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Carburetor

 
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Tue May 21, 2013 11:06 pm    Post subject: Carburetor Reply with quote

FYI Shifter Go Kart Guys,

I'm getting this experimental test carb fitted up to the CR125 Honda.

Mikuni Super Butterfly Type SBN38mm Diaphragm Pump Carburetor
No jets to change ever (well almost never) as it has easy to get to externally adjustable low & high speed mixture screws just like the Vortex RoK-tt carb only a much bigger bore (38mm) to fit the CR125 Honda engine and the fuel pump is built right in too.


I'm getting tired of always taking off the carb to change the high & low speed pilot jets and I don't care for float types of carbs either.

These are one of the best performing and easy tuning carburators that money can buy





[/img]



I still have to add a air box adapter and a choke primer bulb for cold starts

The fuel pump shown in the photo is going to come off of course




Ocono Bob

Robert Horvath
W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.

rhorvath4@wi.rr.com
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Sam Zavaglia



Joined: 23 Nov 2004
Posts: 1203
Location: Australia, Sydney,

PostPosted: Wed May 22, 2013 2:17 am    Post subject: Reply with quote

I wonder if it perform better than float type carbs that Honda, Yamaha, Suzuki etc etc used for in their 2T reed valve engines on their GP and MX production and racing models.

Ian Harrison had a play with one on a CR250 but I think it never made it beyond dyno testing.
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Robert Lawson



Joined: 10 Nov 2001
Posts: 2232

PostPosted: Wed May 22, 2013 7:22 am    Post subject: Reply with quote

Robert,

We first tried a true "pump carb" on Moto's way back in the early 90's when we got tired of watching races from the sidelines.

Tom Cuthberson pioneered this method and used it on all of his kids karts. He loaned a complete set-up to us to try at Mid-Ohio that year and it changed our season. It was just a 34mm Mikuni "clutch kart" carb but it worked flawlessly. Tom and his kids don't get the props they truly deserve for being first to plow the path and build the first laydown shifters in this region.

Later, we grew tired once again with float carb delivery issues (damn PJ) and again turned to a pump carb for answers. In 96' we chose the Keihin CDK II watercraft carb and had great success with it on our newly purchased RS 125. It still worked well when we removed it for a Std. PWM (no pump-around) simply because of the HP gain the float carb provided. It was a proven set-up that worked from the start and still works today.

You will need to plug the manual choke shaft holes and "priming" with a fuel ball should not be necessary. You absolutely can change the jets in the carb to run alcohol, no lead, or hi-test! Being able to tune on the fly is always a bonus but don't think for a second that dropping it on will be bliss. Yes, it will work with the std. intake boot you have.....but not as well as it can. The intake tract length is also a very important tuning device that will hurt or limit your RPM's with an OEM boot. To simulate the same intake length as a float carb (which your engine was designed for) you will have to fabricate a new intake plate and use an aftermarket stubby boot (check the sled shop near you) to completely replace the OEM boot. That will shorten this length considerably and make a HUGE difference in top RPM.

At Blackhawk Farms in 99'we loaned this set-up to a friend on an Anderson/CR 250 and he won his race going away. He too was a believer after that weekend.

We never fought "sea level" carb issues at Daytona with these carbs.....unlike our float carbs!!!

It isn't a "speed secret" by any means, the float carb just makes cleaner-better HP....period. BUT......it is trouble free and will make your weekends at the track more enjoyable while you make all sessions of practice and races.

I may still have those intakes, I know we still have the carbs in the trailer. Always nice to keep that pacifier close....ya know!!!! Cool

Enjoy, you will love the ease of use.

RPM
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Wed May 22, 2013 7:48 am    Post subject: Carburetor Reply with quote

Perform better than float type carbs ? Sam , That is the $64,000 question ?

I will just enjoy not removing the carb for every small weather / jet change I hope.

I have 3 of these exact Mikuni carbs on my 750cc Jetski and they work great on it !

