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Stock Carb Slide Mod (Read 371 times)
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Re: Stock Carb Slide Mod
Reply #15 - 04/15/18 at 16:08:42
 
Did some similar tinkering with the vacuum ports in the slide years ago with some success.  I had read an article on mod's for the carb on a sporty and used that as a guide.  I drilled a couple of sets of holes, both a bit smaller than suggested for the sporty and could feel an improvement in responsiveness.  I added a dial-a-jet and left it like that.
I did not have backfiring issues to  speak of mainly because of the exhaust system I used, so did not do anything to the TEV.

I may still have the article, but would need to dig through boxes if someone wanted to take a look.


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Re: Stock Carb Slide Mod
Reply #16 - 05/15/19 at 19:23:51
 
I did not drill a third hole in the slide but increased both of the original vacuum ports.
   the Gagetman Groove  ,was done mostly to improve fuel mileage , and increased mine by 3.5 mpg /9.8 miles/per /tankful (2.8 gallons) in mixed riding . A side benefit seemed to be a smoother idle ,in spite of less fuel usage , this occurs because the fuel at idle  slides down the back of the throttle plate ,encounters the grove ,bounces off the front of the  basically V shaped groove ,which both further atomizes the fuel and directs this flow upward  in the intake passage. This allows backing out your throttle speed adjustment screw and provides most of your increase in mpg. Without the groove fuel is less atomized , because it merely tries to follow the floor of the intake passage, the opposite of what happens at higher throttle settings.
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Re: Stock Carb Slide Mod
Reply #17 - 05/19/19 at 04:23:40
 
I did some quick calculations on this...

Stock air bleed area = 0.0145 sq-in (2 x .096")

Your air bleed area = 0.0226 sq-in (2 x .096" + 1 x 0.1015")

Therefore total air bleed hole area was increased 56% over stock.

Another alternative would be to drill the two stock bleed holes to a #31 yielding total bleed area of 0.0226" or 56% increase in area.

A 56% increase is quite a bit so I can see why the change would have been very noticeable and why we must be very careful.


If we use a 3/32" for the new bleed hole area will be 0.0214 giving a 48% increase in bleed hole area.

If we use a #41 for the new bleed hole area will be 0.0217 giving a 50% increase in bleed hole area.


Planning on doing this later today and will start with an additional 3/32" bleed hole...
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Re: Stock Carb Slide Mod
Reply #18 - 05/19/19 at 10:34:05
 
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Re: Stock Carb Slide Mod
Reply #19 - 05/20/19 at 13:45:28
 
Just finished this up with an extra 3/32" hole in the slide.

I let the engine warm up in the garage a bit and it takes throttle no problem and sounds a bit snappier but it is meaningless until I go for a ride...

So funny story...  I drained the tank because the last time I had to remove the petcock to get the tank off.  I found if I place the speedo cable under and parallel to the tank bottom the tank WILL come off without touching the frame.

Get the job all done pour the gas back in and fire it up.  Starts right up and takes big throttle input.  A minute or two later off choke no longer takes throttle and sputters.  WHAT???

Turns out the tank was right on the ragged edge of reserve and it was no longer feeding in the ON position.  Now it's all good.

That was a bit scary for a while...
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Re: Stock Carb Slide Mod
Reply #20 - 05/20/19 at 14:09:45
 
Ride Test Done...

The bike has a MAC exhaust, 55 pilot, 150.0 or 152.5 main, and idle mixture screw between 1.5 and 2.0 turns for best fast idle.  The needle is still a tad too low as it is just slightly lean on inputs but it is magnitudes better than it was in bone-stock trim.  The engine pulls hard and strong and throttle feel and response was MUCH improved but slide opening was a bit lazy.

This simple mod really works.  The carb responds as before under normal part-throttle inputs -- Feels no different at all.  However, if you whack the throttle now you immediately hear intake noise and get an instant change in power delivery.  Before the engine would respond and spin up very lazily.  Now it is right there when you hit the throttle.

I've got to say...  This simple little engine when jetted and uncorked really comes alive.  It is still a bit flat on top and I assume that is due to the short/small cam but who cares?  This little gem makes GOBS of TQ in low-mid and that is where it needs to live.

