bajabug12a

I have a 12a that doesn’t start when cold, I had to tow it the other day to get it running. This motor is in my Baja bug and it runs very strong once started and warmed up. This 12a is striped and only using stock coils and distributor with a Weber 48 IDA and a big street port. After it gets warmed up I can shut down and restart without any problems. I’m wondering if the motor is really dead or if I’m having an ignition problem. My tach was acting up, going to zero when trying to start the motor, so I moved it to the trailing tach and it’s working how it should. The motor isn’t even giving me a popping/trying to start sound. I have checked spark on the plugs and I’m getting it. I do a volt reading on the fully charged Optima battery and it’s at 12.6volts before I crank the motor and at 10-11v when cranking the motor. I do a reading on the coils and when cranking it drops to 9-10volts, I have a relay feeding the ignition but not sure whats going on with this motor. I don’t want to rebuild if I don’t need to. Please any input will help…

RotaryRocket88

iTrader: (7)

Generally speaking, you need only a handful of things to get an engine to start/run. You have spark, but is the timing still correct? You can put a timing light on the main pulley and crank it over.

You need compression too, so thread a compression tester into the trailing plug holes, hold the bleeder down (or remove schraeder valve), and crank the engine. You should see a uniform series of bounces hopefully in the 90+ psi range. If the pulses are not even, or there are 1 or 2 missing per rotation, you have a damaged or missing seals.

Lastly, is fuel delivery correct? Too little or too much will keep it from starting. Does spraying starting fluid in the intake help?

bajabug12a

Thanks for the response rotoryrocket88! Here’s what I know, I put a mark on my motor and distributor and it’s at the same mark. Unless the distributor jumped inside the motor then I think I’m good on timing. As for doing a compression and timing test, I always thought you need a special timing light and compression tool for rotary motors. I believe fuel is good but I need to pull my air box off and see what’s going on. It sure seems like I’m getting the right fuel, but I’ll check. So you don’t think its ignition problem? I just was tripping with the tach acting up on one coil but not the other. Anyone else with input?

RotaryRocket88

iTrader: (7)

Well you said the plugs were sparking when you pulled them, right? Unless the issue only comes up when cranking.

You don't need a special timing light or compression tester. For the light, you can put the clip on a leading or trailing wire to check them separately. A standard compression tester just needs to be tweaked to allow pressure to vent between pulses (bleeder button or schraeder valve removal).

What about the starter motor? Is it an RX-7 starter adapted to fit in the transaxle, or some other kind of starter? Rotaries require high cranking speed to start properly, and it would make sense that being warmed up is enough to help get the engine to start even if the speed is on the slow side.

durnzuki

We had that problem when we first put the engine in my sons samurai. Both coils were working but the trailing one was weak. Replaced the coil and it starts right up now.

bajabug12a

Yes it has spark, not sure if its enough.. Good thing to know about the light and compression tester. What should the timing and compression be at? The starter is a high torque modified VW one. It worked fine on the motor before I started having starting problems.

RotaryRocket88

iTrader: (7)

Compression should be in the 90-100+ psi range if the engine is healthy. I think the minimum factory spec is actually 85 psi in the 2nd gen FSM. Anywhere below that will be lower compression than normal, which can easily lead to starting issues. If you had a damaged/blown apex or side seal, you would notice right away the huge lack of power. It's pretty obvious when an engine blows, which is why I suggest it could be compression below spec.

According to a thread in the 1st gen section, timing at idle should be:

12a USDM= Trailing 20º ATDC, Leading TDC
12a EUDM= Trailing 20º ATDC, Leading 5º ATDC

These are the marks on the main pulley, but spark should be advanced during cranking.

bajabug12a

Thanks for all the help!

Sorry on the delayed response, the holidays have been busy! I did a compression test and it was in the 60 for both rotors. I find it hard to believe it’s this low in both and at the exact same pressure. Never the less, I know the motor has 5 hard sessions on it, so I’m pulling it and opening it up. I’m hoping its just as simple rebuild, new carbon apex seals, new gasket kit and back together. This is in an offroad baja and I’m limited on funds.