Air Thumb Screw...a solution !
09-24-2013 | 07:38 PM
#1
Thread Starter
Well take off, eh.
SuperBike
Joined: Jun 2012
Posts: 1,204
From: QC, Canada
Air Thumb Screw...a solution !
For those of you who have been looking for this, you know that I also have been searching for some time now. I have found one that will do the job for the VTR.
The thumb screws I have found are the MSR and a remote adjuster by R&D. Why two ? Because at first, I thought the same one would fit for both carbs. Unfortunately for me, no. The MSR fits perfectly for the rear, but had to get the R&D for the front. Since the MSR screw hit the water fitting on the front cylinder. A little machining, or, a narrower head on the front air screw would of solved the problem, but the thought of the remote adjuster was more appealing to me.
Now there are a few items that need to be said about this screw, it's not a perfect fit.
1- Original screw is 15mm from base of thread to end of screw
2-The MSR/R&D is 17mm
3-Screw profile at the end of the screw is not exactly as the original.
4-The first step of the screw is 1mm shorter then original and needle point
of the MSR/R&D is stockier then the original.
To solve the needle point problem on the screws, I've filed them down to get as close as possible to the original. The first pic below illustrates this.
Once on the carbs, the screws do not give the same depth into the carbs as the originals since they are longer. However, what's important is the number of turns out, not the turns in.
I've been running the rear needle on the carb for the past month, and it's been pretty easy to adjust and play with. I have just installed the front R&D model to the front, and that works also, so, I hope later this week to have time to run the bike, and give it a final fine tune on front cylinder. Second and third pics show the whole kit installed. Eventually, I will get the R&D for the rear also, and fix a bracket on which both remote adjusters will fit. For the moment, I will work with fitting my hand in the engine bay to fine tune the rear.
The thumb screws I have found are the MSR and a remote adjuster by R&D. Why two ? Because at first, I thought the same one would fit for both carbs. Unfortunately for me, no. The MSR fits perfectly for the rear, but had to get the R&D for the front. Since the MSR screw hit the water fitting on the front cylinder. A little machining, or, a narrower head on the front air screw would of solved the problem, but the thought of the remote adjuster was more appealing to me.
Now there are a few items that need to be said about this screw, it's not a perfect fit.
1- Original screw is 15mm from base of thread to end of screw
2-The MSR/R&D is 17mm
3-Screw profile at the end of the screw is not exactly as the original.
4-The first step of the screw is 1mm shorter then original and needle point
of the MSR/R&D is stockier then the original.
To solve the needle point problem on the screws, I've filed them down to get as close as possible to the original. The first pic below illustrates this.
Once on the carbs, the screws do not give the same depth into the carbs as the originals since they are longer. However, what's important is the number of turns out, not the turns in.
I've been running the rear needle on the carb for the past month, and it's been pretty easy to adjust and play with. I have just installed the front R&D model to the front, and that works also, so, I hope later this week to have time to run the bike, and give it a final fine tune on front cylinder. Second and third pics show the whole kit installed. Eventually, I will get the R&D for the rear also, and fix a bracket on which both remote adjusters will fit. For the moment, I will work with fitting my hand in the engine bay to fine tune the rear.
09-25-2013 | 09:32 AM
#4
Senior Member
SuperSport
Joined: Jul 2012
Posts: 582
From: Santa Fe, New Mexico
jack, you are the man! I gave up and thought others did the same. Now that I've bought the motion pro too,l the thumb screws are found. I would still rather have the thumb screws so I'm eager to see how this works out!
09-25-2013 | 09:49 AM
#5
Thread Starter
Well take off, eh.
SuperBike
Joined: Jun 2012
Posts: 1,204
From: QC, Canada
Well Twist, as I said before, I've been running the bike for some time now with the MSR needle at the rear, and, have had no issues, and, have tuned it quite well. Now that the front is on, as soon as I will ride (tomorrow I hope), I will be able to let you know how well I've managed to tune front also.
The front remote is so easily accessible, I'll be able to adjust waiting at a red light !
The front remote is so easily accessible, I'll be able to adjust waiting at a red light !
09-25-2013 | 02:28 PM
#6
Senior Member
SuperBike
Joined: Jan 2007
Posts: 2,167
2. Machining & polishing let alone "filing" the tips cannot provide the precise regulation the OEM "screw" will. Carbs are very precise instruments with high tolerances.
3. maybe the turbulence in the fuel metering created by the "filed" tip (stepped needled) promotes better fueling given the erratic modulation the VTR's huge venturis create! LOL
09-30-2013 | 07:20 AM
#7
Thread Starter
Well take off, eh.
SuperBike
Joined: Jun 2012
Posts: 1,204
From: QC, Canada
You think !? Really !? and I thought by filing it down, I had a perfect match. Well, there goes my plan on reinventing the wheel.
Ok, I've been running the bike for a few days now, and, runs perfectly. It takes 10 seconds to adjust the screws, and, that's where the beauty of this mod is. It takes a few seconds.
As Skok made sure to point the obvious out, it's not a perfect match. Nevertheless, I am very pleased with the outcome, and, will persue this little project with the hopes of improving it even more. Like any other project, there is always room for improvement and positive feedback.
09-30-2013 | 07:42 AM
#8
Senior Member
SuperBike
Joined: Jan 2007
Posts: 2,167
Precision is relative and if it works well enough for you, I guess is all that matters. I'm used to working out to 4 decimal points and finish down to 2000mi.
I modified the $20 Motion Pro cable driven flat blade carb tool by grafting on a a D-head bit and can adjust the fuel screws without removing or even lifting the fuel tank easily (2 minutes) even with engine warmed up. I also plumbed the intake manifolds to balance the carbs with the tank down too. I use an electronic Twin Max unit but also have an ancient mercury manometer.
I modified the $20 Motion Pro cable driven flat blade carb tool by grafting on a a D-head bit and can adjust the fuel screws without removing or even lifting the fuel tank easily (2 minutes) even with engine warmed up. I also plumbed the intake manifolds to balance the carbs with the tank down too. I use an electronic Twin Max unit but also have an ancient mercury manometer.
09-30-2013 | 04:01 PM
#9
Senior Member
Superstock
Joined: May 2012
Posts: 397
From: UK
Bloody hell you've only gone and done it. Well done. I would look at it as a prototype and things can only improve skokievtr does have a point with the accuracy when you consider that 16th of a turn can have an effect, but I bet your dam close. And yes technically it's a fuel screw as it's underneath the float bowl and meters the amount of fuel. Four strokes don't have enough vacuum to draw enough air to make the mixed fuel flow well, whereas on two strokes there is more vacuum so can get away with metering with air.
ThumperFaq: MXA Fuel Screw
(:-})
skokievtr does have a point with the accuracy when you consider that 16th of a turn can have an effect, but I bet your dam close. And yes technically it's a fuel screw as it's underneath the float bowl and meters the amount of fuel. Four strokes don't have enough vacuum to draw enough air to make the mixed fuel flow well, whereas on two strokes there is more vacuum so can get away with metering with air.ThumperFaq: MXA Fuel Screw
(:-})
10-20-2013 | 06:51 PM
#10
Member
Squid
Joined: Apr 2011
Posts: 85
From: Canada
How are these working out for you?
Instead of having the flexible fuel screw with the wrong taper, could you cut that off and JBWeld the original one on the end? Would cut it behind the threads and attach it so you would have the original taper, length, and thread.
Instead of having the flexible fuel screw with the wrong taper, could you cut that off and JBWeld the original one on the end? Would cut it behind the threads and attach it so you would have the original taper, length, and thread.
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