throttle hesetation

[bears4ever]

Hi All

I'm sure someone out there has had or seen this problem. I have a 68 mustang with a 289. The motor,trans,rear end all has been rebuilt. I noticed the other day that it has a hesitation when I'm first taking off. Could this be a carb air/fuel mixture problem. Brand new 650 edlebrock carb with a B & M shifter. Any suggestions would be greatly appreciated.

Thanks

[zgreatwhite]

There are several areas to check. I suggest the easy areas first, as they don't cost any money, though they are time consuming...and usually not the cause of this problem.

First, would be to check your distributor advance. You need a timing light, and a golf tee. As a quick check, when the engine is off, remove the vacuum at the distributor and plug the hose with the golf tee. Start the motor and check the timing. Increase the RPM and see if the timing mark has moved. If it doesn't, your mechanical advance in the distributor is broke. Otherwise it is "probably" ok.

Next, put the vacuum to the distributor and see if the timing has moved. Hopefully it has, and then you know your vacuum advance is "probably" ok. (I say probably, because there is a timing advance curve for both the mechanical/rpm and vacuum advance mechanisms. I am sure there is a discussion here somewhere concerning how to more accurately measure this).

If the above check OK, chances are you need to modify the carburetor, which according to the Edelbrock propaganda is easy to do. I suspect this is the case as a 650 CFM carburetor on a 289 is way more then you probably need, so I suspect a RICH ACCELERATOR PUMP is causing the stall..that is too much fuel for the small amount of air your motor is pulling.

In any case, you will probably need to buy an Edelbrock kit, and change out a few items to get the proper fuel settings. Goto the Edelbrock web site, and you can probably order the parts from Summit.

In all honesty, they should include the kit with the carb. As I recall, the propaganda states "TUNED TO YOUR ENGINE", but I don't understand how any aftermarket bought off the shelf can be tuned for a 289, 302, 351, etc. not to mention the different cams.

Good luck.

[powerband chaser 302]

Originally Posted by zgreatwhite

so I suspect a RICH ACCELERATOR PUMP is causing the stall..that is too much fuel for the small amount of air your motor is pulling.
Good luck.

I second that idea. If you dont have a problem with flat spots in the engine building rpm while driving or any hesatation above 1500 or so then im posative its just the "accelerator pump shot" Check the edelbrock web page to find how to adjust this.

[okiedragster]

ill third the accelerator pump and if that isnt the culprit try the vacuum advance, like zgreatwhite said , pull the vac hose off the carb that goes to the advance(this sounds dirty..lol) and with the motor running suck on the hose and see if there is a change in the motor idle, if so the vacuum pod is prob. good...

[bears4ever]

I will try that this week and see what happens. thanks all

[Rev]

I'm not convinced that it's necessarily a "too rich" situation. A too large carb often gives a weaker signal causing an overly lean situation. But that situation usually occurs higher in rpm range when the main jets are functioning. I'm thinking that it may actually be a "not enough accelerator pump shot" rather than too much.

Is there any black smoke when you nail it from a stand still? That would mean an overly rich situation (too much pump shot). If that's not the case, I think the hesitation means not enough shot.

Rev

[bears4ever]

No I have no smoke when I rev the engine. it runs and idles nice. It only happens when I first go to accelerate. I was able to test run the car on my street a few weeks ago when we had no snow. Unfortunatly living here in Canada with this lovely white stuff on the ground I'm not able to test drive it at this moment. I can only pray that the snow goes away soon. Do you know what i would adjust to get that extra shot.Thanks

[Rev]

If conditions warrant, get someone to stand behind the car when you nail it from a stand still causing the "hesitation". A very rich condition will make black smoke momentarily. If that doesn't happen, I'm assuming a momentary lean condition causing the hesitation.

I'm familiar mostly with Holleys. Check on the Edelbrock website to see what they recommend for tuning the Edelbrock pump shot. You may need a little more. I'll admit that I'm just guessing here, but it is a thought.

Rev

[bears4ever]

Thanks Rev for the information. I will try that.

Thanks again

[bears4ever]

Hi Rev

I was able to have a friend stand behind my car yesterday(not too close of course). When I gave it there was some black smoke that came out. I'm going to look at leaning it out and see what happens. thanks again