No power until I rev it

Lock · Post by **Lock** » Wed Dec 14, 2016 2:05 am

Hey all, as title says I have no power in the first few minutes or until I rev the engine a bit after starting cold. Engine is in tune - valves done, timing set, vacuum hoses all checked. It starts fine, idles fine, runs fine rest of the time, but I notice it doesn't idle any higher when cold than warm (maybe this is related?)

Not a big issue, it's only a problem when I forget, pull out of my driveway into traffic and can't accelerate beyond 5mph. If I hit the gas it revs to about 1200rpm and struggles for 2-4 seconds, suddenly springs to life and then is as normal.

It is a 1979 with the two vacuum lines to the distributor, so maybe vacuum isn't working correctly, almost feels like the timing is way out momentarily. Maybe also related - I also found a crack in my expansion tank that was always there, apparently it's never held pressure above 1psi. Fixing that next week with a new tank.

Can anyone give me any pointers on what to investigate first?

Mike W. · Post by **Mike W.** » Wed Dec 14, 2016 12:03 pm

Check timing. I had the retard side fail on my 79 and while it wasn't gutless, it wasn't right either. But I just timed it by ear. That or a massive vacuum leak, but timing is my first thought.

Lock · Post by **Lock** » Wed Dec 14, 2016 5:01 pm

Thanks Mike, will do. Timing was set by the book recently, but I haven't tested the advance/retard diaphragms to see if they hold vacuum, or affect the timing in any way. I'll check them out.

I'll also check that vacuum temperature valve in between the distributor and manifold. It's hard to test fixes because once the car has been run for a few minutes it is fine - I have to wait until it's stone cold again for the effect.

Merlin · Post by **Merlin** » Fri Dec 23, 2016 7:56 pm

If the problem is only when cold then its in the cold start circuit, however if the problem is always below say 3K RPMs then I would look at the air flow meter. The engine should rev slightly higher when cold to warm the engine. Another odd item that may affect it is a vacuum leak that seals when it warms up.

I always set the timing to the factory spec and then adjust by ear.

Good luck.

Lock · Post by **Lock** » Fri Dec 23, 2016 10:45 pm

Yes, the problem is definitely only when cold, in the first few minutes so hard to troubleshoot because I have to wait until it's cold again to replicate. But it doesn't idle any higher when it's cold ( idle is usually anywhere between 700-1300 depending which 'mood' the car is in) so something is wrong with the cold start circuit and maybe the whole throttle/airflow meter area.

It passes CA smog with flying colors, and the two diaphragms on the distributor are functional and sealed. I'm wondering if it might be that vacuum temperature valve between the throttle and the distributor having some sort of problem. I will bypass it and see how it responds. Will set timing this weekend and see.

RonDwyer · Post by **RonDwyer** » Sat Dec 24, 2016 1:41 pm

you could consider taking apart the distributor, the points assembly and all to clean and lubricate all that. Not sure if that is possible but old lubricants are the cause of so many problems. I have a distributor, ECU and a few other parts if you want to borrow anything to swap in.

Lock · Post by **Lock** » Wed Jan 11, 2017 12:00 am

Thanks Ron - I will check the centrifugal action of the distributor weights/springs and grease as needed. Will also bypass the thermal vacuum valve to the distributor (the one next to the coolant temp sensor) for testing to see if it's stuck. I seem to recall a FAQ mentioning what the two vacuum lines do on distributor on the '79 model, but I can't find it now, be good if I knew what everything did before trying random things. One is advance and one is retard I believe?

I actually suspect that my aux air valve my be stuck shut, after reading this - the FAQ says this only adds throttle, doesn't affect mixture, but wondering if it's making a difference (and could also explain my random idle speeds, esp if it's broken and flapping around).

http://www.firstfives.org/faq/aux_air_v ... valve.html

In a perfect world where time and money was endless I'd replace it with the later model '80-'81 electric AAV, but for now I'll spray some carby cleaner in it and see what does.

I haven't found a good description of the Temp Time Switch, but I think that also/may instead have an issue, as it runs for only about 10 seconds - what I assume is (like the old electric choke on a carby) it has a tiny heater element and a bi-metallic switch, and if the engine is cold the heat from the heater turns the bi-metallic switch off (or on?) after about 10-20 seconds, but if the engine is already warm the switch is already off due to heat - is that right? The wiring diagrams seem to support this idea. If so, then I think that might be culprit here. Either the cold start injector is flooding the engine, or it's not running at all?

It is pouring with rain right now here in the bay area and I live very near a creek that has a flooding and flash flood warning, and I have no garage so the poor beemer is out in the rain. Which is why I'm here inside rambling and not fixing it.

RonDwyer · Post by **RonDwyer** » Fri Jan 13, 2017 12:22 am

I have all those parts you can swap in to try if it can be driven here.

Lock · Post by **Lock** » Tue Jan 17, 2017 12:14 am

RonDwyer wrote:I have all those parts you can swap in to try if it can be driven here.

Thank you Ron, I might take you up on that once I've narrowed down what I suspect is broken. As to whether it can be driven, well currently it only has 1st and 3rd gear, but it's fine on the freeway once you get going!