Fireblade Carb Problems

[Guest scrabster]

hi, ive had a good pinto mechanic come to check the timing and dizzy settings,after a few minor adjustments all is ok,the problem is the carb settings.he balanced them as best he could but said i could realy do with a bike mechanic to do it.spoke to two who said they could only do them on a bike.the carbs are spitting back and popping out of exhaust, number 1 & 2 exhaust pipe feel a lot cooler than 3&4 which spit more petrol out.ive started with mixture screw at 2 turns then 2.5 then 3turns but stil runs unevenly.ive had the carbs on and off 5 or 6 times now.took them back to richard at gbs who took them apart and cleaned them and found nothing wrong.put them back on and same result spitting back and popping.engine has new bestek ignition system,new piper 270 cam kit and vernier pulley.has anyone any ideas before i take it to a rolling road test or will i be wasting my money till its running something like.oh its a zero im building,please help before i have no hair left to pull out.

jess.

[Guest Nigel Novice]

Seen somewhere on here about bike carbs needing a bit off negative pressure ie airfilter/box

[Guest scrabster]

Seen somewhere on here about bike carbs needing a bit off negative pressure ie airfilter/box

thanks for reply,ive tried it with and without filter,result the same.

jess.

[Guest Ian & Carole]

Hi

 

If you still have an extreme of difference on 1&2 compared to 3&4 then it is telling me that the carbs are still not balanced one carb is working harder than the other hence the difference.

 

Give me twin 40's every time.

[Guest scrabster]

Hi

 

If you still have an extreme of difference on 1&2 compared to 3&4 then it is telling me that the carbs are still not balanced one carb is working harder than the other hence the difference.

 

Give me twin 40's every time.

hi,i took carbs of and cleaned them again after they were balanced,do they have to be done again?getting fed up with them now,how easy is it to smash them with a hammer.

[Guest erichetherington]

Almost certainly, if they've been apart you need to start from scratch.

[Peter Bell]

If you haven't got a flow meter try this:-

You can balance them pretty accurately by ear, just like SUs, use a length of hose pipe stick one end at the mouth of the carb, the other in your ear and listen to the volume of the sucking, they all need to be the same. Start at the master carb, the one the throttle cable connects to then compare with the next in line, adjust the throttle screws till that one sounds the same as the first. Then on to the next, etc. you may have to increase/decrease the idle speed as you go, but always compare the sound to the first carb. This will at least have all the carbs working together, when opened up bike carbs do tend to show quite a bit of fuel mist being spat back out, this is known as stand off.

What fuel pump are you using? you need very low fuel pressure otherwise they will flood.

[Guest scrabster]

If you haven't got a flow meter try this:-

You can balance them pretty accurately by ear, just like SUs, use a length of hose pipe stick one end at the mouth of the carb, the other in your ear and listen to the volume of the sucking, they all need to be the same. Start at the master carb, the one the throttle cable connects to then compare with the next in line, adjust the throttle screws till that one sounds the same as the first. Then on to the next, etc. you may have to increase/decrease the idle speed as you go, but always compare the sound to the first carb. This will at least have all the carbs working together, when opened up bike carbs do tend to show quite a bit of fuel mist being spat back out, this is known as stand off.

What fuel pump are you using? you need very low fuel pressure otherwise they will flood.

hi,thanks for reply,its a bike fuel pump supplied with the conversion from gbs,richard reckons this is a first,there are usually no probs with the carbs.perhaps i bought the 13th set?im trying to get hold of a bike mechanic to give me the right advice,no luck yet though.it seems to my untrained eye they are overfueling3&4 and starving 1&2.mixture screws are a bugger to get to.carbs wont come off manifold so have to drain coolant and take them off engine,see what tomorrow brings.bye.

[Andi]

I had over fueling and could not find out why, I had a bike pump also. I needed smaller jets so I got a spare set of and drilled them out to 1.65mm and that cured it.

Dont know why as some jets are going out to over 1.85mm and producing good results. I guess these bike carbs have "individual personalities".

How come you cannot take the carbs off the inlet manifold??

[Guest salty_monk]

The "mixture screws" will only affect the mixture at idle or very low throttle openings, the next stage is the needle jets (a bit like an SU carb) which is also a component of the main jet (as the needle sits in the main jet hole...).

 

There are also air jets to contend with too in most carbs. Balancing them is very important. You will probably find they have balance ports on them, if so easy to balance yourself with something like the Carbtune. http://www.carbtune.com/

 

Yes, you will need to balance them after taking them apart. Also check the float levels & that the float valves are working correctly.

 

Here's some info for you... http://www.dansmc.com/carbs2.htm there's a lot of advice out there.

 

Dan

[Guest scrabster]

I had over fueling and could not find out why, I had a bike pump also. I needed smaller jets so I got a spare set of and drilled them out to 1.65mm and that cured it.

Dont know why as some jets are going out to over 1.85mm and producing good results. I guess these bike carbs have "individual personalities".

How come you cannot take the carbs off the inlet manifold??

hi,thanks for reply.richard at gbs had a real job wrestling them on with his weight behind him.i didnt want to do any damage trying to force them off.

motorbike guy wants £70 to come and try to set things right.almost the price of another set of carbs.

[Guest scrabster]

The "mixture screws" will only affect the mixture at idle or very low throttle openings, the next stage is the needle jets (a bit like an SU carb) which is also a component of the main jet (as the needle sits in the main jet hole...).

 

There are also air jets to contend with too in most carbs. Balancing them is very important. You will probably find they have balance ports on them, if so easy to balance yourself with something like the Carbtune. http://www.carbtune.com/

 

Yes, you will need to balance them after taking them apart. Also check the float levels & that the float valves are working correctly.

 

Here's some info for you... http://www.dansmc.com/carbs2.htm there's a lot of advice out there.

 

Dan

hi,thanks for reply.mechanic used an air flow meter,cant see any where to put tubes to use a carbtune!engine starts ok and idles for a bit then dies,if i try to rev it it splutters and dies.dont know realy what model they are richard at gbs just said fireblade carbs.what type are yours?the float level cant be adjusted they are plastic.i will have another dabble tomorrow.

jess.

[Guest salty_monk]

I would be very surprised if float levels can't be adjusted, normally you bend a stop that touches the end of the float valve but yours are likely much newer than what I'm used to playing with....

 

I play with bike carbs on bikes not cars. It sounds to me like you are either not getting enough petrol in or too much...! Does it restart straight away or act like it's flooded or?

 

Dan

[Guest yokel]

Hi

Float height is critical, with the carbs upside down on the bench and all the float bowls off, use a tyre depth gauge to check the height of the float above the carb body, you will need the correct setting from a Honda dealer, but generally 10 - 14 mm, in the centre of the float, above the float valve there is a small stainless tang that acts on the valve to close it. bend it gently to set the floats at the same height, put it all back together and check fuel pressure is less than 2psi!

 

HTH

 

Tony

[Guest scrabster]

I would be very surprised if float levels can't be adjusted, normally you bend a stop that touches the end of the float valve but yours are likely much newer than what I'm used to playing with....

 

I play with bike carbs on bikes not cars. It sounds to me like you are either not getting enough petrol in or too much...! Does it restart straight away or act like it's flooded or?

 

Dan

hi dan,it starts up again straight away.after last nights efforts i took plugs out which were wet with petrol and black.when i first turned ignition on the petrol pump then stops and i can smell fuel a bit from the carbs,is this normal? im thinking the pump may have too much pressure, overfuelling carbs then flooding engine.does that sound about right.but it does start up again and cuts out when i try to rev it.ive got a man who knows coming tomorrow so ill let you know the results.