Just to verify before I dig into the gulp valve for my
74 E-type, I assumed my valve’s diaphragm was bad because
the vacuum connection leaks through the larger pipe that
connects to the intake. IE, if I suck on the larger pipe it
draws air through the small vacuum pipe (and visa versa),
but if I cover the vacuum bib with a thumb I can’t suck any
air and the valve does not open (can’t blow through the pipe
that went to the air cleaner in either case.) I tried
pulling a vacuum on the small vac connection with a miti-vac
hand pump, but couldn’t pump it fast enough to register on
the gage or open the valve.
Mike suggests to test it in place:
‘‘Take off the air (side) pipe and start the engine. There
should be no air being sucked into the opening. Now rev the
engine and let the throttle snap closed. There should be a
very distinctive whoosh sound as a gulp of air is sucked
into the opening. If it does all that then it’s working.’’
and that is a good idea although I have the valve
off and the elbow to the air cleaner plugged right now.
Before I reconnect it does anyone know how to test it off
the car? Am I correct in thinking that there should be no
air drawn through the vacuum connection with the valve
closed or open?–
Phil W - 87XJ6, 86DD6, 85Sov, 74E, 67DQ450, 67DR450, 67Mk2
Arkansas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from Phil in Ar sent Sat 20 Mar 2010:
This is a smog device the idea being to open the valve when
high vac occurs when the car is slowing down and the engine
is a brake. It allows air into the manifold.
If you dont have smog then you can disconnect and cap off.
New ones are not that expensive. There should be no coupling
between the small vac pipe and the main.
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from alex paterson sent Sat 20 Mar 2010:
Thanks Alex, it was the coupling between the vac pipe and
main I needed to know about; that’s apparently what caused
my engine to suddenly run so lean and have no power.
BTW, ‘‘not that expensive’’ may be a relative thing; the only
place I’ve found one listed so far is XKs Unlimited and that
listing says: GULP VALVE, PN: C34018/RB ($300.00 CORE
CHARGE) Price: $ 340.97 / Each
Guess I’ll leave it off for now and if I get too much
backfiring I’ll try replacing the diaphragm myself per Mike
Eck’s suggestion.–
The original message included these comments:
New ones are not that expensive. There should be no coupling
between the small vac pipe and the main.
alex P
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
Hi we have a backfire on a 1971 etype S3 that seems to be recreatible after about 15 or 20 min of driving and letting off the gas. We are thinking this is the Gulp valve but I have a few questions. 1) Is the Gulp valve supposed to blow Air into the Air filter or suck air? We want to test this and will be following the procedure listed:
Take off the air (side) pipe (Item #5 in Diagram) and start the engine. There
should be no air being sucked into the opening.
Now rev the engine and let the throttle snap closed.
There should be a very distinctive whoosh sound as a gulp of air is sucked
into the opening.
If it does all that then it’s working.
From what I read here the Gulp Valve will suck air out of the air filter area? I have also read that you can bybass the gulp valve by blocking or putting a cap on the intake where the gulpvalve hose enters the air intake. How will this stop a backfire, or why would it. To me it would seem like it may actually cause more issues, this is why I could use some help understanding it better. Thank you all for your time.
Hi Eric,
The gulp valve allows air from the air cleaner to be introduced into the intake manifold when the engine is in overrun mode where you let off the gas to slow down. Normally this event causes the mixture to richen, so more unburned hydrocarbons get pumped into the exhaust system. In previous years that would simply show as a puff of smoke out the tailpipe but since Jaguar introduced the air pump it instead causes an explosion in the exhaust manifold. In the same manner as a doctor prescribing another drug to counteract the side-effects of the first drug, Jaguar introduced the gulp valve to lean out the mixture on overrun so the car wouldn’t backfire. The Stromberg carburetors have a bypass valve which accomplishes the same thing, and if you have not rebuilt them they undoubtedly are not working. They have a little vacuum hose leading to them. I have removed the gulp valve from my car and do not get a backfire, but then my bypass valves are all working. Repair kits are available from the usual suppliers, including DIAPHRAGM KIT, bypass valve | Moss Motors
The “Gulp Valve” is an AC Delco Rochester Emissions component developed by General Motors back in the 1960’s to meet emission standards. Jaguar adopted the GM emission package to field the V12 motor with carbs since the Fuel Injection they wanted didn’t pass Fed standards.
Original Jaguar P/N valves were “Made in England”. This is the only difference. Check eBait… numerous for sale: 1967 Chevy C-10 pickup “Anti-baclfire valve”
WOW, A blast from the past. I still have the E-type, but after discovering the internal leak in the gulp valve system, removing it and taking the E for a test drive, it had a malfunction in the brakes that caused the rear brakes to drag and overheat the rear rotors to the point of becoming bright orange/red It is still awaiting a drop and rebuild of the rear cage to include new calipers and differential seals which were also overheated. My how time gets away and other projects intervene. I didn’t realize it had been so long.