Ocono Bob

rhorvath4@wi.rr.com
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Ian Harrison



Joined: 23 Nov 2006
Posts: 1673
Location: United Kingdom (Great Britain), Manchester

PostPosted: Wed May 22, 2013 8:02 am    Post subject: Reply with quote

Hi Guys

I never had any joy at all getting the Mikuni SBN44 to work on a Honda CR250.

The world and it's wife gave their advice, but in the end you either had fuel running out when the engine stopped (due to low pop-off pressure required to maintain an idle), or no idle at all, and in all the testing I never saw even a hint of what could be described an advantage.



If anyone should be daft enough to want to buy the pictured setup, it has only ever been run on the dyno and is cheap.

I suppose that it was a novel way to waste a month or so of my life, but you have to try these things!

In the end I just asked myself . . . . why?

Changing an occasional jet dosent seem all that hard, does it?

Anyway best of luck Wink

Regarding the jetski, I can well imagine a 38mm working on a 250 single pot (3 on a 750), as the low down vacuum in the venturi would be much greater and hence you wouldn't need as low a pop-off pressure in fact that is exactly what they were made for!! But with a 38mm on a 250, you ain't going to get the top end power (just look at all the restriction in the venturi, a 38 is probbably equivalent to a 30-32mm conventional carburettor! I have a feeling that with an SBN38 on a 125, Robert will have exactly the same issues that I did. Be interesting to hear how it goes.

Best Regards

Ian Very Happy
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Viper Racing UK
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Wed May 22, 2013 9:14 am    Post subject: Reply with quote

Robert Lawson,

This is just a first test and if it pans out to be a good move I plan on fabricating up a very short adapter plate with no rubber boot at all.

Just mounting it by its own carb flange ears directly to a short homemade adapter plate and next a V Force 3 reed box.

I did this for a short while with my smaller 34mm Tillotson pumper carb on the Honda.

It worked out very well so I just decided to move up to the correct size 38mm carb for that CR 125 Honda engine.

Here below: are a couple of photos of the old setup that worked out pretty well.....Maybe my new set won't be any better then the Tilly ?

I trust your advice because you have already done this thing before.

Any more advice or suggestions Robert ?









Thanks Ocono Bob

PS where do live about ?

Do you have a photo of your intake ?

But a Cr125 would use a smaller intake I think ?

rhorvath4@wi.rr.com
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Robert Lawson



Joined: 10 Nov 2001
Posts: 2232

PostPosted: Thu May 23, 2013 5:24 am    Post subject: Reply with quote

Robert,

The RS and CR intakes are interchangeable.

Be careful mounting the BN direct, it is heavier of course and......we had a carb snap off at Daytona. Man that thing flew for about 300 yards!!!!!!!!! Laughing

Flat plate with a stubby flange/boot (maybe 5/8" total length) will get it very close to a float carb. We also fabricated a super short aluminum flange/tube with correct IS and OS dia for the new boot. A little anti vibration here is important, especially if you run some of the rougher tracks (like Grattan back a few years).

I'll get some pic's to you soon.

Robert
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Jim McMahon



Joined: 07 Apr 2007
Posts: 2869
Location: United States, St. Paul,

PostPosted: Fri May 24, 2013 7:12 am    Post subject: Reply with quote

Were you lacking power with the KF carb? Reason I ask is that the ICC\KZ motors run 30mm so I would have expected the KF carb to be in ballpark.

I know Ian had issues getting the popoff right have it work properly on the 250 because the vacuum was so low at idle.
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sat May 25, 2013 1:35 am    Post subject: Carburetor Reply with quote

Jim McMahon & Robert Lawson

I do use both types of boots CR125 & RS125 on the Honda and no boot at all with the TillyCarb :

But you guys seem to think that "RS125" is a better intake so I will use that one with the Mikuni SN38mm...correct ?

