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 MGB Technical - Gulp Valve

My 1980 MGB makes a "pop" sound when I let off of the accelerator while shifting as if it gas is igniting. I have replaced the gulp valve twice. The car also seems to be idling high. How can you tell if the gulp valve is working and where do you get a "good' one, or what else would cause this?
Howie

FWIW, I don't believe NY is a state requiring you to have your emissions control stuff operative. Accordingly, I would suggest you get rid of the entire system - which, of course, will include the gulp valve. Ditch the air pump, remove the air injectors (plug the holes with 7/16 SAE threaded bolts 1/2 inch long) and plug the intake manifold where the gulp valve was hooked to.

The gulp valves were weakly designed and the whole system was devised mainly to comply with U.S. standards at the time. Some may wish to argue that point but I truly don't believe this emissions control system had a lot of great engineering put into it.

I removed this system from my 69 B about 4 years ago and the engine has run much better ever since. I had a backfiring problem (especially when decellerating) and that has gone completely away.

Tom Fisher
Tom Fisher

Howie,
I had the same problem in my '73 B, backfiring and/or popping when shifting, and on the overrun. A new gulp valve did not help. I tried running it with the belt off the air pump and the backfiring was totally gone. I put the belt back on and disconnected the outlet hose to the injectors, and blocked both sides of the line, and no backfiring. I have a Monza exhaust, and even though it still is intact on the outside, some of the baffles have rusted out on the inside (I have pulled some of the remnants out of the tailpipes with pliers)and it has very little back pressure, but sounds nice. My theory, maybe misguided, is that with insufficient exhaust back pressure the air that is injected into the exhaust ports to help more completely burn any remaining fuel ends up doing its job farther downstream in the exhaust manifold, downpipes etc., causing the popping and backfiring.
Like Tom, I removed the system. I was trying to keep the car as original as possible and be a nice guy to the planet, but it runs better and gets better fuel mileage without the system. I kept the parts, though.

Ralph
Ralph

Howie,How is thing going in Syracuse?I was born in No. Syracuse long years ago.I miss the ole place(lived on Gillete Rd)I now live in Toledo,Ohio(what can i say)I also have a MGB,1972.Take care,Rich
Rich Osterhout

Howie-
Interestingly, the most common cause of backfiring in an MGB is the simplest to diagnose and fix: a leak in the exhaust system. As the pressure wave of a pulse of exhaust gases passes through the exhaust system, it leaves a partial vacuum behind it, sucking in fresh air through the leaky joint in the exhaust system. Unburnt fuel condenses in the exhaust system due to the induction of the cooler air and mixes with it, creating a condition rife with the potential for combustion. When a pulse of hot exhaust gases hits it- Bang! This problem can be aggravated by a too-lean or too-rich fuel-air mixture that will result in the production of increased amounts in unburned fuel. To find out if this is the origin of your particular problem, mix up a thick solution of water and liquid dishwashing detergent. Not the kind you put in the dishwasher, the other kind that your wife uses when she washes stuff in the sink. You know, the thick liquid stuff that she uses to cut grease with. With the system cold, squirt it on the joints of the exhaust system (do not forget the joint at the bottom of the exhaust manifold), then fire up the engine and look for bubbles. If you see bubbles, then you have found the leak. If tightening up the clamps does not cure the problem, your friendly local auto parts store or muffler shop can supply you with some exhaust system putty to take up the gaps in the connections that result from poorly matched exhaust system tubing diameters. A set of SuperTrapp T-bolt style exhaust clamps will give perfect 360 degree sealing in order to eliminate the leakage completely. They also have the advantage of being manufactured from durable stainless steel so that they will not corrode and are complete with Nyloc nuts. These are available from Summit Racing in both 1 ¾ “ (Part # SUP-094-1750) and 2” (Part # SUP-094-2000) through their website at http://store.summitracing.com/ . It should also be noted that the juncture of the exhaust manifold and header pipe is the most common location of such a leak. Because the interior of the bottom of the exhaust manifold has a conical surface, the exhaust manifold gasket should be installed with the conically shaped end facing upwards into the recess of the exhaust manifold. The gasket is squeezed between the exhaust manifold and the exhaust pipe flange in order to achieve its seal. Note that the headpipe has a flange welded on it to allow the "triangular" flange to compress the gasket (doughnut) when the bolts are tightened. If you use an old headpipe when you do a rebuild, then you will be running the risk that the welded-on flanges have significant rust damage and that they will eventually fail to the point that they will pull down through the triangular bolt up flanges. If you have an indication of an exhaust leak that you can't find, some backfiring while decelerating down a hill, and maybe even a loud squeaking noise on rough roads, then you might want to check and see if your headpipe is starting to migrate downward toward the pavement.
Steve S.

Hello- Once again Steve, The Virginian Guru, nails it! Cheers, Vem
VEN

This thread was discussed between 06/06/2008 and 15/06/2008

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now