RX7ZOOM

I have disconnected the vacuum advance on my dizzy and have lost a heap of torque down low. Have heard about locking the dizzy. What is this exactly? Is it advantagous? How is it done?

Regards, Pete.

Rx7carl

If you remove the top of the dizzy (look in the shop manual), theres a pair of weights and springs, thats your centrifugal advance. If you remove the springs and tack weld the weights fully out your timing will be locked (assuming you keep the vac advance disconnected). Racers do this to simplify the dizzy (less stuff to break).

WackyRotary

You need to lock the distrubuter if you run a blow through setup otherwise it will be a dog a low rpm. I also agree its a good mod for those who want to simplify things. And you retain max advance at lower rpm with the throttle opened up to produce more torque. I think more people should do this since it is a really cheap easy mod to do.

I used it on my bridgeport for a little while and did notice a little more lowend(if you consider 3000rpm low) I locked it for my blowthrough turbo.

KYPREO

with the vacuum advance, its not that you are losing torque down low in the rev range, its that you are losing torque on light throttle application/low load. because the timing effectively becomes retarded by 7.5 degrees. the timing split also changes with vacuum advance, becoming a 7.5 degree split under low load.

Unless you have a ported engine, why not keep all the vacuum advance and centrifugal advance connected? I've tried both and the stock setup is way better for fuel economy and torque on low throttle. I would only lock the timing for reliability reasons when you are running a lot of advance, eg bridgeport application.

Unless someone else can tell me otherwise?

WackyRotary

Well when ever you get on the throttle below 4000rpm, you lose your vacuum advance and that causes it to bog some. Vacuum advance is good for light throttle only since it advances timing beyond mechanical at low engine loads and thus helps with MPG. But going to full throttle with a un-locked distrubuter hurts lowend since the advance is retarded(since vacuum is 0) and don't get the max advance again till 4000rpm.

So with a locked distrubuter, you got max advance and don't use the vacuum source anymore. Get the good MPG and lowend response a locked will provide.

12abridgeport

I need to do that also, when i try to set timing with the timing light, the marks keep on jumping back and forth sometimes. I was told that if you don't have msd boxes a locked dizzy would cure that.

So basically i need to take the dizzy apart and make sure that the weights don't move? Do i need to adjust them or something before i weld them?

Pedestrian X

yes, adjust them all the way out.

KYPREO

thanks whacky...that makes sense. so basically the extra 10-15 degrees locked advance below 3000rpm more or low compensates the extra advance you would have had at low engine loads.

12abp: if you're timing point is jumping, make sure the inductive pickup is not close to the trailing, when you are measuring leading and vice versa. The timing light might also be shitty.

The timing point should only move when you hope on the throttle and/or the revs lift (up to 3000rpm).

Wankelguy

You'll need to set the timing to max advance at about 6000 rpm. Then, you'll end up being a bit too advanced at lower rpms, but that's the trade-off.

Rx7carl

Funny my good (read $$$$) timing light picks up the trailing spark, but my $10 Wal-Mart one works great. Go figure.

KYPREO

My cheap Kmart one is great too lol

Suparslinc

I've been running without the vacuum advance on a stock engine with a modified carb, and I do notice my gas mileage is down. Maybe I'll go back to stock now.