MGC guy sneaks in... looks around.. asks question.

[Steve_S]

MG owner here. Sorry to intrude, I'll just stand by the door and not sit down. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

I thought you Healey folk might be able to offer some advice. I recently acquired an MGC with a built-up engine, running triple webers. I don't know much about this engine and I know nothing about webers. I understand the engine isn't identical to Healey units but they aren't completely different. Here's my question...

I know my car is running very rich, one reason being the plugs are all sooty and black. However one plug, number 5, is light tan. What would cause this?

I would assume both 5 and 6 would be the same color. I don't know these carbs at all as they are still new to me, but I thought each carb feeds two cylinders. If that's the case, how would only one plug be light tan and the other sooty black?

Other info...

The car runs well although it idles high when warm (cold idle 700, warm idle 1300-1500). There is an occasional "puff" for lack of a better description, as if the engine missed. It happens mostly at idle, and sometimes there is a hesitation at speed when the throttle is feathering between idle and accelerate. Nothing serious though. There is also occasional run-on after shutting down when warm.

Specs on the car and engine can be seen here:

https://www.mgnuts.com/mg/mgcgts/specs

Any input appreciated!

 

[Dave Russell]

Re: MGC guy sneaks in... looks around.. asks quest

Hi Steve,
I would start by verifying that jetting is the same in all six barrels.With an unknown engine the PO could have odd parts in some of the carbs. There are many jets, bypasses, venturi's, etc to check. Also, obviously check float levels. Record ALL present jet & bypass sizes for a reference. Especially check the #5 barrel as it seems to be running lean as compared to the other cylinders. Possibly an air leak somewhere?

Overall, the mixture appears to be rich. This could require jet changes to all six barrels, not a cheap or easy task to find the correct jetting.

This rich mixture may be saving you from more serious problems. ie - I notice that your specs say BP5ES plugs. If true, this is a very hot plug for your engine. If you get the mixture leaned somewhat closer to optimum, you will almost certainly need colder plugs such as BP6, BP7, or even BP8.

If you are not familiar with these carbs, I suggest getting a good book such as the Haynes "Weber Carburetor Manual".
D

PS - Too high fuel pressure could be a major cause of the "rich" condition.

 

[RonMacPherson]

What Dave said, plus. A little elaboration. The weber carburetor is good for performance tuning, in that just about every single stage of fuel air mixture can be controlled. Each piston has it's own fuel supply except for basic float chamber which is shared in each carburetor between the throats and jets.
1st get yourself a good Weber book, or several; Haynes is a good intro book, I think Pat Braden's Weber Carburetors is very well written and Haynes Techbook Weber Carburetor Manual is probably the best all around textbook type.

Then do some web searches. The more info you acquire the better your situation will be.

As Dave said Weber carburetors are sensitive to overpressurizing of the fuel system. A lot of folks do not realize that just 1 lb of over pressure goofs up a whole lot. And yet it requires a goodly volume of flow. Most fuel lines with Webers if not upsized are marginal. Get yourself a GOOD fuel pressure gauge and use it when running to make sure your pressure NEVER goes above 3 1/2 lbs. Some say that is too high, but...

Then, after accessing the books, remove your covers and do a jet survey. fuel jets, idle jets, emulsion tubes, etc. Get a good magnifying glass and a good light. Might be a good idea to get a jet gauge(not that expensive) So you can verify that the size of the jet is correct. A lot of people think that you can drill out a Weber jet if you need to go fatter, not realizing that with Webers you're just goofing up the flow. Each cylinder should be running the same jet pattern, that way each cylinder is equalized. Black smoke is rich, popping and backfiring is lean. Which jets need to be changed? Depends on when the popping and backfiring occurs. Can be idle fuel, can be accel fuel, can be accel stroke. First thing is to inventory what you've got and plan a course of correction.

 

[Steve_S]

Re: MGC guy sneaks in... looks around.. asks quest

Thanks guys. Excellent information! I will investigate the carbs to the best of my ability over the next week.

 

[VelodromeRacer]

Re: MGC guy sneaks in... looks around.. asks quest

If you do your homework well my son, Master Keoke may
answwer all your needs...

(I know, I am still in training as well)

 

[Steve_S]

Re: MGC guy sneaks in... looks around.. asks quest

Hey, I'm a velodrome racer, too! Well, I used to be. I've been planning to get back on the track for years. I spent most of my time at Encino, and also rode Dominguez Hills and San Diego.

 

[Johnny]

Re: MGC guy sneaks in... looks around.. asks quest

Since it is a new car, to you anyway, you might try just running some type of carb cleaner through all the carbs. Even adding fuel injector cleaner to the gas tank. Replace the spark plugs first, then check if they are still sooty.

 

[VelodromeRacer]

Re: MGC guy sneaks in... looks around.. asks quest

Steve S,
Lucky you..CA track time has much more warm days then us midwesterners! I have raced on the Major Taylor velodrome for over 15 years now! I train on a fixed gear on the road, climbing hills of southern Indiana!

Good luck with the MGC.

 

[GregW]

Hi Steve,
Randy Forbes turned me on to the Carbtune synchronizer. I’ve got one if you want to borrow it, though it only has three vacuum lines a present. Here is Randy’s photo of the setup. Carbtune

 

[Steve_S]

Deal, thank you!