Refresh the memory: When was the last time the flex brake hoses (Front - C30755 (2); Rear - C30754) were replaced. As they age (over 5+ years) they then to collapse internally. That traps brake fluid pressure engaging the brakes without the brake pedal being pushed! My recommendation: Change all three; cheap insurance!
In a message dated 12/28/2023 9:47:45 PM Eastern Standard Time, noreply@jag-lovers.com writes:
Hi Mike, this is fantastic information. Now I understand how to check this and why it’s needed. The car is in the shop at the moment so we won’t be able to do any tests until after the new year. We think this issue may be above the shop’s expertise. Just so I’m clear on the Gulp valve and Bypass Valves. Is it safe to say that if either the gulp valve or the bypass valve are working that a backfire, related to this scenario, should not occur? My thought is to test the gulp valve and replace it before digging into the carburetors and replacing the bypass valves. I am still trying to understand where the bypass valves are in the carburetors. Thank you for explaining this to me.
I hadn’t replaced any brake lines when the rear brakes overheated. That day now long ago I had just removed the gulp valve that had internal leaks that caused poor running and took it for a test drive and noticed the first time I used the brakes that the pedal felt very hard, and after a mile or two smelled the brakes. I stopped and found the rotors were very hot but an impending storm was rolling in so I turned around and drove home and by the time I got there the rotors were glowing a straw orange color. I have since heard about something called a reaction valve in the brake system that can malfunction, but I’ve not verified that is the case here. I am still planning to drop the rear cage and rebuild it myself or have it rebuilt, and I will replace the brake lines when I do, but too many other projects have gotten in the way and time seems to pass so quickly I didn’t realize just how long the E has been on the back burner. Good to know that there is a source for the gulp valve if it is needed once the E is on the road again and hopefully that won’t take another 10 years because I figure that is about all the time I have left.
Sounds like you have charted some work to be done. Yes, the Brake Reaction valve has a history of causing brake problems. The Gulp valve, an emission control components, has not affect on brake performance or braking action. Two totally separate systems.
If you’ve never dropped the IRS some points to consider:
When you lift the car you will need a support (i.e. roll-a-round jack, etc.) that can be used to take the weight of the IRS. Don’t let the IRS just hang from the four mounts while the car body is suspended. This is especially critical as the mounts aren’t designed to hold the weight of the IRS. They will separate/break! Not good!!!
If your three brake flex hoses haven’t been replaced in the last 5+ years, do so!!! Cheap insurance!
Don’t use DOT 5 - Silicone brake fluid. DOT 3 or DOT 4 is more than up to the job and cost effective.
Research JAG-LOVERS archives regarding the reaction valve and fixes. There is a small plunger that usually is the cause of problems.
Good luck. Look forward to your future post as you dive into the IRS.
Happy New Year,
Cheers,
Dick
In a message dated 12/30/2023 6:26:35 PM Eastern Standard Time, noreply@jag-lovers.com writes:
Your best bet is to blank off the ByPass valves! They are a known vacuum leak source. Again, another “emission” component that probably isn’t needed if you don’t have to pass a State Emissions Test!
I remember removing the gulp valve but don’t remember blanking off anything on the carburetors themselves. That removal seemed to restore the engine to what had been normal running for me.
Probably unrelated but interesting is that my 2004 Triumph Bonneville America motorcycle would backfire on closed throttle coasting until on advice from a forum I disconnected the throttle position sensor. No more backfiring after that. I assume the gulp valve was supposed to reduce backfiring on the E, or was it’s purpose something else?
Thanks for the advice on removing the rear cage, Dick. I once saw a post on how to make a tool for separating those rear mounts and I even set aside a piece of flat steel to use to make one. Now if I can only locate that information again. Right now the E is in my garage on 4 wheel dollys and I have a Motorcycle lift jack that I intend to use under the cage while lifting the rear end and separating the mounts. any advice on the mount separation?
Sounds like you have a solid game plan! Once the hand brake cable, drive shaft and brake flex line are undone it’s a smooth order to remove the eight mount bolts (noting location of shims!!! - method 2) then lower the complete IRS out. Of course you removed the exhaust system first… LOL
When reassembling your IRS you may want to look into installing a remote bleeder system for the IRS brakes. It really makes brake work MUCH EASIER!!! Money well spent IMHO.
As for Mount Separation there are two methods. First, remove the four (4) nuts/washers from the mount from inside the IRS cage. The IRS can then be lowered and the four mounts remain in place.
If you plan on replacing the four mounts then, IRS supported, remove the eight (8) mount bolts. Then the IRS, complete with mounts may be lowered.
Have a Happy New Year and a “PURRRRRR” fect journey with your kitty!
Cheers,
Dick
Quick Note: While you have the IRS removed you might want to consider removing the drive shaft too. If it’s never been out of the car I’d recommend replacing BOTH U-joints along with having the shaft high speed balanced. I’m sure there is someone in your are that does that kind of work. You’d be amazed with the payoff of doing those 2 things… Just my 2¢…
In a message dated 12/31/2023 4:35:13 PM Eastern Standard Time, noreply@jag-lovers.com writes:
