MGB: SU's

Another GT question/s!:) I know I'll be tuggin at the MGE's mindstrings for I've lost lots of what I used to know about the B's due to disuse atrophy. The SU's are balanced but seem to run rich for when I pulled the plugs, they were all carbonized after a nice 40 mile jaunt, nothing over 45 for I don't know the cond of the wheel bearings or the wire wheels, so I took it slow. Even the OD which the PO said did not work, worked!! Lucky there I guess. Vacuum advance is minimal due to a defective vac mech, so should not more be burned since not as advanced? Been a long time since I used my brain on these ones. Need to get a spark plug blaster. I'll have to look for one at the local Harbour Freight.

I did do a cold compression test, all cyls are at 120 amazingly! I figure hot, that should go up a bit. No visable oil burning. Does not smell of lots of unburned fuel. What is the best way to tune these buggers mixture without fancy equip? Don't want it too lean either. I used to have a Gunsons Colour Tune but that on my '77 B was not too helpful way back in the good old '90s! Would it be now that I'm older and wiser and more patient? Car starts fine with choke on cold and right away warm.
Need to get a dwell meter again also! Indeed the good old simple days.
BJ

Well, the best way to set the mixture is with a wide band oxygen sensor - but since most of us don't have one of those, you will have to follow the manual - but I have had trouble with the procedure in the manual.

Try this in conjunction with the manual http://www.mgexperience.net/phorum/read.php?1,956473,956473#msg-956473

use the procedures here
if this shows its for HIF's

http://www.sucarb.co.uk/Technical.aspx

Michael,

That is what the Dr ordered! :) I remember that photo of the chap with the hose in his ear!! I'd do the balance with my flow meter:)

Many many thanks

BJanos

i am glad to help.

i have a single 44 so i do not get to enjoy the pleasures of carb balancing

Bryan-
When you pulled the plugs after your run, it was after you stopped in your garage or driveway, idled for a few seconds and shut off the engine. The plugs reflect the condition at idle and shut down not at actual running and acceleration. The needle in your carbs has 16 positions. As the needle rises and falls based upon running demands, it creates a different rich or lean mixture. The "plug test" should be done in the range of driving conditions most important to you. For example, if you suspect that the carbs are running too rich during cruising conditions at 3,200 rpm, find a quiet stretch of road, run the car up to 3,200 rpm for a few seconds and then shut the car off. Pull off to the side of the road and then check the plugs. Similarly you could of course get the engine warmed up completely and run the rpm's up to 3,200 in your garage and then shut the engine off. The plug color condition changes hundreds of times during any drive you might take with the idle condition not representing the rich or lean condition during road use. The "right" mixture at idle may be useless at running speeds.

X2 Brian's comment.

I found my car rich at idle and VERY lean at speed, had to change needles to correct.

The hours I have spent with a tube in my ear. You have got to love them, really you have got to love them. How much time would you spend tuning a carb on an American car.

If your vacuum advance isn't working, you're going to have unburnt fuel in the chamber when the exhaust valve opens. Your plugs are telling you that you're not getting complete combustion and you shouldn't until that distributor starts advancing to 30 degrees at 2500rpm. Fix the vacuum problem and put in new plugs. BTW, don't waste the money on spark plug blasters. They make things look pretty but new plugs are inexpensive and a blasted plug with a couple of glass beads stuck between the inner insulator and the threaded shroud can end up doing some damage to your engine. Best of luck. Basil

Bryan ,
Leave the carbs as they are for the moment.
Get the ignition sorted first then go for the SU's , IF they need it.

Personally I used a vacuum gauge to set the carb balance.

Pete.

Good idea, will leave the adjust alone until the ignition is fixed. Thanks