Deceleration Valve Options

[wonkipop]

@Van B

the EGR on the 75 (calif) works off the vac port before the throttle plate on the throttle body when its all hosed up proper stock.

one of those weird things i discovered on the EC-A, EC-B research.

same port worked advance on the distributor of the EC-B 74 engines.

the decel on the 75s still works the same way as it did on the 74s.
off manifold vac.
but its a beefier unit for sure.
maybe letting in even more air on decel than the 74s?

(IMG:style_emoticons/default/beerchug.gif)

[Van B]

@Van B

the EGR on the 75 (calif) works off the vac port before the throttle plate on the throttle body when its all hosed up proper stock.

one of those weird things i discovered on the EC-A, EC-B research.

same port worked advance on the distributor of the EC-B 74 engines.

the decel on the 75s still works the same way as it did on the 74s.
off manifold vac.
but its a beefier unit for sure.
maybe letting in even more air on decel than the 74s?

(IMG:style_emoticons/default/beerchug.gif)

Yeah I saw the T on the parts diagram and rather than try and figure out what was going on there, I was just glad I got a ‘74. I’ll be honest, I knew I wanted a 1.8L L-Jet when I was shopping, but I had no idea how much junk was on a ‘75 model.
I learned to drive in a ‘75 1.8, but all the 75’s I ran across in my search were either 2.0, carb’d, or both.

[emerygt350]

Egr is actually a really cool (literally) addition to engines. My 302 runs so much better with the egr working (correctly). For a hot little beast like these flat 4s egr could really help keep them cooler while cruising.

[wonkipop]

@Van B

the EGR on the 75 (calif) works off the vac port before the throttle plate on the throttle body when its all hosed up proper stock.

one of those weird things i discovered on the EC-A, EC-B research.

same port worked advance on the distributor of the EC-B 74 engines.

the decel on the 75s still works the same way as it did on the 74s.
off manifold vac.
but its a beefier unit for sure.
maybe letting in even more air on decel than the 74s?

(IMG:style_emoticons/default/beerchug.gif)

Yeah I saw the T on the parts diagram and rather than try and figure out what was going on there, I was just glad I got a ‘74. I’ll be honest, I knew I wanted a 1.8L L-Jet when I was shopping, but I had no idea how much junk was on a ‘75 model.
I learned to drive in a ‘75 1.8, but all the 75’s I ran across in my search were either 2.0, carb’d, or both.

(IMG:style_emoticons/default/agree.gif)

as it turns out we know we got the best one. the EC-B. least crippled. (IMG:style_emoticons/default/first.gif)

maybe you learned on a 49 state 75. nearly as pure as an EC-B. just didn't have the advance on the distributor connected.

i'd like to have sympathy for californians. they get experimented on.
but its their own fault? (IMG:style_emoticons/default/stirthepot.gif) (IMG:style_emoticons/default/smile.gif)

[wonkipop]

Egr is actually a really cool (literally) addition to engines. My 302 runs so much better with the egr working (correctly). For a hot little beast like these flat 4s egr could really help keep them cooler while cruising.

you know your stuff emery.
EGR was a kind of substitute for the advance hose hook up on the EC-B of 74.
i believe the EGR also enhanced fuel economy slightly at cruise as well as the cooler running, restoring some of the benefit of the EC-B vac advance operation from distributor.

as far as i can tell the EGR on the 75 californians only kicked in really at cruise, steady part throttle. rest of the time it was out of the equation.

[wonkipop]

It's like an appendix. You could just remove it and not care.

Bad move. The decel valve opens when you close the throttle at high RPMs. It leans the mixture, and also it acts as a dashpot, keeping the RPMs up so the engine doesnt die under decal.

(IMG:style_emoticons/default/agree.gif) good description,my understanding is the L-jet TB's that have only one vacuum port (retard) so that valve would be essential to stop stalling when the throttle is fully closed after acceleration ,right ?
So it serves the above function and also helps to reduce emissions when the throttle is closed @ the same time ?.
Cheers.

there were a variety of throttle bodies on the L jets.

we got the research done on them.

