Bike Carbs - ZX6R & 1800 Pinto

[davidimurray]

I'm running an 1800 pinto, with a set of ZX6r bike carbs and Megajolt. I'm currently setting up the idle but run into a slight problem - let me start at the start -

ZX6r carbs have been respaced to suit the pinto by myself. I aslo took the opprotunity to strip and clean the carbs. Following rebuilding I set the needles one groove lower and the idle jet screw 3 turns out from their home position. I also blocked off the air corrector nozzles as this seem to be the reccomended advice.

Got the engine fired up nicely and now the cooling system is finished I've started some tuning and longer engine run times for testing.

The carbs have all been balanced using a pair of vacuum gauges. I then checked the timing and set it to be correct with the Megajolt. Finally I set the the idle to about 8-900RPM using the throttle stop screw.

Following all this I noticed the car was running very rich so I stuck a borrowed CO meter up the exhaust - to be confronted with a reading of 8%

Since then I've moved the circlips to either end of the needle grooves and screwed the idle screws in until they are all shut - with hardly any affect. When the engine is running, the diaphragms in the carbs are just 'bobbling' from their rest position and I can see fuel coming from the main jets. This is the same across all 4 carbs - even with the needles set in their lowest position (highest groove) there is still fuel coming out of the main jets. Best I've managed to get it down to is about 6.8% CO, but the engine will rev easily and quickly off load to the redline. After idle there is a big puff of smoke from the exhuast but this quickly clears once all the rubbish is blown out of the exhaust.

This seems to suggest that the idle circuit isn't doing anything and that the main circuit is doing all the work. I've checked the float height once and set them I what I though was the correct 17mm with the bowl off and also double checked using a clear tube from the dot on the carb body. Also when the ignition (pump) is on there is no sign of any fuel passing through the jets without the fuel running. The pump is a ZX6R pump to match the carbs

It seems to me that the 'bouncing' diaphragms seems to be the issue, but what do I do about this? I've checked the diaphragms and the little o-ring in the top caps and they all seem fine.

Has anyone got any advice on what to do next? All help much appreciated.

Cheers

Dave

[mark]

Try unblocking the air corrector holes, they were open on my cvh build with zx6r carbs and that ran fine with a rejet, it was well within emmisions limits for iva

They are also open on spuds zetec which also runs perfectly with bigger jets being the only modification

The only point I needed to block them is when I put the carbs on my st engine, it was running very lean on the rollers even with huge jets so I blocked them up and this richened everything up substantially, even at low throttle openings

Blocking them up made an extra 50bhp instantly so they seem have quite an effect on the mixture

It seems that with zx9 carbs blocking the air correctors is standard practice but is less common with the zx6 carbs and only done if required

[davidimurray]

Mark

That's great. So far all the other ZX6R carb users I have asked have comeback with the same thing and run with the air correctors unblocked. Time to get all that solder out

Thanks again

Dave

[baz-r]

dont block the air corrrecter jets thay feed air to the emulsion tubes etc and that is why its co is so high too much fuel in bigger droplets i bet your hc's where sky high.

you should be able to take a stock set of carbs and fit them on and get the motor to run. good to see you ballanced first its always the first place to start then go from there on jetting and needle hights

mixture ballance is the tricky one it can be set by checking exaust gas temps for each cyl header of the manifold im thinking of seeing if a ir contactless heat gun meter we have at work will work
cold is rich hot is lean when thay are all simmular the mixtures are ballanced and total co% will be for all cyl in sync

same can be done if you use megersquirt with 1 injector channel per cyl or bank to get the mixture the same for all cyl's

[baz-r]

ps all the bikes i have had filcker the slides/diaphrams a little at idle thay should it shows the diaphrams are working.
i would say once you get the mix better the throttle stop screw will need winding off letting less air in reducing the vacum and reduceing the pulse to the diaphram and improving the hole thing
its all a knock on effect