Having problems getting a consistent idle rpm.

[BangkokDean]

I have an Edelbrock 750 that has been a good carb for 3 years. But lately I have been having problems that first were a surging feeling when driving at RPMs 1000 to 2000.
See this thread....

http://vettemod.com/forum/showthread.php?t=7750&highlight=idle

I removed the carb and cleaned the all the small holes out, thinking that when the car sat for 4 months during the rainy season the gas had gummed up. This did help but now I am having problems getting it to idle. Using the idle screws I get a nice idle and no hesitation just off idle but after a few minutes the RPMs jump around and finally drop 100 RPMs. I then readjust and the same thing happens. Also when driving in low RPMs, there is a slight missing feeling.
I am thinking that there is a vacuum leak, but I have tried blocking all the vacuum hoses off the intake and carb, no difference.
Any ideas folks?

 

[SmokinBBC]

Did you check for vac leaks around the base of the carb and intake mani?


Could be that your fuel pump is clogged up as well. It sstarts out idling ok and getting enough fuel, but maybe not getting enough when cruising and coming back down to idle? how is it when you put your foot to the floor?

Did you ever have problems with the gas over there disintigrating the rubber parts on the needle or accel pump?


Does the timing mark jump or float at idle? Maybe sticking weights or corrosion under the cap? maybe the mech advance not returning to rest properly when coming down to idle?

 

[DeeVeeEight]

Remove the air cleaner and with the engine running cover the top of the carburetor with a rag. If the carb. is good it will stall, if the base has vacuum leaks the engine will still run (poorly). I don't know if it applies to the Eddies but the Rochester 4 bbl throttle shafts can get so sloppy that they allow vacuum leaks, enough that the above test applies.

Another idea - throw a bottle of Techron fuel system cleaner in the gas tank.

 

[BangkokDean]

I have now replaced the base gaskets and it is better but still a little jerky when acceleration off idle, If I very slowly give it gas off idle it is a little smoother. If I give it loads of pedal its good.

I am now thinking the carburetor is the problem, no vacuum leaks plenty of fuel but still not fun to drive.:crutches:

 

[big2bird]

I have now replaced the base gaskets and it is better but still a little jerky when acceleration off idle, If I very slowly give it gas off idle it is a little smoother. If I give it loads of pedal its good.

I am now thinking the carburetor is the problem, no vacuum leaks plenty of fuel but still not fun to drive.:crutches:

I bet its more of that famous Edelbrock "green sludge."

 

[BangkokDean]

I have now replaced the base gaskets and it is better but still a little jerky when acceleration off idle, If I very slowly give it gas off idle it is a little smoother. If I give it loads of pedal its good.

I am now thinking the carburetor is the problem, no vacuum leaks plenty of fuel but still not fun to drive.:crutches:

I bet its more of that famous Edelbrock "green sludge."

OK I give.......WTF is green sludge???

 

[big2bird]

The shiney silver looking carbs get a green oxide type sludge inside when exposed to moisture.

 

[BangkokDean]

I just took the carburetor apart and soaked it for 24 hours in lacquer thinner, blew out all holes and installed new gaskets and a new accelerator pump. New base gaskets. but it still wont hold a steady idle when hot. Giving it gas it seams fine but I have not driven the car yet but will try tomorrow.
the front idle screws I have turned out two full turns but there is little to no isle changes when turning it out more or in more, unless I turn completely in and then it wants to stall.

BTW the intake is a spread bore with a separation on either side but the gadgets are open or no separation and carb is A square bore. Not sure this makes a differences?

I'm beginning to think the Edelbrock carb is the problem. I wonder if this will be a better carb for me?

http://www.summitracing.com/parts/SUM-210216/

 

[mrvette]

I just took the carburetor apart and soaked it for 24 hours in lacquer thinner, blew out all holes and installed new gaskets and a new accelerator pump. New base gaskets. but it still wont hold a steady idle when hot. Giving it gas it seams fine but I have not driven the car yet but will try tomorrow.
the front idle screws I have turned out two full turns but there is little to no isle changes when turning it out more or in more, unless I turn completely in and then it wants to stall.

