Hi,

My rx7 seems to die a few minutes after starting it up sometimes, and then really has trouble starting again. It seems to lose power, such that the gas pedal does nothing, and then the engine will just stop.

Last time it happened, I started it up after work without a problem, was letting it idle for a minute or two to warm up, then the engine started sounding strange, car started shaking. I thought maybe the carb was still cold, so I tried giving it gas, but it kept sounding really weird, hard to describe, sort of a slow "whump-whump" noise and it died despite giving it gas. I got it started after a bit of cranking, but then the same thing, and after that I couldn't start it at all. Mashed the gas pedal while cranking, etc, but nothing. It did start the next morning after quite a bit of cranking though, and sounded fine.

Set up is a street ported engine with a weber carb (not sure what kind). If previous owner wasn't lying, the engine has around 5k miles on it. Not sure what exhaust, but the header merges into one pretty small outlet, maybe 1.5 in ID I would guess. Not sure about the fuel pump, but as far as I can tell the Weber does not have a fuel return system. Seems like there's just the one line into the carb. Ignition is dual MSD system, I have checked all the connections, they look ok.

Edit: Also, I don't think the car has an oil cooler... I can't see it anywhere. Where is the stock oil cooler location? How bad is this?

The strange thing is that the car runs great when it doesn't enter this fail mode. Has excellent power (although I have noticed power seems to drop off at higher rpm). So it seems like a random chance whether or not it's going to get into this state when I start it up.

Thanks

 

How old are your plugs?

 

Mine started to not want to start anymore in the morning so I bought all new NGK's. Every morning I hold the choke all the way out and start the engine, rev up to about 1500rpm and push the choke all the way in. Since its cold in Northern Michigan I have to keep my foot on the gas @1500rpm and wait a few minutes for the engine to warm up to idle by itself. But in the summer I don't have to. So first bet would be plugs.

 

Plugs are actually brand new. I experienced the problem before and after installing the new spark plugs, should have mentioned that. Weber carb doesn't have a choke unfortunately.

Thanks for the suggestion.

 

Could be crud built up in the fuel system. Czech your filter first.

 

That too, and maybe you're getting too much fuel?

 

It looks like there are two fuel filters on this setup. One just before the carb and one kind of hanging below the gas tank. They both looked spotless last time I checked (they are some generic K&N filters with transparent plastic housing). I'll try and take some pictures later.

Maybe so, especially since the Weber doesn't have a return fuel line that I can see. How would I fix this, or even determine that this is for sure happening? I know virtually nothing about carburetors .

What about fuel pump? It's not the factory pump, as I can barely hear it when it's running, and I know the OEM pump is quite loud. Can't imagine why the fuel pump would be failing intermittently though.

Thanks for help so far guys.

 

how long have you had the car?

with the Weber, you really need to find out what model/size you have and you NEED to know what fuel pump is feeding it. so those are the two biggest pieces of info that you should obtain before trying to "fix" it.

Webers (no more so than most other carburetors) are sensitive to pressure and will flood if the pressure is too high.

feel free to post photos if you remain unsure about anything you find.

also, just to be clear, when you said dual MSD system, do you mean just the coils or does it have amplifiers ("boxes", e.g. 6A, 6AL, etc.)?

EDIT: in my quest to get details, i forgot to keep it simple ... check your plugs and see if they are wet.

stock oil cooler should be the beehive, under the filter. if it's not there, then it may have been converted to an air-type oil cooler somewhere up front. either way, you NEED to know what you have and know that the oil is being adequately cooled.

high RPM power loss could be either too much or too little fuel. confirm the parts you have and we can move on from there.

cute.

 

Thanks diabolical1.

Only a couple of weeks. I bought it from a guy who rebuilt the whole thing, I had assumed he knew what he was doing since he had like 4 other rotaries and was a nice guy... maybe not though.

Yes, it has the 6AL, two red boxes.

Here's a picture of the carb, which will have to do until I get home and can see if there is a model number on there. Can anyone identify this?



Not sure how I can identify the fuel pump. Do I need to empty the gas tank?

Will check the plugs, thanks.

 

it's a DCO. you just need to figure out what size now ... 40, 45, 48, etc.

as far as the pump goes, find it, photograph it and post it. there should be no need to empty the tank. unless there was some kind of funky relocation, it should be under a plate near the filter by the rear driver's side wheel.

okay, so you've only had the car for a few weeks. has it ever started and run well?

 

I think it has always been a little bit rough since I've had it. As I said, it usually starts up fine as long as you hit the gas a bit while cranking.
The first problem I had was just a few days after I bought it, it died in a similar manner to what I described, sudden loss of power trying to accelerate from a light and then died, this was just a few minutes after starting it up. Probably 60-65 F ambient temps though, so it wasn't cold. I managed to start it again after quite a bit of cranking and gas pedal usage, and it was fine. I did drive it 400 miles round trip without any issues, plenty of power on the highway.
At that point I had a problem with the ignition wires, which had burned through due to previous owner routing them right over the engine... You can see in the pic above. That is fixed, and I believe is unrelated to this issue. I changed the spark plugs at this time.
Then same problem last Thursday. Started up fine, started sounding weird, died. Got it going once more, and then it shut down, couldn't start it until the next morning. Haven't had time to do anything to it since then.

So that number is just the diameter in mm of the intake tubes right?

 

have you changed the cap and rotor since you got it?

 

You mean the distributor? No.

Is it prone to failure?

 

not the distributor itself, just the cap and rotor. they are wear items and can cause hard/no starting, misfiring and stalling when worn. actually, the MSD ignitions have been reported to accelerate wear on them (i've read that, not experienced it). i suspect changing them won't cure your issues, but it's possible it could help. it's simple maintenance so you're not losing anything by doing it. might as well check the timing whenever you do it as well.

 

Well I ended up taking it to a local mechanic that I've dealt with before. I realized I just have zero time to debug this at the moment, and I wanted to get it running reliably again.

They found (only took them about an hour!) that the fuel pump was badly wired up, resulting in intermittent power to the fuel pump. They rewired it properly to the ignition switch. Not sure what it's usually wired up to, but I think this is a good solution.

Thanks again for everyone's help!