Veritas-Aequitas

Started off the day with a goal. Simple one at that.

Get the 250 started.

It's left me with a carburetor sitting on my desk, and me with no idea how to clean it. Big pile of parts on the ground that I'm going to try and put back together whenever I clean this carb. I guarantee I'm going to end up with misrouted hoses and at least one extra bolt.


Funny how you can tear **** apart with the best intentions, it goes well up until you finally realize you have no clue what the hell your doing. I don't even feel like putting it all back together anymore. Fawk.


Sorry for the rant. Anyone have any sites that explain the parts to a carb?

Odiedogcx

i know what you mean .. i like to tear things apart .. then i lose pieces, don't know what i'm doing, get bored, etc

try here .. http://auto.howstuffworks.com/question377.htm

Odiedogcx

http://auto.howstuffworks.com/....html

this one may be more useful

integrator43

post some pics..... i may be able to help

Veritas-Aequitas

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by integrator43 &raquo;</TD></TR><TR><TD CLASS="quote">post some pics..... i may be able to help </TD></TR></TABLE>

I'll post up some pictures tomorrow of what I managed to clean you can see if I missed anything.

3.50 a gallon is killing my wallet

ScareyH22A

Same **** happened w/my friends dirt bike. He tried everything to start it like towing it w/a truck and stuff but no luck.

He's gonna take it to a shop now. Fuel tank seems to be delivering into the carb fine, the filter lets air in ok, and there's spark. I dunno

Good luck.

UTCiv

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ScareyH22A &raquo;</TD></TR><TR><TD CLASS="quote">Same **** happened w/my friends dirt bike. He tried everything to start it like towing it w/a truck and stuff but no luck.

He's gonna take it to a shop now. Fuel tank seems to be delivering into the carb fine, the filter lets air in ok, and there's spark. I dunno

Good luck. </TD></TR></TABLE>


Try taking out the spark plug and squirting a little fuel in the cylinder to fire it.

My brothers 85 YZ125 wouldn't start cold any other way. Pushed, pulled whatever. Throw some fuel in the cylinder, wrench the plug in, starts on first kick every time and as long as you keep it warm after shutting off, starts first kick after that.

I don't know, I just don't like taking my bike to shops.

ScareyH22A

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by UTCiv &raquo;</TD></TR><TR><TD CLASS="quote">Try taking out the spark plug and squirting a little fuel in the cylinder to fire it.

My brothers 85 YZ125 wouldn't start cold any other way. Pushed, pulled whatever. Throw some fuel in the cylinder, wrench the plug in, starts on first kick every time and as long as you keep it warm after shutting off, starts first kick after that.

I don't know, I just don't like taking my bike to shops.</TD></TR></TABLE>

Tried it already. It'll run for a second and die again. I'm thinking that if there's fuel in the cyl and it starts, then the fuel from the tank isn't reaching the cumbustion chamber but when we mess around with the plug and stuff, there's fuel in there. I'm stumped. I told him to take it to a shop.

smokee

here is a good general carb site, with definitions and pictures of all the parts in your average carb

http://www.dansmc.com/carbs.htm

snowman95

this is a guide for the cbr250rr

but alot of the theory should stay the same

http://www.cr-x.org/cbr250/for...aning

Cheers to CAMD for the write up

Guys the following is a basic guide to carbs and how I go about cleaning them. For the last ten years I have worked on Aussie imports and particularly CBR250R’s and RR’s….. probably 100’s of them, no exaggeration.

We use two types of cleaner.
1/ A really heavy duty chemical that breaks down fuel deposits
Subaru Upper Engine Re-conditioner or Quicksilver “Power Tune” available from marine shops. Both come out of the spray can in a white foam. Bloody nasty to humans so use surgical gloves and eye protection and use it in a well ventilated area. I use Power Tune.
2/ An acidic chemical to wash the carb bodies with.
We use a product called Marine Clene which is a septone product. It is a citric acid based stain remover used for cleaning boat decks. Great for cleaning carb bodies but again a bit nasty on hands eyes and lungs.

**CAREFULL!! There is a chemical that is not as aggressive and good for just washing away dirt and grit etc… basically plain old carb cleaner from super cheap. Comes out of the can clear and is cold on the skin. It evaporates quickly. * DO NOT USE THIS TYPE OF CLEANER ON ANY RUBBER COMPONENTS AS IT WILL MAKE THEM SWELL…. eg: o rings, float needle tips or diaphragm rubbers. Best not to use it at all.

**NB: Before anyone starts getting excited and thinking to themselves that this guy is full of ****, and that there is heaps more to a carb than that, I’m only putting this together for the guys that have no experience or knowledge of carbs and don’t have the time or space to go through all the physics of carb operation.


Some Basics….
They worked out ages ago that approx 14 parts of air to one part of fuel, in this case petroleum, burns really well. Carbs are basically designed to make sure this is the mix of air/fuel that we get through the rev range of our bikes.

The first three things to remember with carbs is you need:
1/ Air in.
2/ Fuel in.
3/ Air/Fuel out.

