jetting 95 vmax 600

coreysask

New member
Joined
Dec 23, 2004
Messages
79
Age
54
Location
Balgonie
Website
corey.cabler.com
Hi,
I'm wondering what the air screw adjustment should be on a 95 Vmax 600.

It has deltaforce reeds...if that makes a difference.

The trouble is that between 30-50 mph it seems to be rather unresponsive. At 50 it goes like hell. Being my girls machine I'd like it to run a bit smoother.

Might be the clip on the needle too...if anyone has the specs on that I'd check those too.
Thanks,
Corey
 
I'd love to know this too, mine has always been boggy in that range, I put GYT twins on it and clutched/jetted according to Yami hoping that would clean it up and make it more responsive, but nope, it's still boggy in that 25-50 mph range, after that, it goes like hell too. It's also the sled my girl will ride when she can get out, so I was hoping to make it nice and responsive on the lower end. The plugs are a nice cardboard brown so it isn't running rich, the air screws are 2 turns out as specified. I'm running out of things that could be causing the bog. Carbs are cleaned every year, just put a new rear suspension underneath it, new ultimax 3 belt on, new chain case oil. Any ideas..? I'm sick of having to hold thr throttle 2/3rds open and only going 40-50 mph.
 
The air screws regulate how much air is allowed into pilot circuit. The more you turn them out, the leaner you are in that low-to-mid range.

If you do a 1-mile WOT blast, then kill the sled at the end of it while still pinning the throttle, then let off throttle, then brake to a stop, you can pull the plugs and examine your fueling through the main jet. Cardboard color is good. Darker is richer, lighter is leaner.

You can do the same test across a 1/2 mile at the "problem" area. Get the sled going about 35 and running like shit, hold it there for a 1/2 mile, then kill - let go of throttle - brake to stop. Check plugs, see what you have for fueling in the low-to-mid range.

I suspect 2 turns out for you low elevation guys is too lean. If it's too lean, it'll bog coming out of the mid range.

On a 2-circuit carb, you have pilot and main circuits. With no throttle, the sled idles through the pilot. It mainly runs on the pilot up to 1/4 throttle. Vacuum is the primary determinant of air/fuel delivery through the pilot. The harder the motor sucks, the more a/f mix it can sip through the pilot. This works fine up to about 1/4 throttle.

As throttle is increased beyond 1/4ish, the needle mechanically starts to pull out of the main jet, allowing more fuel to be mixed with the ever-increasing amount of air being sucked in by the motor. This is where the needle clip/washer is a factor. If there are 5 settings on the needle, with #1 being farthest from the needle point and #5 being closest to the needle point, then #1 is leanest and #5 is richest. If you use #1, the needle taper is lower in the main, therefore the needle must be pulled farther before it's taper begins passing through the main allowing more fuel to get past the needle. At WOT, the needle is either barely in the jet, or totally clear of it, allowing maximum fuel flow through the main jet.

Remember a three simple ideas for optimal tuning.

1 - the motor is an air pump. The faster it runs, the harder it will suck air in and push air out, and also the higher the volume of air it will try to move through itself. Your first job it to make sure the intake and exhaust tracts are relatively unrestricted and perhaps even properly "tuned" to optimize laminar air flow through the pump. Yamaha engineers did most of this work for you. If you modify intake or exhaust for even less restricted airflow, the sled will want more fuel because it is getting more air. But, flow may be more turbulent after the mods, which robs power. This is the catch-22 of mods: Anyone can give it more air, but can you make it smooth (effective) air? This is why Daman could be considered to be right when he sez Stock Rocks.

2 - once a clear air path and volume has been established, the carbs regulate how much fuel is mixed with that air. Too lean = low power, poor fuel economy, & excessive engine wear. Perfect lambda = optimum power and fuel economy and normal engine wear, but difficult to achieve perfectly. Way too rich = low power and poor fuel economy, but dranatically reduced engine wear. Just barely too rich (staying conservative) = good power and fuel economy and reduced engine wear. Since no one can be perfect, always try to err to the rich side.

3 - a fueling curve is a transition, especially as the sled moves into the mid-to-higher rpm ranges. If you have a dead range, it's because of a problem with your transition. Fuel is always flowing through the pilot, so be sure that the pilot circuit is not too rich or lean. Main size and needle clip determine how soon fuel starts flowing through the main and also how much fuel flows through the main. At WOT, the main is ALMOST all that matters, because so much fuel is flowing through it that the pilot is hardly of concern, and the needle is totally clear of the main, so clip setting doesn't matter. But the holy grail is a nice transition from 1/8 all the way to 5/8 throttle. This is where the 3 critical variables must be optimized: air screw, needle setting, and main size.

Only really high riders (always 8000+) should consider reducing pilot jet size.

Start by getting a proven expert recommendation for pilot and main jet sizes and needle clip location for your sled setup. This will vary according to elevation and engine mods and exhaust.

