85RX7GS

iTrader: (1)

My car has recently developed a series of strange problems. Not really sure why, but here's what's happening...

*Engine will cold start with the choke, but will not stay running if the choke is set below about 2200 rpms. If it is set below that, the engine will immediately die as if the ignition was cut unless I pump the pedal. After the choke has pulled in AND the water temp gauge has reached normal operating range, the engine idles rock steady at 750 rpms. With the choke on while warming up and even after the engine has warmed up, the exhaust smells pretty rich...more so than before.
*While parked and accelerating the engine, there's a miss that starts around 2200 rpms and remains present until about 4500 rpms. Sounds like it may be running rich during this span of rpms and then stabilizes once it reaches higher rpms.
*After any sort of extended cruise on the highway with the engine turning around 2300 rpms, the RR of the car near the tail light will be covered in soot. I've also had people who were following me tell me that the exhaust smells horrible. This made me curious, so I had someone else drive my car while I drove behind it and the exhaust does not smell normal. Honestly, the smell isn't a big issue, but I figured it was worth mentioning as it might be useful info to this problem.

This all started about 2 weeks ago. Car is a 79, 12A Atkins street port with the RB 12A street port exhaust. Stock carb, stock points ignition with a recent complete overhaul on the distributor. Aside from this problem, the engine runs great, pulls strong and doesn't exibit any signs of low compression or failing internal components. Only thing I did (not recently) that I can think of which could be related to this problem was that I completely rebuilt the carb last winter.

I'm thinking that these individual issues might somehow be related since they both happen within a similar rpm range. Right now, I'm trying to figure out what happens within the 2000-3000 rpm range in terms of the ignition, carb and emissions related hardware.

Any thoughts?

Kentetsu

I would start by making sure that you still have spark on the leading plugs. After that, we're on to the carb. I suggest that you check in with Sterling and see what he thinks; www.sterlingmetalworks.com/bymc


Good luck.



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85RX7GS

iTrader: (1)

Thanks, I'll have to check that now that the weather has cleared up. Is there anything that would cause the leading ignition to cut out at certain rpms? I read that the trailing ignition is cut under certain circumstances, but didn't see anything about the leading.

Also, I was thinking about this yesterday and one thing that came to mind was the possibility that I installed one of the jets in the wrong place on the primary side. My observations while driving to work this morning were that while operating over 2000 rpms, the throttle seemed to be noticably less responsive than when the engine is under 2000 rpms. Almost seemed like it wasn't getting enough gas over 2000 rpms until the secondaries opened up. Maybe I swapped jets accidently?

Kentetsu

Installing the jets in the wrong position could result in the issues that you are seeing. Sounds like something worth adding to the list...

85RX7GS

iTrader: (1)

Made some progress last night. Turns out there was a vacuum leak at the ACV block off plate that was noticeable when the engine was cold, but not so much when it was hot. Must've been the difference in temp of the metal that caused it to seal a little bit better when warm, as I didn't notice it until the engine was running while cold. Needed an automotive stethoscope to hear it...I guess my hearing isn't so good. Once that was fixed, I had to re-adjust the idle speed and mixture. I'm at 3/4 out on the AAS and 2 1/4 on the MAS.

Also, no more missing or hesitation while under load, but there's still that mid rpm miss while parked and revving the engine (no load) up to about 4000. Dynamic timing seems fine and the advance diagphrams seem to be working fine. Points are in good shape and gapped correctly, but I don't have the right meter to check dwell. Never have bothered with that though...

I have a feeling that the miss may be carb related at this point. Seems like everything ignition wise checks out. I found a diagram, which I wish I had PRIOR to rebuilding the carb, which shows which jets go where and what their sizes are and what circuit they are for. I'll be going through that to make sure everything is in the right place and if that doesn't work, I'll try swapping carbs.

Kentetsu

I'd keep my eyes open for a later model dizzy while you're at it. Messing around with points has always been a futile experience for me.

Good luck, sounds like you're making some progress...

85RX7GS

iTrader: (1)

Thanks man, yeah...slowly but surely I'm chipping away at it. I guess I've baffled the minds of the others with this problem

True, I guess I could pop a later model distributor in there and wire it up, but I'm saving that as a last resort. I actually had one in there a few years ago, but I honestly didn't notice much of a difference in performance or fuel economy to keep it in there, so I went back to the points. Even with the points distributor, I wasn't having this missing before, so I'm thinking it's gotta be a fuel/carb issue. I'm hoping to get some time today to dive into it further