Would anyone know? On left air intake box, on the engine side, there’s a round hole between the carbs. Does this need to be open? If not, what do I plug it with?

 

I believe that hole is supposed to have a rubber elbow that connects to the metal pipe that goes to the gulp valve. It definitely needs to be covered as it is inside the air filter so any air that gets sucked in to the carbs from there will not have gone through the filter.

 

thanks very much for your reply. i think i know the rubber elbow - on my xke the rubber elbow is on the right hand side air intake box, and it's on the outside side. the one i'm interested in is the left air intake box, on the engine side, there's a round hole in the box. i can't find any images for this area. however, your general comment makes a lot of sense - it maybe should be plugged up to keep all air going through filters.

but i would welcome any further comments

thanks very much for your reply. i think i know the rubber elbow - on my xke the rubber elbow is on the right hand side air intake box, and it's on the outside side. the one i'm interested in is the left air intake box, on the engine side, there's a round hole in the box. i can't find any images for this area. however, your general comment makes a lot of sense - it maybe should be plugged up to keep all air going through filters.

but i would welcome any further comments

 

There's also a rubber elbow on the inside (carb side) of the LH airbox. It's #5 on the upper left diagram on the page from Moss attached below. The elbow connects to a metal pipe that then connects to the gulp valve. If you're not familiar the purpose of the gulp valve it's to "gulp" additional air into the manifolds when you suddenly take your foot off the gas. When they close suddenly the carbs create a temporary over-rich mixture and the "gulp" helps keep the air/fuel ratio in line so there is a cleaner burn and less chance of a backfire. If your car has had most of its emissions system removed then it's likely the gulp valve is no longer there and the connectors removed. If so you need to cover that hole in the airbox or you're getting unfiltered air in your engine.

V12 Gulp Valve system

 

This is what it should look like if you still have a gulp valve connected.

 

this is fantastic help, thank you. in the morning i'll check for pipework that goes to the LH hole. However from memory i don't think that pipework is there. the rubber elbow and logical connecting pipes are not there. this is very helpful, thanks.

 

thanks for the photo. here's one from mine - maybe my gulp valve system is absent.

 

Here's what the original plumbing looks like. The gulp valve is the small round item at the end of the intake pipe. When triggered it draws air from the filter housing (that's why that hole is behind the air filter) and sends it to the intake manifold just downstream of each of the four carbs - rear side on the left bank and front side on the right bank. You can see the metal pipes that connect to the back of the carbs in my photos. If your gulp valve is missing it's likely all that plumbing is too.


Gulp valve viewed from right side.

Intake pipe from air box to gulp valve. Note air injection pipe crossing over the top of intake pipe and dropping down to rubber connectors behind carbs.

 

thanks, this is very helpful. really helpful. here's a photo before the air intake box was put back on. i don't seem to have that big pipe for the gulp valve. i'll check tonight if there's any gulp valve infrastructure in the V. Again, thanks very much.

 

hi lr grindley. yes, my car doesn't have any of the gulp tackle. you might be able to help with another topic. there's a pipe coming from distributor, over the V and snakes under the rear throttle body. The Al pipe here is then , but it's open ended and terminates under the rear left throttle body. i can't find a logical nearby place to connect it. do you think it was part of the gulp assembly? there's a vid here, correct orientation, looking fwd from behind left rear throttle body. you can see the pipe on the right in the last second or two - has some green paint on it.

 

photo here might be more helpful. it's interesting, i come from england so we didn't have to go through any of this smog situation.

 

English - I'm away from my car until tomorrow but will check then and get back to you. I'm pretty sure that's a vacuum pipe that runs between the intake and distributor but want to double check. If so it should have a rubber connector that connects to the intake manifold on one end and a rubber connector to the distributor on the other end. I'll confirm tomorrow.

In the meantime do you have a vacuum line connected to the distributor retard capsule? Also do you have a group of black rubber vacuum hoses (4 IIRC) coming out of a thermal switch on the right side, rear end of the intake manifold water pipe? If not your whole vacuum system may have been removed. Most of it is emissions related so the engine will run fine without it but you want to make sure all the inlet manifold vacuum ports are plugged or you'll get a lean condition on one or more of the carbs. Vacuum leaks in that system are a common cause of poor engine performance, especially if someone has tried to tinker with the carbs to offset the leaks in an attempt to get it running right.

