A "HOW TO QUAD CARBY" THREAD PLEASE!

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A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Fri Jul 15, 2011 3:10 pm

This one is aimed straight to Superscan- can you do a thread on a "how to quad carby" build. This has been bouncing around the site for a while and we are too lazy to search the mis-information highway for tips and advice and you seem to know what you're doing. Can one inlet runner generate enough vacuum to actuate a brake booster? How do you operate the choke from the cabin? Should the carbies be fitted with individual air filters or can an air box be applied to filter them collectively? We would be most appreciative of you offering your R & D experience in this matter. Please- pretty please? 8-)
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby webby » Fri Jul 15, 2011 5:10 pm

viewtopic.php?f=30&t=4016&start=0&hilit=quad+motorbike
This's the link to the original thread :thumpsup:
A "How-To" would be awesome though, as would jet sizes, needle settings etc if you ever got it running right :)
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Sat Jul 16, 2011 2:12 am

geezer101 wrote:This one is aimed straight to Superscan- can you do a thread on a "how to quad carby" build.
No problem, I'm in the middle of making a quad carb setup so I guess I'll just have to take a few more pics.

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Sat Jul 16, 2011 8:24 am

Yay! Thanks for taking this one up. :thumpsup:
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Wed Jul 20, 2011 12:44 am

A few things to check before you decide to use a quad motorbike carb setup.

Probably the most important thing to decide is what size and type carbs you are wanting to use.


1. CV or NON-CV
I chose the CV (Constant Velocity) style with flat slide because they are the most forgiving and cheaper than the non-CV carbs.
I can put my foot flat to the floor any time and the engine won't bog down.
Basically they are an advanced SU carb.

The non-CV carbs will give you better throttle response "IF" you know how to operate then correctly.
They can bog down if you give it too much throttle but, if you know what you are doing, they are the better choice.
The problem is the price. On average, they are between 2 to 4 times the price of the CV style.


2. Carby size.
Considering the standard carby for the 2.6L have a 30mm primary and 32mm secondary, quad 25mm carbies would be be a 25% increase in size, which would also be the same size as a 34-36 weber.

I initially chose 40mm angled inlet carbs, but, because I wasn't confident enough to make an angled manifold myself, I ended up going with the 38mm straight port carbs.

For a daily drive with a relatively standard to a mildly worked engine, quad 34mm to 40mm will work great and I would rate them to be better than a twin 40mm side-draft setup.


3. Room
Another thing to consider in your carbie choice is the room in the engine bay. If you don't have much room between the head and the strut, an angled intake may be helpful, so you can fit the air cleaners on.





The Manifold


I start with a standard manifold, cut the pipes off and then weld on some straight tube, spacing the ends the same as the carbies.
That way, there is no carby modification required.
Image
Not pretty, but functional.

Do NOT use standard silicon tubing to join the carbs to the manifold, the petrol will wreck it very quickly.
The tubing I use is internally coated and fuel safe.
Just search EBAY, there are plenty of people selling fuel safe silicon tubing.





Basic CV carb setup

You will need a fuel pressure regulator that can regulate down to 0.5psi. These carbs are gravity fed on the motorbike so pushing anything more tha 1.5psi isn't a good thing.
I modified a standard holley carb fuel pressure regulator by compressing the internal spring a bit. This allowed me to be able to regulate the fuel pressure down to 0.25psi.



Based on my current setup of the quad 38mm Mikuni's off a 1995 Suzuki GSX-R750:


1. You shouldn't need to change either of the Idle jets (fuel and air blead). The idle AFR I'm currently running is around 17:1, without any issues.

2. Standard float height.

3. Main Fuel jet size 1.55mm.

4. Needle position will be determined by the wear on the "needle Jet", try the middle position first.

The only other thing to I'd recommend is to attach a cable for the choke. I only use it to start the engine on a cold morning. For the rest of the day, it isn't needed.
Because CV carbs don't have an acceleration fuel pump, pumping the accelerator when trying to start the car does nothing.

