TWegs

Hello all, I am new to the forum and need some help/advice.

I recently purchased a '65 Mustang GT Fastback with a 302 V8, 4brl, C4 Auto. The car starts great, idles fine but when I put her in gear she stutters for a few seconds and then dies. If I give her some gas while in gear she will continue to run for a minute but I need to rev her pretty good to go anywhere, I have only been able to get her to the end of my driveway and thats it!

At idle she is at around 1200 RPM when in gear the RPM drops to around 700. With a Vacuum gauge to the carb. while idling it is reading around 15 dropping to around 10 when I give it gas, no noticeable drop when in gear. Need help locating the leak, any common areas to check and good ways to do so?

Not sure if this is enough info, I am not the best with engines so if more info is needed i will do my best.

Any help or suggestions is greatly appreciated.

Tim

kenash

Hi Tim,
Checking and know the eng. vac is a good start. But, know depending on where you pick up the vac source, is going to offer a different reading. First, your idle appears to be too high unless you have an aftermarket "hotter" cam, in which case, it would be normal to is have a lower than normal vac reading. Otherwise, it's typical for the vac to "fall-off" when raising the Rs above idle. If too your knowledge, it has a stock cam, your vac readings at 800-900 Rs should be near the high teens/low twenties, depending on other wear factors. It's quite normal for the Rs to drop off when placing "in gear". This is why automatics have a higher idle speed compared to manuals.
So, why is it idling at 1200, when it should be 300-400 Rs lower? Is the carb's idle mix set correctly? The carb's idle circuit is dependent on good engine vac to pull fuel from the fuel bowl. clean? BTW, the vac needle should be fairly steady at idle, it should drop to "0" when you "goose it". Just some things to consider...

jlg2002

Keash makes good points- 1200 is too high and 15 in is too low for a "good" engine. try setting the idle speed down to 700-800 in park to close up the throttle blades. then, measure your vacuum iirc, i rarely saw a car idle in the low 20's but 19 and steady is a good number with a stock cam. You also need to look at the carbs accelerator pump to see if it's shooting a jet when you step on th egas. check dwell 28-32, timing6-10 deg, and then adjust idle mixture screws and set idle speed in that order. the best way to isolate a vac leak is to spray carb spray around the intake system. don't forget to check the PCV valve.

TWegs

Thank you both! I did lower the RPM's and checked everything else the vacuum pressure is still a bit low, but the car is running much better and after a few trips around the block it appears to have just needed to be driven a bit to "clear her out".

Simple problem...just foolishly exaggerated a bit.

Thanks again!

kenash

First, as a follow up, insure all of the simple stuff is correct, wires are clean and in good working order. If points, they have the correct gap. Insure the inside of the cap is clean and the rotor is not "overly" worn. Now that you'e reduced your idle re-check the timing and adjust, if needed. You can use the vac gauge to adjust your car idle mix quality. Basically, you want to turn each screw very slowly in/out to determine at what point, you achieve the highest RPMs. If the RPM rises too high (outside 800-900 band) adjust the idle speed screw to reduce. Do the same for the other idle quality screw.
One of the attributes of a good idle vac (within specs), the smoother your engine will idle. The carb idle circuit is wholly dependent on a clean idle circuit with a good vac source. All else being within specs.
Do the easy basics and you'll feel the difference. BTW, vacuum is a measurement in terms of inches of mercury, not the result of an induced pressure.
Good Luck with your project.