Honda RS125 Intake Manifold w/ 5į Boot...
This pre-1995 Honda RS125 intake manifold (P/N 16220-NF4-900) has a 5į boot and can be mounted to 1999 Honda CR125 Moto engines, without having to remove the kick starter boss.

and the

The 5-degree angle design makes it much easier to mount the seat strut, on the engine-side of a 125cc shifter kart, versus using the 1999 CR125 OEM 30-degree intake





Jim McMahon,
I plan to be at Blackhawk Sat. June 1st with this Birel Shifter # 92 in the photos of Craig Hemmen as Tuner/Mechanic and here is a photo of our old Tony Kart KF-1 with my driver/grandson.....I put front hand operated brakes on this Tony Kart and they work out to be very useful.

I'm old guy in back of him kneeling down so you'll know what I look like when we get to Blackhawk.

[/URL










And as far as the performance of the Tilly KF1 34mm carb on the shifter it seemed great in the corners & at the way top end too...With plenty of ZIP !

Did you notice the exhaust note change with a pump carb??? Robert asked > yes we did > a sharper higher tone coming out of the corners.



But my testing was cut short and inconclusive because my buddies thought the carb might be too small a bore for a shifter and wanted me to get going on the larger SN38 pumper to be used on there machines.

I am going to get KF Tilly back on the Honda as soon as I finish developing the SN38mm for them as I thought it ( the Tilly) was a perfect combo > CR125 and the Tilly HW12 34mm carb !




I posted my homemade axle driven H.D. 24 volt starter pack before..but here is it again because it works so well .




And also a few more pics. of the SN38mm....A work in progress :







Ocono Bob

Robert Horvath
W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.

rhorvath4@wi.rr.com
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sun May 26, 2013 6:32 am    Post subject: Carburetor Reply with quote

This carb is going to be a nice clean install.





Note ! That other fuel pump in the photo will be coming off soon as is not needed with this SN 38mm carb I believe ?


Ocono Bob
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sun May 26, 2013 6:35 am    Post subject: Carburetor Reply with quote

Brian Degulis,

The Coleman can take 24 volts for 20 to 30 seconds at a time.

I did this for one year...But as you say it was just "HIT OR MISS" in its ability to start a shifter at the axle.

And this is when I said "There has to be a better way" and came up with the setup in the post.

It did take me most of the winter to perfect it. And I did build a pair of starter packs at the same time . I sold extra to friend for $285.00 and he's pretty happy with it.

It's always best to start any engine in the highest gear it has.

I like to make strange stuff Brian ...I even made a device to adjust the carb mixture from the pits by ear for my grandsons KF1 TaG Tony Kart Not too many people even know what a KF1 Kart is.

And that thing worked pretty well too.

I did put a limit on the high speed needle so I did NOT "COOK" the engine.






Ocono Bob
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Wed Jun 05, 2013 8:58 am    Post subject: Carburetor Reply with quote

Go Kart Friends,

I have almost finished the externally adjustable mixture control Mikuni carb install on the CR125 Honda shifter.

I'm now going have a grand total of about $200.00 involved not counting labor which I did myself.

A small set back is that without a restrictive type airbox / air filter like the factory uses on a OEM setup... I have to set the pop off pressure from about 30psi down to 10 to 18psi or lower for better throttle response just off idle they say.

They also say to use a four hole air box ?

So the kart still is not ready for "Prime Time"

I have just ordered off ebay this low pressure pop off spring : Mikuni Spring Arm-Sq Bn @ 65Grams 730-03030

But even with the wrong pop off pressure the throttle response is pretty impressive on the kart stand...She really "Barks" !

Very nice to have that primer bulb in the photo when you need just a squirt of gas in the carb...Seems to be better then having a choke.

Again of course the external fuel pump seen in the photo will be coming off as it's not needed because the mikuni has its own pump built right in the carb itself.














I have been trying to get this experimental test carb fitted up to the CR125 Honda.