LG

 

Hi lrgrindley, thanks for your message. i wanted to write and clarify my mistake. the open metal pipe from under the rear left carb/ throttle body does not go to the distributor. it goes to the other side of the engine (video), where there's a group of three tubes, with horizontal yellow stripes, going into what might be a part of the RHS air intake. I don't know the meaning of this.

 

I checked my car and that thin metal tube you showed should connect on one end to the intake manifold just behind the LH side rear carb and the other end to the black plastic part with the four rubber lines in your photo (not directly to the distributor as I thought). That black plastic part is a thermal switch and is screwed into the back end of a coolant pipe. The rubber and metal line that connects to the back of the LH side manifold connects to one of those four rubber lines and supplies vacuum to the switch. The vacuum it provides is switched to the other three rubber vacuum lines depending upon the engine temperature. One of those other three rubber lines connects to the distributor to retard the timing when cold, another runs to the gulp valve (which you no longer have), and the third (I believe) runs to the two air boxes to open and close the warm air intakes (for emissions control, to warm the engine up faster when cold). As long as the vacuum supply line from the manifold and line to the distributor are connected you should have all you really need. Just block the other two lines on the thermo switch (to gulp valve and air boxes) so you don't have a vacuum leak.

 

thanks lr gridley. this is fantastic help, i'm really impressed with your knowledge and understanding of these systems. you're definitely on my christmas card list. I'll take some time to digest but i think i've got the gist of what to do as first step. for the floating thin pipe, i'll search for a connection to a similar sized metal pipe coming that ultimately comes from the intake manifold just behind the LH rear carb. the floating tube is currently capped.

as an aside, i made three changes yesterday, which had significant impact. on the left air intake box, I blocked an open round hole on engine side. did this with electrical tape as the assortment of plugs i ordered from moss didn't fit (my fault). then i repositioned and hose clipped the main hose going from LH air box to carbs. that had been shown to be leaking on a carb cleaner test. and third, i put a new rubber elbow on the outside of the RH air box. I drove the car to work this morning and there was noticably more power and acceleration - and the idling when warm, after 15 mins driving, was down from 1300-1400 rpm to 1050/1100 rpm. none of which i expected. going thru these vacuum pieces is really having an effect.

 

Hi lrgrindly. Is this the nipple on the air intake that I should route to? In the middle of, slightly right. I uncovered the nipple-was capped before.

 

The open nipple in your photo is blanked off on my car too. Not sure what it was intended for but it's not used so keep it plugged. The small metal pipe attaches to a rubber elbow below and just downstream of the LH rear carb. If you can get your hand in there you should be able to feel the nipple. You can just see it in this photo.



There are lots of places where you can get vacuum leaks and as you have found out they can really hurt the performance so are worth tracking down. All too frequently ill-informed mechanics have screwed up carbs and timing trying to make the engine run right, not realizing that a vacuum leak (or two) was the cause of the problems. Keep at it. I'll try to help as much as I can.

 

hi lrgridley, thanks very much for your photo. its that your "hanging" thin pipe routes under the LH rear carb, as mine does. and i see there's a stout rubber connection on yours. you describe the rubber piece as an elbow. would you know what the elbow connects to - is it another thin metal tube? if so, could you describe in which direction does the elbow point? is it 12 o clock, 3 o'clock etc? i ask because i cannnot for the life of me find a receiving end near the front of the rear left carb i the space between the two carbs.

or am i being dimwitted - does it go to the gulp circuit that i no longer have?

 

There is a short thin tube (nipple) that's attached to the very back underside of the LH rear carb sticking straight down. You should be able to feel it next to the fiber gasket between the carb and the manifold. The rubber elbow is attached to that carb nipple, goes straight down then turns 90 degrees to attach to the metal tube on it's way across to the engine to the thermo switch. That's the black plastic thing with the 4 black hoses (it's one of those hoses). It supplies the main vacuum to drive the thermo switch that diverts the vacuum to the other 3 hoses - going to the gulp valve, distributor and intake heater valves.

 

thank you lrgidley. great commentary. your directions are great, I just was waylaid by my dimwittedness. i had been looking for the nipple on the carb side facing the firewall. i've found the nipple now that i've searched at the back of the carb, facing the manifold. excellent. i'm just trying to figure out finding a 3/16" rubber or silicon elbow, so that i can avoid using four clips. thanks again, great help all the way along.