Slide drilling

Is a common practice? What size drill bit? Would I see a benefit?

4300 ft ele. 4 into 1 exhaust. Stock carbs/airbox.

I am having an extremely difficult time getting rid of the 3500-4000 rpm sputtering. At cruise only. Accelerating through it its not there.

Thanks a bunch fellas.

 

Drilling the slides affects how fast they come up and down when you twist the throttle, which gives you slightly better WOT response.. Dunno if it will help with a sputter at a specific RPM. I hear of a lot of people do it to Harley CV carbs... Also, the Dynojet kit requires drilling as part of the installation.

You might try this, to see what's causing your sputtering -- apply just a tiny bit of choke when it happens, and see if the sputter goes away. If it does, then you're lean. if it makes the sputtering worse, you're too rich. At 3500-4000 RPM, the mixture is affected slightly by the idle jets/mixture screws, and more so by the jet needle position. You can try shimming up the needles with some thin washers, and see if it helps.

 

Thanks for the reply.

Will try. Whats weird is (might not be all that weird) just below that spot and idle is great. Just above, its great(throttle setting wise).

I do get a bit of a hanging idle after being ridden for awhile...

 

I now know I'm dangerously lean.
I went out on the highway, set the throttle at a steady 60 mph, 4,000 rpm.
For a few miles. Killed the engine and checked my plugs.... BONE white. All four.

So I got back on the highway, did it again only now with the enrichener on about half way. I noticed the sputtering was gone. Killed the engine and the plugs now were just beginning to get some light tan color.

Question, my pilot screws are already 3- 3 1/4 turns out... How much more can I get out of them?

Or should I richen another part? Shim the needle up? Drill the slide?

Thanks again fellas.

Rich

 

Drilling the slide will not make you richer. You could get into trouble with the thing opening too fast on a quick throttle snap and leaving you lean.

Shim the needle. You may find you need larger main jets.

 

What size shim would be appropriate for a first start? Just thick enough for one needle clip position i assume...

 

If you haven't already increased the main jet size with the mods that you have done, that would be my start. Chacal has a neat little formula for determining the starting point for a new jet size but I can't find it now. The IDLE air screw has little to do with air:fuel mixtures at 4,000+ RPM, this is where the main jet comes in under the emulsion tube.

I just read your signature. You changed the exhaust w/o changing the jetting. Time to enrichen your main jet (up size it) to compensate for the change in engine breathing.

 

OK, thanks for the advise.
By the jetting calculator, I have come upon the needed 122/41 jets.
Will probably order through this sites parts master on monday and give er another go!

Thanks,

Rich

 

Here you go:

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Hi xyz!.....we've never used pods on any of our bikes, they just seem like way too much trouble to me! BUT, here is the "standard" re-jetting recommendations from people who fool around with them....although, please be aware that every situation is different, and you should expect to go through some amount of trial and error (and frustration!) before you get it as close to right as is possible.

By the way, the most important part of the information below is in the section titled "PRECAUTIONS"!:

So here is the info regarding jetting that you might find helpful:


MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

+4 main fuel jet sizes for 4-into-1 exhaust

+4 main jet sizes for no muffler (open headers)


Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

+2 main fuel jet size for drilling holes in the airbox

+4 main fuel jet sizes for individual pod filters (no airbox)


Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.


PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.



PRECAUTIONS:

- Make sure your carbs are in perfect working order before making jet changes....meaning fully cleaned internally and rebuilt.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!




EXAMPLE:

Stock Carb Settings:
#120 Main Fuel Jet
#40 Pilot Fuel Jet
Y-13 Needle

MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet
----------------------------
Equals: +8 main fuel jet sizes baseline
Subtract: -2 main fuel jet size per formula above
----------------------------
Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #120
+ 6 additional sizes
= a #126 main fuel jet size
---------------------------
Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

= #126 calculated from above
-2 jet sizes for altitude adjustment

= a #124 main fuel jet size.


PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #40
+ 2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in)

= a #42 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' asl.


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RESULT:

A #124 Main and #42 Pilot is A GOOD STARTING POINT.

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