SINGLE CARB MOD

well i said i was going to do it, and my rack of 4 CV carbs acted up on the way home from storage today so........

i started making an intake manifold, i have a take-off harley carb. its a side draft keihin, single bore, throttle plate, pumper carb. i have not looked up the numbers to see exactly what it is yet but i will post up once i figure it out.

this will unfortunately be a LOOOONNNG project because i just do not have much time to do anything on the bike, quad, truck, or mustang lately because we are working in long island. i am home weekends but i just dont have enough hours in a day. at $4 per gallon for diesel i will need to make some time, because 5mpg on the bike saves me some cash.

discuss. 8)

 

Is that 5 mpg or 50 ?

 

What's your ideas for the intake? Someone on this site said that they had done this but took a long time to get the intake right. All the port tubes had to be the same length if I remember correctly. :roll:

 

eek! 50mpg!!! if it only got 5, i would have to scrap it!

as for the intake....

let me start by saying, this is not going to be for performance. this is primarily to RETAIN or IMPROVE the 50mpg it currently gets while eliminating a ridiculous rack of 4 cv carbs.

with that being said, i have a few designs for intake manifold that all attempt to keep the runners as close to equal length as possible. the better ones may not fit, so i need to do some mach up and see what works and what doesnt. i also do not think equal runner length is going to be quite as important as it would be if i were doing to do this for performance reasons. just thinking "aloud" here, but if we pry away from the MC world of thinking, and look at some auto inline engines...even the performance offenhauser manifolds do not have equal runner length. only the most "extreme" high rpm full race engines have manifold designs aimed at equalizing runner length.

one design that i keep coming back to resembles a 5.0ho style upper manifold or as some gm guys like to call them, a tunnel ram. the only thing i dont like about this design is i do not think i can keep the runners long enough. it would help if i had the bike here in my hotel room so i could see how much room i actually have.

for those inbterested, i have not molested my cv rack yet, because if this fails i will tear into the rack, fix it and get the bike on the road for summer while i do some more in depth R&D so i can take a better and more prepared "swing" at it next winter.

 

I think the tunnel ram idea is probably your best bet. I don't think it would need to be all that big and would allow you the most equal intake runners with the least amount of work.

Then put a pod on it because you can!

 

I think the difference will be downdraft principles (automotive) vs sidedraft principles (motorcycle). That was my thinking on the manner but I might be wrong. There was some cool 4cyl. car manifolds designs from the past that could work, like the 240z Datsun/Nissan, that goes back a ways but I hope your getting the picture. And by all means put some pods on it.LOL

 

Weber makes some side draft intakes you might look at them for ideas. A buddy of mine had a two carb side draft intake on his pinto back in the early 80's.

 

2into1 carb setup on a XS650 Yamaha

 

this is how someone else is trying to do it

http://www.google.com/imgres?imgurl=htt ... 29,r:2,s:0

 

I had a look at the image you linked to..

Will there be a delay for the mixture to get to carbs 1&4 with this setup, or is it compensated for by using different diameter on the outer ports?

 

This style of manifold was common on cars in the 1960s. Not that efficient, but will certainly work.

 

That is exactly what I was getting at (not that efficient), getting all the tubes to deliver the right mixture will be difficult. Hope it works out for you, keep us updated.

 

i am attempting to use a holley 2bble. will use copper 1 /2 copper pipe from carb adapter plate to middle of homemade aluminum intake.

 

Id like to see the mpg with this.

 

i wanted to use a 390 4bbl i had, but it got used for a truck instead. the only problem i saw with using a holly was the physical size of the thing! i would be very interested in seeing how yours comes out!

i just walked in my door, back from LI. tomorrow i have a long list of things i need to do but i hope to work on the manifold. i am going to trial the tunnel ram style first.

