hapamoto

Hello and thank you for reading and in advance for any replies.

I recently purchased a 72 510 with what I have been told is a J bridge ported motor...Well that is where the story begins I dont know crack about rotary motors other than they sound sweet. My questions are these and I have done some research but can't find conclusive answers...

About the motor: Running what I have been told is a Holley 750 (trying to confirm based on numbers on the carb) intake by racing beat, custom exhaust.
Oil injection disconnected, Stock distributor pointless ignition, with MSD spark control. From a friend I have been told if it is a J bridged motor that it should be mild due to the idle RPM...Idle is just above 1K.

Questions:
1- what should the ignition timing be I know that you are supposed to set the timing based on leading or trailing and then adjust the vacuum advance for the appropriate timing after. Problem neither advance control is hooked up at this time. Should it be for a motor like this? Ported or manifold vacuum? (thinking ported...but) What is the correct or better timing? When I bought the car the bolt for the timing adjustment was missing so....
2- any recommendations on 2 stroke oil or ratio. currently running 1oz per gallon
3-any recommendations on motor oil weight? I plan on running synthetic for ***** and giggles but which weight?
4-the car has a very slight hesitation near closed throttle but it seems to only be there until you pass that point in that gear and then it seems to go away? Carb fuel delivery issue? Seems to be worse when you are babying the throttle if you push it a bit or full throttle no issues.
5-thermostat.....think it might be stuck slightly...low water flow and issues on hot days in traffic. Should I run no thermostat? On normal mid 80 days it runs on the road at 190. In traffic it was reaching 210+ very low coolant volume in the radiator.
5-spark plugs run whats in there? NGK BUR9EQ leading and trailing.
6-any suggestions on exhaust...mufflers this thing is pretty loud it seems to have what was told to me as a resonator but looks like a large glass pack? Limited ground clearance and hope to resolve this by modifying the exhaust.

Thanks again and if anyone might know who could have built this motor.....I have was told it came from OC CA???

Cheers!

rx_214

Uh... What exactly is your friend telling you? It should be mild due to the higher idle? Does he really know what he's talking about??

J-ported engines are pretty loud and is one of the wildest porting method available, take a look here: Porting

1 - You should consult a Mazda turning shop for this.
2 - 100:1 to 150:1 is the range most people do the pre-mix.
3 - Should use 20W50 given the condition of the engine modification. Do you know if the engine was running synthetic before? There isn't a huge amount of advantage switching over to synthetic, unless you have the extra money and really needed the extra cooling ability that is hard to notice.
4. Carb, fuel, throttle... there can be fair bit of possibilities here.
5. If it's stuck, then go get a OEM one from the dealership, also get a thermostat o-ring gasket, that should clear the issue. And NO, you should run a thermostat to ensure the ECU is communicating correctly; unless you want overheat without you knowing on a normal cruise.
6. Smaller diameter exhaust pipe? You should probably get a new exhaust made and use a fairly low-tone muffler to keep the exhaust noise down. But only make it in the fashion that it won't kill your performance.

Shop wise, you can contact Racing Beat, Mazdatrix, Rotary Performance (rx7.com), and SA-Motorsports.

hapamoto

rx 214 Thanks for the reply and all your info. As for the thermostat I don't have an ecu issue so the only concern is warm up time and running too cool. I do appreciate all your input though

rx_214

I think a thermostat would still help, regardless of whether you have an ECU or not (you're running aftermarket I guess? Microtech, Megasquirt, Haltech?).

With how the thermostat works, based from what I know, it also receives communication from the coolant sensor to decide when to open and close. Having no thermostat and just let the coolant flow may end up with undesirable cooling results, because everything flows a lot faster. Unless you have a very good radiator and lots of cooling ducts, I don't see why you shouldn't run a thermostat, given that it would work with the engine.

Anyhow, that's mostly what I think.... hopefully everything gets figured out.

Baldy

ECU doesn't control t-stat opening and closing. But, engine temp needs to be at an optimal point, and the t-stat keeps it there. It's only about $10 at the dealership and it's not difficult to change.

rx_214

You're right, my apologies. Electronics are not my strong point...

$10? That's pretty cheap. Last time I bought it, was around $25 or so. Then again it's not that much, lol.

hapamoto

Okay I did some tuning and found out that someone before me had swapped the leading and trailing coil wires. I could not time this motor....although it ran okay. I corrected the coils set the timing to what I have found online for a j bridge ported motor which I read was 20 degrees advanced and 8 degrees advanced. Well the car ran but bad backfires, less power, and on shut down I would get a nice back fire as well.

After playing with it for sometime I advanced the timing to about double plus some and it runs much better. My fear is that I might blow a rotor seal?

Dont know enough about rotary motors yet. Guess i will run it at its best and hope I don't blow it up?

BTW no Vacuum advance is hooked up yet.
But damn this little motor can pull.

rx_214

Wanna give us a video and we can all hear the engine roar?

Lynn E. Hanover

The vacuum advance holds in about 16 to 18 degrees of advance. Then when you open the throttle the vacuum drops away (Manifold pressure) and the vacuum bellows relaxes and advance drops to the static setting about 6 to 8 degrees. So there is too little advance because of no vacuum lines, then you advance the distributor and it runs better, (at 16 to 18 degrees). But when you rev it up you have way too much advance. So, don't do that.

Make maximum advance 24 degrees. Measure it at 4,000 RPM. With the vacuum line disconnected. Once you have it set, reconnect the vacuum lines.

A straight weight racing oil in 30 or 40 weight, in the sump. Or a 40 weight synthetic, A name brand 2 cycle oil as a premix at one ounce per gallon. Use a thin multigrade in very cold areas.

Most "J" bridgeports do not idle well at all, but tend to surge under low speed and unloaded Rump, Rump, Rump. My racer idles at 2,200 RPM

The stock thermostats are a goofy looking piece. Be sure nobody has plugged the lower hole in the thermostat housing. If that is the case, a conventional thermostat will work fine.

Those plugs are fine for just driving around. For hard driving use the dash 10s or really hard driving use Autolite AR2593 Or NGK R6725-11.5

Lynn E. Hanover

The picture is a "J" bridgeport

hapamoto

At Lynn E. Hanover!!!!

Thank you very much for your information and time taken to write. I apologize for my delayed response. I think I have worked the bugs out of this timing issue I have been having thanks to you! She runs much better now without all the backfires and popping.
I'm new to rotory motors and it took some time to figure out what was going on. I found the last owner had the coils swapped so the leading was the trailing etc. and then we had to reset the distributor so we could get the timing close. After that your info came in to play and really helped me finish it off.
I still have a slight stumble mid range rpm 2k to 3k as I change gears and begin to accelerate. I am moving towards carb adjustments. These Holleys have all kinds of variations I learning about.......

Thanks again!
Kyle