QUAD Motorcycle Carbs

[Zufer]

to be honest the reason i went with the plenum was i had all the stuff to make it and i am extremely broke at the moment. Also i gain the benefit of cold air, which i would have lacked with velocity stacks and foam filters as they would have been right behind the engine and above the exhaust. And yes all the fabrication and welding was done by myself.

Thank you all for the great comments, i'll try to get a vid of it running sometime, but i don't know how much how well you will be able to see anything if i driving, but i can get a free reving vid soon.

[87lxiaccord]

You should dyno it!

[bushbean]

What is the reasoning behind having four little carbs instead one big azz one?

[Legend_master]

What is the reasoning behind having four little carbs instead one big azz one?

It's like EFI before computers were around.

[Zufer]

the idea behind 4 little carbs is that each cylinder gets the precise amount of air and fuel as opposed to a single carb which is a generic tune so the cylinder just get whatever mixture there is in the plenum when they are sucking. Also 4 carbs give better response which was the main goal. Because i autocross and track my car i am not really worried about peak horsepower and more worried about a flat torqure curve, this was the best way to do that NA.
and yes i plan on dynoing it. But before i do i have a teg tranny and a lightened flywheel to put in, and some porting and tuning to do.

[2ndGenGuy]

Sweet setup man! You should PM me next time you head to an autocross. I do some up here, but I would totally drive to Portland for a chance to go with another Accord.

[Zufer]

ya i will for sure let you know when i'm gonna be running, i don't know how much autocross i'll be doin but i definitely am gonna get to a couple trackdays in august, well atleast thats the plan. you should come run one of those.

[Justin86]

nice!!!

[sb_hbackDX]

I have been pondering with the idea of quad carbs for looooonng while and now that money is... somewhat abundant I think Im gonna go through with it. Since your one of the few guys on here with quad carbs I figured I'd ask a few questions...How is the car/carbs holding up since the conversion? Did you ever fab another intake mani? With four carbs...how is the gas mileage(important for poor college students!) Now I have access to a MIG welder for the aluminum and I also know how to use it so that shouldn't be a problem...But how long were your runners? I saw that they were pretty long for torque reasons due to your large cam...but I have a mild cam, Colt Triflo Stage 1. I have some measurements for the runners already but I would like to get your input. Now to the carbies
Did you create a fuel rail for them? What was your PSI in the line? I have been tuning and tinkering around with carbs for years and I'm sure you know how to tune also but how tough were those to tune? I have a Weber 32/36 and 38 also and those were not to bad to tune even thought I didn't have a Wideband O2 sensor...Growing up me and my dad worked on Holly's, Edelbrock's and SU's...Weber was a new one for me and I must admit there pretty badass but I want better throttle response too and I'm not really into the dual DOEC 40's...i hear there gas guzzlers and not half as cool as 4 mini carbies. Damn this message is long! Im sorry to make you read all this shit hahaha Well whenever ya free give me a write back. Adios man!

[lostforawhile]

I have been pondering with the idea of quad carbs for looooonng while and now that money is... somewhat abundant I think Im gonna go through with it. Since your one of the few guys on here with quad carbs I figured I'd ask a few questions...How is the car/carbs holding up since the conversion? Did you ever fab another intake mani? With four carbs...how is the gas mileage(important for poor college students!) Now I have access to a MIG welder for the aluminum and I also know how to use it so that shouldn't be a problem...But how long were your runners? I saw that they were pretty long for torque reasons due to your large cam...but I have a mild cam, Colt Triflo Stage 1. I have some measurements for the runners already but I would like to get your input. Now to the carbies
Did you create a fuel rail for them? What was your PSI in the line? I have been tuning and tinkering around with carbs for years and I'm sure you know how to tune also but how tough were those to tune? I have a Weber 32/36 and 38 also and those were not to bad to tune even thought I didn't have a Wideband O2 sensor...Growing up me and my dad worked on Holly's, Edelbrock's and SU's...Weber was a new one for me and I must admit there pretty badass but I want better throttle response too and I'm not really into the dual DOEC 40's...i hear there gas guzzlers and not half as cool as 4 mini carbies. Damn this message is long! Im sorry to make you read all this shit hahaha Well whenever ya free give me a write back. Adios man!

i was going to ask him how they were running also. just to compare notes,i got some more done on mine recently and i've got some pics and a couple of videos up on the site. https://www.3geez.com/forum/showthread.php?t=61333 as far as pressure most of these side drafts run about 2-3 psi,it's fuel flow thats important on a carb not pressure. as long as the bowl can be kept full you're fine. on mine i'm running a holley low pressure regulator,i've got it set up on the factory carb right now,and i run about 3 psi. i built another pickup for the tank and i'm going to run a walbro pump under the body,that pumps fuel on demand. the stock fuel line is actually pretty decent,it's just the pump that sucks. we need to start a thread on here,just for those of us running multiple carbs,so we can all compare notes.

[cygnus x-1]

...Growing up me and my dad worked on Holly's, Edelbrock's and SU's...Weber was a new one for me and I must admit there pretty badass but I want better throttle response too and I'm not really into the dual DOEC 40's...i hear there gas guzzlers and not half as cool as 4 mini carbies.

Better throttle response than Webers? How do you mean? My 38/38 had awesome response; barely any throttle needed to cruise. If you want it to rev faster you need a lighter flywheel.