Mikuni Super Butterfly Type SBN38mm Diaphragm Pump Carburetor

No jets to change ever (well almost never) as it has easy to get to externally adjustable low & high speed mixture screws just like the Vortex RoK-tt carb only a much bigger bore (38mm) to fit the CR125 Honda engine and the fuel pump is built right in too.


I'm getting tired of always taking off the carb to change the high & low speed pilot jets and I don't care for float types of carbs either.

These are one of the best performing and easy tuning carburators that money can buy .


Ocono Bob

Robert Horvath

W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sun Jun 16, 2013 11:55 pm    Post subject: Carburetor Reply with quote

James Bell

So how did testing go with this 34mm Tilly carb Thursday you asked ?

Answer > Spectacular, Marvelous, and a dramatic increase in the low end performance coming out of the corners...no lag at all----always a crisp throttle response!

No need for a "GFS system" or a "Pump around system" or a outboard fuel pump either...And such ease to tune with no taking off of the carb anymore !

Just a slight tweak of the two mixture screws while watching the ETG gauged.

But about the same performance on the way top end as we expected ...but no slower then the too big of 38mm Keihin Carb

A few more tests with Tilly and then on to the Mikuni 38mm carb Bruce.

Ocono Bob

Robert Horvath
W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sun Jul 21, 2013 9:13 pm    Post subject: Carburetor intake manifold Reply with quote

UPDATE :

FYI Shifter Go Kart Guys,

For the open/modified
class of Honda CR125 Shifters.

The very short fuel path direct fit Honda CR125 Shifter intake manifold for 38mm 2 flange bolt types of carburetors is all done .

It has a 11 degree right rotation angle
to to clear the kick start bump ( Carbs like the externally adjustable Mikuni 38mm Carbs work really well )

No more rubber boots with right angle turns to disturb the fuel flow !

And even a more perfect fit when used in conjunction with the V-Force 3 Reed Cage box .

I'm getting this experimental test carb fitted up to the CR125 Honda.

Mikuni Super Butterfly Type SBN38mm Diaphragm Pump Carburetor
No jets to change ever (well almost never) as it has easy to get to externally adjustable low & high speed mixture screws just like the Vortex RoK-tt carb only a much bigger bore (38mm) to fit the CR125 Honda engine and the fuel pump is built right in too.


I'm getting tired of always taking off the carb to change the high & low speed pilot jets and I don't care for float types of carbs either.

These are one of the best performing and easy tuning carburators that money can buy.

see below:








Thank You

Bob

Robert Horvath

W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.

rhorvath4@wi.rr.com
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Robert Horvath



Joined: 11 Jul 2010
Posts: 83

PostPosted: Sun Sep 08, 2013 9:39 am    Post subject: Custom Honda CR125 intake manifold and the Mikuni carb setup Reply with quote

Results now are in

On using the :

Custom Honda CR125 intake manifold and the Mikuni carb setup

Hi back shifter guys.

It's been about six weeks now that we have been using the new setup

I didn't want to say anything before until the unit was thoroughly Race track tested.

The answer is easy ..JUST ONE WORD > Awesome Performance!

We have taken a full second off our own personal best time at our local track ( Badger Raceway Dousman wi.) and after hundreds & hundreds of laps with absolutely no Carb trouble at all.

A good lap time at Badger is anything under 38 seconds....We are consistently in the 37.20s with the Honda CR125/Mikuni now,

I'm not setup to "Retail a kit " to the general public.

But I'm making arraignments now to sell it through a few of the better shifter kart shops and on line from them also.

It will be priced about on par with the Swedetech Honda intakes.

The complete intake kit would consist of the intake, all gaskets all, hardware,throttle cable, bar type throttle cable bracket, 38mm air filter/box adapter and to inc.this disclaimer below :

"As when installing any performance product, a degree of mechanical ability is required. If after reviewing the parts you don't feel that you can properly complete this installation, take your kart to a competent professional. Proper installation and adjustment will save time, money and aggravation."

