Distributor advance springs.

[beebo]

When i first got the car started up, i would rev it and it would not idle back down; stayed at ~2000rpm. i took the distibutor apart and found that it had one incorrect spring on the centrifugal advance and one correct one. the only springs i could get were from a SBC. When i installed this, i think the springs are a little stiff because when i drove it, it felt like it had 0 power until about 2500 when the dist. finally advanced. when should the vaccuum advance cut out and the mechanical davance take over or where can i get the correct little ditributor springs.

[Myphisto]

I'm no expert, but I believe the mechanical advance is the first stage and the vacuum is the second stage. That's why you would have minimal power until enough vacuum built up at a higher RPM to actuate the advance. As far as springs, try the dealer and or some of the online vendors. You might also check ebay as I thought I saw some distributor rebuild kits on there.

[spyder]

Fuel burns at a specific rate. As the engine spins faster the spark is advanced in order to get the peak maximum cylinder pressure/power at top dead center. Mechanical and vacuum advance are designed as a best guess as to where that advance curve needs to be. If the base timing is not correct the power will be wrong at any rpm. if the curve are incorrect, (wrong springs or weights) the curve won't match the rpms. So what does this all mean? In general, timing too early you get pinging or knocking. Too late you loose power. Notice no where in here I mentioned idle rpm. If the timing greatly affects idle than it is likely your carbs idle is set too high and the timing is very retarded to slow down the idle - hence low power. What I do is to adjust the base timing for the fastest/smoothest idle, set the idle where it is supposed to be and than tune the advance curve to the engine power. This might be overkill on a stock motor but mine is not, however if the time is taken to do this you can get improved mpg and hp! This is some of what a modern engine does many times a second to maximize it's efficiency

[dbrick]

The distributor "desmog" kits on ebay have new springs and weights. Mine came in Nissan packages, might be avail at dealer if you can get the part #.
What year and engine do you have?

[beebo]

70 2000

[dbrick]

Contact this Ebay seller, http://stores.ebay.com/Datsun-Parts-Exp ... eZL2QQtZkm ask for a recurve kit. I got mine from him. You have to reset your timing after to 15 BTDC. If you have a smog dist.car and timing is set at 15, will cause problems

[beebo]

ah i just ordered a pan gasket from that guy. very quick shipping. i got it 2 days after i sent payment.

[gboone]

The original distributor was designed with a dual slope advance curve. This is why there are 2 different springs in the mechanical advance mechanism. One of the weights doesn't engage the rotor cam until 1700 rpm.

There seems to be a lot of misunderstanding of ignition timing advance. The mechanical and vacuum advance features are completely independent of each other. The mechanical advance is strictly a function of engine speed. It maxes out at 15 degrees (at the crankshaft) at 3800 rpm. So if your timing at idle speed is 16 degrees BTDC, the total advance at 3800 rpm or higher is 31 degrees BTDC (16 + 15). If using a timing light, make sure your engine is at least temporarily down at 700 or 800 rpm while setting the timing. Otherwise, if the engine speed is too high, the mechanical advance mechanism may already be advancing. You want zero advance occurring at idle while setting the timing. While you have a timing light connected, rev the engine to make sure the timing is advancing by about 15 degrees at 4000 rpm.

Regarding vacuum advance, it is a function only of the vacuum signal from the carburetor. The vacuum signal increases with a combination of medium to high engine speed and little to medium throttle opening. The advance from the vacuum actuator maxes out at 5 degrees (at the crankshaft). The intent of vacuum advance is to reduce exhaust emissions and improve fuel mileage while cruising. There is no performance advantage to vacuum advance because when the throttle is wide open, the vacuum signal drops to almost zero. Actually you don't want maximum mechanical advance to combine with maximum vacuum advance under full throttle anyway because it would result in too much advance.

The last time I ordered the spring sets from Nissan, they were NLA. Bruce must have bought many, many sets a while back and is selling them with the rotor cams on eBay.

I've torn down about 250 roadster distributors and they have dried or no grease, lots of wear and rust, frozen parts, and are severely out of adjustment. It would surprise me if the better ones operated even decently.