, you can use a mirror to look up in there, and use a properly fitted 90-degree screwdriver to carefully and firmly unscrew the pilot jet. It is somewhat meticulous, but way way better than pulling the carbs out of this bike.

Sea Foam works best in the piston chamber, it is good in the fuel flow system but takes time. (I actually pull off the fuel lines where they attach to the carburetor body and then inject my float chamber with ChemTool and let that sit overnight, then use the drain plug to let it out, but that is a little scary since ChemTool attacks rubber, so you might want to have replacements on hand for the jet chamber o-rings (the manual calls it the drain chamber, P/N 92055-1290).

But for me, if there was an issue bad enough to clog a fuel jet, then I would want my entire fuel system flushed out and cleaned. Whatever clogged it could clog other things. Don't know how meticulous you are, and as Spockster pointed out it may be limited to the pilot jet in your case.

If you don't want to mess around and wait, then take action on the most-likely fix scenario: pull off the jet chamber cover, pull out the pilot jet, see if it is clogged, clean and re-install. See how that goes, do the other carb if necessary.

If you have tons of energy and time and want to do a job that will suffice for years, then do the whole fuel system: take off gas tank, disassemble petcock and clean/flush it out, drain and clean out tank, and then pull carbs off and disassemble them, clean them thoroughly, blow out with compressed air, then rebuild or re-assemble. This is a very major undertaking, to be very clear.
 

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What the heck, I dug up one photo showing what it looks like up in the jet chamber. If you want more info, I am a virtual fountain of it. :)

53457
 

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Discussion Starter · #19 ·
An update: I turned the pilot screws all the way in then back out 2 and a half turns. I drained the gas out of both carbs (the drain screw on the bottom of course) and filled both carbs with Gumout and let set for a few days. Moments ago, at full choke, I started it up. It ran for a short time, dropped form 3,000 RPM to 2,000. Then it went down to zero and now I can't get it to start for nothing. I did check each drain screw and gas came out so it appears to be getting fuel.
 

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An update: I turned the pilot screws all the way in then back out 2 and a half turns. I drained the gas out of both carbs (the drain screw on the bottom of course) and filled both carbs with Gumout and let set for a few days. Moments ago, at full choke, I started it up. It ran for a short time, dropped form 3,000 RPM to 2,000. Then it went down to zero and now I can't get it to start for nothing. I did check each drain screw and gas came out so it appears to be getting fuel.
Sounds like it might have flooded.
 
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