Carb Help Needed

[BlindSquirrel]

Hello, Guys and Gals,

I apologize in advance for sounding like an idiot, and not purchasing a "Holley Tuning" book yet, but stuff happens.

I have a 1967 Barracuda with a 360 and a Holley 750 that I have been driving on a daily basis. The fuel pump was just replaced, and now when the car warms up, the idle runs high - around 1600 to 1700 RPM's. The idle is fine when cold, and the problem just started after the fuel pump was replaced. Do you have any suggestions on the cause, and how to fix it?

Also, while I like the power that the cas has, the 6 MPG fuel economy is starting to put a hurting on my wallet. I'm not planning to race the car, so do you have any suggestions on a carburetor that would give me better fuel economy while not completely killing the performance?

Thanks for any help that you can provide.

BlindSquirrel

 

[mopar head]

Sounds like once it`s heated up, expansion maybe allowing an air leak, thus leaning it out/higher rpms? or fuel pump not delivering enough fuel? Check all hose/hardline connections. Spray carb cleaner around carb and base, also intake manifold. If you have pretty paint substitute with wd40. A rise or drop in rpm will indicate a vac leak, in that area. Could be time for a good carb rebuild. I assume you have a mechanical secondary carb? If so, you`ll have some serious tuneing to do. to get economy. For economy and not too shabby performance, a spreadbore intake, thermoquad, can get you 20+ MPG or a holley Vac secondary carb.

 

[jimmyray]

My Holley 750 DP got 8 mpg on the highway, and ran 12.26 best. My Thermoquad gets 14 mpg on the highway, and has run a best of 12.09. (same 408 through auto with 3.73's) I have heard many say that Holleys are bad for mpg, and i could not get it any better. But then I never learned how to tune it, either.

 

[BlindSquirrel]

Thanks to those who have responded. I tried checking for a vacuum leak, with no luck. I am including some photos of the carb set up - maybe someone can help me solve the immediate problem with the added information.

Thanks for any help you can provide.

BlindSquirrel

 

[70aarcuda]

have you adjusted the idle speed down ....

check all vacuum plugs also....check the pcv valve...

 

[JoeDust451]

I'm looking at the writting on that bowl, are you running 75 jets up front?

 

[BlindSquirrel]

JoeDust,

I have to claim ignorance. The Previous Owner could not tell me anything about the car other that the fact that it is a 360. I have been driving the car and working on it a little bit at a time, so I don't know anything about the carb or jetting. I would have to assume that you are correct on the jetting. Do you have any suggestions on that?

Thanks,

BlindSquirrel

 

[JoeDust451]

JoeDust,

I have to claim ignorance. The Previous Owner could not tell me anything about the car other that the fact that it is a 360. I have been driving the car and working on it a little bit at a time, so I don't know anything about the carb or jetting. I would have to assume that you are correct on the jetting. Do you have any suggestions on that?

Thanks,

BlindSquirrel

If its the 3310, they come with 72s up front, now on mine, i dropped down to 70s, but realized my engine feels more comfortable with the 72s, i just need to dial-in the idle curcuit. You may want to check that jetting & see, maybe drop it back down, it'll improve your mileage.

 

[1968FormulaS340]

I would start with the basics.

•Float levels.

•Idle screws (bottom them out then back out 1 1/4 turn. Some say 1 1/2 turns).

•Hit every air bleed with carb cleaner.


Those are the first 3 things I do if a Holley is acting up.


If those 3 things don't work……

•Pull the bowls

•Hit every hole with carb cleaner

•Replace the power valve (because you are in there, may as well)

•Pull the needle and seat out of the bowls and hit with carb cleaner.


By this point every Holley I have had is running smooth.


•You may also want to check (replace) the secondary diaphragm and make sure the check ball is in place.

•Get one of these http://www.holley.com/20-59.asp


I would also reset the stock jetting.


At 6 mpg you are getting 1/2 to 1/3 what you should be getting.