BTW the intake is a spread bore with a separation on either side but the gadgets are open or no separation and carb is A square bore. Not sure this makes a differences?

I'm beginning to think the Edelbrock carb is the problem. I wonder if this will be a better carb for me?

http://www.summitracing.com/parts/SUM-210216/

try taking the carb off the intake, and look at the gasket really good, both on the intake and on the carb, keep same position of gasket sides as you compare the footprint/indentations for air leaks, if you can't spot it that way, try spraying some carb cleaner around the base with engine idling...make that just a little spray, not a lot otherwise the fumes maybe affect engine and you think you found something when it's just too much carb cleaner, giving a false positive....

:crutches::bonkers:

 

[BangkokDean]

I just took the carburetor apart and soaked it for 24 hours in lacquer thinner, blew out all holes and installed new gaskets and a new accelerator pump. New base gaskets. but it still wont hold a steady idle when hot. Giving it gas it seams fine but I have not driven the car yet but will try tomorrow.
the front idle screws I have turned out two full turns but there is little to no isle changes when turning it out more or in more, unless I turn completely in and then it wants to stall.

BTW the intake is a spread bore with a separation on either side but the gadgets are open or no separation and carb is A square bore. Not sure this makes a differences?

I'm beginning to think the Edelbrock carb is the problem. I wonder if this will be a better carb for me?

http://www.summitracing.com/parts/SUM-210216/

try taking the carb off the intake, and look at the gasket really good, both on the intake and on the carb, keep same position of gasket sides as you compare the footprint/indentations for air leaks, if you can't spot it that way, try spraying some carb cleaner around the base with engine idling...make that just a little spray, not a lot otherwise the fumes maybe affect engine and you think you found something when it's just too much carb cleaner, giving a false positive....

:crutches::bonkers:

Gaskets are new and good. Carb cleaner is not available here. I still am thinking about getting a spreed bore carb to fit the intake better. Although the present carb had been good before.:suicide:

 

[mrvette]

I just took the carburetor apart and soaked it for 24 hours in lacquer thinner, blew out all holes and installed new gaskets and a new accelerator pump. New base gaskets. but it still wont hold a steady idle when hot. Giving it gas it seams fine but I have not driven the car yet but will try tomorrow.
the front idle screws I have turned out two full turns but there is little to no isle changes when turning it out more or in more, unless I turn completely in and then it wants to stall.

BTW the intake is a spread bore with a separation on either side but the gadgets are open or no separation and carb is A square bore. Not sure this makes a differences?

I'm beginning to think the Edelbrock carb is the problem. I wonder if this will be a better carb for me?

http://www.summitracing.com/parts/SUM-210216/

try taking the carb off the intake, and look at the gasket really good, both on the intake and on the carb, keep same position of gasket sides as you compare the footprint/indentations for air leaks, if you can't spot it that way, try spraying some carb cleaner around the base with engine idling...make that just a little spray, not a lot otherwise the fumes maybe affect engine and you think you found something when it's just too much carb cleaner, giving a false positive....

:crutches::bonkers:

Gaskets are new and good. Carb cleaner is not available here. I still am thinking about getting a spreed bore carb to fit the intake better. Although the present carb had been good before.:suicide:

I was trying to say take a good look at the PATTERN of the impressions on the gasket, from the intake and the carb side and see how those line up that there should be no air leaks....look closely....

 

[CLASS OF 69]

idle problems

I have an Edelbrock 750 that has been a good carb for 3 years. But lately I have been having problems that first were a surging feeling when driving at RPMs 1000 to 2000.
See this thread....

http://vettemod.com/forum/showthread.php?t=7750&highlight=idle

I removed the carb and cleaned the all the small holes out, thinking that when the car sat for 4 months during the rainy season the gas had gummed up. This did help but now I am having problems getting it to idle. Using the idle screws I get a nice idle and no hesitation just off idle but after a few minutes the RPMs jump around and finally drop 100 RPMs. I then readjust and the same thing happens. Also when driving in low RPMs, there is a slight missing feeling.
I am thinking that there is a vacuum leak, but I have tried blocking all the vacuum hoses off the intake and carb, no difference.
Any ideas folks?

try disconnecting the vacuum advance. had a problem in the vacuum advance on a friends car 2 weeks ago.

