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Timing/Tuning Question

Greggers

SAOCA Vice President
Platinum Level Sponsor
Let's say for sake of argument that I have a 1725 that's running nice but occasionally stumbles and/or pops into the carbs a bit under load.

1. Checked the timing. It landed at 2.8 degrees BTDC (too retarded).

2. Checked carbs and found them to be out of balance. Got them synched and set the mixture according to WSM (deferring to forum suggestions for number of turns).

3. Car wouldn't start unless I set the timing at 22 degrees BTDC (way too advanced).

4. Put on Colortunes and got the front carb nice and bunsen blue. Couldn't get the back carb to blue.

5. Started the car again and it wouldn't start unless I set the timing at 35 degrees BTDC (way, way too advanced). Lots of backfiring, both exhaust and carbs.

6. Shut it down and got it to idle at 22 again. But at 22, the car was gutless. With any single-digit timing, the car won't even come close to starting.


Could it be the distributor? If the mechanical advance were sticking or otherwise not functioning properly, would it cause the variable timing (and the intermittent stumbling/backfiring that started this journey)?
 

Bill Blue

Platinum Level Sponsor
Greg, I don't know what is causing your problem, but my attack on the problem would be:

Start it up and rev the engine while the timing light is hooked up, but the dizzy vacuum line blocked. You should see a progressive increase in timing as the engine revs and the progression should end at about 3k. The timing should return to the same base as it comes down to idle.

If that looks good, hook up the vacuum line. The spark should now "dance" up and down as the rpm/vacuum changes. If it passes these tests I'd say the problem is not in the dizzy.

Next, test for vacuum leaks. I don't know what not being able to get a blue flame means. If it means it is lean it means a vacuum leak is present somewhere in rear carb. The propane torch method seems to work well.

Last, look at the coil, capacitor, cap, rotor and wiring. The spitting at load could be from running lean or weak spark.

I wouldn't be terribly surprised if you have two separate problems. These tests should tell you what is working, what is not.

Good luck.

Bill
 

W_Pierzga

Platinum Level Sponsor
Hi

Just a thought. Have you considered that the PCV valve may be causing a vacuum leak? Disconnect the hose and plug the PCV valve and see what happens.

Cheers,
Wayne
 

beamdream

Gold Level Sponsor
Amongst other things have you checked that the throttles are synced ? or possibly a bad diaphragm in the rear carb. :confused:
 

Greggers

SAOCA Vice President
Platinum Level Sponsor
The carbs were synched in the first step. It'd be super if we could find a good solution to the sloppy synch linkage issue. There's just too much chance of slipping.

It ended up being a confluence of factors causing the crap running. A mixture that was a little off combined with a high idle (caused by the WSM's idle-setting procedure not being too relevant 50 years on) combined with a little miss (which caused the timing to "waggle"). After a couple of hours of a couple of guys throwing every trick in the book at it, we managed to get it running better than it was before. After a bit of driving, we'll get a look at the plugs to check if it really is better.

For some reason, the squirrel-cage-style flow meter says the front carb is sucking 12 and the back 10. So I guess the carbs could stand to be synched again. We aren't keen on doing it for fear of starting the whole process over (and due to the variability of the aforementioned sloppy linkage).

If I had to do all over again, and as a note for future me reading this next time I run into this problem, I'd probably set the timing at max centrifugal advance (allegedly 32 degrees at 3500+ rpm) and let it fall where it may at idle (hopefully around 8). That said, the idea of setting timing with the engine screaming away at 3500 rpm is a little frightening.
 

RootesRacer

Donation Time
That said, the idea of setting timing with the engine screaming away at 3500 rpm is a little frightening.

Why would it be frightening in the driveway but not tooling down the road?

IMO this is the ONLY way to set timing (along with an obligatory validation that the idle timing is close to what it was specified to have been).
Do disconnect the vacuum advance line since at 3500 RPM at light load, the carb vacuum port may still have significant signal.
You should also verify that the vacuum advance is DONE by 3500 RPM or you may get an extra amount of unplanned advance.

Oh and 32 degrees is a max figure, 31 is where I would put the timing on an engine not listening with det cans.
 

Greggers

SAOCA Vice President
Platinum Level Sponsor
I only say timing at 3500 rpm is frightening because:

A. I can't hold my car above about 2500 rpm in the garage before the sound and fury make the neighbors start wondering what the hell that weird guy with the old car is trying to blow up.

B. I usually can't keep a steady 3500 rpm without leaving a couple of layers of skin on the flaming hot linkage (assuming I can hold the linkage, timing light and dizzy with just two hands). Perhaps I should get smart and do it with a friend's foot on the pedal.
 

Bill Blue

Platinum Level Sponsor
By this time, your neighbors should have given up wondering what the hell your doing with that old car.

I don't have any friends to help by holding the revs, but my wife is always willing to do that kind of stuff. I'm sure she thinks it beats the hell out of a carburetor on the kitchen table.

Bill
 
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