No Decel Valve, no problem? Except a lil popping Options

[nditiz1]

2.0 76 GC motor -

So I went through my entire FI system to find out if any vac leaks were present as well as learn the ins and outs. I did find some things interesting and enjoy what they mean except for a slight popping I get on deceleration. Now, this could be caused by two things, exhaust leak (have new gaskets to be installed) lack of decel valve.

If the car still runs by removing certain items I am all for it, especially ones that are over priced due to NLA. My AAR is in good working order, but if it ever does go belly up I may just remove that too. Currently I have the cold start valve disabled (no connector, no fuel) I was trying to diagnose a rich running issue and read it only kicks in at real low temps. I can always properly test it and hook it back up if need be - one item down.

I was looking for my decel valve and could never find it because I don't have one. Now, how much of a burden is this causing me. The car seems to motor down the road fairly well. It idles great (steady) after being warmed up. I get a popping inside the exhaust on deceleration.

I have gone over the timing was at 27 but put it to 28 after finding out I have a Raby 9550 cam.

So now I have a more simple system without two factory things, but is not having the decel valve causing more issues like the popping or even worse? What say you decel valveless FI guys (I think t_rowle runs his that way).

[jcd914]

One advantage of the decel valve is that it reduces the suden high vacuum spike you get when you decelerate. This extends the life of the diaphragm in the MPS.

As you stated, the cold start valve is only energized at low temps, it is also limited to just while you are cranking the engine over.

Neither item is critical to the operation of the FI system but neither is a common failure item.

Jim

[nditiz1]

One advantage of the decel valve is that it reduces the suden high vacuum spike you get when you decelerate. This extends the life of the diaphragm in the MPS.

As you stated, the cold start valve is only energized at low temps, it is also limited to just while you are cranking the engine over.

Neither item is critical to the operation of the FI system but neither is a common failure item.

Jim

So what you are saying is that the decel valve won't prevent the popping and I should adjust the ecu?

[jcd914]

One advantage of the decel valve is that it reduces the suden high vacuum spike you get when you decelerate. This extends the life of the diaphragm in the MPS.

As you stated, the cold start valve is only energized at low temps, it is also limited to just while you are cranking the engine over.

Neither item is critical to the operation of the FI system but neither is a common failure item.

Jim

So what you are saying is that the decel valve won't prevent the popping and I should adjust the ecu?

I don't know if the decel valve will prevent or reduce the popping in the exhaust or not.
You should get a leaner fuel mixture on decel with the decel valve installed and working.
I don't know if that translates into less popping or not.

I would put the decel valve back on, if only to extend the life of the MPS diaphragm.

I would also make sure the head to exhaust gaskets seal well and get the fuel mixture checked and adjusted.

Jim

[troth]

There was a time when I wanted to be able to shift a little quicker, but couldn't because the decel valve was holding the revs up higher than ideal. As an experiment, I tried disabling the decel valve by putting a little BB in the vacuum line. The revs dropped MUCH quicker, but I did get some slight crackling under deceleration. Ended up not liking it this way, so I took the BB back out.

This was on an L Jet car, so take this for what it's worth.

[era vulgaris]

I used to get popping on deceleration with my old 72 1.7. It turned out the decel valve was out of adjustment. There's a little threaded adjuster type thing on it. After setting it correctly my popping on deceleration stopped completely.
Not sure if it would be the same issue for you since you don't have one at all, but it's the experience I had with it

[jim_hoyland]

I used to get popping on deceleration with my old 72 1.7. It turned out the decel valve was out of adjustment. There's a little threaded adjuster type thing on it. After setting it correctly my popping on deceleration stopped completely.
Not sure if it would be the same issue for you since you don't have one at all, but it's the experience I had with it

Hmmmmm. Anyone have a pic of the adjuster ? I'm running a '73 or '74 development valve on the 1.8L L-Jet. There is popping on developing, even during gear shifts...?

[jcd914]

I am not sure about the decel valves on 914s but not all decel valves are adjustable.
The common adjustment is a bolt with a jam nut, loosen the jam nut and tighten or loosen the bolt to adjust how fast the decel valve closes after the vacuum spikes and opens it. tightening the bolt increases the spring tension on the diaphragm in the valve.

Jim

[worn]

I am not sure about the decel valves on 914s but not all decel valves are adjustable.
The common adjustment is a bolt with a jam nut, loosen the jam nut and tighten or loosen the bolt to adjust how fast the decel valve closes after the vacuum spikes and opens it. tightening the bolt increases the spring tension on the diaphragm in the valve.

Jim

A helpful tool in working with the system is something like the mighty vac, which couples a vacuum pump with a gauge. Helps for setting decal valve and testing for leaks. You can for instance put different levels of vacuum on the decel valve and blow through the other port to see at what vacuum the valve opens and closes. Then you can adjust. I don’t run my decel valve and get no popping.