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Running rich
Mark O - 15/11/20 at 10:09 PM

Gents

I have Zetec 2.0 blacktop mated up to ZX9R CVK carbs. I have the following set up.

Checked needle jet - it is shimmed by one 0.5mm shim. This is standard.
Airscrews turned 2.5 turns out.
Main jets are 165.
Air corrector holes open.

With this set up, it starts fine enough, but on blipping the throttle when warm it does emit black smoke. Not alot, but definitely some there and it does leave a residue of black against a piece of cardboard at the tailpipe. It is also a bit smokey at idle.

No tuners up here know about bike carbs so it's a policy of try it and see.

First things

Air screws - is it out to richen or vice versa?
Air corrector holes - I believe 0.7mm is about right. I have some brass inserts en route. Not sure if this will make much difference.

To lean it out, what do you recommend?

Will a smaller main jet -155? make a difference? I thought main jet only acted on the final 3/4 throttle.

Many thanks

robertst - 16/11/20 at 01:43 PM

quote:
Originally posted by Mark O
Gents

I have Zetec 2.0 blacktop mated up to ZX9R CVK carbs. I have the following set up.

Checked needle jet - it is shimmed by one 0.5mm shim. This is standard.
Airscrews turned 2.5 turns out.
Main jets are 165.
Air corrector holes open.

With this set up, it starts fine enough, but on blipping the throttle when warm it does emit black smoke. Not alot, but definitely some there and it does leave a residue of black against a piece of cardboard at the tailpipe. It is also a bit smokey at idle.

No tuners up here know about bike carbs so it's a policy of try it and see.

First things

Air screws - is it out to richen or vice versa?
Air corrector holes - I believe 0.7mm is about right. I have some brass inserts en route. Not sure if this will make much difference.

To lean it out, what do you recommend?

Will a smaller main jet -155? make a difference? I thought main jet only acted on the final 3/4 throttle.

Many thanks


My Pinto on R1 Carbs was running stupidly rich until I found out the Air corrector holes were blocked. Yours are open and it's still quite rich by the looks of it. I think it's your idle circuit. Check your needles, you'll probably have to lower them one or two notches, then your idle screw. Out to richen, In to lean. Check the diaphragms on each carb to see if there are any cracks or tears. Also check out your float levels (this had a massive impact on mine, as they were too high)

As you say, the main jet is irrelevant until 3/4 throttle and beyond so it's not that.

Are you sure it's not burning oil? have you checked the plugs? Mine was leaking in two valve stem seals. It was a right bummer to fix, but she ran sweet after all that.

Hope it helps

Atb

Mark O - 16/11/20 at 02:49 PM

Yes -I too think it is idle circuit - they are actually CVR carbs by the by..... Airscrews were well out - certainly over 4 turns, so I think that is what I will try first. Any recommendation as to what to set them to as a good first start - 1.5 out? Float levels - not checked them. Will do so.

robertst - 16/11/20 at 05:39 PM

quote:
Originally posted by Mark O
Yes -I too think it is idle circuit - they are actually CVR carbs by the by..... Airscrews were well out - certainly over 4 turns, so I think that is what I will try first. Any recommendation as to what to set them to as a good first start - 1.5 out? Float levels - not checked them. Will do so.


whoah 4 turns out! that's your ticket right there then! yeah 1.5 turns out from fully closed is ok as a starting point.

Normally, if the idle screw is more than 2 turns out you need to change to a smaller jet, less than 1 turn out change to a larger jet. But you need to adjust everything in the right order:

1: Make sure carbs are balanced
2: Main jets - your's seems to be fine at 165
3: Adjust needle jets
4: Adjust Idle circuit

just in case, you need to do this with the engine at operating temperature. Don't bother doing it on a cold engine

Do you have a wideband? If not you could use an infrared thermometer aimed at each exhaust branch to get the temps roughly equal and a visual inspection of the plugs straight after shutdown. That is a rough and dirty method to get the engine running acceptably well, but by no means will it be spot-on without a wideband.

[Edited on 16/11/20 by robertst]

[Edited on 16/11/20 by robertst]

Mark O - 16/11/20 at 07:16 PM

Yes - many thanks for that. Just an aside, why should airscrew settings matter so much ref running rich? I understood they affected about 1/4 throttle, so I can understand them the affecting idle, but after that? I guess they are still leeching fuel through all the time the engine is running? It's actually using fuel like a drag racer! I stuck 5 litres in from empty just to test in on the road - all gone after 10 miles! Goes well though!

Carbs balanced by the kit supplier - not actually checked them though.
Main jets agreed are OK
Needle jets - now reverted to stock with just the one shim
Idle - will set all at 1.5 out

Pump is a bike pump which came with the kit
CVR carbs - float heights all checked - all now around 4mm - a couple were low - and therefore possibly contributing to the rich mix - at 2mm or so.
Air correctors now 0.8mm hole.

Agreed about the plugs as a check. Pity. They were brand new Motorcraft for the Zetec put in yesterday - now 'orrible, sooty and black.

Mark O - 19/11/20 at 05:26 PM

Nope - no good. Car still runs way too rich with airscrews 1.5 turns out. Black smoke and it stinks.

Any further advice as to how to lean it out considerably would be greatly apppreciated.

Many thanks

Mark

Wildnz - 24/4/21 at 07:55 PM

I have an identical issue and a very similar setup - I would greatly appreciate any additional steps or advice here...