throttle hesitation

[Iceman247]

Can someone tell me what would cause a hesitation in throttle response on my 1974 360 after the engine comes up to temp?

 

[DetMatt1]

Have you been running pump gas with ethanol in it? Do you use additives to help combat the negative effects of the ethanol?

 

[moparleo]

In other words ,check your accelerator pump. If it doesn't work or is very weak, the diaphragm could have failed. How long has it had this problem ? Did it happen after any work you may have done recently ?

 

[Iceman247]

Yes I run pump gas in it with ethanol with no additives. freshly built motor brand new Holley 670 street avenger with about 50 miles on it. i say new but i put it on there first of Jan. hardly gets driven. when it is cold its a nice crisp response.

 

[burntorange70]

Do you run a carb spacer? That may help.

 

[Iceman247]

yes i have a spacer

 

[Iceman247]

Sorry guys what i meant to say is that I have been using one, any other ideas?

 

[Chryco Psycho]

If it is crisp in cold air assuming the choke is off at this point you are going rich so lower fuel level in the bowls , have you set them since you started the engine ? Tuning the accelerator pump circuit with less accelerator pump shot / smaller cam & squirter , the cam controls the total amount delivered , the squirter controls the deliver speed , also more initial timing usually around 14* at idle with 36* total will help

 

[DetMatt1]

Hard to imagine that the ethanol could have caused any damage in such a short time but you should really be using an additive with every gallon of ethanol gas you put in your tank. I've purchased a couple of Edelbrock carbs more recently than a Holley but the owners manual that comes with them said not for use with ethanol. I'm sure the Holley manual says the same thing. It will reap havoc on the entire fuel system front to back. I'd start by opening that carb up for a visual inspection including seeing if there's any gunk in the bowls.

 

[AUSTA]

Hard to imagine that the ethanol could have caused any damage in such a short time but you should really be using an additive with every gallon of ethanol gas you put in your tank. I've purchased a couple of Edelbrock carbs more recently than a Holley but the owners manual that comes with them said not for use with ethanol. I'm sure the Holley manual says the same thing. It will reap havoc on the entire fuel system front to back. I'd start by opening that carb up for a visual inspection including seeing if there's any gunk in the bowls.

Is the flat spot from idle or at any throttle position if it was at any position you would think it was not getting enough initial fuel when the butterfly opens have you tried opening the idle air jets up

 

[Iceman247]

thanks for the comments, yes the flat spot is from an idle. I'm going to get some additive and take a look into the carb. Right now I'm running a total timing of 38. I also am running a vacuum advance with my 360 bored .020 heads shaved with oversized valves with a .238 cam. i did find a fuel leak around my sending unit seal last night that i plan on fixing tomorrow, could that be contributing to the problem? thanks again for all you all's input.

 

[Chryco Psycho]

I would disconnect the vacuum advance bring up the total timing to 36* approx , this will give you a lot more initial timing & more response at low RPM .
Make sure there is no play in the accelerator arm / linkage & adjust if nessisary there should be a shot of fuel immediatly as the throttle shaft is moved .

 

[AUSTA]

flat spot

thanks for the comments, yes the flat spot is from an idle. I'm going to get some additive and take a look into the carb. Right now I'm running a total timing of 38. I also am running a vacuum advance with my 360 bored .020 heads shaved with oversized valves with a .238 cam. i did find a fuel leak around my sending unit seal last night that i plan on fixing tomorrow, could that be contributing to the problem? thanks again for all you all's input.

I had the same problem with a new street avenger 670 on my 340 ended up going with a black diamond qfs 780 run perfect from day one had to jet down at bit on the primaries.
see comments on video

 

[Racer57]

DetMatt1, I'm currently using an Eldebrock that I purchased last year. Please tell me what page the owners manual that comes with them says not for use with ethanol ? I'm unable to find it anywhere.


I have used ethanol in every vehicle I have ever owned for the over 30 years that its been in our fuel supply. I have never had issues due to its use. Currently its in a 1976 C70 2ton worktruck with 360, 1979 CJ7 Jeep with 304 and my '70 Cuda with 383.

 

[moparleo]

Here you go Mr.Racer 57.
http://www.edelbrock.com/automotive...1000/Performer_Thunder_Carburetors_130815.pdf

Second page, at the bottom.

 

[Iceman247]

does anyone know if the flip top gas caps are vented or not. i have a locking cap now and no canister and when i opened the cap today after a test run it sucked in alot of air and i actually heard the gas tank pop (yeah not) I assume because of no ventilation. could be part of my issue as well.

 

[Iceman247]

i will definitely try unhooking the advance and setting the total timing thanks.

 

[moparleo]

The flip-top is a cover only. The cap is under it. The cap should be non-vented.

 

[DetMatt1]

I run 1 ounce per 5 gallons of gas of good quality 2 cycle oil with TCW-3, it's not terribly complicated.

 

[Racer57]

here you go mr.racer 57.
http://www.edelbrock.com/automotive...1000/performer_thunder_carburetors_130815.pdf

second page, at the bottom.

Edelbrock carburetors are not calibrated for or compatible with alcohol race fuel or e85
pump fuel. Use of alcohol or e85 in your edelbrock carburetor will damage your carburetor and void
all manufacture’s warranties. These fuels can also damage other fuel system components, unless
specifically designed for use with alcohol or e85 fuels.

Their not calibrated for Diesel either !!! ROFLMAO !!