Using those recommended jets, set the air screws 1.5 turns out and the needle at #3. Ride for a while, do the mid and top range plug check.

Then use the air screws to try to eliminate any bogs as she's transitioning from pilot to main circuits. If you are unable to make it sound and feel right with the air screws, then move the needle clip 1 position in the indicated direction. This will change the "timing" of when the main circuit becomes a factor, and will require that you sort of "start over" with the air screws to get everything just right.

Your tools:
- plug checks at both mid and high ranges
- how does it start when warm? If you are using recommended jets and it's hard to start when warm, you are likely too lean on the air screws, turn them in a little.

You can never get it perfect everywhere, especially with a 2-circ carb. but you can get close.

The reply button sez "Post Quick Reply". That buttons obviously isn't working today. :D
 
Last edited:
Thanks for the detailed reply, I guess I have some testing to do. From what you say it sounds like my needle position may be the problem and those needles are such a pain to get at! I was also wondering if the float height could be an issue as well and if so, how do you check that to make sure it is at the stock setting of 24-25mm? If it's at the correct setting all should be well and either air screw or needle postions will need to be adjusted. I will do the plug checks to see how it's running in the problem area and go from there. If you have any advice on checking the float height I'd appreciate it. Thanks!!
 
Last edited:
the best advice is to get a service manual and follow their protocol and spec for float height.

Another approach would be to remove the bowl and hold the carb upside down to see what the float looks like when it is sitting on the needle (closed). Bend the adjustment tab (carefully) to make the horizontal plane of the float parallel with the lip of the bowl.

This latter approach is widely know as the "**** it, just make it level" approach. It has served me well for years.
 
I have a 94 with single GYT pipe from a 96 XT and carbs from a 96 and I have mid-range to top-end bog. Up to 50 is good. What should I do to adjust. The 96 carbs are a little different and I don't know how to adjust them.
 
I'm no expert on all the different year models, but I was under the impression that everything from the 90's had 2-circuit carbs.

If you're bogging coming out of the mid, its a transition problem. That could mean your pilot jet is wrong, your pilot air screws are set wrong, your needle clip is too high or low, or maybe your main is off by 1 size.

Pilot jets are rarely changed, but if you bought the sled used, the only way to know what's in the carb is to look for yourself.

My 94 was jetted for 10K feet when I bought it. I foolishly put 100 miles on the thing before ever looking. It's a wonder I didn't fry it.

Other than the idle adjustment screw, which should be set to make the sled idle at 1500 (i think that's right) and then left alone, there is only one other adjustment screw on the outside of each carb - the pilot air screw.

Other than the location of that screw, these carbs all work the same.
 
One other comment about aftermarket mods, relating mostly to air flow issues (laminar vs. turbulent).

Many available aftermarket pipe or intake manifold systems purposely sacrifice something in the low or midrange in order to increase peak HP.

When you modify a performance engine system, you can never really have your cake and eat it too (unless of course you are willing to spend heavily).

The factory engineers design the entire engine system to provide good performance across the entire rpm range.

If you modify that system to create more peak HP at high rpms, it is almost unavoidable that you will cause a deficiency somewhere else in the power band.

Problems like this are partly solved by better engineering for the engine system (example = fuel injection with hi-res mapping that allows precise regulation of fuel delivery at 100 or better rpm increments), or perhaps better engineering for the desired mod (example is $1200 Akropovic pipes for the Busa; they are amazing).

An old Yam VMax sled will run pretty good stock if you get the carbs and clutch set up right. A pipe will add a few peak HP, but also will likely make a weird spot or two in the midrange that is difficult to tune out.

You frequently have to choose between perfect "driveability" and peak HP. It's hard to get both.
 
Last edited:
While I'm rambling, here's another comment regarding pilot air screws:

They should be between 1 and 2.25 turns out.

If you're 3/4 turn out, well then you're using a very "rich" pilot circuit to overcome a lean dificiency somehwere else.

If your'e 2.5 turns out, then you're using a very lean pilot circuit to overcome a fat problem somewhere else.

Ideally, you're between 1 and 2 turns out, except maybe for the really high guys.

For perfectionists, 1/8 turn increments are a reality when tuning.

If you live at elevation, go find some room at your average riding elevation, and tweak it there. Then you'll have best results across your whole range.

Finally, the biggest ***-biter on a carb is the air screw assy. This assy is comprised of a screw, spring, washer, and o-ring. When you remove the screw, the washer and oring usually stay in the hole. The hole frequently gets contaminated with white crusty oxidation. The washer and o-ring frequently get shot to the moon with compressed air by people who had no idea they were in that hole.

If you have midrange weirdness, confirm that you are still in possession of all parts of each air screw assy, and that each assy and air-screw hole are not full of the crusty stuff. Good carb cleaner is designed to dissolve both gasoline varnish and white crusty stuff. In the past, I have squirted a very little WD40 on the assy and in the hole after cleaning white crusty stuff from both.
 