In a simplified version of a motorcycle carb there are three main metering systems plus the choke system:
1/ Pilot Jet (also called – slow jet or idle mixture and is adjusted by the pilot or mixture screw )
from idle to ¼ throttle
2/ Needle / Needle Jet Nozzle (in this case the nozzle and emulsion tube are separate)
from ¼ to ¾ throttle
3/ Main Jet
from ¾ to full throttle
The Choke System
stand alone system in the carbs that gives you a lot more fuel for a cold start.


Each one of these systems has three parts to it (it all comes in three’s)
1/ Air jet – for air in
2/ Fuel Jet – for fuel in
3/ Orifice - for air/fuel mixture to come out of (in the case of the pilot system some times 2 orifices)
So think of each system as a “Y” . If you were to spray carb cleaner into one leg of the “Y” and block off the second leg, it should come out the third leg if it has no obstructions. This is probably the most important thing to remember. I use this method to make sure my jets and orifices in the carb are all clear. It is also a great way for those learning to trace where the different jets and passages in the carb connect to.


If any of these systems or air/fuel paths are blocked a part of the rev range will not be getting a correct mixture of air/fuel. For example: A partial blockage in an air jet in the pilot system will mean more fuel than air and therefore a rich mix at idle and probably darker colour spark plugs. If a main jet was to drop out the spark plug in that cylinder would be very dark. On the other hand if a jet is blocked you run lean on that cylinder and the plug would be a very light, almost white colour. Not good as you run the chance of burning a hole in the piston. So it is important to clean and tune the carbs correctly. Better power, better fuel economy and less hassles.

Rich = more petrol not enough air (dark colour spark plug)
Lean = more air not enough petrol (light colour spark plug)


OK…first off take the carbs off and get a clean area where you can lay out the components in order. If you have a bad memory or will be doing this job over a week, use a digital camera and take pics before you pull things apart. Makes it a lot easier to re-assemble. I have spoken to plenty of people that have been mechanics for a long time and they still aren’t systematic about the way they clean carbs. The only way to be confident they are clean is to take it step by step and don’t cut corners because you think you know better. Make sure you have heaps of light (very important), compressed air and a magnifying glass handy. Get a small glass jar and spray about a ½ inch of Cleaner 1 (Power Tune) in, so that as you take the jets out they can soak in it.

For this first cleaning stage use Cleaner 1… eg: “Power Tune” which comes out as a white foam.

Remove the float bowls and the floats. If the float bowls have crud in them spray some cleaner in them to soak. To remove the floats just take out the pivot pin. You will notice that there is a small needle shaped object attached to the float that was sitting into a special brass seat in the carb. This is what they refer to as the float needle and seat. The needle has a small sprung loaded nipple (ooh he said nipple) at one end. It is important that this nipple moves freely, so push it in with your fingernail a couple of times. If it is stuck, try to gently turn it with a pair of pliers. Be very gentle with it though. The MC19 also has a small wire clip attached to it at the same end, so be careful not to lose it. The other end has a black rubber taper on it. Clean this gently with a rag and inspect it with a magnifying glass for damage. I have hardly ever replaced them, only when people have damaged them, and even then probably only a dozen in ten years as they normally don’t play up.

The brass seat should be inspected for pitting and general dirt/crap. A good way to clean these is to polish them with a cotton bud soaked in brasso in a cordless drill. Again I haven’t had to replace too many as this normally cleans them up. The seats come out of the MC19 but are part of the carb body on the MC22. Each removable seat has an alloy washer under it and it must go back when you reassemble. If you buy a carb kit it will have a replacement washer in it. Soak the needle, seat, washer and float pin in the glass jar.

Next flip the carbs over and take the diaphragm caps off. Inspect the rubber diaphragms for holes or tears. They must be intact so that they respond well to vacuum. If they are holed throw them away and get some second hand ones from the wreckers. Sometimes you can repair them but it’s a bit tricky. Take care not to get any of the spray cleaners on to the rubber, as it may make it swell and assembly will be a pain. Inspect the diaphragm springs. They should all be the same length. Inspect the needles for stale fuel deposits and wear. A little wear won’t be a problem, but major wear or damage is not good and can cause a rich mix in the ¼ to ¾ throttle range. Leave the needles in the slides and spray them with cleaner A to soak.

In the top of the MC19 carbs you can see 2 little brass jets. One is for the choke and the other is for the idle mix. Spray some cleaner down both jets and see where it comes out at the bottom of the carbs. (in the float chamber).

Flip the carbs over. You should be able to see a fixed brass tube which is the choke jet, a long skinny removable jet which is the pilot/idle/slow/mixture jet, a larger diameter round jet which is the main jet. It screws into a tube with a hex head on it. This is the emulsion tube. It mixes (emulsifies) the fuel and air that flows up past the needle. On MC22’s you should also see a mall tube with a brass screw in it. This is the mixture screw we hear so much about. On the MC19 it is the brass screw on the side of each carb. You must be extremely careful with this screw. If you are heavy handed you can stuff the screw, or even worse the carb body. Very gently turn this screw in clockwise until it seats home. Do not tighten it! Screw it back out anti-clockwise 2 whole turns. This is the standard factory setting for this screw. Turn it out 2 more turns so that we open up the pilot system for cleaning. Don’t remove it yet. Actually I leave all the jets in at this stage. It helps me to see if any are blocked. I remove them at the end and let them soak while I acid wash the bodies. If the screw is jammed and won’t move I sometimes get them loose by heating the carb bodies, but you have to be very careful doing this. Best done by a mechanic.