C|

[sb_hbackDX]

Yes I hear the 38/38 has damn good throttle response and in fact I have one but don't you think 4 39mm mini carbs would have slight better response that a large 2 barrel 38 carb? Thats a 39mm carby per cylinder I don't want to junk my Weber's but its just a recent project i was working on...
http://cgi.ebay.com/ebaymotors/ws/eB...ayphotohosting
I already have cut the aluminum runners and an old EFI intake mani(using injector sites for vac log) I just have to make time to weld them together...What do ya'll think? This is also a cheap mod, well for me, the carbs were under $200 and apparently they were rebuilt and with low miles...I'm just concerned with the MPG with 4 39mm's Another issue is that the carbies are "electronically controlled"... The on board CPU apparently controls the lift of the beveled slides of the carb by regulating the pressure above the diaphragms...could be a problem but hey a carb is a carb right

[cygnus x-1]

Not necessarily. In fact carbs that are too big can be worse than smaller carbs. They need to be matched to the engine so that it gets the right air/fuel mixture when the throttle is opened. A small engine may not draw enough air volume through a large carb to create the velocity needed for good fuel metering.

I'm not saying they won't have better response, but I think you'll be hard pressed to get better response than a properly tuned Weber.

C|

Yes I hear the 38/38 has damn good throttle response and in fact I have one but don't you think 4 39mm mini carbs would have slight better response that a large 2 barrel 38 carb? Thats a 39mm carby per cylinder I don't want to junk my Weber's but its just a recent project i was working on...
http://cgi.ebay.com/ebaymotors/ws/eB...ayphotohosting
I already have cut the aluminum runners and an old EFI intake mani(using injector sites for vac log) I just have to make time to weld them together...What do ya'll think? This is also a cheap mod, well for me, the carbs were under $200 and apparently they were rebuilt and with low miles...I'm just concerned with the MPG with 4 39mm's Another issue is that the carbies are "electronically controlled"... The on board CPU apparently controls the lift of the beveled slides of the carb by regulating the pressure above the diaphragms...could be a problem but hey a carb is a carb right

[Zufer]

sorry double post

[Zufer]

ok i know this is my thread and i haven't been posting in it.... but i will beg to differ with the hard to beat a weber comment. I had a very well tuned weber and when my carbs were properly tuned on the first try at my manifold it had way better response. however i also went with 34mm carbs because i felt from reading and calculations that it was all i would need to fuel properly up to 7k rpms. I have yet to get my newer shorter manifold tuned properly so i can't say how responsive it is... but hopefully in the next week or so.

Also for those thinking of trying this... all i can say is it is not for the feint of heart as my car has yet to idle properly for more than a few days because as the weather changes so frequently here in portland the mixture changes as well. This is also partly due to the large cam, but a lot of it is the carbs. that being said i am glad i have done this setup although i'm kinda frustrated with tuning right now

[lostforawhile]

Not necessarily. In fact carbs that are too big can be worse than smaller carbs. They need to be matched to the engine so that it gets the right air/fuel mixture when the throttle is opened. A small engine may not draw enough air volume through a large carb to create the velocity needed for good fuel metering.
I'm not saying they won't have better response, but I think you'll be hard pressed to get better response than a properly tuned Weber.
C|

this is one advantage over the webbers that the SUs have,they are a variable venturi carb, the piston controls the size of the venturi, by the amount of air flowing through it. less air needed,idle and cruise, the venturi gets smaller,open the throttle and the engine demands more air,the piston rises and the venturi gets bigger. this assures the mixture is always correct under all conditions. lets see a webber adjust itself like that. thats the inherent problem with all fixed venturi carbs, you can tune them at a comprimise at one point, but at the opposite ends of the operating range,they will always be out of tune. there are various fixes for this,such as power valves,accelerator pumps, booster venturis,etc. etc. etc. but it's still always a compromise. the SU is like having a carb that has almost infinite adjustment over the entire operating range. almost like a mechanical fuel injection system. this is also the reason that the same Su carb can be used on a number of different sized engines. the carb adjusts itself to the airflow of the engine.

[cygnus x-1]

Variable venturis are cool.

But my main point was that a larger carb does not necessarily equate to better throttle response. Manifold design and tuning has a lot to do with it as well.

C|

[lostforawhile]

right,but these carbs can act as both a larger carb and a smaller carb. smaller carb is better for cruise and low speed larger carb is better for wide open throttle. the venturi changes the size of the carb in essence

[A20A1]

Are your runners the same inner diameter all the way through or do they get wider as they get closer to the head or is that just the extra thickness of the stock manifold?

[hondaman1986]

any updates on how its running? what part of portland are you from i live in clackamas and would love to see this in person

[2oodoor]

He was on the other day, I would like to know how it runs as well, hearing it would be a bonus too

[Ichiban]

Unfortunately, electonically controlled carbs are usually a disaster. Best of luck on that one.

Also, look at any (most) 2 or 4 barrel progressive carb. The primaries are way smaller to maintain high velocity required for good driveability and throttle response. The secondaries are huge, the assumption being that the engine is turning fast enough when they open that it's producing enough vacuum to support the added airflow, and thus meter the fuel properly.

[Zufer]

this is not an electronically controlled carb. And also it runs, hopefully in a couple weeks it'll have a better tune on it. and the it has a vacuum controlled slide to keep the velocity constant.

[Ichiban]

This is also a cheap mod, well for me, the carbs were under $200 and apparently they were rebuilt and with low miles...I'm just concerned with the MPG with 4 39mm's Another issue is that the carbies are "electronically controlled"... The on board CPU apparently controls the lift of the beveled slides of the carb by regulating the pressure above the diaphragms...could be a problem but hey a carb is a carb right

This is what I was referring to.

[2oodoor]

^^^those were 1996 suzuki GSXR750 carbs^^^