Mixture setting

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milfredo
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Mixture setting

Post by milfredo » 24th February 2008 - 3:36pm

Hi,

I've got the CO meeter to set the mixture on my carbs.

I set the carbs to a standard setting, 1.5 turns out on each and balanced/ set the idel to about 1000.

I follwed the manual of the tester and set it in air over an 8 minute period to 2% CO. I then put it in the exhaust and the reading dropped to 0.8%ish... now I would have thought that it should have been richer as it was 1.5 turns on the volume screws and not been leaned out yet?

Now should I be turning the mixture up i.e. turning the volume out? I'm confused.
Just out of interest I put the meter onto my Dad's new Mini and got a reading of 0%. I know it is a new car, but why would I want mine at idol to be 2.5%?

Can anyone help?

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Editor
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Post by Editor » 24th February 2008 - 6:57pm

The volume control screw controls the flow of fuel in the idle circuit, so unscrew it a bit to get a richer mixture. The 1.5 turns is just a starting point - can't adjust anything unless the engine is running!

I usually go for a figure of around 3% CO for carbs for a Type 3. Worn carbs sometimes draw in a bit of extra air around the throttle valve, so it doesn't pay to be too lean.

What you do notice is that with around 8% the exhaust sure smells nasty! In fact you get to smell this when there's a classic car in front.

Modern cars have a catalytic convertor that chemically combines the exhaust gases with oxygen and gives out minimal CO. FI Type 3s produce about 0.5%. Also modern cars have engines designed to burn the fuel better, so there's less CO being produced.
Dave.

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milfredo
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Post by milfredo » 25th February 2008 - 11:02am

I think there might be something else going wrong then. It is still plainly too rich when set to 2.5, it pops on unburnt fuel and the plugs are seriously black. I think there must be something wrong with the ignition.

I just posted this on the Samba:

Thanks guys.

This is the route I've been taking although I must be doing something wrong somewhere.

I have a 009 (I know) with petronics timed to 30degs at 3000 revs, all new leads and plugs (gapped), valves checked and correct, idel was set to 900 although I had to bring it to 1000 to keep it ticking over as it's so lumpy, carbs balanced by ear, both mixture screws turned out 1.5 turns, linkage and chokes look like they are working in unison... and this is where I get stuck.

As the idel is so lumpy it's hard to turn the mixture in and notice the engine stumble. Then I repeat on the other side. I think I get there but am unsure. I have not balanced the carbs at 2500 revs as I didn't know I had to.
It drives nice, until the plugs soot-up so I'm thinking that it's still too rich, maybe there is something else going on, something with the ignition, again I'm just stuck on where to check.

I can't afford a new dizzy so the 009 will have to do for now. Are there any tests to check the rest of my ignition?

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nidge
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Post by nidge » 25th February 2008 - 8:32pm

Does it pop through the exhaust or back through the carbs?

How did you set the timing to 30 degs advance?

Is it a stock engine? no leary cam or anything?

Do the revs rise and fall randomly? if so could be an air leak. Have you got an in let gasket between the head and manifold and a paper gasket between the manifold and the plastic riser and another between the riser and the carb?

Stock carbs? Rebuilt?

have you balanced the carbs with a balancer?

Is the balance pipe between carbs in place not blocked and or leaking ?

Check the condition of the pointed ends of the volume control screws they could be worn or even missing the seal.
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milfredo
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Post by milfredo » 25th February 2008 - 10:15pm

Hi Nige,

Through the exhaust, advance timing gun, stock new 1600, stock cam, stock professionally rebuilt carbs.

Revs stay steady until it seems to miss or bump, sometimes followed by a pop. It never raises. All proper gaskets installed while engine was out of the car. I've used a piece of fuel pipe as the balance pipe.

Carbs balanced by ear as my balancer doesn't fit the odd top on the solex's.

cheers,

Will :)

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Post by purplepeter » 26th February 2008 - 12:49pm

Make an adaptor for your balancer..a bit of pipe/hose will suffice

mine is the top of a road cone,as thats all i could find when i needed an adaptor!

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Post by nidge » 27th February 2008 - 10:05pm

I too made an adapter for a carb balancer but didn't have a road cone handy. made mine from the lid of an aerosol.

If it's popping through the exhaust there could be an air leak on the exhaust somewhere ? which could explain the unexpected reading on the Co meter?
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Post by veedweeb » 29th February 2008 - 6:01pm

milfredo wrote:
I've used a piece of fuel pipe as the balance pipe.
I could be wrong here, but doesn't the balance pipe 'carry' a vacuum?

I remember a problem a while back when I pipe that was designed to carry something under pressure (like a fuel pipe) was partially collapsing because of the vacuum.
Steve.

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Editor
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Post by Editor » 29th February 2008 - 11:08pm

There are times when it would - never heard of it as a problem though, as on over-run, the carbs aren't really passing much air so no fuel either.
Dave.

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Post by the_hotrod_freak » 2nd March 2008 - 9:22am

milfredo wrote:Hi Nige,

Through the exhaust, advance timing gun, stock new 1600, stock cam, stock professionally rebuilt carbs.

Revs stay steady until it seems to miss or bump, sometimes followed by a pop. It never raises. All proper gaskets installed while engine was out of the car. I've used a piece of fuel pipe as the balance pipe.

Carbs balanced by ear as my balancer doesn't fit the odd top on the solex's.

cheers,

Will :)
if you have knacked carbs no amount of tunning will help. as with the balance pipe you need to fit the largest diameter pipe you can fit. as it will help the two carbs.
if its poping check the exhaust for leaks. also the rough idle could be down to worn out carb. its common for them to leak fuel at the base of the carb.

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