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Idle mix adjusting tool

  • Thread starter Thread starter Greg O.
  • Start date Start date
G

Greg O.

Guest
I know I have seen this come up before, and did a search but could not find what I was looking for. The idle screws on the bottom of the carbs are a bear to get to with just about everything I can think of to use. Espeically #2 and 3 on my 750L. I remember someone using a piece of hacksaw blade. I tried that without much success. Any ideas what works well? It is tough when the engine is off, and even worse while it is running.

Thanks,

Greg
 
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Greg O. said:
I know I have seen this come up before, and did a search but could not find what I was looking for. The idle screws on the bottom of the carbs are a bear to get to with just about everything I can think of to use. Espeically #2 and 3 on my 750L. I remember someone using a piece of hacksaw blade. I tried that without much success. Any ideas what works well? It is tough when the engine is off, and even worse while it is running.

Thanks,

Greg
Click to expand...

Short screwdriver (2") with a wide handle. And a glove.
 
Would it make a differance in the mixture if the airbox was removed, because that would make it easier to reach the two inside carbs.

Greg.
 
Since you said "pilot screws on the bottom of the carbs", you have VM carbs because CV's dont have those screws. The fuel pilot screw setting for a stock airbox/exhaust on a VM 750 is 1 3/4 turns out. Air screws set 2 turns out. There is no reason to try to set them with the engine running.
They should all be set the same. I always set mine before installing the carb rack. However, a small mirror under the float bowl, a flashlight and a 1 1/2" long screwdriver will work just fine for access, but your hand will block your vision enough that accurate setting is nearly impossible. Take the rack off and set them precisely. It matters.

But looking at other comments, now I think you may be misnaming what it is you want to adjust. There are no mixture screws on VM carbs and there is no fuel pilot screw to adjust on a CV carb. What year of 750?

Earl



Greg O. said:
I know I have seen this come up before, and did a search but could not find what I was looking for. The idle screws on the bottom of the carbs are a bear to get to with just about everything I can think of to use. Espeically #2 and 3 on my 750L. I remember someone using a piece of hacksaw blade. I tried that without much success. Any ideas what works well? It is tough when the engine is off, and even worse while it is running.

Thanks,

Greg
Click to expand...
 
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Actually they are pretty easy, any auto parts store has a short screwdriver. Get one with a blade that fits the screw properly. Airbox removal will change things, but you don't need to adjust these with the engine running. It's not the idle mixture, it's just above idle, when you barely crack the throttle. The idle mix is the screw up on the side of the carb, adjust this one for highest idle. The ones underneath, set them all the same, test ride. These only effect the mixture when it is barely cracked open. Ride around at something like 10 - 20 mph for a while, it should have good crisp throttle response in this range, If you open the throttle more than an RCH it is running on the needle position, not the fuel screw... look at a spark plug. If it's too lean, turn them all out a little, too rich, turn them all in. Keep the screws all even as well as you can.
 
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I made a good fitting device for this purpose from a shorty flat driver tip (from one of those cartrige screwdrivers) which I JB welded into a mar-connector (for joining electrical wires). Works nice. You can fit it into the smallest spaces and is easy to hold in place while turning. You could even mark it with a reference point to help keep track of the # of rotations.
 
I took a 6mm bolt with built in washer and ground down the threads to a little flat head. You can look at the side of the flat head as it turns to count half or quarter turns. The washer part of the bolt sits just below the bottom of the mixture hole. You can even clear the cam chain tensioner. The clutch cable gets in the way sometimes on #2, but if held out the way with one hand the screw can be adjusted with the other.

If I'm having a good day with hand dexterity I can access #2-#3 without using a 10mm socket attached with electical tape.
 
79 750L. VM carbs. I was under the impression they needed to be set for best idle, just like the air screws. I will give them all 1 3/4 turns, then re-adjust the air screws.

THanks,

Greg
 
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Earl, you are right, it isn't that hard to pull the rack, and that will make it much easier to set them all the same to start with.

Thanks again,

Greg
 
After owning a 79 vm carb 750 for years that had a stock airbox and exhaust, I can say with reasonable certainty that it will idle best and run smoothest with the pilot fuel screws set to 1 3/4 turns out and the air screws set 2 turns out. :-)
You want the pilot fuel screws set between 1 3/4-1 7/8ths turns out and the air set between 2 and 2 1/8th turn out.
Thats the "sweet spot".

Earl

Greg O. said:
79 750L. VM carbs. I was under the impression they needed to be set for best idle, just like the air screws. I will give them all 1 3/4 turns, then re-adjust the air screws.

THanks,

Greg
Click to expand...
 
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Earl,

Thanks, I can't wait to give it a try, but it is time to go to bed for now.:cry:

Greg
 
earlfor said:
You have a stock airbox and exhaust, 79 model 750 with vm carbs and it will not run on those settings?

Earl
Click to expand...

'78 750, stock box and pipes. about 1 1/4 turn out works the best.
Right now it won't run because the pistons and cylinder are on the kitchen table.
 
Hmmmm, well...........I am certain you can tell the difference between when your bike is running and when it isnt. LOL I have no explanation for those settings. I do know when I bought my 79 750, it had very low miles on it and the fuel pilot screws still had the unbroken yellow sealant stripes on them. The bike had those screws set to 1 5/8th turns out from the factory across the board. I've set up VM carb 750's and 1000's and they all ran best between 1 1/2 and 1 7/8ths out. Go figger. :-)

Its probably not running because the idle mixtures were too lean, or did you just run out of paper plates? LMAO

Earl


tkent02 said:
'78 750, stock box and pipes. about 1 1/4 turn out works the best.
Right now it won't run because the pistons and cylinder are on the kitchen table.
Click to expand...
 
earlfor said:
Hmmmm, well...........I am certain you can tell the difference between when your bike is running and when it isnt. LOL I have no explanation for those settings. I do know when I bought my 79 750, it had very low miles on it and the fuel pilot screws still had the unbroken yellow sealant stripes on them. The bike had those screws set to 1 5/8th turns out from the factory across the board. I've set up VM carb 750's and 1000's and they all ran best between 1 1/2 and 1 7/8ths out. Go figger. :-)

Its probably not running because the idle mixtures were too lean, or did you just run out of paper plates? LMAO

Earl
Click to expand...

It's not running because the 750 pistons and cylinders have been removed, and the 850 piston rings have not arrived yet. :-)
 
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