I have a 1985 Mazda RX-7 GS with a stockport 12A and a recently rebuilt Nikki carb, the vehicle has 60,xxx original miles on the odometer. The car has had a GSL rear swapped in and it has racing beat headers with 2 1/4 piping (with cat) back to a Magnaflow muffler. The rat's nest is still on the car and as far as I know, still functioning.

The car has had high idle trouble since I bought it, nothing insane but it would stay at right about 1,100 RPM. This last weekend my friends and I attempted to solve the problem by hunting for vacuum leaks. After finding one and correcting the issue we adjusted the carb to bring the idle down. After a bit of playing with it we were able to fix the idle at 800 RPM. The next day I went outside, choked the car off and started it to let it warm before I drove it to work. Immediately upon backing out of my spot, I noticed that the RPMs wouldn't come down unless I pulled the choke out and let it slap back into the warm position. After this was done, the car would idle right back at 800 RPM although it did drop below that (I assumed this was because the engine was decelerating quickly since it was coming down from anywhere in the 5-8K RPM range). However, any time that the gas pedal was touched in the least, the revs would continue to climb until I pulled the choke out and let it slap back into the warm position. I limped to work this way, hoping that it was stuck for some reason that I couldn't figure out and it would correct itself during my trip. When I arrived, I cut the engine and opened the hood to have a look. The throttle cable was extremely loose and would move out of the bracket with a very light touch. My friend came over with some tools and we tightened it back down. After having a close look around we found what I believe I have read called the "teeter totter spring". It was not attached to the throttle return spring assembly at all. After fitting the smaller piece back into the nook we thought it belonged in we started the car and allowed it to warm again using the choke. While giving my friend a ride back to his place of employment we found that now the RPMs would not come below 2k unless the choke was pulled and allowed to slap back into the warm position. When the choke was pulled the RPMs would come down to 1500 or so and stay there. The engine doesn't seem to hunt as much as before but I have no idea what I've done. I've poured over the FSM and Haynes manual and everything looks like it's set up correctly but very obviously, something is wrong. I didn't want to continue troubleshooting until I'd consulted with the gurus on this forum for fear that I might do something dumb. I apologize if this is an easy fix and it's something I just didn't see or look for yet but I do really appreciate all of your time and effort. I look forward to speaking with someone soon, thanks again!

Regards,
Alex

 

I was thinking about this some more. When I reattached the throttle cable to the mounting bracket I tightened down the 12mm nut on the driver's side enough so that the cable wouldn't move from the bracket. Is it possible that the throttle cable at the bracket needs to be adjusted on the passenger's side to provide more slack? Why do you suppose the RPMs would go down when the choke is pulled out and allowed to slap back to it's released position? Sorry for posting again before getting a response. I'm confused...

 

See my post at SMW.

 

1. The throttle cable length is adjusted in this way: starting with lots of "slop" in the cable, pin the gas pedal to the floor using a 2x4 or whatever. Under the hood, take up all slack in the cable using the adjuster, then tighten everything down. Remove 2x4. The key is to make sure that the cable is not so tight that it is trying to force the throttle open farther than it is capable of going, which can spin the shaft and fubar the carb.

2. Once, while working under the hood, I moved my throttle cable out of the way (stuck it under something). Then, while trying to drive the car later, the throttle kept sticking. Moved cable back to the proper position and it was okay.

3. Make sure everything is properly lubricated.

4. Read Sterling's Idle Tuning section if you haven't so far.

Good luck!



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Hey, guys. Thanks so much for all of your help. I really appreciate the responses both on here and on the BYMC.

I'll follow both of your suggestions and report back on what happens.

I still wonder why if I pull the choke out and let it slap back into place (with the engine warm) the RPMs drop and stay there (at about 1500) until I press the go pedal again. When I saw this I thought that a part of the mechanism was either hanging on another part not letting it close without the force of the choke slapping open or that something was seized. I checked for anything that could keep it hanging and saw nothing, I sprayed as much of the linkage as I could with PB Blaster but that didn't help either. Does anyone have any ideas as to why the operation of the choke while warm would lower the RPMs?

I ordered the Racing Beat air pump blockoff plate last night. When that comes in I'll remove my emissions equipment and plug up all of the vacuum sources. When that's done and the throttle is free again I should be able to set the idle as it should be set. If that doesn't work at least I'll be closer to diagnosing the problem.

Thanks again, guys! If you have any more ideas please let me know!

 

I rebuilt a carb for a member and had a high idle issue. I knew it wasn't a vacuum leak. After checking and fiddling for some time, I found that the cruise control cable was too tight, raising the idle. Check that cable and the hot start assist cable. I suspect though that your throttle cable may be kinked or has a wear spot in the covering that has allowed moisture to corrode the wire cable inside the spring sheath.

 

Trochoid, thanks for the response. I remember talking to you about 3 years ago when I got my first FB. Good to see that you're around here still.

The car doesn't have cruise control, it just wasn't equipped with it from the factory. I'll check the hot start assist. Is there a cable with that?

I think the same thing about the throttle cable. I have a feeling it might be seizing somewhere. Do you think this could be a reason why pulling the choke and letting it slap back in to place lowers the RPMs? I'll shoot the throttle cable again with PB Blaster if I look it over and there is a wear spot somewhere. I'll have to look for a new one (probably Mazdatrix) and replace it when I pull the emissions equipment.

Thanks so much for the response!

Regards,
Alex