I'll post a few more pics in a few days. Just thought I'd better put a bit of blurb down while I'm in the mood.


Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby webby » Wed Jul 20, 2011 2:36 am

Winner. Nice writeup :)
Now to find a set of carbs, probably use them on a 2L to begin with as that's what my car'll be running while the 2.6 is being built.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Mon Jul 25, 2011 10:54 am

I've been doing a bit of research on the CV carby set up. These carbies are very vacuum sensitive and need a restricted air box to get the slides to actuate properly. Without an air box they won't work properly at low to mid range. I had a talk to a bike mechanic this morning and he said the most common mistake made on road bikes is the removal of the air box for individual K & N filters. He also warned me that CV carbies only have an efficient life span of 60-70,000 kms before the slides are worn out and require replacing- these are big bucks to rebuild (2 grand for a kit!) I think fabricaing an air box should be an easy enough affair though and will have a big impact on driveability and response. Now for the mental part- I am investigating the feasabilty of actually getting a manifold cast for this application. Redline make a 45 DCOE manifold that retails around the $320 mark- the quad carby manifold is actually simpler in design and would require less machining to reach the final product. All I need is the cash and time to develop it... :lol: :lol: :lol: :|
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Mon Jul 25, 2011 6:28 pm

:thumpsup: :thumpsup: :thumpsup: geezer101, good to see you doing some research. :thumpsup: :thumpsup: :thumpsup:
Originally (back in 1988) when I first decided to use motorbike carbs, I wasn't told any of this info, I just made it and it worked very well.

Recently, when I decided to try it again, I was told a lot of what you had been told.

BUT they are talking about a motorbike engine, NOT a car engine

geezer101 wrote:These carbies are very vacuum sensitive and need a restricted air box to get the slides to actuate properly.
This is true for motorbikes, for a 2.6L car engine, which is nearly 3.5 time the capacity, the "longer and stronger" vacuum pulse is more than enough.

geezer101 wrote:Without an air box they won't work properly at low to mid range.
Again, true for a bike, but consider a car engine's (2.6L) low end rev range is 1500 rpm, (multiply that by 3.5) which is around 5250 rpm on the motorbike.
Most decent cams come in around 2500-3000, which would be between 8750-10500rpm on the bike.

geezer101 wrote:He also warned me that CV carbies only have an efficient life span of 60-70,000 kms before the slides are worn out and require replacing- these are big bucks to rebuild (2 grand for a kit!)
On the cabies I use, the slides and the plate they rub on are plastic. I have done the best part of 80k on 2nd hand carbies and they are still going fine. Yes there are some scores on them but they still move freely and it doesn't seem to affect their function at all.
On a bike, that would most likely be a different story.

BTW:
What typically wears out first are the Needles and Needle Jets. At $55 a pop for each carby($220 a set), this can get expensive. The solution is to have the "Needle Jets" Nickel-Teflon coated.

geezer101 wrote:the quad carby manifold is actually simpler in design and would require less machining to reach the final product.
The problem is which quad carby setup do you make it for? The carb offsets are different for each bike.
I've been looking at a way to simply mod one of the redline manifolds but in the end, it's just as easy to mod a standard manifold.



Cheers.
Last edited by Superscan811 on Mon Jul 25, 2011 7:36 pm, edited 1 time in total.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby webby » Mon Jul 25, 2011 7:07 pm

When did I write that? :think:
Anyway. Carry on lol
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Mon Jul 25, 2011 7:37 pm

Sorry webby,

Fixed..

