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1979 RX7 Carb help
Hello every one, I’m a new member here. I recently picked up a 79 RX7 with only 77K miles. It runs fine until I come to the stop light and the idle just drops and the car would stall if I don’t give it gas. I have replaced the fuel filter, spark plugs, dist cap and rotor. I’ve been searching the forum. Some people mentioned adjusting the Mixture Screw, checked for vacuum leak, etc.. I couldn’t find any vacuum leak. I read the Sterling post on tuning the carb. However, my S1 Carb looks a little different. I hope someone can help me point out which screw is the mixture and which is the idle speed. Thank you! https://cimg6.ibsrv.net/gimg/www.rx7...1a3c0dbe66.jpg |
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red: air screw
green: mixture screw blue: idle speed (or throttle stop) screw |
Thank you guys. I’ll give them a try. Hopefully it’ll fix my problems |
Don't over-tighten any of the screws or you will damage them.
Drop a can of Seafood into the gas tank (full) will help clean out the fuel system... Keep checking the fuel filter. If the car was in storage for long, before you bought it (or the PO didn't drive it much), the tank may be compromised (rust) and shedding its innards into the fuel. Not likely since you say it runs well except idle... Stu Aull 80GS AZ |
Thank you so much. I have gone through 3 filters. The problem is when it comes to stop light, the idle drops unless I give it gas. Since this has carb has separate Air / Fuel mixture screw, how do I adjust them. Can I use the same concept on Sterling post? |
Originally Posted by 7aull
(Post 12321338)
Drop a can of Seafood into the gas tank (full) will help clean out the fuel system...
just joshing .... Seafood should be Seafoam |
lol. I figured it was just probably auto correct. This forum is so helpful. many thanks!
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screw in blue is throttle stop. no need to adjust unless a PO messed with it.
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Originally Posted by rxtasy3
(Post 12321409)
screw in blue is throttle stop. no need to adjust unless a PO messed with it.
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it should have something like paint marker on it so it's noticeable if it's been turned. maybe back it out and let the butterflys seat, screw it in til it touches, then tighten to like the one o'clock position. don't want to uncover too much of that slot, forget what it's called. now if i had one that wouldn't idle down enough with the other screws, then i might back that one out slightly.
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Thank you. I'm going to give it a try.
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Thank you every one for the help. I was tinkling around with the carb last night. Car runs much better. The problem now is the car drops idle on deceleration especially when it comes to full stop then the RPM picks itself backup. I had to set the idle to 1500 RPM in order for it to stay idled at red light. Could it be some thing else?
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Sounds like your fuel bowls might be flooding (or overfilling) when you let off the gas. Will it do the the stalling thing the driveway too - like if you hold the pedal for a little and let off, does it do the same thing as when you're coming up to a stop?
If it does, either have a friend work the pedal, or just use your hand on the throttle arm for the dashpot (the arm is on the firewall side of the carb and is relatively flat compared to everything else), and do the same testing while looking through the fuel sights in the carb. The sights are located on the front and back of the carb and you'll probably need a mirror to see the one on the rear. At idle the fuel should be about halfway up, and while driving or whatever, it shouldn't deviate much from that. If when you release the throttle the gas level rises significantly, you most likely have either a sticky float, needle, or a dead/stuck vent solenoid. Do this test for both float bowls (both sight glasses). This same issue happened to me when one of my needle valves kept sticking down, and then again when my vent solenoid died. Back when my needle kept sticking, I noticed that it happened most often if I had just accelerated relatively quickly. While testing, you may find that you have to either punch the throttle or bring up the rpm enough to have a quick enough change to cause a needle to stick. If it's the vent solenoid, the issue should happen regardless of rpm/acceleration because the float bowl simply can't breath which causes all sorts of weird things. I'm going to bet it's not the vent solenoid since it sound like it drives normally otherwise. If you do find that the fuel level rises significantly in these tests, refrain from tearing into the carb just yet. Let us know the results, and best of luck :). Oh, and how did you set the idle up at 1500? Did you use just the throttle stop, or a combination of things? Perhaps that fact could be of use while troubleshooting. Also, does the issue still "occur" now that you've set the idle up - as in, maybe it's just slight enough that it doesn't stall the car? |
Thank you for the info. I’m gonna give it a try. I used the idle screw and air screw to get the idle up to 1500. That’s the only way to keep it idle at red light. |
I found that If I richen it up. It'll run better. However, found out that my gas tank is all rusted and filled up with debris. I've gone through 4 fuel filters already. Should I drop the tank and clean it or just buy a new tank if there's one out there?
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If you've got the time and patience, I would drop the tank and either send it to a local rad shop to do the job, or you could try it yourself. I cleaned and coated my own tank recently and so far it's working great. New tanks are fairly difficult to find, especially for the SA's (1979-1980) as they have a slightly smaller tank due to the 'full' sized spare tire.
As for the tuning, being that you said richening the mixture helped, I would now bet on there being a vacuum leak. Depending on the leak, the car may idle decently (perhaps a little high) and rev/drive okay, but upon returning to idle it will stumble or die. This happened to me during my ACV delete when my block off plate wasn't sealing properly. Since the SA vacuum rack is fairly simple, you could either pull some vacuum lines and inspect them individually (take pictures before so you don't forget where they go), or spray some ether or similar around the vac lines and see if the idle raises. Best of luck. Oh wait, just reread your post. Did you mean richening the mixture fixed the issue, or just made it better? |
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