Need Input--kfx Carburetor Conversion!!!!??

[PeterBenincasa]

Hey guys I need your (WELL KNOWLEDGED) Imput on this:

I am in the process of Building my race motor and the idea came up about getting rid of all that electrical nonsense and converting it to a carb setup!

I've seen a couple Suzukis with this done to them, and the dynos look impressive!! Many people are not convinced it is a good idea but fact is, a well tuned carb will put out way more fuel/air mixture in the intake manifold than a stock efi throttle body.

I was doing the calculations and it looks like I would be looking at a 34 or 35 mm setup. Has anyone seen this done, or done it on a KFX!!?

I am aware of costs, and a bit less throttle response, and how I would need to remove the fuel pump, besides for that, anyone have ideas on how to rip the sensors out, and how to keep the crank positioning sensor running and throttle positioning sensor.

Any (well knowledged) input will help me here!! So shoot!

[eastside 400]

BCS has a kit and its like 2500 bucks, its not as easy as just removing the FI stuff and adding a carb. also your carb size is way off, most 450's use anywhere between 39mm(stock FCR) and 43.5 bored for MX use

just sell it and buy a honda

[RobRacing]

Well IMO if the factory race teams are using the EFI system then there is no benefit to switching to a carb. This is the future and there is no point in denying it just stick with the EFI and tune it to your liking.

[FHKracingZ]

Originally posted by RobRacing
Well IMO if the factory race teams are using the EFI system then there is no benefit to switching to a carb. This is the future and there is no point in denying it just stick with the EFI and tune it to your liking.

Good luck getting the fuel injection stuff the factory teams run. the factory suzuki stuff cost over 15,000 per quad.

[lilguy450]

there is plenty to gain when going to a carb especially in power...i felt a BIG gain when i switched my suzuki to a carb and i bored out the carb to a 43.5mm..the stock throttle body on a ltr is bigger i think its like 50mm....by switching to a carb and boring it out i gained a good amount of power and not to mention tuning was easy..i didnt have to worry about bringing a 500.00 laptop to where i was gonna ride..all i had to do was change jets and be done also the weight savings was worth it too ..... jmo

[MtnEX]

Look... If you are going to do this... do it because you want pure simplicity... and for no other reasons.

Understand that it is going to loose some throttle response and not gain any power from the TB to carb swap.

The MX bikes make more power because they have hotter cams, lighter weaker internal rotating mass, and a better ignition curve.

Guys have bored out throttle bodies, installed bigger injectors, etc... and actually lost power.

If you want every last bit of power for your race motor, then make sure you have a good intake, good exhaust, and get yourself a Procom ECU like I have listed in my signature. It gives you control over everything the ECU controls and allows you to adjust that ignition curve... which is where the rest of that missing power is hiding.


Now if you want to do it for simplicity... if I were you I'd purchase the following from a part-out...

KFX450R kick start kit
KX Head
KX CDI
KX Carb
KX stator assembly w/ everything including crank sensor.
Some good wire to make a new harness.


I'd try hooking up the carb, and the CDI and wire everything first. Then if it will not work, change out the crank sensor and stuff.

That should get you going and if it doesn't work, you should not be out much and should be able to unload the stuff for your money back.


For me, this is a quad I will probably keep absolutely as long as I can... meaning I may have to resort to this conversion down the road... but I don't want to until I have to.

I miss the simplicity... but don't miss carbs.

[lilguy450]

the reason why people loose power when boring there throttle bodies is because there taking a throttle body thats already matched to the setup that thier running and making it too big..i think its 50mm and there taking it to a 52 or 55mm correct me if im wrong....

and have you tried a carb swap to begin with on any bike? im basing my info off an LTR which i know is a completly different bike but they both run the efi....and the ltr gained alot more then simplicity! and im sure if done correctly, any bike that is switched from efi to carb will gain some sort of power

[lilguy450]

and as far as throttle response....you wont notice a differnce at all

[MtnEX]

Originally posted by lilguy450
the reason why people loose power when boring there throttle bodies is because there taking a throttle body thats already matched to the setup that thier running and making it too big..i think its 50mm and there taking it to a 52 or 55mm correct me if im wrong....

and have you tried a carb swap to begin with on any bike? im basing my info off an LTR which i know is a completly different bike but they both run the efi....and the ltr gained alot more then simplicity! and im sure if done correctly, any bike that is switched from efi to carb will gain some sort of power


Originally posted by lilguy450
and as far as throttle response....you wont notice a differnce at all

The KFX is my first EFI bike, so I have not done that yet.

It has a pretty good flowing 42mm throttle body and the head is pretty well set up for this. In order to get more power from a larger mm setup on the KFX, you have to increase displacement quite a bit and do head work... otherwise it usually nets a power loss.

The suzuki is different in that respect, as I've talked to a guy who did the switch. But I do not believe he gained anything but simplicity that he could not have gotten from a larger throttle body.

And generally, a throttle body of the same size will flow more than a carb.

In the end, it's all about tuning the entire intake to the right flow cabibility to match the head flow, displacement, and general amount the engine can suck in.