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby webby » Mon Jul 25, 2011 7:41 pm

All good mate, just had me a little confused is all :)
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Mon Jul 25, 2011 9:42 pm

Did you find out what is causing both the 'pinging' and running rich? Both events seem to contradict each other. Another item which is sort of related- on a standard carby what fuel pressure is going through the accelerator pump?
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Mon Jul 25, 2011 11:45 pm

geezer101 wrote:Did you find out what is causing both the 'pinging' and running rich? Both events seem to contradict each other.
The issue was unevenly worn Needle Jets.
2 were worn badly and this was giving a false "RICH" reading in the exhaust gases. Cylinder 1 and 4 were a bit lean causing, the pinging. Bought a new set of needle jets and the problem disappeared.

geezer101 wrote:Another item which is sort of related- on a standard carby what fuel pressure is going through the accelerator pump?
The motorbike carbs are gravity fed so they only require 0.5psi of fuel pressure. They can handle up to 2psi but you have to change the float levels.
I just modified a standard Holley fuel pressure regulator (compressed the spring a bit) so I could adjust the pressure down to 0.5psi rather than the standard 3psi.

Also, the CV style carbs don't have a accelerator pump.

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Tue Jul 26, 2011 11:51 am

Yep. know that. Was referring to the accelerator pump on a standard single mikuni/solex factory carb originally fitted to our engines. Was thinking could it be possible to reconfigure a fuel recirculation cannister to feed fuel to the quad rack and have the main fuel outlet from the cannister hooked up to the fuel return line?
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Tue Jul 26, 2011 1:17 pm

geezer101 wrote:Was thinking could it be possible to reconfigure a fuel recirculation cannister to feed fuel to the quad rack and have the main fuel outlet from the cannister hooked up to the fuel return line?
Good idea in theory but the problem is on a hot day, the return line to the fuel tank will be pressurized by the evaporated petrol in a warm petrol tank.

This, in turn, will cause the fuel pressure, at the carbies, to be too high.

You could make it work, but it would require a bit of creative plumbing and a small reserver tank.


Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Tue Jul 26, 2011 2:56 pm

Thought about the reserve tank idea but decided against it (no space elevated enough for a tank, didn't like having a fuel reserve in the engine bay). My brother's old scorpion used to suffer from vapour lock funnily enough, I had to pull over and crack the fuel cap to depressurize the tank on really hot days... Back to the thread. So you gave the idea of having inlet manifolds cast up serious consideration? If the inlet runners were cast short enough, wouldn't it be possible to use longer silicone joiner hoses to adapt to virtually any carby set up?
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Tue Jul 26, 2011 3:40 pm

geezer101 wrote:If the inlet runners were cast short enough, wouldn't it be possible to use longer silicone joiner hoses to adapt to virtually any carby set up?

Again, good in theory but silicon is flexible and if you pull 15-20lbs of vacuum, when you take your foot off the accelerator, a large long silicon tube will collapse in on itself.


geezer101 wrote:So you gave the idea of having inlet manifolds cast up serious consideration?
The majority of my brothers work is for some of the main foundries in Brisbane. Both Machining and die making.

My original idea was to have straight runners and then space out the carbies to suit. The manifold could also be used for a quad throttle body setup OR add a plenum chamber and use it for a Turbo or standard EFI setup.
The problem is the minimum run number for each of the foundries was high. Smaller foundries will do smaller numbers but at a much higher unit price.

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Tue Jul 26, 2011 6:00 pm

Bummer... :( I'll check it out one day as there's plenty of alloy casting foundries here in S.A. Maybe Kilkenny castings? :think:
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby woops » Tue Jul 26, 2011 9:15 pm

Have you considered getting a rapid prototype part to manufacture a mould for sand casting. If you designed up something in solidworks you might be able to get something reasonable. You'd just have to do a bit of thinking about the casting shrinkage etc.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Tue Jul 26, 2011 9:33 pm

I could make the casting relief myself (used to work in a foundry) and a model of the inserts but a: need to find an alloy caster willing to take the time out for one trial mould and b: find a machine shop to mill up the mounting face of the manifold, the thermostat housing seat and cut and drill the threads for the bolts and extraneous fittings. There's a lot in making a decent alloy casting and as I don't have the training in materials tolerancing I could end up with an expensive piece of aluminium for my efforts! Look over in the U.K. and you can buy off the shelf carby manifolds for VW Golfs and popular 4's- if there was enough interest in bike carbies for sirius/saturn/astron engines the market would make the R & D worth while...
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby A112H » Tue Jul 26, 2011 9:40 pm

