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Cleaning Carbs

130405 Views 144 Replies 57 Participants Last post by  mat
If a spark plug change and air filter replacement do not have the desired effect on your bikes performance, the three golden steps you need to follow to get your bike running smooth are

- Clean your Carbs
- Set the Float Heights
- Get them Balanced

For Cleaning the carbs

Items needed

1. Aerosol Carb Spray Cleaner
2. Clean Petrol in a Plastic “Squeezy” type bottle
3. compressed air (if available)
4. new screws for the top and bottom carb covers (check for correct length)
5. new fuel filter
6. soft brush and toothbrush

Tools needed

1. Very long (12 inch) Phillips screwdriver
2. Stubby flat and Phillips screwdriver
3. 8,10 and 12 mm spanners (ring preferred), and 2 fixed 10 mm spanners
4. pliers (to undo the clamps holding the fuel pipes)

Getting to the Carbs

1. Disconnect the fuel / vacuum pipes from the tank
2. take off the tank after making sure that the tap is off and place it gently on a discarded car tyre – the edge of the tank will rest on the sidewalls of the tyre while the tap can hang safely in the middle
3. undo the air filter box from the carbs
4. loosen the screws holding the carbs to the manifold – you’ll need the long Phillips head screwdriver for this.
5. pull the carbs out firmly but gently (this is the first hurdle – get ready for some bruised knuckles)
6. undo the accelerator and choke cables with two 10mm fixed spanners and screwdriver (choke cable) making note how they should go back in.
7. the carbs should be free now – wash them from the outside liberally with petrol and a soft brush and toothbrush
8. tap each screw on the top and bottom of the carb gently with a hammer
9. mark the top and bottom of each carb with numbers from 1 to 4 to ensure that you don’t mix the internals / covers up.

Opening Process

1. Open the screws from the bottom of each carb – do this one at a time (this is the second hurdle – have someone experienced at hand and an impact driver if possible) make sure you don’t “round” the heads of the screw.
2. take the cover off and place the screws in it
3. gently slide out and remove the float pin, needle and float and place them in the bowl
4. with the correct ring spanner (8mm I think) and flat screwdriver undo each jet gently !!! the metal is very soft !!! – place it with the respective carb cover
5. repeat this over all 4 carbs
6. turn the carbs over
7. maintain the same sequence – don’t turn it around else you will interchange the order – ie . from left to right (look at your earlier number markings for a confirmation)
8. undo the screws
9. place the top covers with the respective bottom covers
10. remove the diaphram, needle and spring and place each with the respective top cover.
11. wash the carb bodies liberally with petrol, a small paint brush and toothbrush. Spray carb cleaner everywhere very liberally – let them stand for a while – and wash once more with clean petrol
12. wash each jet with carb cleaner and petrol, blow air through them but don’t insert any pins or sharp objects through them – this will damage them.

Closing up

1. fit the jets back and tighten them gently – not too tight (use your brain here – not your muscles)
2. wash the floats, pins, etc with carb cleaner and clean petrol and fit it back on carefully – refer to Shadows manual for specifications if you want to be a perfectionist (I do it just by sight cause I don’t need performance in India)
3. fit the bottom on with new screws and gaskets if possible.
4. wash the carb tops, diaphrams (don’t pierce them by mistake) and springs and fit them back together.
5. its dicey getting the spring back in the MC-17 and 19
6. make sure that the diaphram is not kinked or sticking out of the cover at any place.
7. make a final check to see if all the screws are in – nice and tight.
8. push each slide up gently and release – they should smoothly slide back into place
9. fit the carbs in the manifold – apply a light layer of grease and slide them in after connecting the throttle cables, choke.
10. tighten the clamp clips, connect the fuel pipes with a new filter
11. fit the air filter[hr]

Thanks to RPM's for the write up and pictures

First, some decent pics of the carbs (finally!)
(you may want to set your screen res to 1024x768 or higher for viewing this)

This next pic is of the rear of the carbs, if you could get your head where the rear shock absorber is.
Simply undo the clamps indicated to get the carbs off.
Note I have replaced the crappy screws with torx heads as the heads do not stuff up as easily.
Also I wrapped teflon tape around the threads to make it easier to undo them.