For example, the Kawi may be able to respond differently to a larger throttle body or carb... provided the right things are changed... and furthermore, if the intake itself is tuned to go along with it. But nobody has solved that equation yet, which is probably highly linked to popularity.


In the end, if you could find the right TB layout with the right intake layout to match your suzuki build, you would gain a little power and response over your carb setup.

Is it enough to be worth switching back now... no probably not...

[MtnEX]

And I wouldn't say anything on the subject as I am pretty divided between EFI and carb for off-road purposes....


But you just don't see people buying new sports cars, and ripping out the EFI to install a big carb.

It just doesn't happen, and in my opinion shouldn't happen on off-road applications either...

The components should just be higher quality and more engineered for off-road use... They should be of the toughest design, and use the most sealed connectors, and heaviest shielding wiring, and on and on....

So they don't become a problem out there...

I am all for reduced liability... but I don't think it should come in the form of stripping them off... but instead reducing the liability of the extra stuff by making more suited to the application so it's a non-issue.

[lilguy450]

well the efi systems on these quads are nothing like the ones on cars and I woulnt even think of removing the one off my truck lol but all the high performance drag cars and race cars are running carbs..

[sexysilverado45]

in all honesty i would keep the 2500 dollars and put it towards suspension, or a house, apartment, car you name it. the f.i on a quad and vehicle are identicle except for quads have less sensors. also f.i is better in my opinon because its really not that hard to understand and fix a problem on it. sure a carb is easy but if you crawl around your quad long enough you'll learn it pretty quicly.

basically don't fix what ain't broken, the manufactur put it on there for a reason trust their work and leav it alon.

[MtnEX]

Originally posted by sexysilverado45
in all honesty i would keep the 2500 dollars and put it towards suspension, or a house, apartment, car you name it. the f.i on a quad and vehicle are identicle except for quads have less sensors. also f.i is better in my opinon because its really not that hard to understand and fix a problem on it. sure a carb is easy but if you crawl around your quad long enough you'll learn it pretty quicly.

basically don't fix what ain't broken, the manufactur put it on there for a reason trust their work and leav it alon.

I have to totally agree....

I was an absolute electrical system moron. But I had to learn it, and you'll be surprised how much you can learn when the urge to ride is eating at you. And now people turn to me like I'm some sort of guru when something goes wrong on a KFX.

I'm no guru on electrical systems. I've just learned the KFX system the hard way and understand the electrical diagram when I look at it, like you would understand a map of your neighborhood.

[lilguy450]

i disagree with the efi being exacly the same as a car the manufactuers barely started putting efi on quads...efi has been around for years on automobiles so it does differ alot yes it does do the same job but ive never had to put a tuner on a gas vehicle to run an aftermarket exhaust and intake however i would also take that 2500 and spend it on something else lol the LTR kit was half of that

[MtnEX]

They don't have the ability to adjust themselves for mods because they lack an o2 sensor, MAF/MAP sensor etc...

Therefore they are "open loop" systems... which are generally preferred for performance applications.

[scotturban]

Has anybody done this? I know its been talked about a lot and has anyone (without buying the 2100 bcs kit) has swapped there kawi to a carb?? All this electrical junk has screwed me one to many times now and I set i want it gone! Any Info ?????? Pics Would Be Better and Parts List

[MtnEX]

Originally posted by scotturban
Has anybody done this? I know its been talked about a lot and has anyone (without buying the 2100 bcs kit) has swapped there kawi to a carb?? All this electrical junk has screwed me one to many times now and I set i want it gone! Any Info ?????? Pics Would Be Better and Parts List

The short answer is no.
Nobody has done the conversion like that to my knowledge.


The carb and TB seem to be a direct swap.

CDI & coil swap could be done.

Electric start can be retained, kick start could be added.


Where the big mystery lies is inside the left engine cover.... the crank sensor.

None of us have any idea if the KFX crank sensor is compatible with the KX or KLX CDI?

Now if it is not, that is as simple as cutting the two wires and installing the KX or KLX pickup.

But then that draws a second question... is the KFX flywheel and KX or KLX pickup compatible?

Now the whole flywheel off a KX should fit the KFX, but then you loose electric start. And so to keep that you would have to see if the KLX flywheel is compatible with the KFX starter gears.

In the end though, the pickup position on the KX and KLX is different than the position of the KFX crank sensor. And the engine bottom end and case covers are a little different.

[MtnEX]

So, the first step would be to realize that the bike carb also has a TPS and you would want to go to thumper talk forums or something and ask the bike guys about this... rather it is a problem and if guys run without it, etc...


Then the next step would be to be brave enough to pick up a CDI and coil... try hooking it up and see what happens to find out if that stuff will work with the KFX crank sensor and flywheel.... if not the ignition timing will be all off or no spark at all.


Then you would have to buy a KX/KLX pickup and splice it into place of the KFX crank sensor.


It will no doubt take a gambler to see if it will work as you can see.