Thanks for the ramble Baker. I suspect the needle isn't set right...probably on the lean side being that whoever put reeds in it. I'm going to try to raise the needles when I have time and see what the plugs tell me.
I think I read that the air screw starting point should be about 1.5 turns out. Sounds like as good of a place as any to start. :-)
Corey
 
Reeds tend to make it run rich. Does your eyes burn a little while it is idleing or is the fuel smell really strong. I had boyeson reeds in mine and took them out because it was running rich.
 
baker said:
The air screws regulate how much air is allowed into pilot circuit. The more you turn them out, the leaner you are in that low-to-mid range.

If you do a 1-mile WOT blast, then kill the sled at the end of it while still pinning the throttle, then let off throttle, then brake to a stop, you can pull the plugs and examine your fueling through the main jet. Cardboard color is good. Darker is richer, lighter is leaner.

You can do the same test across a 1/2 mile at the "problem" area. Get the sled going about 35 and running like shit, hold it there for a 1/2 mile, then kill - let go of throttle - brake to stop. Check plugs, see what you have for fueling in the low-to-mid range.

I suspect 2 turns out for you low elevation guys is too lean. If it's too lean, it'll bog coming out of the mid range.

On a 2-circuit carb, you have pilot and main circuits. With no throttle, the sled idles through the pilot. It mainly runs on the pilot up to 1/4 throttle. Vacuum is the primary determinant of air/fuel delivery through the pilot. The harder the motor sucks, the more a/f mix it can sip through the pilot. This works fine up to about 1/4 throttle.

As throttle is increased beyond 1/4ish, the needle mechanically starts to pull out of the main jet, allowing more fuel to be mixed with the ever-increasing amount of air being sucked in by the motor. This is where the needle clip/washer is a factor. If there are 5 settings on the needle, with #1 being farthest from the needle point and #5 being closest to the needle point, then #1 is leanest and #5 is richest. If you use #1, the needle taper is lower in the main, therefore the needle must be pulled farther before it's taper begins passing through the main allowing more fuel to get past the needle. At WOT, the needle is either barely in the jet, or totally clear of it, allowing maximum fuel flow through the main jet.

Remember a three simple ideas for optimal tuning.

1 - the motor is an air pump. The faster it runs, the harder it will suck air in and push air out, and also the higher the volume of air it will try to move through itself. Your first job it to make sure the intake and exhaust tracts are relatively unrestricted and perhaps even properly "tuned" to optimize laminar air flow through the pump. Yamaha engineers did most of this work for you. If you modify intake or exhaust for even less restricted airflow, the sled will want more fuel because it is getting more air. But, flow may be more turbulent after the mods, which robs power. This is the catch-22 of mods: Anyone can give it more air, but can you make it smooth (effective) air? This is why Daman could be considered to be right when he sez Stock Rocks.

2 - once a clear air path and volume has been established, the carbs regulate how much fuel is mixed with that air. Too lean = low power, poor fuel economy, & excessive engine wear. Perfect lambda = optimum power and fuel economy and normal engine wear, but difficult to achieve perfectly. Way too rich = low power and poor fuel economy, but dranatically reduced engine wear. Just barely too rich (staying conservative) = good power and fuel economy and reduced engine wear. Since no one can be perfect, always try to err to the rich side.

3 - a fueling curve is a transition, especially as the sled moves into the mid-to-higher rpm ranges. If you have a dead range, it's because of a problem with your transition. Fuel is always flowing through the pilot, so be sure that the pilot circuit is not too rich or lean. Main size and needle clip determine how soon fuel starts flowing through the main and also how much fuel flows through the main. At WOT, the main is ALMOST all that matters, because so much fuel is flowing through it that the pilot is hardly of concern, and the needle is totally clear of the main, so clip setting doesn't matter. But the holy grail is a nice transition from 1/8 all the way to 5/8 throttle. This is where the 3 critical variables must be optimized: air screw, needle setting, and main size.

Only really high riders (always 8000+) should consider reducing pilot jet size.

Start by getting a proven expert recommendation for pilot and main jet sizes and needle clip location for your sled setup. This will vary according to elevation and engine mods and exhaust.

Using those recommended jets, set the air screws 1.5 turns out and the needle at #3. Ride for a while, do the mid and top range plug check.

Then use the air screws to try to eliminate any bogs as she's transitioning from pilot to main circuits. If you are unable to make it sound and feel right with the air screws, then move the needle clip 1 position in the indicated direction. This will change the "timing" of when the main circuit becomes a factor, and will require that you sort of "start over" with the air screws to get everything just right.

Your tools:
- plug checks at both mid and high ranges
- how does it start when warm? If you are using recommended jets and it's hard to start when warm, you are likely too lean on the air screws, turn them in a little.

You can never get it perfect everywhere, especially with a 2-circ carb. but you can get close.

The reply button sez "Post Quick Reply". That buttons obviously isn't working today. :D

Nice wright up Baker, ;)!,, ,should be a Sticky!!
 


Back
Top