This is basically everything dismantled,
but the intake trumpets and plastic bit in the above photo are not shown.
The perspective is if you had your head where the engine is,
looking back up at the carbs.

This is a pic of the vacuum chamber and all associated parts:

This is a pic of the float chamber and all associated parts.
The carb on the left still has the cover on,
the next one is with all the parts as they will look once you undo the cover,
3rd +4th carb from the right is with the jets taken out:

Last pic is where the two jets + pilot (air/fuel) screw goes.
I noticed the pilot screw and drain screws all had anti-sieze compund on them,
so I assembled them with some more of that stuff...

[br]Okay, I did this, I'm a defintite noob, here's what to avoid:
As mentioned previously, all the vaccum slide things got mixed up (what are they called anyway? the four black things that look like female contraceptives[?]), as I couldn't write on them. [B)]

Somehow, I managed to mix up the float bowl covers too,
despite the fact that they were all numbered properly.[:I]
Someone was talking to me when I assembled the carbs.
The worst part is I only figured this out when all the carbs were back on the bike, and the accelerator + choke cables were attached (and that took a while[B)]).
I peered into the bike and saw that all the float bowl drain screws were all pointing inwards!! "Oh fer chrize-sake" was my first thought.
I'm leaving it that way until I have to take them off again for whatever reason.[B)][B)] *shrugs*

EDIT: Oh yeah at about this point, a good jet of carby cleaner spray ricochet(ed) off the carbs and DIRECTLY INTO MY EYE![B)]
Fuck! You shut your eyelid really tightly by instinct & it feels like your eyeball is vaporising from the inside out. Run to the tap, flush my eye... omg I can still see![hyp]

The bad/good news is that there was one sticking vacuum slide thing
-- turned out to be a very tiny raised bur (sp?).
I fixed that myself with a bit of 1000 emery paper in less than a minute.[HB]

It took 4 to 5 attempts to get the hang of balancing the carbs.
This was because the 3rd balancing screw works the opposite way to the other two.[B)]

I spilled a load of mercury (three times) from the stoopid gauge trying to get rid of the "bubbles", and once the toxic shite ended up in my shoe of all places - and I only deduced that it ended up there after the entire bike was put back together, and I thought "Geez where'd all that mercury from the second spill go?
Kinda went near my trouser leg. Let's have a look in my shoe".
Sure enough it was in my foot for at least half an hour.[xx(]

I thought I did a good job of balancing the fourth or fifth time...
I go up the street and there appears to be a flat spot at roughly 6-8k.
I'm not too sure about this though, as I could only ride in peak hour and it was difficult to tell.
As soon as I hit the powerband the acceleration was decent enough.[^][:S] It idles better than before, but I think it could be even better.

EDIT: more photos of carbs here:
Dunno why his floats are so white...[:S]

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141 - 145 of 145 Posts
Thanks Aduro, i will do that then. Although i was afraid that would be the answer! Iv only stripped carbs from single cylinder bikes so this will be a learning experience. All good fun though im sure. What should the standard jet size and pilot screw settings be? It was the mechanic at the MOT place that advised me to get the hi flo filter! I will just get a standard filter then as my current one is pretty dirty.
Iv just found your post about setting pilot screws so will use that info, thanks again.
What is the drain screw for in the float bowl.. and how do you set it? on a 1999 cbr250rr
drain screw for the float bowl is just a screw that...lets you drain the floats. (for when you're cleaning them/for some reason need to drain the float).

You don't have to set it. As long as it's not leaking then it's fine.
great write up mate wish i had joined a couple of days ago to see this but i figured it out haha im new here the names matt pleased to meet ya all im from n.s.w australia
141 - 145 of 145 Posts
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