takvanvi

Hello,

Similar threads - 3800 RPM wall...accelerates poorly. Sorry in advance for the novel, but hopefully the extra detail will eliminate a run of leading questions.

i've read ~100 threads on rev limit and acceleration problems. My symptoms sound real similar, but very few threads end with a smoking gun. There must be a common solution to what seems like a relatively common problem.

I will note the following in this order - .1. car detail. 2. what's been tried 3. the symptoms

1. the car - stock 83 rx7.

2. Already done.....new cap, new rotor, new plugs, new plug wires, new fuel filter. I swapped (not new, just flip-flopped the 2 that were there) the 2 igniter modules on the distributor and this didn't change the problem. Checked the fuel flow and it is in spec per Haynes. Tried to check the fuel pressure, but difficult to find an accurate gage in the 1 to 5psi range. Timing is good. Everything is sparking (checked at the distributor cap by pulling 1 cable at a time. fuel flow in the primaries is good. Fuel flow in the secondaries IS FLOWING (looks like a lot) when i manually open the primaries and secondaries in neutral.

The Symptoms
3a. Car idles fine. Car revs fine in neutral to ~5k if done slowly. Just a little more gas to get past 5k and it sputters out. Enginge runs rough and rpms drop. When doing this, 5k is about the time the secondaries start to open and gas starts to come through the secondaries.

3b. Similar to 3a, while driving, car will come up to speed to about 3-3.5k if gas is applied gradually. just a little more gas and the car will sputter and run rough with no further acceleration. I tried this with choke and w/o with same results.

3c. Plugs are generally running a little on the white side, but running temperature is normal.

3d. The problem came on slowly over a couple weeks. I noticed by the fact that acceleration got a little slower day over day. cruising to work, it took longer to get up to 80-85mph on the freeway. then i coudn't get to 75, then 70, then 65.

I am thinking I either have a spark or fuel problem.

Best I can tell, the spark is doing what it is supposed to. I can see the timing advance when the RPMs advance on both lead and trailing circuits.

the fuel would be next. primaries are gunning fuel in the bowl. and when i actuate the secondaries manually (in neutral), I can see a steady flow of fuel coming out there too. But everything seems to fall apart when I believe the secondaries would be kicking in.....during hard acceleration or to get past 3500rpm when driving. I don't think it is the accelerator pump because it is not a temporary stall, but a sustained rev problem. If the accel pump was bad it would just be a temporary hesitation.

Is there an obvious fix? I think I have run out of the easy things to do. I can try to rebuild the carb, but I am not convinced if this is the problem, or where I might focus my attention.

Thanks in advance for your advice!
Tom

Rx-7Doctor

iTrader: (13)

1). Check compression, if 1 of the 2 have problem it is going to be the rear housing. 2). Remove the pipe from the exhaust mnaifold and rev it up, if it easily revs, you have a clogged cat problem. 3) inspect the carb at the right rear near the firewall. Your looking to
make sure that both springs, the lower and the top are connected. let me know, rx7doctor

takvanvi

thx for the advice. I will give those a try.

couple questions for education/understanding. Why would either a clogged cat or low compression become such an issue as the secondaries start to kick in? Everything runs fins and smooth in Neutral or while driving as long as I stay out of the secondaries.

Also, which 2 springs are you talking about (upper lower). Just let me know which component on the carb they are attached to.

And what typically causes a cat to clog?

thx again!

RXTbone

The internals of the cat breakdown over time. A lot of forum members will punch a hole through it and run it open. Nice time to replace some exhaust components if you can afford it. I ended up buying a RB exhaust and it was the best money I ever spent...

I had a similar problem to the one you describe, and I followed similar procedures to fix - to no avail. What ended up solving my problem was a carb rebuild. I know this is a general fix - but it worked.

I guess I'll throw the softball and ask how many miles the carb has on it?

takvanvi

you have a great looking car. My car has 205,000. I've had it for at least 15 years, so I can guess that the carb has never been rebuilt.

Well, I cracked (didn't even fully remove) the exhaust pipe at the manifold donut connection. WOW! what a difference. I can really get into the gas and it doesn't exibit any of the problems that I had explained. sitting at idle, almost all the exhaust is coming out of a relatively small split at the donut, so the cat must really be plugged.

I live in Phoenix and we have to pass emissions. So if I punch the cat through, eventually I will need to put a cat on to pass emissions. Will that RB exhaust keep me in the "pass" mode? What all is included in the RB exhaust? How much?

bahlorm

It should have all that information you need to know at http://www.racingbeat.com/Mazda/RX7-...ml?id=dhiEuTC5. Just check out their complete exhaust systems.

PercentSevenC

No, you won't pass emissions with an aftermarket exhaust. You might be able to get an RB short-primary exhaust and stick a cat in place of the presilencer and be able to pass the sniffer test, provided all your other emissions junk is in good working order. But if they do a thorough visual inspection (and actually know what they're looking at), you're boned - you can get an aftermarket rear muffler, but that's about it.

I mean, if you want to you could get an RB exhaust and just swap back to stock for a day when emissions time rolls around. In that case I would recommend the long-primary system, because it's just better.

LizardFC

iTrader: (1)

lol blasted by the past.