EC-B (49 state) 74 had both ports and both vac lines (adv + retard) connected to dist.
EC-A 74 (cal) had no connection of advance vac line to throttle body and port capped in throttle body in front of throttle plate. only retard connected.
75 EC (49 state) had only one port in throttle body. connected to vac retard on dist.
75 EC (calif) had both ports on throttle body. had retard connected on dist.
and had same port as EC-B in front of throttle plate connected to EGR.

finally got to the bottom of it all.

and all the different stories about them being two ports or one port, advance + retard,
or only retard.

folks saying one or the other were right (and wrong) in the past.
only had part of the story.

jeff bowlsby opened up the question recently and we cracked the mystery.

which means yeah.
a californian EC L jet coming down off throttle closure with or without a decel might behave slightly differently to a 49 state EC coming down off throttle with or without a decel? ?? (IMG:style_emoticons/default/confused24.gif)

i have a 74 EC-B. no decel. has had no decel for 33 years at least. no problems.
except when cold. rest of time i must admit i really like how it comes down when i back off the gas. no backfires either. which aren't backfires anyway. its fuel dumping in the hot exhaust and detonating. never get that. sometimes can hear a slightly burble.
but its pretty mild. keep it well tuned which might help.

yes i know there are some say you have to have them.
and i don't disagree. might even reinstall a decel just to see what its like as i have found one and have it racked and stacked. but for now. all is fine.

you certainly do need them for D jet.


EDIT.

here is stuff i pulled off an old 911 intake system.
think its for a K jet?
salvaged a decel valve and probably only have to adjust spring pressure for the 914.
bracket is wrong orientation but probably adaptable.



also have an aux air valve, which looks almost like a 75 decel valve. (almost but not quite)
the aux air valve is hooked up to an aux air regulator, which is what we would call an aux air valve on the 914. they seemed to need to use the two to do cold start extra air for warm up.

they just made these kind of standard parts and they had a nipple closed or open, or a diapram maybe stiffer or a spring adjustment different and used them on anything and everywhere.

in australia there is a mob in queensland who can rebuild these things.
they open them up and recrimp them, so long as they are made of metal.
so if your WD 40 trick doesn't work and you can't get hold of one down here, they are a good way to go here if you have a core you can send them.

[Blue Lightning]

It doesn't "control the vacuum" (if I understand you correctly); it uses manifold vacuum to open itself, to add un-throttled air to the intake to lean it the mixture on decel to reduce backfire (and excessive emissions) due to a rich mixture.

Modern EFI simply backs off the injector pulse (or shuts off the injectors entirely) when the throttle is closed (as indicated by the TPS) and on engine over-run to lean out the mixture. For whatever reason, D-Jet was not able to do that back then (or maybe they didn't think of it?)

Testing the decel valve is fairly straightforward. With no vacuum on the port, the valve should be closed and you can't blow through it. Adding a vacuum via a Mity-Vac and the valve should open and you can blow through it. As I recall the desired setting for that cutover is 17mmHg?

If you can blow through it when it's off the car, and/or cannot blow through it with vacuum on it, then it's bad and/or out of adjustment. I wouln'dt be surprised if a prior owner danked around with the adjustment...

If it works fine but the cutover vacuum is either too high or too low, then it can be adjusted via that locknut and screw to ~17mmHg.

What are your current symptoms when testing in this manner?

The thing is, it kinda does control vacuum. As you state, it allows more air in when the vacuum is above the set value. Adjusting the screw outward increases my idle significantly, which in turn increases manifold vacuum, so it is almost a positive feedback loop.

I agree on its function, and that you really don’t need it. But set incorrectly (or if it is broken open) it seems to cause high idle (since it is basically an air leak).

And if your manifold vacuum is too high there are implications regarding the vacuum advance/retard on your dizzy, as well as the MPS, both of which affect engine operation.

[Ron914]

@GregAmy , I was looking at your old post here about testing the decel valve and your information about a prior owner adjusting it wrong was spot on . I removed my decel valve and could not blow through it when no vacuum was applied to it . I loosened the adjusting locknut and opened the valve and the decel opened as you stated 16-17inHG . I want to adjust it but need a small clarification . If I am reading correctly I should adjust it until I can no longer blow through using my Mityvac somewhere around 17inHG correct .
Glad I found this information as I was going to start searching for a hard to find decel valve but now I do not have to .
Thanks

[GregAmy]

GregAmy, I was looking at your old post here about testing the decel valve...

Hey man. To be honest, I was looking back at that post with awe, myself, it's been way too long since I messed with those and I converted my D-Jet to Microsquirt soon after (see sig)...I'd say just go with that info.

Sorry. (IMG:style_emoticons/default/wink.gif)

[Geezer914]

I have a2056 with Ljet. Ditched the decel valve long ago, never had any problems.

[Ron914]

GregAmy, I was looking at your old post here about testing the decel valve...

Hey man. To be honest, I was looking back at that post with awe, myself, it's been way too long since I messed with those and I converted my D-Jet to Microsquirt soon after (see sig)...I'd say just go with that info.

Sorry. (IMG:style_emoticons/default/wink.gif)

That' is the setting I went with but your post was very good information for Anyone that thinks their decel might be bad . Mine was plugged until I loosened the lock nut and opened up the adjustment screw and suddenly I could blow through it . I have a 76 so I need all equipment present and operational to pass a California smog test .
Thanks for the information .