High revs on start up

[Thin Lizzy]

Hi All,

Is it normal to have high revs on start up? The car seems to increase it's revs to around 5000rpm. Then after 3 minutes, it returns to normal revs. It sounds like the chock is out, but I've checked it and it's not.

Is this normal or do I need to get this checked out?

Thanks for any help you can give.

 

[will e]

That is not normal and it is bad for the engine. Something is wrong with your choke system. What kind of carb do you have?

Do you have a tach or does it just sound faster?

 

[Thin Lizzy]

I'm not sure which carbs I have. No tach, but I know its reving way to high. When I put it in to drive the rev's go down, but put it into neutral or park and it high. It only seems to happen when the engine is cold.

 

[Boss1Ray]

Sure sounds like a carb/choke adjustment...

I had a similar problem with an old pickup. It was the throttle linkage. It had been bound up (sharp bend) where it went through the firewall. I tried to lubricate it but ended up replacing. I would take linkage loose from carb and make sure there is no friction just to rule that out.

Good luck.

Ray

 

[71/351c/darkhorse]

also look for the high idle screw on your carb. on my edelbrock i have its underneath where the throttle cable attaches. As soon as the engine warms up it will drop back down. is in an electric choke or pull style?


Whats your usual idel set at? when you drop it into gear when it is high idling does it drop down to normal op. rev or still elevated? find a decent tach/dwell meter if you can so you see what your really running at.

 

[Thin Lizzy]

Thanks for the information. Does the choke cable runner near the drivers pedals? A cable was hanging down the other day and I caught it with my foot.

 

[Jim and Jutta]

Mine "sounds" like it's 5000 RPM upon start up but it's actually around 1700, then after a couple of minutes it drops down, even a 1700 start up is pretty fast for an engine that's been sitting for a long period. If it's been sitting for several days without starting, I normally crank it over a few times prior to pumping it, just to get a little oil on top of the engine, then I pump it once and it springs to life. If that helps or not, I don't know, but it makes me feel better.

Jim

 

[Don C]

I agree with Jim, it probably sounds faster than it is. If you placed it in gear at 5,000 you would likely have a wild ride, even with your foot on the brake.

I would recommend getting some kind of test meter so you can verify the engine operations. Some are inexpensive, the second one also does volts, amps, and ohms.

http://www.amazon.com/Actron-CP7605-Tachometer-Voltmeter-Analyzer/dp/B00062YUUS

http://www.amazon.com/Winmax-WIN6899-Automotive-Digital-Multimeter/dp/B0062CVSZ6/ref=sr_1_9?s=automotive&ie=UTF8&qid=1416593235&sr=1-9&keywords=engine+analyzer

 

[Thin Lizzy]

Mine "sounds" like it's 5000 RPM upon start up but it's actually around 1700, then after a couple of minutes it drops down

So yours does a similar thing. I'm only guessing it's 5000 rpm, as it doesn't have a rev counter.

Is it normal for 71-73 Mustangs to have what appears to be an automatic choke like this?

 

[Jim and Jutta]

Mine "sounds" like it's 5000 RPM upon start up but it's actually around 1700, then after a couple of minutes it drops down

So yours does a similar thing. I'm only guessing it's 5000 rpm, as it doesn't have a rev counter.

Is it normal for 71-73 Mustangs to have what appears to be an automatic choke like this?

They make carbs for our cars with both automatic and manual chokes, I have an electronic automatic choke, some like the manual chokes which is what those with automatic chokes wish they have "if" the automatic choke starts giving you issues.

 

[Thin Lizzy]

A manual choke sounds much better. I'll see if I can get this fitted. Thanks for the info.

 

[ceheler]

If you are looking to fit your carburetor with a manual choke and already have an automatic choke Napa makes a kit for that part number 732-1153. It comes with a cable as well as a plastic piece that replaces the automatic choke piece and several bracket. Our store sells it for a little under $20. Works great on forklifts i sell lots for those. Apologies if i missed what you meant.

 

[Thin Lizzy]

That sounds great. I'll find someone that can look at my car.

This place's got some much knowledge .

 

[ceheler]

Not a problem. We have a great group of guys here and a lot of experience coming from the other side of the counter. Me being a diesel mechanic and my manager being a speedhead as well helps. If you ever have a question regarding napa part numbers or mustang parts feel free to PM me and chances are i can help you out

 

[rutkak]

1600 or so is about right for a cold start on the fast idle. There is an adjustment screw on the right side of Edlebrocks and I think left side of Autolites. You just turn it to adjust but you'll need a tach or timing light with tach. As the choke opens it drops the revs down until the car is warmed up and choke is fully open.

 

[judge]

If still have the factory style carb, it's probably not just a choke problem. I believe it will do the same with a manual choke. There is a 5/16 screw on the right side of the carb to adjust the throttle position when the choke is on. You simply need to back that off some.

 

[c9zx]

Just information. Cold start fast idle speed for 302 auto trans = 1500 RPM. Manual = 1400 RPM. I would verify/adjust cold start RPM before changing any parts. Chuck

 

[Thin Lizzy]

Is this the screw on the right that needs adjusting?

 

[c9zx]

It looks like it could be and it on the highest step in the picture. Is that a Weber carburetor? If so please post a picture of the carb. Thanks, Chuck