David
One thing you might want to consider for tuning your carbs is a
Colortune. I've seen lots of pros and cons about using them but I
like it. It really lets you see what is happening in the combustion
chamber. I found that my engine runs better if it has a rich mixture.
Go from the bunnson blue color to orange. I'm not sure this would
allow you to pass the smog testing, but at least you will have a fuel
mixture that will give you some pep.
Marty Schlining
57 MGA Coupe
75 MGB
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Subject: MG Tuning
Author: David Hall <dhall@hp-vcd.vcd.hp.com> at BALT.SMTP
Date: 8/16/95 9:12 AM
Hello All!
I've got a 72 MGB/GT. I've recently put in an electronic ignition,
replaced the vaccuume advance, put on a tuned exhaust header, a new
muffler and pipes, and rebuild the carbs. With all of these mods, one
would expect a nice running MG, no? (p.s. Dual SU carbs.)
Now to the fun part - tuning it all up! Here's what I've done:
1. Removed vaccuume hose from vaccuume advance. Set static timing to 10 BTDC.
Hooked the vaccuume hose back up.
2. Adjusted the mixture jets so they were even with the bottom of the carbs,
then backed them off two turns each.
3. Set the idle adjust screws so that it's idling at approx 800 RPM.
4. Tried to do the adjustment on the mixture so that it is at the knee of
the curve. (Fastest lean speed.) This is a hard one to do.
Voila, should have a tuned MG, no? Well, it doesn't run very well. It's
week in acceleration, when cruising at most speeds, it kinda stutters.
Something which I observed however: Before I did the tuning, I drove it around
after I got it all back together. Really Peppy! However, it was idling around
1500 RPM. When I put the timing light on, it appeared to be ruuning about
20 BTDC. When I changed the timing to 10 BTDC, it dropped down to a nice slow
idle.
The PPO has put a High-performance cam in. Would this affect the
timing?
So, here's what I'm going to try:
Slowly keep advancing untill idle speed starts coming up. Stop when it gets
to 1000 RPM. Try it there. (See if pep comes back, smooth running, etc.)
Buy a carb balancer so I can for sure get the carbs in synch.
Any other suggestions? Am I missing something? (Valves? - I haven't touched
them yet.)
Thanks for any help! :)
David Hall
dhall@vcd.hp.com
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