Backfire and won't idle-only running on 2 cylinders-all sorted!

[Deicide]

Have a problem with my CBR600, 1994 model

Haven't started the bike in ~10 months. In that time ive checked the valve clearances, replaced spark plugs, and stripped off the exhaust. I finally have the bike at a stage where I could start it.

Yesterday, drained the fuel tank of the old fuel, drained the carbs and put fresh fuel in her. Hooked it all up last night and tried to crank her over. Battery was very weak and only had ~4 cranks before it died. Put on charge and tried it again, another 4 cranks and died. Jump started it this morning and managed to get it to start, after a couple of loud backfires.

The bike will run with the accelerator but when you bring it down to idle, it will just die and backfire at the last second. I cannot get it to idle at all, even using the choke.

Im guessing maybe one of the plugs is fouled because of the initial cranking causing flooding?
Would pulling the plugs out and checking the spark plugs be the first step?
Would any unburnt fuel then evaporate?

Also not running with air filter or air filter housing in place if that makes any difference

Any help is greatly appreciated.
Cheers

*****UPDATE***** 16/4/09
Ok, so Duffman and I where going to sync the carbs tonight until I found out that "the cool V-Twin sound" my bike makes is actually because its only running on 2 cylinders!

Cylinders 1 and 3 aren't firing. I get spark, appear to have compression, air but no fuel is getting to the spark plugs (plugs where bone dry)

I have fuel in all of the floats on the carburetor but it dosn't get to cylinders 1 and 3.
Im guessing maybe one of the jets is blocked on 1 and 3????
Would my first course of action be to pull the carbs out again and check the jets???
They where clean when I put them back in, anything else I need to check?

Cheers

[jules_1972]

Hmmm, carbies flooding??

Check carb floats...

[Deicide]

Excuse the noob question, what am i checking on the carb floats? Never pulled a carb apart before so not too sure what im looking at/for?

[druu]

If it's flooded, get it started, hold the revs then once it's warm enough, start blipping it in the high rpm to clear it, or just go for a fang.

[Deicide]

If it's flooded, get it started, hold the revs then once it's warm enough, start blipping it in the high rpm to clear it, or just go for a fang.

Hmmm might go give that a go first. Unfortunatly, bike's not quite at the road legal stage yet so i'll try blipping it at high rpm

Would being flooded stop the bike from idling?

[Surly]

The carbs have lots of small orifices for things including the idle circuit.

If the bike has been let sit with fuel in it these orifices will be blocked with the dyes and other crap left when the fuel evaporates. Pulling the carbs to bits and cleaning everything you can get to is the best start.

Hope this helps

cheers
Surly

[druu]

Oh, and don't use *any* choke, you'll just add more fuel to the mixture.

[Deicide]

The carbs have lots of small orifices for things including the idle circuit.

If the bike has been let sit with fuel in it these orifices will be blocked with the dyes and other crap left when the fuel evaporates. Pulling the carbs to bits and cleaning everything you can get to is the best start.

Hope this helps

cheers
Surly

Thanks Surly, guess im pulling apart the carbs today, can't hurt to give them a clean regardless.

[jules_1972]

Get some CRC Carb cleaner and give them a good clean out.

Some compressed air (Not to high pressure) thru orifices will also assist
in cleaning out any residue..

[Deicide]

Ok, i managed to get the carbs off. Ive pulled the float body covers off,






what should I be cleaning? and what else do I need to pull apart?

Can I use pre-cleaner or degreaser, or is carb clean the best?

[druu]

Take each jet out (one by one as to not confuse) and spray carb cleaner into each one, then blow it out with some air, then replace. Do for the main jets, pilot jets and spray some carb cleaner in the orifices too.

At this point in time it's a good idea to confirm you're running the right jet sizes (if stock, compare with a manual) and also checking the float heights are good on each float.

Also check your needle position to see if it's at the correct setting (if it's adjustable).

Spray carb cleaner in the fuel areas to clear any crud too.

[Sumatie]

While your at it you may as well clean your fuel tank and replace the fuel lines, cheap and ensures it is clean.

[jules_1972]

use carb cleaner as it wont attack rubber seals or damage the plastic floats.

The float bowls clean them out to.

The 2 brass screws on the right are the main and pilot jets.
The center one is the main, the metering needle slides in the center of the main jet.

Use plenty Carb cleaner, low pressure air also good to.

[druu]

Oh, and don't forget to set the mixture screw (the + head screw at the bottom of the pic) according to the manual as well. Screw it in lightly until it stops, then unscrew however many turns the manual states.

[Deicide]

Well I finally sorted out the problem,
Cleaned out the carbs this afternoon, gave everything a good clean-a few of the jets where gunked up but overall it was pretty clean. Got the carbs back together and back on the bike, started cranking her over-note: for future reference-make sure ALL the float drain screw are done up! it wasn't until I was halfway through cranking her over when I noticed fuel leaking everywhere!

Eventually got her started, let off the accelerator and...nothing, no idle, just dies...hmmm I though, I wonder what happens If I adjust the "Throttle Stop" hanging off the carburetors..Success!! im now idleing nicely at 1300 rpm!
It must have been thrown out at some stage of the build

Oh well at least my carbs are clean, and I now know what parts make up a carb, and what the inside of one looks like!

For anyone else about to clean there carbs, I found this link very helpful, step by step guide with pictures on carb cleaning:
How to Clean a Motorcycle Carburetor, the RIGHT way. Evan Fell Cycle Works

Cheers for all the advice guys

[jules_1972]

For anyone else about to clean there carbs, I found this link very helpful, step by step guide with pictures on carb cleaning:
How to Clean a Motorcycle Carburetor, the RIGHT way. Evan Fell Cycle Works

Cheers for all the advice guys

Way to go....

Good link to....

[Deny-It]

Hey Souter, good to hear the progress on the big girl. Looks like you have sorted through a few issues to get to this stage and its all coming together. Last time I spoke to you, you were dealing with a snapped off bolt, ah know all about that . Is it ride-able yet?

[Deicide]

Ha ha, yeah mate its going REALLY good,
snapped a total of 3 bolts thus far-have now learn't patience and how to use my torque wrench! Gavin from GD engineering helped fix the last bolt-broken fork pinch bolt (with an ezy out snapped off in it! ) ) you can ask him how much fun he had getting the bolt out and heli-coiling it! The guys a dead set legend!

Ive got my R class test beginning of May so Ive dedicated all of April to her. Have the motor all back together, just wanna synch the carbs and then ive just gotta bleed the brakes, new chain and sprokets and put the busted ass fairings back on and its good to go!.

Will be putting new fairings on soon after that, just wanna get out on the road though-im having withdrawals from selling the 250!!

[HotelBushranger]

Won't running with no air filter or housing fuck with the carb settings? That's what it says in my XS manual:

On no account run without the air filters attached, or with the element missing. The jetting of the carburettors takes into account the presence of the air filters and engine performance will be seriously affected if this balance is upset.

And again

If this precaution is not observed, the engine will run with a permanently weak mizture, which will cause overheating and possible seizure.

Just for XS's or for everyone?

[Deicide]

Hmmm not sure, you need the filter and housing off to sync the carbs so i figured it would be ok????