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FAQ - Carbs

327K views 314 replies 120 participants last post by  joshuaj 
#1 ·
Quote, originally posted by GTaye »
Ever wonder?

(Stolen from Sport-Touring.net):
Basics of Motorcycle Carburetor Operation
The basic secret of carb function is that inside each carb are thousands of tiny gnomes; each with a small bucket. As you open the
throttle, more of these gnomes are allowed out of their house and into the float bowl, where they fill the buckets and climb up the carb's passages to the intake, where they empty their buckets into the air stream.

But, if you don't ride the bike for a while, bad things can happen.
Tiny bats take up residence in the chambers of the carb, and before
long the passages are plugged up with guano. This creates a gnome
traffic jam, and so not enough bucketfuls of fuel can get to the
engine. If it gets bad enough, the gnomes simply give up and go take a nap. The engine won't run at all at this point. Sometimes you'll hhave a single dedicated gnome still on the job, which is why the bike
will occasionally fire as the gnome tosses his lone bucket load down
the intake.

There has been some research into using tiny dwarves in modern carbs. The advantage is that unlike gnomes, dwarves are miners and can often re-open a clogged passage. Unfortunately, dwarves have a natural fear of earthquakes, as any miner should. In recent tests, the engine vibrations caused the dwarves to evacuate the Harley Davidson test vehicle and make a beeline for the nearest BMW dealership. Sadly, BMW's are fuel injected and so the poor dwarves met an unfortunate end in the rollers of a Bosch fuel pump.

Other carb problems can also occur. If the level of fuel in the float bowl rises too high, it will wipe out the poorer gnome housing in the lower parts of the carb. The more affluent gnomes build their homes in the diaphragm chamber, and so are unaffected. This is why the bike is said to be "running rich".

If the fuel bowl level drops, then the gnomes have to walk farther to
get a bucketful of fuel. This means less fuel gets to the engine.
Because the gnomes get quite a workout from this additional distance,
this condition is known as "running lean".

The use of the device known only as the 'choke' has finally been
banned by PETG (People for the Ethical Treatment of Gnomes) and
replaced by a new carb circuit that simply allows more gnomes to carry
fuel at once when the engine needs to start or warm up. In the
interests of decorum, I prefer not to explain how the 'choke'
operated. You would rather not know anyway.

So, that's how a carburetor works. You may wish to join us here next
week for basics of electricity, or "How your bike creates cold fusion
inside the stator, and why the government doesn't want you to know
about it."


Modified by GTaye at 4:59 PM 9-8-2004

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Later,
Thomas


Modified by the12for12 at 10:37 AM 6-21-2007
 
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#106 ·
Re: FAQ - Carbs (OnTheRunDCI)

Quote, originally posted by OnTheRunDCI »
Running a 2L 16V with dual weber 45's and have the carter pump. Which fuel filter should I run? I've heard of a 3 port filter than I can run the nipple on the tank that was for the return line to instead of capping off that nipple.

I use a ~'89 Maxima fuel filter. It has 5/16 (8mm) nipples on both sides.
 
#298 ·
Quote, originally posted by mofoco »
what about blockin off the frigin injectors how to?

cheap and dirty - use dimes and some high temp silicone in each injector port.
or, go buy 4 trans drain plugs from the dealer and screw them in.
Transmission drain plugs don't fit, but that was my initial assumption as wall. It's a 1/2" NPT (national pipe thread) I threaded a reducer bushing (for clearance issues) to reduce it to 3/8" I used a little JB weld on the threads because they were questionable. From there thread a barbed fitting into that bushing giving me a vaccume port pre throttle plate to sync the carbs and more than abundant vaccume for the brake booster.
I modded a lower intake manifold on my 9a 16v 2.0 and got r1 carbs to just clear the hood, but just.
Any advice on throttle cable?
I'm thinking of stealing the lines off my old BMX (never used them any way)
 
#109 ·
I got a couple questions about my carb set up
-the carter 4070 pump i got didnt come with any wire harness, where can i get some wires that will hook up to the terminals on the pump?
-I plan on running new fuel lines what size should i go?
-I wanna run a fpr, how much pressure is good for dellorto 40s?
Thanks very the help
 
#110 ·
Re: (6thGearGLIGuy)

Concerning Flat Slide Motorcycle carbs
......to be continued
Quote, originally posted by Jeprli »
Flat slide main jets only come into action at top quarter of throttle, midrange is controlled by the size and position of needle(you move a clip on the needle to a different position, upwards leaner, downwards richer, it basically controls when the main jet will kick in) and for first half of throttle it's all in the a/f mixture screw. If engine is running too rich with these carbs, it will bog down at lets say 4000rpm, if it's too lean it will let you know a lot sooner as it will have hard time starting. These type of carbs use very low fuel pressure as most are gravity fed so don't go crazy with pressure 2-3 psi the most. Oh and there is the float bowl which has a fork that controls these floats, you can bend that tab and allow more fuel into the bowl, but that is only for those who really know what they're doing. Also adding a little bit of high quality 2 stroke oil as a premix to your tank will keep flatslides smooth , and keep them from seizing(16:1-10:1 premix ratio). Balance and lighten your engines when using these as they rev up a lot quicker than fuel injected motor. These are practically impossible to synchronize, so the best you can do is have each one set exactly the same. I'll be doing this for my winter project, using a 2l aba motor with most probably yamaha R1 slides.

All additional info IM the original quoter, Udig?
 
#113 ·
Re: (chopWet)

Quote, originally posted by chopWet »
yep we need more on bike carbs, I have two magazine articles that give an overview of the conversion, if someone could host them they could be put up for refrence....





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#115 ·
Re: FAQ - Carbs (Big CADDY)

i have a 2L 8v counterflow (rv head) im gonna run sidedraft from a cbr 900rr any extra info would be wasome thanks my only main concern now is my ignition comes from my digifant box and i need to know how im gonna get my spark these setups appear to be for a cis or cis-e box help on ignition


Modified by bradford_ramage at 8:44 PM 9-21-2007
 
#116 ·
Re: FAQ - Carbs (bradford_ramage)

okay, lets take this to the top with some real crazy idea's
I have recently acquired a mk2 8v along with a dual 40mm mukini carb setup and cam.... I really want to run nitrous with that setup and don't even know where to start.
12for12
I'm gonna need ur help on the carb side of this from A to Z, its gonna be rather ground breaking and a spare 8v motor has been donated for the cause to see what this will produce. I have some help from experienced tech's awaiting the neccessary info to install the carb setup. Just lay it out here for them and we'll be testing the nitrous grounds shortly there after.
Yes I said nitrous, everyone can keep their negative comments to themselves.


Modified by GermanRob at 11:22 PM 10-10-2007
 
#121 ·
Re: (RaceJetta)

I have a 92 16v gti. And a pair of 45dcoe's, now since i have no ignition control unit. Can i just use a MSD6AL with my factory computer and Dizzy? Or will this not work? And what size fuel line are you using from the pump to the front?


Modified by DriVeWaY2L16V at 1:49 AM 1-11-2008
 
#122 ·
Re: (DriVeWaY2L16V)

you can use one of the existing lines for fuel, swap out fuel pumps, run a regulator and filter and your good to go. no return needed with 4psi
use the factory dizzy and a MSD 6A or 6AL. you can add the 8990 timing computer for more advance also. the diagrams are above. The ignition control units are a dime a dozen in junk yards.
 
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