Rich Idle

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fstarockr
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Rich Idle

Post by fstarockr » Sat Sep 10, 2016 6:20 am

My zxr400 has been running rich since I bought it, idling rough, black powder on plugs and after a 150 mile journey the inside of exhaust was also black, after I cleaned that with a wire brush..


It's a 90 H2 model, according to manual stock jetting is
Mains 98
Pilot 35

Which I have (po had 102 mains in)..

Fitted new plugs, they fouled up after 35 seconds running. All 4 powder black..

So in desperation I pressed out needle seats, could barely make out possible wear, but not sure.. And damaged the needle sleeve bits..

Should the needles be totally blocked at idle? As an experiment I decided to hack mine as an experiment..

I found the shank of a 2.5 mm drill fit very snug inside, so I drilled out the needle jet to 3.5mm, and turned down an aluminium pop rivet jacket to fit inside, and drilled the sleeve out back to 2.5, as far as I can tell the needles fit a little bit more snug than before..

At least I can raise the needle if I'm too lean.

Anyway, after studying this diagram , am I on the correct path or should I rather have dropped the pilot jets before ruining my needle seats?

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banner001
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Re: How a ZXR400 CV Carb Works.

Post by banner001 » Mon Sep 12, 2016 9:21 am

your needles should not make a perfect seal at idle, there is always a good bit of wiggle room, and your main jets will only really affect high rpm WOT running.

are your float heights set correctly? if they are then your only other source of fuel is from your pilot adjuster screw, what are they currently set to, what pipe/can/airbox combination are you using? what psi compression readings are you getting across all 4 cylinders cold/with oil?
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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fstarocka
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Re: Rich Idle

Post by fstarocka » Sun Oct 02, 2016 9:21 am

Hi banner thanks.. Sorry for the late reply, I got the bike going with my hacked needle seats..

Pilot is at 2 1/4, I've raised float heights to 12mm from 11mm, air filter is a very thin spandex thing I got with the bike but running with it off seems to make little difference.

I rode 160 miles, and my the mid range power is great.

I had to catch a flight but in my haste it seems like the bike was running better, I'll be back this week.

I've ordered some 4mmx2mm brass tubes from China including some very fine carbide drill bits so will redo this with better equipment.

Pilot screws all cleaned with springs, washer and oring checked.. No damage.

I still have to drill out an old plug as my compression kit doesnt fit :)

My shims are also out of whack, new ones have arrived,

I managed to balance the intake and exhaust shims evenly but they are all about .05-.1 mm over on all..

But that shouldn't cause over fueling.. Besides bike still has great power..

So despite the screws being engine side they are in fact air screws so I'll try back them out half a turn each..



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fstarocka
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Re: Rich Idle

Post by fstarocka » Sun Oct 02, 2016 9:27 am

Not sure what pipe it is, stock?

Image

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banner001
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Re: Rich Idle

Post by banner001 » Mon Oct 03, 2016 12:32 pm

fstarocka wrote:So despite the screws being engine side they are in fact air screws so I'll try back them out half a turn each..
the screws are mixture screws, you turn them out/counterclockwise to let more mixture through, and turn them in/clockwise to restrict the amount of mixture going in.

if you are sure its petrol causing the blackening of the plugs, and not oil past the rings, then by increasing the float height from 11mm to 12mm you have leaned out the fuelling of the whole bike, you can try screwing in your pilot adjuster screw 1/4 turn as that should lean the idle (do you need choke to start it from cold/hot?). you have also dropped the size of the main so that should further lean out your WOT running.

you need to sort out the shims and compression check, then once it idles fine you need to do a carb balance as that can affect idle massivly.

the exhaust looks aftermarket, the downpipes look to be original (i think i can see a weld seam running along their top).
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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fstarocka
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Re: Rich Idle

Post by fstarocka » Mon Oct 03, 2016 1:43 pm

Tx, wouldn't oil leave wet black? Its dry powder so most certainly fuel?

The screws are air screws, mixture is ambiguous because u adjust the mixture either via fuel or air control, its important to know what you are mixing.

The 12mm float height is still within spec, it was just preventative measures to reduce the chance of a rich float bowl level..

More work to try find the issues.. Had carbs and tank off so many times.

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banner001
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Re: Rich Idle

Post by banner001 » Tue Oct 04, 2016 9:21 am

fstarocka wrote:The screws are air screws, mixture is ambiguous because u adjust the mixture either via fuel or air control, its important to know what you are mixing.
its not an air screw, if it was an air screw then when you fully screwed in the pilot adjuster screw you would fully block air coming from the pilot air jet...but not the fuel jet, i.e. this is the possible way it would work...so next time you have your carbs off fully screw in your pilot adjuster screw, remove your float bowl, and fire fuel down your pilot jet, there is only 1 place the fuel will come from, and thats from the transfer ports that are partially covered by the butterfly valve...

...so tell me, how is it working as an air screw (i.e. it only affects the volume of air in the pilot mixing chamber), and how will screwing it in richen your bike if it fully blocks the flow of fuel from the pilot hole in the carb venturi?
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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banner001
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Re: Rich Idle

Post by banner001 » Tue Oct 04, 2016 9:22 am

or in other words, please alter the diagram in this post to how you believe the carb to be working

viewtopic.php?f=115&t=16915#top
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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fstarocka
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Re: Rich Idle

Post by fstarocka » Sat Oct 08, 2016 7:08 am

Image

Not sure what you mean? There are fuel metering screws and air metering screws ,depends on carb design.

The 400-H model carbs are air screws despite being on the engine side.

I have yet to verify whether its rich at low or high rpm.. I cruise around 8500-10000 rpms on the highway..

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banner001
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Re: Rich Idle

Post by banner001 » Sat Oct 08, 2016 1:29 pm

Rmkd is wrong, and has a long running feud on here.

Please, remove your carb, screw in the pilot screw, squirt fuel through the pilot jet in the float bowl and tell me if it squirts out of the pilot hole in the Venturi...because if you think it's metering the air only then the fuel will squirt out of there with no restriction.

Do that test as an Independent person and report back here, but I'm telling you that you, rmkd, and factory pro are wrong.

With the pilot screw all the way screwed in you can almost see the end of it in the Venturi fully blocking the pilot hole...it's posts like this that take other people's opinions ahead of testable facts that fucks up everyone's point of view.
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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fstarocka
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Re: Rich Idle

Post by fstarocka » Wed Oct 12, 2016 5:32 pm

hi banner - just remove the erroneous posts above, i was really unsure - i pulled a plug today and it seems to be burning better although I havent changed much.. one plug was so fouled it wasnt even firing - I was running diesel injector cleaner thru to clean any carbon - so maybe that caused issues - i backed out all mixture screws a 1/4 turn and will see how it goes.. but will have to get an afr gauge at some point.

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