Because of all the tight quarters I recommend installing the carb & and intake as one piece with a very long ball type allen wrench.

Then it's easy to do.

I got so tired of always having to take the stupid Honda CR125 Keihin carburetor
off to change jets I'm taking a lot of them off the shifter Karts in our little classic shifter club and tossing them out or selling them....I think they are all JUNK.. pump arounds too....But maybe that's just me ?

Here below is a long story of what I'm doing for carbs instead ...AND I'LL TELL YOU THIS SETUP REALLY WORKS WELL ON THE CR125s.

This below looks very clean and it solves all the fuel system issues.

Robert Horvath

Participant
UPDATE :

FYI Shifter Go Kart Guys,

For the open/modified
class of Honda CR125 Shifters.

The very short fuel path direct fit Honda CR125 Shifter intake manifold for 38mm 2 flange bolt types of carburetors is all done .

It has a 11 degree right rotation angle
to clear the kick start bump ( Carbs like the externally adjustable Mikuni 38mm Carbs work really well )

No more rubber boots with right angle turns to disturb the fuel flow !

And even a more perfect fit when used in conjunction with the V-Force 3 Reed Cage box .

Iím getting this experimental test carb fitted up to the CR125 Honda.

Mikuni Super Butterfly Type SBN38mm Diaphragm Pump Carburetor
No jets to change ever (well almost never) as it has easy to get to externally adjustable low & high speed mixture screws just like the Vortex RoK-tt carb only a much bigger bore (38mm) to fit the CR125 Honda engine and the fuel pump is built right in too.

Iím getting tired of always taking off the carb to change the high & low speed pilot jets and I donít care for float types of carbs either.

These are one of the best performing and easy tuning carburators that money can buy.

see all photos below:

at this new link :

http://ekartingnews.com/forums/topic/results-are-in-on-using-the-custom-honda-cr125-intake-manifold-mikuni-carb/

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6132.jpg" alt="Intake" />

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6145.jpg" alt="Carb &amp; Intake" />

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6151.jpg" alt="Carb &amp; Intake assembled" />

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6220.jpg" alt="Intake on the Honda" />

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6396.jpg" alt="Tilly" />

Or a big bore Tilly is a good fit on the Honda too for short tracks!
Note &gt; a primer bulb also for easy starts :


Important note below :

Road America is a famous road course located near Elkhart Lake, Wisconsin


Here are the results of the first time out at Road America with the new intake set up.

I installed the kit on team Craig Hemmen / Bob Horvath (That's me)

We ( Craig Hemmen age 61 the driver of Kart # 92 &amp; me Bob Horvath the mechanic age 6Cool were competing all day at Road America) and of all the Pro shifter Karts (about 22) there today...We got fast time of the day and that gave us the Pole Position for the feature race and a First place Win in for our Honda class too.

The ICC shifters and the Honda's all run together in one class due to the small number of each

Date 24-08-2013 13:36
Length 0.8000 Miles
Best lap time 44.463 In lap 4
Best speed 64.773 By competitor Craig
Hemmen/Bob Horvath
pos start no. competitor laps total time diff best time best lap best speed
1 Honda engine 92 Craig Hemmen 6 04:36.982 44.463 4 64.773
2 ICC type engine 65 Darrick Lang 6 04:54.457 17.475 44.690 5 64.444
3 ICC type engine 17 Dayton Bender 6 04:56.302 19.320 44.829 2 64.244

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6218.jpg" alt="The Intake on the Honda" />

<img src="http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6216.jpg" alt="The Intake on the Honda" />

http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6218.jpg" alt="The Intake on the Honda" />
http://i954.photobucket.com/albums/ae24/roberthorvath4/DSCN6218.jpg" alt="The Intake on the Honda" />




Thank You

Bob

Robert Horvath

W352N6446 Road J
Oconomowoc Wi 53066 U.S.A.
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