 

[MYBAD79]

if you can't get any carb cleaner, you can detect vacuum leaks with shaving foam..... engine obviously has to be cold and you need a helper to start the engine while you look... easy cleanup too..... :smash:

 

[BangkokDean]

if you can't get any carb cleaner, you can detect vacuum leaks with shaving foam..... engine obviously has to be cold and you need a helper to start the engine while you look... easy cleanup too..... :smash:

I have a stumble not a stubble....JK, so what do I look for using shaving cream?

 

[BangkokDean]

try disconnecting the vacuum advance. had a problem in the vacuum advance on a friends car 2 weeks ago.

Was the vacuum advance causing the idle to fluctuate after warm up?

 

[BangkokDean]

I just took the carburetor apart and soaked it for 24 hours in lacquer thinner, blew out all holes and installed new gaskets and a new accelerator pump. New base gaskets. but it still wont hold a steady idle when hot. Giving it gas it seams fine but I have not driven the car yet but will try tomorrow.
the front idle screws I have turned out two full turns but there is little to no isle changes when turning it out more or in more, unless I turn completely in and then it wants to stall.

BTW the intake is a spread bore with a separation on either side but the gadgets are open or no separation and carb is A square bore. Not sure this makes a differences?

I'm beginning to think the Edelbrock carb is the problem. I wonder if this will be a better carb for me?

http://www.summitracing.com/parts/SUM-210216/

try taking the carb off the intake, and look at the gasket really good, both on the intake and on the carb, keep same position of gasket sides as you compare the footprint/indentations for air leaks, if you can't spot it that way, try spraying some carb cleaner around the base with engine idling...make that just a little spray, not a lot otherwise the fumes maybe affect engine and you think you found something when it's just too much carb cleaner, giving a false positive....

:crutches::bonkers:

Gaskets are new and good. Carb cleaner is not available here. I still am thinking about getting a spreed bore carb to fit the intake better. Although the present carb had been good before.:suicide:

I was trying to say take a good look at the PATTERN of the impressions on the gasket, from the intake and the carb side and see how those line up that there should be no air leaks....look closely....

After thinking about my Idle problem I have been thinking that the problem might be heat related. The carb has an aluminum heat shield between the intake and carb with gaskets sandwiched one both sides but when hot and the car is left sitting for 5 minutes or more it is difficult getting to start. The fuel is boiling out. I will check today to see if there is room under the hood for an insulation spacer to reduce the heat from the intake manifold transferring to the carb.

 

[BangkokDean]

Well after soaking the carburetor body in Lacquer thinner for 24 hours and blowing our all the small holes then installing a new gasket kit and accelerator pump the motor is running much better. It still has the fluctuation idle that I think is heat related. I have bought a 1/2 inch spacer as there is room under the hood for it but wont have it till April in a hand carry from Texas.

So I am getting there....

 

[big2bird]

Well after soaking the carburetor body in Lacquer thinner for 24 hours and blowing our all the small holes then installing a new gasket kit and accelerator pump the motor is running much better. It still has the fluctuation idle that I think is heat related. I have bought a 1/2 inch spacer as there is room under the hood for it but wont have it till April in a hand carry from Texas.

So I am getting there....

Get any green crap outta there?

 

[BangkokDean]

Well after soaking the carburetor body in Lacquer thinner for 24 hours and blowing our all the small holes then installing a new gasket kit and accelerator pump the motor is running much better. It still has the fluctuation idle that I think is heat related. I have bought a 1/2 inch spacer as there is room under the hood for it but wont have it till April in a hand carry from Texas.

So I am getting there....

Get any green crap outta there?

Yup, the green giant shit is out..............for now.