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SU adjustment.

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burgundyben

Jedi Hopeful
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I pulled the plugs out to clean and gap them, they were black and sooty.

I'll check the choke is fully off and cleant the filters, then maybe I want to adjust the mixture.

How many flats to adjust and whcih direction weakens the mixture?

Is 2 flats a lot or not much at all?

Other than that she's running like a dream.

Thanks

Ben
 
Looking down at the carb, counterclockwise will raise the jet and lean out the mixture, remember you are looking at it upside down so opposite from you would think, if the car is close to stock, I suggest the jet to below the bridge about .070", I measure them with the end of a dial caliper, just take the dashpot and piston out to do it, or you can adjust it up (lean) until it stops and then turn it down (rich)12-13 flats. two flats will net you about .010-.015" change in jet position change, if my memory serves me right a flat equals about .006"-.008".
 
Thanks for that, a colleague has just given me a colourtune set he no longer uses, I'll give that a whirl.

Not sure what type of filters I have, they are not paper so I assume they are washable, I might give those a wash first.

Were the original filters paper ones on a 1500 MGA?

Thanks.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]a colleague has just given me a colourtune set he no longer uses[/QUOTE]

On dual carbs, its best to get the car to which fuel comes first adjusted properly before moving to the 2nd carb.
 
tony barnhill said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]a colleague has just given me a colourtune set he no longer uses
Click to expand...

On dual carbs, its best to get the car to which fuel comes first adjusted properly before moving to the 2nd carb. [/QUOTE]

How do you know when you're at that point? My experience has been that the car runs pretty badly until both carbs are pretty close to being adjusted.
 
You can tune the engine on one carb at a time if you raise the piston way up on the other and have em seperated. In fact this is one of the factory accepted methoids to get things going the first time.
 
wkilleffer said:
tony barnhill said:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]a colleague has just given me a colourtune set he no longer uses
Click to expand...

On dual carbs, its best to get the car to which fuel comes first adjusted properly before moving to the 2nd carb.
Click to expand...

How do you know when you're at that point? My experience has been that the car runs pretty badly until both carbs are pretty close to being adjusted. [/QUOTE]

Yup, but if he's using a colortune he can check the mixture on the two cylinders that run off of one carb, then move onto the other. At that point it's not a matter of how the engine runs, but how the cylinders run.

Similar to a 2-cylinder motorcycle engine with 2 carbs, it's like tuning two engines that just happen to run together. One cylinder can make the engine run lousy, while the other cylinder can be close to perfect.
 
You know I wish I had a color tune. I am just too Scotch to fork over the funds.
 
They're a VERY handy tool to have lyin' around, Jack. I've two and it makes setting the mix on a dual SU engine a less-than ten minute job. Bit pricey if you don't do it a lot, but it sure cut time down for shop tune-ups. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
I notice a few on ebay. Is one the same as the other or are they specifically designed for MGs?
 
Hello all,
i have always worked on the principle of the same number of colourtunes as carburettors. Don't forget that there is a balance pipe between both carburettors and so there is some interaction, i.e whichever cylinder is drawings draws from both, but not equally I suppose.

Another factor that upsets a colour tune is if the engine draws in oil at idle, (worn guides\seals) that cylinder will always be rich.

Alec
 
You're all making me feel old. I set my SUs by ear with a screwdriver, a flow meter and an SU wrench. If I can't find my flow meter then I use a piece of rubber hose.
 
Steve,

The rubber hose is a new one to me, I am going to have to try that one.

Pat
 
Classically called a "listenin' pipe" in England, Patrick. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
Hold it up to the intake and listen through the hose. If both carbs make the same sound, then the flow is matched. It's pretty accurate actually.
 
all this tak about balancing, and tuning and what not makes me ~almost~ happy to have only 1 carb to play with... /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif
 
I ain't gonna say NOTHIN'... /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif
 
....wow...
 
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