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 over rich at high revs 
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Firing on two.

Joined: May 26th, 2010, 5:34 pm
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Post over rich at high revs
Im running a 602 9.1 nearly run in but take it up to 65 now and then but not labouring it .. I have a lambda sensor fitted the primary main jet has been opened up to 105 up to 55 mph it runs with the mixture perfect but higher than that as it gets on to the 2nd choke it starts to run richer .. the 2nd main jet is 90 so I replaced it with a 75 but that has made no difference to the mixture reading at high revs ( I was expecting it to be much too weak).. .. the float level is perfect there are no signs of the carb flooding it starts easily when hot when it was running in it did 36 mpg I can see no signs of the accellerator pump dripping petrol into the carb when the engine is running,, any ideas before I have another crack at it tomorrow :?


May 1st, 2011, 10:05 pm
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Agony Aunt - You have a car problem? Speak to Ken

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Post Re: over rich at high revs
Kevin,
if it's a standard narrow band lambda sensor, it will detect 'rich' or 'lean' of stoichiometry, but won't indicate by how much, as its accuracy is limited to about 1 step in AFR.

For best power, the mixture needs to be about 10% richer than 14.7:1 air fuel ratio anyway, but if you want to tune for maximum mpg, you could lean off the top end of the primary choke by opening up the primary air corrector jet.

It's probably an 1F1 jet, measure its bore and take it out in stages to judge the result, but be very wary of going too lean... ;)

ken

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Last edited by ken on May 2nd, 2011, 10:18 am, edited 1 time in total.



May 1st, 2011, 11:19 pm
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Firing on two.

Joined: May 26th, 2010, 5:34 pm
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Post Re: over rich at high revs
Ta Ken ..its a wide band sensor will check corrector jet first to see what size it is then to drill it out ... have to admit I"m not 100% sure what it does.. also I"m hoping its the wrong one in there ..Should I first disable the 2nd choke opperation to get the mixture correct on the first choke at max revs ????


May 2nd, 2011, 10:16 am
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Agony Aunt - You have a car problem? Speak to Ken

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Post Re: over rich at high revs
Kevin,
the size of the air corrector jet controls the 'slope' of the mixture as rpm rise and the air speed through the venturi increases.
The larger the air corrector jet, the lower the level of mixture in the emulsion tube will be at higher rpm.

Have you got CHT gauges fitted?
If so, might be an idea to keep an eye on them if you're leaning off the mixture, rather than relying solely on the lambda readings...

ken.

( Edit: I'd leave the secondary choke connected, on the basis that there's an overlap between the effects of the separate chokes.
You'll get a different result if you try to tune them individually. )

notsmartcar wrote:
Ta .. will check corrector jet first to see what size it is then to drill it out ... have to admit I"m not 100% sure what it does.. also I"m hoping its the wrong one in there so will get the book out ..... its a wide band sensor

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May 2nd, 2011, 10:23 am
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Firing on two.

Joined: April 22nd, 2009, 11:06 pm
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Post Re: over rich at high revs
notsmartcar wrote:
Ta Ken ..its a wide band sensor will check corrector jet first to see what size it is then to drill it out ... have to admit I"m not 100% sure what it does.. also I"m hoping its the wrong one in there ..Should I first disable the 2nd choke opperation to get the mixture correct on the first choke at max revs ????


it introduces air into the petrol thats being fed to the main jet(s), it foams it up. This stops the engine sucking in too much neat petrol at full chat

you have cleaned all the jets with brake cleaner (carb cleaner is often for the outside and usually contains some sort of keep it clean oil) and blown through all the drillings ?

you wont be able to tune the first choke at full revs as you wont get there. you'd need to get it to the point just before no2 opens up, its not like they work independantly at max revs.

what carb is it BTW as the 21 23 was jetted slightly diffrently

clean air filter, standard exhaust etc?

edit- must refresh the cashe before replying to stuff thats been replied to!

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May 2nd, 2011, 10:39 am
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Firing on two.

Joined: May 26th, 2010, 5:34 pm
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Post Re: over rich at high revs
The air corrector jet was 1f2 rather than play with that I put in a 1F5 been out for a run it runs slightly richer on the 1st choke but when I plant my foot to the floor at 55 it goes down off the scale weak which I didnt get before when I dropped the 2nd main jet from 90 to 75 (75 still inthere) am going out now with a 1f4 which I hope will drop the 1st choke mixture strength a little so I can than play with the 2nd main jet.............. am I right in assuming a 1f2 has smaller holes Top and sides than a 1f5


May 2nd, 2011, 11:16 am
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Agony Aunt - You have a car problem? Speak to Ken

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Post Re: over rich at high revs
Kevin,
sounds as though you're changing the emulsion tube as well as the air corrector jet, which is complicating matters.
You should only be changing one thing at a time, so either separate the tube from the jet and fit it to an air corrector with a slightly larger aperture or drill out that original IF2.

Haven't got time today to search around in my stuff, but if the 1F5 corrector has a larger bore than the 1F2, maybe try that? ;)

ken



notsmartcar wrote:
The air corrector jet was 1f2 rather than play with that I put in a 1F5 been out for a run it runs slightly richer on the 1st choke but when I plant my foot to the floor at 55 it goes down off the scale weak which I didnt get before when I dropped the 2nd main jet from 90 to 75 (75 still inthere) am going out now with a 1f4 which I hope will drop the 1st choke mixture strength a little so I can than play with the 2nd main jet.............. am I right in assuming a 1f2 has smaller holes Top and sides than a 1f5

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May 2nd, 2011, 12:29 pm
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Firing on two.

Joined: April 22nd, 2009, 11:06 pm
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Post Re: over rich at high revs
And i was going to post before i got dragged off to the garden centre

notsmartcar wrote:
The air corrector jet was 1f2 rather than play with that I put in a 1F5 been out for a run it runs slightly richer on the 1st choke but when I plant my foot to the floor at 55 it goes down off the scale weak which I didnt get before when I dropped the 2nd main jet from 90 to 75 (75 still inthere) am going out now with a 1f4 which I hope will drop the 1st choke mixture strength a little so I can than play with the 2nd main jet.............. am I right in assuming a 1f2 has smaller holes Top and sides than a 1f5


personally id go back to standard and work from there
your 105 and a 1f2/1f1 for the primary
87.5 2nd main and air correction at 2AA and see how that goes? (18 26)

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May 2nd, 2011, 2:04 pm
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Agony Aunt - You have a car problem? Speak to Ken

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Post Re: over rich at high revs
Kevin,
just noticed these plots on the 2CV racing forum, on which the AFR ratios might be of interest to you, even though they're for a perishing Land Rover carb... ;)

< http://www.2cvracing.org.uk/forum/index ... 5.html#new >

ken

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May 2nd, 2011, 7:53 pm
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