[scotturban]

thanks a lot for all the wisdom, but Im still a little confused here, already installed the kick start kit on my quad and its already a strictly mx bike anyway, Only ridden on a track, I want to get rid of electric start and battery all together and be just a kicker,,,,,I Know that BCS has sold a machined side piece for the left side of the motor with there kit, But for this to work what parts can I buy from a used part out (Ebay) such as carb, harness, flywheel, and what parts must I resort to bcs for? Thanks a lot for the help :) :ermm:

[MtnEX]

That is the problem, because nobody has been enough of a "GAMBLER" to find out the answer to that question so far.


If they sell a side cover for this conversion it makes me think they use a KX flywheel and all in their kit.

Is this required? I don't know.

If I had a friend with either one of the bikes I'd dang sure find out though!


You'd just have to buy, try and resell parts if it did not work.

I've almost gotten brave enough to try it by sourcing parts from a bike part-out and just seeing what happens.

[scotturban]

Hey MtnEX Can You Make a little list of parts i would Need? I emailed BCS about the parts they sold, will see if they emailed me back tomorrow or next few days hopefully, I think If I bought The Following iT Could work at Least to my Understanding

Honda 450r 41mm FCR Carb
KX450f Wiring Harness
KX450f Stator
Kx450f Flywheel
BCS Side of Motor To Accept KX FlyWheel??
BCS Part That Goes On Tank To Get Rid Of Fuel Pump

[MtnEX]

Originally posted by scotturban
Hey MtnEX Can You Make a little list of parts i would Need? I emailed BCS about the parts they sold, will see if they emailed me back tomorrow or next few days hopefully, I think If I bought The Following iT Could work at Least to my Understanding

Honda 450r 41mm FCR Carb
KX450f Wiring Harness
KX450f Stator
Kx450f Flywheel
BCS Side of Motor To Accept KX FlyWheel??
BCS Part That Goes On Tank To Get Rid Of Fuel Pump

No idea on the Honda carb....

KX Carb
KX wiring harness to mod
KX stator
KX flywheel
KX CDI
KX ignition coil
KX cams
BCS engine cover
BCS tank adapter

I swear though that I would look into trying not to change out the engine cover and what is inside there. I don't know that going to the KX flywheel will generate desired results on power delivery on the quad. I think the flywheel is already too light as-is and bike guys are known to add flywheel weights.

[scotturban]

Why The KX Cams? Already Running The Hetrick Mx kfx450 Cams? But would kx cams be neccesary?

[MtnEX]

No... KX cams wouldn't be needed... especially not if you already have aftermarket cams.


I was just saying to point out you'd be leaving some on the table with the bike CDI timing curve and stock KFX cams.... not having any idea what your mods were.

[RATPACK Z400]

wow a total waste of money!you could buy another used bike with carb then insert it in frame for that money! some people just dont listen or want something different so bad they,ll sacrifice loads of money to have it!

[scotturban]

No Im Not going to buy the two grand bcs kit, But If there is a cheaper way to buy the individual parts (Ebay) Then Im all for it, Will save tons of weight and make this bike easier to find out whats wrong, then going through days of wiring, Can shed off tons of weight get rid of the battery and all that stuff,

[MtnEX]

Yeah, and I doubt a bike bottom end would stand up real well in a high performance quad application.

Yeah people did hybrids in the 400 glory days, but they beefed up the bottom ends... and this ain't exactly 400 days we are competing in anymore.


But yeah, the cost of the BCS kit is just too much in my opinion. For that kind of money you could have a spare EVERYTHING for the KFX system to swap out with known-good parts if something goes wrong.

[PeterBenincasa]

Yeah I completely agree with Scott
I have a strictly racing KFX450 and since I modded it I have wanted to switch it over to Carb.

The suzuki's have nearly the same EFI system and I have seen a few LTRs with the Carb conversion, putting out even greater power and shaving tons of weight!

I am no genius with all the sensor crap, but I know how to work on a carb, and I know that by adding a properly working carb and lossing 5-10 pounds will make the Kawi faster..

If That company makes a kit I'm guessing somebody has done it, just the matter of talking to BCS and seeing if it was sucsessful.

[scotturban]

I shot them an email, heres what I got back... So they Can do it, and ive heard of it working, But the way it sounds is the only hard part involves stator/flywheel and it sounds like bcs is the only ones that can help with that because they made there own stator cover

I shot them an email, heres what I got back...


You can convert the bikes to carb, but it is really expensive and also requires a completely differant stator cover. If this is something you are interested in let me know and I can get a complete quote together for you.

Another solution to your problem may be to send your harness in for us to rework it in to a race harness which pretty much eliminates all the problems with the electrical as well as cleans it up good, That cost is $150.

[bimcgo1]

Heres a picture of a BCS race harness installed.

[scotturban]

for the price sending them your harness seems like a really good route, Looks like it cleans up under the hood so much,

[PeterBenincasa]

Wow thats way better! I definately will have to check that out LOL

[Kawie450r]

The BCS harness mod is great. I have it done to mine and have not had any electrical problems ever.