For those of you wanting that last little bit out of that dull carb this is what you need.  Total bleed area was increased from 0.0145 sq-in to 0.0214 sq-in for an increase of 47.7%.

Just do it...

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Re: Stock Carb Slide Mod
Reply #21 - 05/20/19 at 14:43:20
 
DragBikeMike wrote on 04/12/18 at 17:35:17:
I liked the results of the additional vacuum port created when I left one screw out, so I reinstalled the screw and drilled a permanent hole.  I can still reverse the hole by simply tapping to 6-32 and installing a third screw.  If any of you have tried either of these mods, or if you try them in the future, LMK if you like the results.



LOVE the results and thank you SO MUCH for sharing!
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« Last Edit: 05/21/19 at 07:44:12 by VortecCPI »  
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Re: Stock Carb Slide Mod
Reply #22 - 05/21/19 at 07:40:58
 
I am going to go for a longer ride later today and/or tomorrow.

One thing I would like to mention is that I experienced none of the fluttering I have so often read about in other forums.  This likely happens when the slide hole(s) are already large and you increase them further and/or add additional hole(s) and/or the spring rate is already low.  I can definitely imagine this happening on a Hi-Po bike that already comes from the factory with a pretty good state of tune.

However, with respect to this mild machine my guess is the spring rate and slide holes are on the conservative side (i.e., small) so we will not have such an issue unless we drill way too much.  This is a very common mod for the Kawi KLR650 which has a similar Keihin CV carb and riders never have issues after doing it.

Also...  I run the bike with the right-side airbox lid removed.  Would not be too good in the rain but it makes some intake noise and my wife likes it.  Have any of you done the same?

And...  My SRX600 has a Dynojet Stage 3 kit with slide drilled and new slide spring and the secondary CV carb responds instantly - I might even call it explosively.  The Yamaha engine has a comparatively light flywheel so that plays into it as well.
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Re: Stock Carb Slide Mod
Reply #23 - 05/21/19 at 09:05:49
 
Cool!  Thanks for the feedback.  Looks like we have 3 or 4 of us that have tried the drilled slide with some degree of success.  Seems to be a decent mod, and super easy too.
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Re: Stock Carb Slide Mod
Reply #24 - 05/21/19 at 09:45:28
 
DragBikeMike wrote on 05/21/19 at 09:05:49:
Cool!  Thanks for the feedback.  Looks like we have 3 or 4 of us that have tried the drilled slide with some degree of success.  Seems to be a decent mod, and super easy too.


100% agreed and since so many of us do "The White Spacer Mod" this is the sensible thing to do while we are in the carb.  Add to that the fact it can be done by simply removing the seat and tank and you may be a little nutty NOT to do it!

I have ridden bikes with CV carbs and I've got to say this is THE LAZIEST one I have ever been on top of.  Pretty happy for now...
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Re: Stock Carb Slide Mod
Reply #25 - 05/22/19 at 13:29:02
 
Another test ride...

Pulls like a freight train and makes me wonder if the stock slide EVER found its way to the top.  I also put the right-side airbox cover back on and while it does not sound as cool it pulls harder on top than it did yesterday which leads me to believe it was a bit lean.  If an airbox is too open you lose pressure drop and signal across the mains so I am fairly sure this was the case.

The needle is still just a tad low but it is close enough for my wife.  It may also be the fuel/float level is too low causing the carb to meter a bit lean.  Throttle response is nearly instant compared to what it was and I think this is all a stock engine needs - A larger bleed hole is not necessary.

I got it out on some twisty curves and it exits corners nice and hard now.  Good power everywhere at any engine speed in any gear.  No issue at all whacking the throttle WOT in fifth at 40 MPH.  No hitches, no fluttering nor stuttering...  No issues at all.

This is definitely a MUST DO modification in my opinion...
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Re: Stock Carb Slide Mod
Reply #26 - 05/22/19 at 14:59:18
 
I just checked the fuel/float level with a length of clear line and it is just below the gasket so it looks pretty good.

Either the needle is too low or it is just too fat.  A larger slow jet would help but I am already between 1.5 and 2.0 turns with the #55 out so it is what it needs.

I'm a throttle feel/response junkie so I may looking for a little too much out of this thing but the next time I'm in there the white spacer is coming right out.

Does anybody know if the older needles were richer?
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