MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Fuel Mixture To Rich

After the 60 mile run yesterday and after checking everything out, I noticed the exhaust pipe is a little black, not heavy, but enough to tell me the mixture is a little to rich. Can I lower the needles a bit to lean out the carbs? If so, how much should I lower them initially? Is there a rule of thumb? PJ
Paul161

Is there a reason why you prefer to lower the needles rather than the usual raising of the jets?

Don't forget that the rule of thumb is better a bit rich than even the slightest lean...

Tom Lange
MGT Repair
t lange

Paul, I generally tweak in 1 flat increments. But I do it by checking the plugs after a decent run at cruising speeds. I don't bother with the bit of shutting off the engine, and pulling over. Just don't to too much low speed running. Bud
Bud Krueger

Have you tried the SU piston lift test?
With the engine at normal temperature and running at idling speed lift a piston by 1/32 inch. This weakens the mixture slightly and the engine may speed up slightly for a few seconds. or remain unchanged or decrease speed.
If unchanged the settings are correct.
If the speed increases the setting of the JET is to rich If the speed decreases the setting of the JET is is too lean.
Lowering the JET enriches the mixture, raising it leans the mixture.

You can also check at 2500 to 3000 rpm. Lifting or lowering the piston by 1/8" should not effect the speed.
If correct at idle but not at speed the needle may need attention.

The above is condensed from the instructions on the PSW SU adjusting tools kit.


Jim B.
Jim B in NJ

If it is running perfectly and the plugs look pretty good as per Bud above, I would forget about the tailpipe color and leave it alone. If plug(s) are sooty black, then maybe try adjustment as above. If the engine is brand new, it could be oil due to rings not being totally seated, etc. George
George Butz

Guys, Reason I thought of lowering the needles is that the jets are all the way up with the bottom nuts and rather pulling the carbs to insert a couple washers, lowering the needles is easier, I don't have to pull the carbs to do that. Remember this is a TF and the front carb is a task.
Thanks George, I haven't pulled the plugs yet, but will do that next, if their ok and not sooty, I'll leave everything as is. It does run like a champ and has no hesitation when punching the throttle. I have the recommended Champion plugs in it. The number eludes me right now, but their the ones in the book. Also I burn non ethanol gas, which I can get a mile from the house. I would only use corn gas in an emergency.
Paul161

George, I pulled the plugs and they are a dark brown. No three and four are darker, indicating to me a richer mixture in the rear carb. Reset the timing as it was a little advanced too much. I lowered the idle RPMs and the engine runs smoother than before but will crack to life with no hesitation if the throttle is punched. I think it's where I want it, but will know better when I take it out on the road. Thanks for your input. PJ
Paul161

If the rear ones are a bit dark, make sure the rear jet lever (choke) is positively returning fully up. They tend to hang up and not fully return. George
George Butz

@Paul161: You did not tell us what the number on your needles is.

You can get three types of needles: standard, rich or weak.

http://sucarb.co.uk/carbspec/carburettor/spares/id/1546
Christopher Couper

Chris, I really don't know what number needles are in the carbs. They were in the carbs when I got the car, I'm just assuming their standard.

George, The choke levers are returning fully up. The needle wasn't exactly flush with the bottom of the piston and I dropped it 010. to make it flush, the front carb needle was flush with the bottom. Now I need to drive it and check the #3 & 4plugs again to see if they lighten up some. PJ
Paul161

Paul,
You are probably checking the plugs correctly, but just to make sure,,, As you are driving at road speed, go to natural, shut the car off and coast to a safe spot. Then check the color,, The idea is that you let the engine idle,, it will probably give an indication of being "rich"

Steve
Steve Wincze

Paul. The needles are usually stamped with the reference code, though you need to remove them to read it.
Dave H
Dave Hill

Thanks for the info, all well received. After a good run, the plugs for 3 & 4 have lightened up slightly and pretty much match 1 & 2. I'm going to a show in Fayetteville, Arkansas, about 60 miles away from here, Saturday, that should be a good run to clean up the plugs.
Hey, anybody else going? PJ
Paul161

This thread was discussed between 26/08/2015 and 07/09/2015

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now