mikuni 33 smooth bores vs. lectron 40's

hey all, building a 75 kz900 drag bike. have 1400 kit in it, extended swing arm, drag slick, back cut gears, etc. i have both mikunis and lectrons. any racers out there have a preference of one over the other? why? let it all hang out cause i know u have an opinion or two. Thanks all!

Lectrons are probably the best pure HP making carbs out there. Simple to use and once set up, they need very little work afterwards. They sorta compensate for small weather changes and don't need to be re-jetted all the time whenever weather changes to get max HP. Mikunis will require more to get jetted right and may need to be re-jetted slightly for max HP if there is a swing in weather conditions but...lectrons are harder to drive around the pits or back from run. Not hard but trickier as there is no idle circuit in them. Mikuni's are full-function carbs and can be driven around. Lectrons on my bike seems to make it very abrupt on throttle response...imagine at idle and then jumps to 4000 rpm. Doesn't do that but the feel is there as the bike doesn't transition from idle to part throttle very good where the mikuni's will as they have all the necessary circuits. Local racer here that was the 2009 NHRA World Motorcycle Champion likes to use the mikunis over the lectrons. He has been doing this for decades and knows what he is doing, so either carbs will work. Lectrons seem to be the choice of most racers out there that are running serious bikes though. What cams are you using, porting done to the head, weight of you and the bike, compression of motor, etc. These things WILL make a difference in what you use.

Well i can only lend you my experience as i have put together many kawasaki drag bike engines. now if i had the choice between 33mm round slides or lectrons I would pick lectrons W/O hesitation. that being said the mikuni flat slides are a much nicer carb than the old round slides, but i would still favor the lectrons for a drag bike application. as far as what cylinder head is on the engine if its a Z1-KZ style cylinder head i would use a 38mm lectron. I know a lot of racers run 40mm lectron with KZ style head and a lot of my customers rum them but i have never seen any gain using 40mm. My own drag bike [ now sold ] was a 1294cc with KZ style head and 38mm lectrons and it went consitant 8.80-8.90s with me on it at the time i weighed 220lbs. I've dyno tested my bike with 40s and 38s and the 40s made slightly more top end Hp but the 38s made better overall hp. now if you had a good ported "J" or 83/84 "GPZ" head i say i would used 40mm. Larry what are your thoughts on this ? i came to the conclusion that a early head cannot flow the air to warrant a 40mm carb. I would be interested to hear your thoughts.

If this is a drag race only engine, you have only ONE throttle position.....WIDE OPEN. Go with the Lectrons. They may be worth as much as .10sec in the 1/8. More in the quarter. 33 smoothies will get the job done though if your on a budget(if you can find them nowadays cheap enough) and I think they look sweet with a set of stacks! :woohoo:

As the last poster said, 40 may be one size too big. find some 38's. You need to match your carbs closer to the intake port and valve size.

i'm running 40 lectrons on a real mild big block combo with a kz head that is actually set-up for 33's in my 7" chassis super consistant and fun to ride but it way more carb than i need with this head, i'm going to get a set of 38's this winter for it and put my 40's on a big bad combo that's going in my cartire bike this spring. the 33's i'm going to use on a 1200 motor that i'm putting together for street bike shoot type bike i'm building. so i guess the answer to your question is i like them both but definitly lectrons for the dragstrip if you have the choice.

timebomb33 wrote:

i'm running 40 lectrons on a real mild big block combo with a kz head that is actually set-up for 33's in my 7" chassis super consistant and fun to ride but it way more carb than i need with this head, i'm going to get a set of 38's this winter for it and put my 40's on a big bad combo that's going in my cartire bike this spring. the 33's i'm going to use on a 1200 motor that i'm putting together for street bike shoot type bike i'm building. so i guess the answer to your question is i like them both but definitly lectrons for the dragstrip if you have the choice.

timebomb do you happen to need a big block ? i have a brand new FBG big block and a set of JE 1397cc 14.1.cr pistons Bored, honed, decked, oringed ready to go brand new.

pm me we will talk

timebomb33 wrote:

pm me we will talk

just email me direct at b.flood@myactv.net i will be away from time to time i will reply and send pics.
Barry

DFIGPZ wrote:

Well i can only lend you my experience as i have put together many kawasaki drag bike engines. now if i had the choice between 33mm round slides or lectrons I would pick lectrons W/O hesitation. that being said the mikuni flat slides are a much nicer carb than the old round slides, but i would still favor the lectrons for a drag bike application. as far as what cylinder head is on the engine if its a Z1-KZ style cylinder head i would use a 38mm lectron. I know a lot of racers run 40mm lectron with KZ style head and a lot of my customers rum them but i have never seen any gain using 40mm. My own drag bike [ now sold ] was a 1294cc with KZ style head and 38mm lectrons and it went consitant 8.80-8.90s with me on it at the time i weighed 220lbs. I've dyno tested my bike with 40s and 38s and the 40s made slightly more top end Hp but the 38s made better overall hp. now if you had a good ported "J" or 83/84 "GPZ" head i say i would used 40mm. Larry what are your thoughts on this ? i came to the conclusion that a early head cannot flow the air to warrant a 40mm carb. I would be interested to hear your thoughts.

My thoughts are simple " YOU are right on the money"

KZ runners are pretty limited to what can be cut away at the port entrance so 38's are the "effective" limits.

To really make use of 40mm carburetors a J head pushing 105 - 110 CFM is more appropriate.

Lectrons are a heck of a carb in certain respects and a total piece of shit in other respects. They make HP. They have excellent throttle response.

What they don't do is idle stable below about 2500RPM. They also can be a bitch at the line after the burn out because they want to idle even higher. It makes the bike hard to get into first gear..

Bracket racing is about repeating the number [for most people] so which ever carburetor you can tune to do that will work just fine.

Let's look at some real world aspects of a rack of conventional carbs vs Lectrons.

Do you like to have the bike idle good and return to idle reliably? Then conventional rack carbs are the ticket.

Do you need to wring the last bit of power out of the engine? Then Lectrons are the way to go.

All kinds of people go drag racing. We have a crowd that only goes on T&T night for bragging rights. Then we have a crowd that heads back on Saturday to hopefully bring home the money :laugh:

Funny part is on more than a few occasions...it's a fat chick on a snowmobile that brings home the money!!! :laugh:

taildragger1197 wrote:

If this is a drag race only engine, you have only ONE throttle position.....WIDE OPEN. Go with the Lectrons. They may be worth as much as .10sec in the 1/8. More in the quarter. 33 smoothies will get the job done though if your on a budget(if you can find them nowadays cheap enough) and I think they look sweet with a set of stacks! :woohoo:

As the last poster said, 40 may be one size too big. find some 38's. You need to match your carbs closer to the intake port and valve size.

I have a nice rack of 33's available if anyone is interested. PM me for a price.

Larry C

another thing to look at is your valve sizing if your only running stock sized vales does it make much sense to use a carb that is 3 or 4 mm bigger. thats the main reason i'm going down to 38's for my 7 inch bike i'm using 37.5mm valves in it.

timebomb33 wrote:

another thing to look at is your valve sizing if your only running stock sized vales does it make much sense to use a carb that is 3 or 4 mm bigger. thats the main reason i'm going down to 38's for my 7 inch bike i'm using 37.5mm valves in it.

Good thinking Tim Glad you're back online BTW.

I'll tell you what bud. I don't even bother with 37.5 intakes anymore unless someone absolutely wants them. I found some nice stainless 37mm J intakes that make life so much easier.... Price is excellent also. If you want some, let me know and I"ll get them for you.

Larry C