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MG MGA - Carbs sound loud.

I have a 1962 MGA, with 1622 engine. I put a new exhaust system on and it seems that the carbs sound loud, and not as powerful. I have checked plugs and wires. When reving up it spits gas out the carbs. When pulling plug wires off during idle, the 2 and 3 do not make as much difference in idle as 1 and 4. I will check compression tomorrow.
Eddie Davis

have you checked the valve timing?

Peter
PC Cirillo

I agree with Peter - spitting back at the carbs usually shows the timing is incorrect.
Cam Cunningham

Or that the mixture is too lean...
dominic clancy

Eddie,
You mention that you put a new exhaust system on it. Was the car running OK before you did this? What exactly did you change? Seems odd that an exhaust would cause this symptom.
Good luck,
Gerry
G T Foster

Yes or I thought, the old exhaust was straight through. The engine has 2k to 3k on the rebuild. I will check timing again. I check valve clearances, all is good.
Eddie Davis

I wonder if this is one of those cases where the rear carburrettor filter box has been fitted on upside down, blocking the air balancing hole to the piston. I am guessing (don't quote me) that this may also affect the vacuum advance in that the airflow through the carb throat is out of sync with the engine RPM, resulting in ignition timing mismatch.

Steve
Steve Gyles

Steve, I will look at this, I had also thought that timing was not advancing. By the way thanks for all the feedback, that is what makes this BBS so important, especially, since there no MGA's locally, to go compare to. Eddie, Tuscaloosa,AL, USA
Eddie Davis

Eddie

I know it's only a half chance. But with you probably removing the carbs when you fitted your exhaust I thought it worth a mention. I have done it and, speaking to my MGA supplier (Bob West), he says that about 50% of his customers who come in with not dissimilar symptons, have the rear box upside down. See this page on my website, second small article: http://www.mgaroadster.co.uk/odds_and_sods.htm

Steve
Steve Gyles

Steve, I checked this today, It is ok, but I found a kink in the copper tube, coming from carb, I gonig to get some tubing to correct this. I will go from there.
Eddie Davis

I'm not familiar with the term "filter box". Filter screen...yes, box....no. Clerification please. Thanks!
Robert Maupin

Robert, Steve is talkng about the metal "can" that holds the air filter on the rear carb. He has some info and pictures about this on his web site (see http://www.mgaroadster.co.uk/odds_and_sods.htm).
Andy Bounsall

Thanks Andy!
Robert Maupin

OK, I have done some more test, I have tested compression, and found the following. 1=133psi, 2=30psi, 3=30psi, and 4=133psi. I checked the torque, it is ok. My next step is to remove the head, I believe and hope a failed head gasket. I am thinking of starting a youtube of the sound and how carbs are reacting and my results to help others in the future.
Eddie Davis

Before you remove the head, check the valve clearance on all valves. If for some reason the valves are not closing due to little or no valve lash clearance, it will spit back and have little or no compression. It's a long shot, one more clue to work with.
Russ
Russ Carnes

Russ, I did check and all was in spec. Another check was to ensure the valves on # 2 cylinder was closed, and apply air pressure through the #2 spark plug hole with all plugs out. The result is you could hear and fill air in the # 3 cylinder. The head is coming off this Saturday.
Eddie Davis

Got Head off tonight, as I thought, gasket between cylinder 2 and 3 is blown. Now I will check block and head to find out why the gasket failed. Attached is a picture.
Eddie Davis

Here is the picture.

Eddie Davis


Here is a link to the Youtube I have posted.


http://www.youtube.com/watch?v=dGJsUXBRSew
Eddie Davis

The good news is that you have found a well defined problem! As you mentioned, check flat surfaces and clean really well. I recommend ARP stud sets, de-burr the block around the stud bores, follow their instructions about installing studs finger tight, re- torque and adjust valves several times after re-installation. Remember to change your oil after having the head off. Enjoy that nice car!
Russ
Russ Carnes

Strange it should go at that point, as it is the widest partition of the three. Any theories anyone?
A Pearse

Surfaces not flat, stretched studs, not re-torqued? Apologies to Eddie, if you built the motor you probably checked all the above. I would replace the stud, nut, washer set.
I've heard lots about using the 3 main MGB head gasket, the black one, what is the best?

Russ
Russ Carnes

I would be careful about changing the washers on the head studs. The thickness and hardness of these washers are not standard. Normal, soft washers will give problems.


Mick
M F Anderson

Must use the correct hardened washers. Standard ones will gradually compress, and then you don't have the head torqued down any more.

The copper head gaskets are useless. Use a Payen resin one for early MGB and it will last forever in comparison to the copper ones.
dominic clancy

The reason the head gasket commonly blows between #2 & #3 cylinders is because there are two exhaust valves side by side making for a hot spot in the middle.

I used to have many problems with laminated copper head gaskets. I have used the black Payen head gaskets exclusively since the early 90's with never any problem. These were standard issue for MGB from 1975 on. Moss Motors part number 296-405.

Barney Gaylord

Barney, thanks for your feed back, on your comment I noticed that on the copper gaskets, the bottom side was not full metal at the cylinders, but on the payen gasket it was full metal on both sides around the cylinders. This was the one I used. The A is running great now, I took it out yesterday, it is so good to ride in when the engine is running good.
Eddie Davis

ARP stud kits have the correct hardened washers, nuts, and studs, and are beautifully manufactured in the USA. Standard issue for competition engines. Seven Enterprises specializes in Mini parts, have raced Minis for lots of years, have a great, renowned engine shop that has built motors for many successful racers over the years, and a great staff with MGs and Minis. The Moss part number listed below is ARP, the price is equal to lots of peace of mind.

http://www.arp-bolts.com/

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29855

http://www.7ent.com/page.cfm?pageid=6

Russ
Russ Carnes

I had several of the laminated copper ones go as well in a short period of time. Took Barney's advice and replaced it with the Payen type. Three years and no issues. Last June I replaced the 15 head with an MGB 18 head and added a supercharger. Again no head gasket issues. I even had to slacken the head nuts to replace a broken rocker arm then re-torque. All is still well.
Tom Baker

Thanks for all the feedback, that is what makes this website so great. Here is a link to my youtube account, with a short clip with the sound of my carbs, before and after I replaced the head gasket. http://www.youtube.com/watch?v=zgw6LQiTfVs
Eddie Davis

It has been 2 weeks since I replaced the head, all is good, we have been on several trips around town, again thanks for all the feedback.
Eddie Davis

Chaps,
Ref Steve's comments about fitting the air filters upside down, here's how I avoid this problem (with dymo)! AB

A Bennett

AB

Spot on. One less. Apparently it is a very common fault. I have only done it the once!

Steve
Steve Gyles

This thread was discussed between 24/01/2009 and 03/03/2009

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