Th0m4s

Because my 12A with BAE turbo conversion tried to eat itself last year (sucked in a part of the carburetor through the first rotor, spit it out and back in some rounds through the second rotor) I had to replace the engine with one I found at a scrap yard. The engine itself is in an extremely good condition because it must have been rebuilt only months before the car ended at that scrap yard.
Here starts my strange problem: The engine seems to be kind of a Frankenstein model. The front cover is from a 79-80 12a, the front iron is from a later 12a, the middle iron seems to be from a later model, too and the rear iron is from a 79-80 12a again because there's no oil pressure sender. The housings are completely unknown to me because they look nearly like early housings because they don*t have the "H" on top but the "12a Mazda" sign is different from any other housing i've seen before and there are also some other small differences.
By the way the strangest part of the engine was the oil pan. That part has two oil drain plugs, one on the left side and one on the right.

Today I started the engine for the first time and set up my new carburetor. Everything worked like it should till I tried to adjust the ignition timing. The timing was round about 5° too early but the engine was running totally smooth. Then I turned the distributor till the marks pn the pulley matched (both leading and trailing match up now). When I did that the idle rpms went lower and the engine started running very rough. I have a wideband afr gauge installed and it showed 13:1 afr so that's still ok.
Could it be that the spark plug holes are at a slightly different position or that the pulley is from a different rotary engine? i really don't know what I should do now... try to use the iginition timing matching the marks or use the timing where the engine runs smooth?

t_g_farrell

iTrader: (1)

I would determine where TDC is by using the manual methods of looking at the flywheel and in the plug holes. Then if the timing marks on the pulley do not match up, you know its a pulley issue. The pulley may be 90 deg out of phase or more.

Th0m4s

Interesting idea. I'm going to check that. But would the car even be able to run with the timing 90° off?

t_g_farrell

iTrader: (1)

Absolutely. When I had leading only DFIS setup for my ignition it ran great being 90 deg out of phase. I only discovered it when I added back in the trailing and was trying to time the trailing ignition. My issue wasn't the pulley, I had stabbed the dizzy incorrectly and it was 90 deg out.

Get the rotating assembly to TDC (it can't lie) and then make sure the pulley marks line up and your dizzy is on the mark. Being off by one or two teeth on the dizzy is worse that being off 90 deg.

yeti

iTrader: (1)

Just curious, how much timing is a tooth? I realize this is probably dependent on which distributor you have. I don't think mine is off and it's easy enough to check but just curious.

t_g_farrell

iTrader: (1)

If the bolt that tightens down the dizzy adjustment is not almost in center when at TDC then you are probably off by a tooth. You can be off by a tooth and still compensate by adjusting the dizzy but if you are more than one tooth off its almost impossible to get to the correct timing.

yeti

iTrader: (1)

Guess I'm off a tooth. I'm almost all the way to the right, but I am running around 5 degrees BTC since I have a Weber 48 IDA and a streetport.

I guess if I have any other questions or concerns I'll open a new thread. I don't want to take the focus away from the original poster.