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Stalls when put in gear

P

panteramatt

Member
I can start the car and it idles great but as soon as I put it in rev, it dies. Same with any gear. Now I think I know my problem but need help with it. The car is a 69 mach1 with a fmx. Car ran great till my buddy tried adjusting th ecarb. Its all stock with an edelbrock. He adjusted the idle and then adjusted th e2 front screws to bring the idle back down and ever since, it doesnt run right. Whats the correct way to set the idle and mixture?
 
Your buddy used the mixture screws to lower the idle.
THATS NOT GOOD !!!!!
At idle , after regulating the 2 front screws ( mixture screws)fully clockwise till you feel resistance, regulate , one at the time , each mixture screw counter clockwise and look when you have the highest idle read out and stop turning.Same with the other mixture screw.
After that ,set the idle and your done.
I asume your timing is ok.
 
Timing and everything else is fine cause it ran great before he messed with it. If I have it idleing and I turn the screws all th eway in, it will stall. Do I have to set idle and mixture while its in drive? Whats the proper way to set idle and mixture on the edelbrock?
 
You have to get both sides at an equal base line, so you screw them in until they (lightly) bottom. Then back them out two turns each. From there, adjust each one (maybe in, maybe out) until it sounds the smoothest. You want to turn them both the same amount, if possible.

After you get to this point, then you adjust the idle speed with the screw on the side. Go back and "touch up" the mixture screws one last time.

Ideally you would use a vacuum gage to set the mixture and a tach to set idle RPM. You set the RPM while in DRIVE, not park.
 
Ok, I messed with the idle mixture screws today. I turned the idle up a little more in park and had th e2 screws out 2 turns. I noticed when I turn the left screw out, the idle will raise but when I turn the right screw out, nothing happens. I had it idling pretty high and when I put it in reverse, it still dies right away. I also noticed that it will turn over while in gear, but I think it did that before. This is on a fmx.
 
Since you started your adjustment at 2 turns out on each mixture screw, where are you now?

Also, did you back off your throttle plate screw until the plates are completely closed, counting the turns? If yes, what was that number?

There are a combination of steps in idle tuning, the major ones being ignition advance, idle mixture and throttle plate opening. They all interrelate.

My QD method is get the engine to idle around 1K rpm by any method, set the timing at 12 BTDC, then set the mixture screws at 2, the plate screw at 2 and work from there, looking for the highest unported vacuum reading. To do this properly, you need an engine tuneup set, or at least a tachometer and vacuum gauge. Call someone who has this stuff, give them a beer and borrow it. They can 'help'.

Pat
 
What do you mean by the throttle plate screw? If your talking about the screw on the plate inside the carb with the spring on it, its closed. I dont thinks its the carb for some reason cause all he did was mess with the idle and mixture screws and I have the idle around 1000 rpms and the mixtures screws out 2 turns and it stalls as soon as I put it in reverse. What else could it be?
 
Most people call the idle plate screw(s) the 'idle speed' screw(s).

Once you have a timing light, vacuum gauge and tachometer in hand, we can work the problem. Things can be measured and diagnosed then. Everything now is a shot in the dark.

In the meantime, with the engine idling in neutral/park, snap the throttle open where rpms rise to 4K or so, then release quickly and observe how the rpms fall. If the engine quickly comes back to idle, normal; if it settles slowly, there's a vacuum leak somewhere.
 
Ok, did a couple quick tests as thats all I had time for. The coil is getting the full 12 volts at idle so thats not the problem. Hooked up a vac gauge and Im getting 16" of vacuum at around 800 rpm. Is this good. I did notice once I removed the cap that the engine didnt noticably run worse. Any thoughts. Tomorrow Im gonna time it and clean the carb. After that, I dont know what it could be.
 
16" isn't bad for a stocker, IMO. Baseline your advance at 10 and see what happens. Opening a vacuum port should make a minor difference in idle quality. The larger the port diameter, the more the difference/deterioration. This is one of those times an audio/video of engine operation would be helpful/revealing.
 
As your idle speed rises from fine tuning adjustments, the timing will advance. You can experiment. IME, 10-12 is a normal 'range'. Much will depend on ultimate advance and the engine's detonation resistance at that level. Once it will idle in gear, then that stuff can be worked out. Personally, I set all my parameters with the engine loaded in gear; others might do it differently. It might help you to have a friend available to operate the car while you do measurements and settings, or vice-versa.
 
Found the problem. After all the tuning and checking, it was a DIRTY CARB!!! Go figure. Thats why that mixture screw didnt do anything. Took it out, blew into the carb, and voila, she runs great. So I got the vacuum to 19" and theres no leaks anywhere. Cleaned the carb out, and got the timing to 10. Now I noticed it runs hot so I belive it to be a thermostat, it never ends. Anyway, thanx to yall for your help and wisdom, I learned a LOT!!!
 
Try advancing the timing until you encounter detonation (either hear it or read it on the plugs) at WOT and then backing it off a couple degrees. I generally advance it two degrees at a time. You will find more ignition advance generally mitigates coolant temps a bit. Optimize that first, then look at the cooling system. If you observe good coolant flow (cap off test) when the thermostat opens, it's likely not the thermostat.

Glad you figured the carb issue out. It's always something LOL
 
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