Gbs Bike Carbs Please Help

[Guest ticeysoft]

just a quick help request...

 

i have the GBS bike carb kit bought from stafford show on sunday.. i have fitted them and all is good ion tik over an revs free but it really really is over fueling.. to the point where i have frequent backfire and a trip to the shop eats a quarter of a tank of jiuce..

 

 

can any ony point me in the direction of the fuel mixture screw for the carbs? i can seem to find it

 

many

thanks

[Guest chris brown]

I know little or nothing about bike carbs but this has come up before and it would appear bike carbs are very fuel pressure sensitive so what pump are you using? As too much pressure can overcome the float valves and then fuel just gets thrown straight down the throat.

Just a thought

[Guest ticeysoft]

ATM im just using the pinto fuel pump but i was going to add an in line filter, as the chap from GBS siad if the engine flooded to start with but it never flooded.. its just when you start to put your foot down it drinks the fuel

[Guest Takumi]

The pinto pump gives too much pressure as std, really needs to be dropped to 1-2psi at most. It might well be forcing fuel past the needle valve..hence your appauling economy. Recommend using a regulator with a fuel return.

 

-tak

[Greenie]

just a quick help request...

 

i have the GBS bike carb kit bought from stafford show on sunday.. i have fitted them and all is good ion tik over an revs free but it really really is over fueling.. to the point where i have frequent backfire and a trip to the shop eats a quarter of a tank of jiuce..

 

 

can any ony point me in the direction of the fuel mixture screw for the carbs? i can seem to find it

 

many

thanks

I run a set of Yamaha R1 Carbs combined with the same pump used on the bike on a 1.8 16V Zetec, had the carbs jetted to suit, they run at 2psi performance and fuel economy not really an issue.

 

Mine runs in conjunction with a Megajolt Ignition System whichs really enhances the performance of the car.

 

Do recommend the fuel regualtor.

 

Perservere and you will be overwhelmed by the results.

 

Good Luck!

 

Greenie

[Guest graham dockerill]

Had the same problem with flooding , ebay item 230291404429 is a fuel regulator for £23.50 with carriage, i'm going to fit one of these with the pinto pump.

[Andi]

GBS did say that maybe 1 in 5 carbs wont work with the pinto pump. They do sell a pressure regulator to go with the carbs,

or you could use "filter king" which are quite popular or as greenie said even the fuel pump that originates from the said bike

especially if your near any bike breakers. Should be a cheaper option.

GBS should have re jetted the carbs to .80.

[Guest ticeysoft]

many thanks guys for the info... i will give the regulator a go as im still using the motorcraft amplifier at the mo.. bu i plann to go to an RS Turbo lump with in the next year or so...i hope

 

 

i will try and post some pics of my car when i get chance

 

thanks again..

[Mitch]

Hi Tim

 

you will need a regulator or a bike pump, i have a bike pump on mine, and its running a just under 2psi, which is enough.

 

fill in your location to, as there maybe members near you who would be interested in kicking tyres with you

 

Mitch

 

PS anyone wanting to fit bike carbs DO NOT get gsxr600 srad carbs, as the set i have will not fuel a modded 2,1 pinto,(or wont on mine may ave a bad set!!!) maybe okay for a 1600 but not my 2,1 with 285 piper and ported head.

[Snapperpaul]

Having some problems with my Mikunies, massive over fueling, so much it diluted the oil.

Reduced fuel presure to absolute minimum (about 1 psi) and still no good.

I will get some advise then rolling road for me.

[Guest Takumi]

Can yo confirm the jet size from GBS. as 80 thou is massively too big, thats 2mm.. it need to be 1.7mm at most..

 

You might need to solder up the main jets and re-drill them to an appropriate size.

 

 

-tak

[Andi]

Sorry 1.8mm I was told

[Guest Takumi]

1.8mm is far too big, it will be overfuelling badly..GBS C***ked up

 

1.7mm is closer the mark. easiest way to sort it, is take them out , solder them up and re drill them. Otherwise you'll have to buy new jets.

 

 

-tk

[steve in stockport]

Running bike carbs is about more than just the main jets.

you have to balance jet size against needle size and position, and also set the idle air mixture for tick over.

Once you have these somewhere near you then need to balance all of the carbs against each other.

 

I'm running a vauxhall 2.0 red top with kawasaki zx7r carbs, the main jets are drilled out to 1.7mm and the needles have been dropped as low as they will go, fuel pump is a facet fast road solid state, without a pressure regulator, so far I've done 5000 miles with this set up and fuel consumption is pretty good - 30mpg on average, mid 20's mpg if the right foot gets heavy and as high as 35mpg when taking things steady

 

Steve

[Guest salty_monk]

Steve,

 

You're the first person on here I have seen that has done something to tune them properly!

Most just drill out the main jet & hope it seems. That would never work on a bike, I have no experience for tuning on a car but have done quite a few sets of Mikuni's for bikes in the last year or two.

1.7 is a big main jet but then dropping the needles (down into the emulsion tube) would lean off the mid range of the throttle opening. This would suggest to me that the main jet is too big & the needles could come back up a bit, could get you more MPG under heavy throttle with no loss of performance.

Balancing is very important too as you say. Did you have to mess with the idle jets at all or could you find enough just using the pilot air screws?

 

If anyone wants an easy comparison to tuning bike carbs the neareast you can get in the car world is a set of Twin SU's. They work on similar principals.

 

Dan