At the back of the carb you will see the induction flutes. These are a funnel shaped piece through which air is drawn into the carbs. Rubber on the 19 and alloy on the 22. On the 19 there is a small brass tube at the base of it. This is the air intake for the pilot system. If you pull the rubber flute to one side you can see a hole in the carb body, this is the air intake for the needle jet/main system.
On the 22 there are 3 brass tubes. The one in the center is for the needle jet/main system, the two together are for the pilot system. The other is for the choke.

Spray cleaner through the brass pilot air intake and watch where it comes out. It should come out the pilot jet at the bottom of the carb and at the front of the carb near the throttle butterfly. If you open the throttle while you do this you will see there are actually 2 orifices where the spray comes out at the front of the carbs. One is for when the throttle is closed and the other comes in as the throttle opens. It makes for a smoother throttle response off the bottom. On the MC19 it should also come out the small brass jet up where the diaphragm seats. If every thing in the carb is open the spray should come out each jet/orifice. If it doesn’t then there is a blockage. Repeat this step spraying through each jet/orifice and watch where the spray comes out. After doing all four carbs you should have a good idea what passages and jets are connected.

Remove the jets, taking note where they came from and put them in the jar to soak. I have left jets and float needles in this stuff for several days and it doesn’t hurt them. Just cleans the fuel deposits off.
*NB.. Take the mixture screws out and inspect them for damage. Be careful with them and use a small piece of wire with a hook on the end to get the washer and O ring out.. The order of assembly is mixture screw, spring, washer and then O ring. Doesn’t matter too much if the O ring is a bit old, as long as it is there they don’t normally leak. Seen heaps of carbs run alright with out them.

Cleaning the choke system. Open the choke mechanism by hand while you spray through the choke jets. Also make sure that the choke arm that opens all the choke buttons has a small amount of free play at each choke button. You don’t want it to be holding a choke partially open.

Take the carb bodies out and give them a good spray with cleaning agent 2 “Marine Clene” and let them soak for ½ hour. Give the carbs a good hose off and blow through every passage you just put spray through. Really dry them off so that there is no water left in them. Take your time and be sure.

Put the mixture screw back in and take it all the way home, carefully. Wind it back out 2 turns. Standard is always the best setting to start with.

Take the jets out of the carby cleaner and wash them off with water. I put them in a large tea strainer so that I don’t lose any. Replace all the jets. On some MC22 models the larger main jet go to the outside. Make them tight but don’t go crazy. They are small and brass…. easy to break. Re-fit the floats and float needle and seats. Make sure that the needle is sitting in the correct position on the float. You can’t adjust the float on a MC22. On MC19’s it is important to set the float height. MC19’s will run a bit rich under braking if the float level is too high. They get fluttery when you brake hard at the traffic lights and come good again after a few seconds. Stand the carbs up on one end and lean them back until the floats just close. Standard setting is 7mm from the bottom of the carby where the float bowl mates, to the bottom of the float. We set them at 9mm. There is a small metal tag that the needle attaches to. If you bend it towards the carb body it leans the float level by making the float close earlier. If you bend it away it makes it rich. When you are finished look down through the line of the floats. They should all be roughly the same height. Replace the float bowls. Quick tip…. MC19’s have little alloy tags that get in the way of mixture screw adjustment. Grind them off…makes tuning on the bike easier.

Wipe off the diaphragms and needles with a rag and replace the diaphragms and springs. Be careful to make sure the outer of the diaphragm rubber is seated properly and the spring is aligned before putting the cap on. After the caps are screwed down lift each diaphragm by hand. They should all feel the same. If you feel one that comes up easier than the others the diaphragm rubber is not seated. Lift the cap and reseat it.
I then set the carbs in their running position and attach a dummy fuel tank to make sure none are flooding. If a carb does flood give it a tap with the plastic end of a screw driver to help the needle and seat do it’s job. If this doesn’t work drop the float bowl on that carb and check the needle and seat. It may need a bit more polishing to clean the seat

Check the inlet manifolds for damage. Replace if necessary. Spray a bit of WD40 on the inlet manifolds and replace the carbs and get the bike running. Let it get up to operating temp and then adjust the pilot/idle mixture screws. Turning them in, clockwise, makes a leaner mix. Turn them out to make them richer. I turn them ½ turn out and see if the revs pick up. No change…? Then I screw them back in ½ turn. I then screw them in another ½ turn and see if the revs pick up. No change…? Then I turn them back out ½ turn to the original position. Basically I set them by ear. If the revs pick up that means the motor wants a bit more fuel to run properly. Idle should be 1500rpm

That’s pretty much it. If you don’t have the gear, take it to a mechanic and have the carbs synchronized. It shouldn’t cost too much.

Hope this helps…… Cam

integrator43

very good write up............. i love learning!