 

i think a 4bble would be overkill. ditto on how yours turns out. good luck

 

cb550 with updraft tractor carb

 

ok so its a Keihin butterfly non-cv for harley davidson. i cannot seem to find any info on a real model name for it (FCR for example) but all over harley forums thats how it is recognized. good enough i guess.

the number on it is 27029-83D, so its the 4th version of the carb that was used in 1983 on basically all of the bikes. the harley guys claim that this carb is where the term "Keihin cough" originated, because of the super lean jetting and elimination of a check valve in the pump for epa compliance. the part number still doesnt tell me the advertised size of the carb.

now i am going to measure it and scavenge materials for an intake.

 

41 or 42mm carb, cannot be 100% accurate with my "home" set of calipers. they are very old and sloppy. close enough to kill my curiosity though.

 

i started fabbing a manifold. i am going to tack this up, and see where i can put the carb, i want to make another runner that feeds the carb charge into the center (between 2 and 3) to keep the distances as close as possible.

not much to look at, 5 minutes only gets you so far :lol:

 

This should get interesting...

 

Ditto on that. I just hope that the pictures keep coming as progress is
made.

 

Zookie are you going to retain the stock carb mounts to attach the manifold? Is the bike your building this for currently running?

 

i know it wouild be a total pain in the butt to make,but since you plan to stik a runner tween pots 2 n 3,would it not b better to use a couple of runners tween 1 n 2 and 3 n 4,and maybe angle them together to form a 1 into 2 into 4 mainifold.they would then b more or less identical lengths.

 

ditching the manifold rubbers and flange mounting to the cylinders?

 

theres guys on tcu that have single carb mods.

one guy has a kz1000 with a single carb that he just uses to ride around the farm, lol.

 

here you go bobe....not much but i worked on it for a few minutes again today. dont laugh at the welds, my smallest wire i have for the welder is .045, a little too hot for the thin stuff function over fashion!

i will be using the stock rubber intake flanges to save time.

this is how i got the runners lined up to be sure they would fit perfectly into the rubbers:


then i welded it up:


i broke my good camera, in case you didnt notice.

 

It certainly looks cool Zookie, but don't you think you may have problems with equal distribution to each cylinder. Think about it, it will be a short trip to the closest cylinder (Probably will run rich, but the one on the opposite end will be sucking wind because of the air fuel mixture being used up before reaching it. My opinion, it would work better with the single carb in between the number 2 and 3 cylinder, but try it your way first, I wouldn't want to interrupt you.

 

Welds look good to me. Putting the carb between 2-3 would probably give
the best fuel air mix to the cylinders. 2 and 3 will be a little bit richer but
for this experiment should not be a problem. When you get it running the
plugs will tell the story. If nothing else this mod has caused a lot of interest.

Bob

 

i am going to try and get the intake charge to come into the rail between 2/3 if i can. if not, i am not too concerned because it has never been a problem when tuning an inline 6 with unequal runner lengths.

 

That may be because the internal of the manifold are drilled to give equal flow, as is hinted by the separation of the chamber on the image you posted.

 

To help with the problem of a "dry" charge here, and a "wet" charge there, depending on the different runner lengths, you could secure a stainless scrubbee under the carb, so that the droplets wet-out into the mesh, helping to evaporate and homogenize there. Then each CYL gets a more uniform charge regardless of runner length.

Get fancy and plumb-in an oil line for extra vaporizing heat.
Check out vaporizer carbs here -

http://www.rexresearch.com/auto/carbusp.htm

 

the manifold i posted is a dual port, each runner has 2 ports in it, one for primary and other for secondary feed. its not for equalizing flow, but for keeping low speed velocities high. it just broadens the torque curve.

a heated carb spacer could be an option. a lot of people run them on the 300ci fords to improve vaporization.

 

Zookie do you mean dual plane?

 

Wouldn't the vacuum pressure of all 4 carbs create an equal amount of volume being distributed to each carb?