Don't know what these are worth new but they might be suitable
http://www.redlineauto.com.au/products/ ... y/BRCNFUOG

Scott, can you measure the spacing across the outlet of the carbs please?
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Tue Jul 26, 2011 9:47 pm

The twin DCOE manifold was the one I was referring to earlier @ $320ish. Delete the weber mounts and taper the inlets closer to each other and there's your quad carby manifold...
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Thu Aug 04, 2011 11:10 am

Just had a look @ the quad set up you made for damian- very nicely finished superscan! I see you put the redundant injector ports to good use- is this for the brake booster? :thumpsup:
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Thu Aug 04, 2011 8:12 pm

geezer101 wrote:Just had a look @ the quad set up you made for damian- very nicely finished superscan!
Thanks, they are a bit rough but it will work fine. I just "finish" them in the sandblasting cabinet. :D
Covers a multitude of sins...

geezer101 wrote:I see you put the redundant injector ports to good use- is this for the brake booster?
Yes they are for the brake booster. The "ports" are just a lump of aluminium I welded on there to give me "a bit more metal to thread" for the vacuum ports. I had to put them on the bottom because they are using a standard mechanical fuel pump and if I put the ports on the top, they would interfere.

I use a vacuum port in each of the 4 runners because I have noticed my car idles better after I did the same to my manifold.

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby dvsfin » Thu Aug 04, 2011 11:28 pm

I had the pleasure of going for a nice little ride in superscans car today and I would have to say I am quite impressed with the performance of a relatively standard motor with the quad motorbike carbs
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Fri Aug 05, 2011 2:32 pm

...lucky bastard dvs! I should've had a better look at the pics- didn't realise the vac ports were on the bottom of the manifold, still very tidy work on your behalf. My hat off to you. ;-)
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby dvsfin » Fri Aug 05, 2011 5:07 pm

oh and I am also very jealous of all his toys and bargain ebay finds :P haha
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby natsroy » Fri Nov 11, 2011 5:37 pm

Hey great write up superscan seriously considering it myself,Just wondering what mods did have to do to the timing did the standard vacuum advance cope with the extra vacuum pressure? what timing settings did you use
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby Superscan811 » Fri Nov 11, 2011 8:23 pm

natsroy wrote:Hey great write up superscan
Thanks.

natsroy wrote: seriously considering it myself
Give it a go, it's definitely worth the effort.

natsroy wrote:Just wondering what mods did have to do to the timing... ...what timing settings did you use
I ended up with fairly standard timing, just 10deg initial and a little quicker initial ramp.
If you get hold of a Scorpion dizzy, it's easy to change the advance curves.
The 2 springs are readily accessible under the rotor button cap and they are on an eccentric cam.
Loosen the "thin" spring a little (no more than 1/8th of a turn) to increase the initial ramp.

Give it a test flog (wide open throttle) and see if the engine starts to ping between 1500-2500rpm, if not, give it another 1/8th turn.
When it does start to ping, note what RPM it happens at then tighten the "thin" spring 1/8th of a turn.

Changing the timing will also affect the air fuel ratios.

natsroy wrote:did the standard vacuum advance cope with the extra vacuum pressure?
No issues as far as I can tell. When you have your foot to the floor, there is very little vacuum.. :D

Cheers.
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Re: A "HOW TO QUAD CARBY" THREAD PLEASE!

Postby geezer101 » Sat Nov 12, 2011 5:57 pm

I've been giving the fuel pressure regulation thing some thought (verging on the dodgy side...) and is it possible to drop fuel pressure from an electric pump by lowering the input voltage to it? Had a chat to sparkington and his thoughts were it would be the amperage that would make this idea unviable... Anyone?
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