Delay in throttle response when giving it more gas

[zuburg]

Finally got my 1956 T-bird running pretty smooth at idle, but when I give it more gas to increase the RPMs, there is a delay in the throttle response (almost feels like it is going to stall but recovers), then it revs nicely once it gets past the delay. What are the possibilities that could cause this? Would a bad dual vacuum on the distributor cause this? Vacuum leak somewhere?

 

[fordor41]

The way I understand the loadomatic dist operation they change vac from above the throttle plates at idle to below the plates above idle, thus both vac circuits advance the dist at different throttle postions. there is a valve in line to dist vac advance that switches the 2 vac signals. Hope I got this correct!

 

[Lanny]

Could be the accelerator pump diaphragm that's bad or not functioning right.





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[zuburg]

On my car, there is one rod going from the dual vacuum advance into the distributor and attached to the plate. Then there are two hard lines, one from the front of the carb to the larger vacuum closest to distributor and one that goes from the brass block at rear of carb to the smaller vacuum farthest from distributor. I don’t see any inline valve unless it is in the hard line fitting or the vacuum advance assembly itself.

 

[dmsfrr]

If either of the rubber diaphragms in the (dual) vacuum canister is leaking, the ignition timing can't advance correctly and you'll have a vacuum leak.

You can test them by connecting a length of clean tubing to each one and sucking on it to see if it holds pressure, and slightly turns the plate the points are mounted on. (photo two)

 

[zuburg]

If memory serves me the accelerator pump is in the carb. The carb was rebuilt 2-3 years ago, but has not been used until the last month as we started this engine for the first time. I would not guess it would be bad but stranger things have happened. I would like to eliminate other possibilities first.

By the way if it runs really well when I rev it to higher RPMs once I get past the delay, does that confirm the dual vacuum advance is holding vacuum and working correctly?

 

[zuburg]

I borrowed a vacuum pump with gauge at parts store to test for vacuum but had trouble connecting the tubing. I ended up removing the vacuum advance and just sucking on each hole (it was nasty but I was determined) and they seemed to hold vacuum. I will try to find a hose or fitting that I can attach a hose and see if it is moving the plate.

 

[dmsfrr]

I borrowed a vacuum pump with gauge at parts store to test for vacuum but had trouble connecting the tubing. I ended up removing the vacuum advance and just sucking on each hole (it was nasty but I was determined) and they seemed to hold vacuum. I will try to find a hose or fitting that I can attach a hose and see if it is moving the plate.

If the plate hasn't moved in a while it may stuck and need to be cleaned and lightly lubricated.

. . . By the way if it runs really well when I rev it to higher RPMs once I get past the delay, does that confirm the dual vacuum advance is holding vacuum and working correctly?

If the timing marks advance when lit up by a timing light, that's a basic test.

 

[zuburg]

When I re-attached the vacuum advance to the distributor and attached the rod to the plate the plate seemed to move freely.

 

[scicala]

There is no inline valve that switches back and forth between venturi suction and ported manifold vacuum. It's all modulated within the carburetor. Max of about 4" of vacuum at the distributor.
I would investigate the accelerator pump like Lanny mentioned above in post #3. It is a rubber cup piston (not a diaphragm).
Also there are two holes in the throttle lever for the accelerator pump link to attach too. The outer hole will give you a quicker, and longer pump stroke. Also make sure the accel pump rod moves down even with the slightest throttle movement. Might be some slop that delays the squirt. Or internal carb issues with it. I've done hundreds of these carbs, and it's amazing how many things are assembled incorrectly. A difficult carb to get correct.

Sal

 

[KULTULZ]

Spark Control Valve

 

[Late model]

Hello,
First post on the forum so I hope I did this right.
I have tried to post the pages from the 1956 Ford Service Manual on the operation of the Lodamatic system used on the four barrel carb as PDF files.
The 2 barrel and 4 barrel system are somewhat different, and as as KULTULZ mentioned, the Spark Control valve plays a part in it.
This is not a simple system, and it did not work particularly well, especially on the two barrels. A lot of the systems have been replaced over the years with the replacement of the 55/56 distributor with a 57 model and plugging the in the carb and SCV passages where required.
I switched my 56 Victoria over when I changed to a 3-2 setup.
It seems most likely that your problem is with the accelerator circuit or or the ignition advance.

Don

 

[paul2748]

What are you running for initial advance. 6 is the factory, but 10 to 12 works really good and may help in the bog.

 

[KULTULZ]

Hello,

First post on the forum so I hope I did this right.

Don

Damn if you didn't. Good Post!

 

[zuburg]

OK. Some have mentioned checking out the accelerator pump. My first photo has two arrows. I believe the top arrow may be pointing to the accelerator pump, and the bottom arrow points to a connector that attaches to the accelerator linkage.

I read on another forum that their may be two holes where this connector could be attached. They called it a summer and winter connection. My second photo has a yellow arrow pointing to where my connector is attached (the hole facing left or front of the carb and a blue arrow pointing to an open hole just to the right of my current connection. Should I move this connection to the open hole on the right?

It would be great if this would fix my delayed throttle response.

 

[KULTULZ]

Some have mentioned checking out the accelerator pump. My first photo has two arrows. I believe the top arrow may be pointing to the accelerator pump, and the bottom arrow points to a connector that attaches to the accelerator linkage.

I read on another forum that their may be two holes where this connector could be attached. They called it a summer and winter connection. My second photo has a yellow arrow pointing to where my connector is attached (the hole facing left or front of the carb and a blue arrow pointing to an open hole just to the right of my current connection. Should I move this connection to the open hole on the right?

It would be great if this would fix my delayed throttle response.

Sal mentioned this is an earlier post in this thread -

I would investigate the accelerator pump like Lanny mentioned above in post #3. It is a rubber cup piston (not a diaphragm).

Also there are two holes in the throttle lever for the accelerator pump link to attach too. The outer hole will give you a quicker, and longer pump stroke. Also make sure the accel pump rod moves down even with the slightest throttle movement. Might be some slop that delays the squirt. Or internal carb issues with it. I've done hundreds of these carbs, and it's amazing how many things are assembled incorrectly.

A difficult carb to get correct.

Sal

Also make sure there is no slop in the entire fuel linkage. A lot of things can wear out or become out of adjustment.

 

[zuburg]

Which hole is the outer hole? The left one (where mine is attached in photo) or the right one when looking at the carb linkage from the drivers side fender?

 

[zuburg]

Thanks to all who pointed me to the accelerator pump. I moved the pin on the linkage from the accelerator pump to the right of the two holes on the accelerator linkage and problem appears solved.

 

[scicala]

Yes, the hole on the right is for more stroke of the pump. Your carb looks similar to a lot of rebuilts I see, as in missing parts. Supposed to be a spring, a felt seal and two washers on the pump rod where it goes through the aluminum base. Not a big deal but a small leak for air to bypass the air filter.
Also looks like you must have the choke adjusted open, or using an electric heated choke thermostat, since the hot air tube in the manifold for the choke appears to b blocked off.

Sal

 

[zuburg]

Yes, the previous owner did not have all the hoses/tubes connected for the automatic choke and I was not smart enough to know stuff was missing. I didn’t learn about all of the parts required until after I had the engine installed and I didn’t have any more motivation to remove the intake to clean out and replace the heat tube so I converted to an electric choke. Way easier and less expensive.