 

the longer the intake tract the worse the throttle response will be.
when it goes from one throttle setting to another the charge in the intake has to get used up first.
when going from idle to 1/2 or full will there be enough vacuum to draw fuel through the mid or main circuit ?
remember how bad a 4 barrel ran when the accelerator pump wasn't working

 

The subject line says single carb mod?
You have 4 hooked onto the pipes.
I guess Im not really seeing what the end result SHOULD be.

Is this going onto a car? I cant see how this will bolt up or squeeze into the manifolds OR are you trying to run two pods?

 

Bill, he is going to make a carb attachment of some kind on the middle of his creation similar to the last image on page two of this forum. The 4 pipes you see coming off the one or to attach to the intake side of the motor.

That why we are having this discussion of putting the carb in the middle, and the pipes closest to it would receive more fuel mixture than those on the outside.

Hope that helps.

 

And I assume he plans on capping off the ends of the main pipe. I see what you are meaning as far as the pods, but those will be closed.

 

wow lots of questions! ok....
-ends will be capped
-the higher volume intake tract should be ok when giving more throttle, but will have a "drive by wire" like delay when returning to idle. i am ok with that, within reason.
-Bill, i used the carbs to position the runners. now i know it will fit into the same rubber flanges that the carbs do. (the ones bolted to the head)
-waldo, dual port, very different than dual plane. there are not many good pics of it, this was the best i could find. each single intake port on the head of the engine would equal two ports on the manifold, each runner is actually two runners feeding the same single port on the head.


and for some more pics (yes thats a pipe fitting, i could not make a true bend that tight so i gave up and farmer'd it!)



and this is where the carb will sit, i havent made a mounting flange for it or welded the pipe in place, need to check it on the bike for position first!

 

Hey now, I get it. LOL
The first production run is always the toughest. Dont give up!

 

ya, i am just using what i have in the shop to slap something together, see how it runs, and if it works out well this coming winter i will buy tight bends and make a nice spaghetti monster intake for it that is much more compact with shorter intake run and a smooth flow path throughout.

this is just the beta tester

i dont have any new pics, i just plasma cut 2 flanges for the intake and charge side of the carb. i havent smoothed or welded them yet. i did transport my bike from home to the shop, so i can "button it up" tomorrow hopefully and i can start jetting it.

 

This has been a fast build. It would have taken me 3 months to get the parts
and work it all out but this is welded up already and looking good. It will be
interesting to see when it starts up. (possible YouTube pics). This is really
different and great to see as the whole concept evolves.

 

I need a plasma cutter...

 

we all need one! very expensive for a non commercial operation (hobbyists like most of us) but i am fortunate enough to work for someone who has a lot of toys

my work on the bike got cut short today, barely got the shop warm before i had to leave

in these pics the manifold is not inserted to the rubber boots, just held up in front of them so there will be a little more clearance between the manifold and tank/frame. i will be welding tabs to the frame and manifold to bolt it into place, otherwise it will just fall out of the boots. (pipe fitting added some unforeseen weight, what a hack! )





i dont know if i will be able to get to a point of running it this weekend, we had a horse rupture its stomach after we rushed it out to the vet hospital, so now i am tending to an emotional minefield wife.

 

and youtube will happen 8) even if it fails horribly 8O :lol:

 

If the youtube vidio is as good as this build it will be ok. I hope that the horse
gets well soon.
Bob

 

Im inspired... I want duals... one on each side!!!

 

bill- these carbs are being thrown out by many harley guys in favor for an aftermarket s&s or other performance carb.

bob- unfortunately, my wife is a wreck because the horse has been put to rest. i dont mean to sound incompassionate but things like this always have the perfect timing to ruin plans.

 

Hi Zookie Sorry to hear that the horse did not make it. I was a bit worried
when you said that it had ruptured its stomach. I thought with shock and
everything it would be a hard one to turn around. It is always worse when
a loved animal is involved.

The harley carb that you are planning to try do you know what size harley it
fits.

Bob