Hello

Been a long time reader of the forum but this is my first post.

For the past couple of years I've been building a haynes roadster - lots of pictures in my signature.

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

Where do you live ?

All engines don't need the air correction holes blocking off
the air screws are only in use at idle then the main jets come in to play
What size main jets have you ?

THE ONLY WAY TO GET THEM RIGHT IS TO HAVE IT ON A ROLLING ROAD

And welcome to the site
Jacko

PS we don't all use face thing so can't see your photos sorry

[Edited on 5/6/11 by jacko]

welcome to the mad house carnt help with ur prob but im useing same carbs i havent bloked air pipes off as yet but mines only ran for short time i would be intersted to no to

Don't forget different exhaust systems and air filters can and will alter the carb settings
Jacko

Jacko

Thanks for your replies - the car will be going on a dyno at some point. I am lucky enough to have spent some time on engine dynos with bike engines and a mate of mine has access to a rolling road. In the interim I plan on doing a rough setup to check CO and AFR. Tuning carbs is not really my forte - more used to laptops and ECU's.

At the moment I haven't actually measured the jet sizes - I was told the carbs came from a standard bike that had been crashed - but they need checking. I may well redrill the air correctors - when I first had them open I found I got some spitting back through the carbs but that was before they were properly balanced.

Hopefully if you click on the links in my signature you should be able to see the pics. No need to be on facebook as the galleries are public. When I first posted the signature I hadn't quite mastered the forum code

Cheers

Dave

[Edited on 5/6/11 by davidimurray]

What pump are you using? you need very low pressure otherwise the carbs will just flood. Use a regulator set to minimum, or the original bike pump.

I have ZX6 carbs on my Zetec and havenīt blocked anthing off. The only mods to mine are: carbs respaced, jets to 1.6mm, needle mooved one groove down and idle mixture screws 2.5 approx turns out.

Mine has been on the road for a few years and the carbs work great.

I checked my mixture using a wideband lambda sensor, and basicall fiddled about with needle position to get the mixture as close as I could across the range of light throttle to WOT.

Stu

Dingz - the pump is a zx6r pump. I got a bike one to ensure it was matched to the carbs and should have plenty of HP capacity for my little Pinto.

Stu - thanks for that info. I'm thinking the blocked air correctors may be the problem - will redrill and see whay happens. Out of interest have you noticed if your diaphragms move / flutter when you are at idle?

Cheers

Dave

Same as stu nothing blocked off and they run great on my zetec too.
MOT was an issue for me as I should of had a cat on the car, luckily my MOT garage is flexible so to speak and had the sensor up something else.

quote:

---

Stu - thanks for that info. I'm thinking the blocked air correctors may be the problem - will redrill and see whay happens. Out of interest have you noticed if your diaphragms move / flutter when you are at idle?

---

Im concious that this is an old thread, but many of the people in here have a close setup to me so want to use their knowledge!

When people are quoting main jet sizes, are you just looking at the head of the jet, seeing, for example, 140 and assuming thats 1.4mm etc. Or have you actually seen 1.4mm printed somewhere?

My jets say 140 on them, but someone in work (whos into bikes) has said that doesnt neccasrily mean 1.4mm, depending on manufactuer it could just be the part number which actually refers to a different size.

What Im really asking is, am I looking at my "140"s and should take them as 1.4mm (which by the looks fo this thread is too small judging by 1.6mm etc^^^)

OR is my "140" a part number which actually IS a 1.6mm jet??

Do you have a small set of drill bits? It might be worth getting a 1.6mm bit and seeing if it will fit.

I redrilled mine to 1.6mm so know that's what size they are.

Stu

I bought a modelling drill bit set and drilled them out bit by bit till ide got it running right at wot
Then i bought a set of jets in the size i last drilled them to as drilling will give you a 'tube. ' shaped hole,not the reamed funnel theyre supposed to be
Only a couple of quid each

I meant use the drill to see what size the jets are rather than drill them out - if a 1.5mm drill bit will fit inside is can't be a 1.4mm jet.

Just out of interest where did you buy the jets from?
Mine seems quite happy on drilled jets.

Stu

[Edited on 15/9/14 by whitestu]

Good old ebay
On keihin and mikuni theyre the same as weber dgav jets
Just for info,on these jets 140 is 1.4 etc
Mine ran fine on drilled one too,i just replaced then so i know the spray pattern is correct
Probably makes little difference tho

Well I managed to get a 1.5 and 1.7mm drill bit in work, 1.5mm goes in and 1.7mm doesnt, guessing they have been drilled out to 1.6mm, so the search continues :-(

Has everyone kept the standard pilot/idle jets? any numbers on these?

Yes, the only jets I changed were the mains.

Stu

I had zx6r carbs on my 1640 pinto and 2040 pinto i drilled the main jets only 1.6 to 1.7mm the air corections were left standard.

I ran this set up on a bogg brothers manifold with no vac advance pipe and ran faultless.