Bad idle, fuel pressure

[Kai23]

Moin moin,

I have a 84 CJ7 with the AMC 258 i6 / 4.2l with Weber 32/36 carb and HEI Ih´gnition

It has a pretty low idle, around 400 rpm...
And i don´t get it higher.

I read that a fuel pressure regulator is recommended, so i installed one.

Now i see the fuel pressure does weird things, with or without regulator...

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

I have tested a new fuel pump, no change...

What do you think could be the cause for this?

Thanks,
Kai

 

[Lumpy Grits]

A fuel pressure regulator will not raise your idle speed.
Where's your idle adjustment screw?
Confirm that your fuel filter's return line is connected to the outside fitting and the center fitting is connected directly to the carb.
PLEASE-fill out your vehicle info.
LG

 

[Kai23]

Fuel filter is mounted correctly.
Center fitting to the regulator and carb, outside fitting to the return line,
positioned at the top.

I thought maybe the low pressure could be the cause for the bad idle?

The idle mixture screw is 2 1/2 turns out, the idle speed screw is 1 1/2 turns in.

Is the vehicle information ok this way? Did i forget anything

 

[Lumpy Grits]

Turn the idle speed screw in till the idle speeds up.
Get a vacuum gauge and use it to set the correct idle mix.
LG

 

[Kai23]

The vacuum gauge was a good hint.
The idle speed screw was way too far in.
Set it to zero vacuum at "S" port.

I installed a bigger idle jet in the secondary (65 instead of 60),
now the idle is fine about 750 rpm when hot.
Idle mixture screw 2 turns out, idle speed screw half turn in after touching.

Manifold vacuum is around 15-17"

Onlybad thing is it gets hot (100°C) when i drive longer than a minute with full opened throttle...

PS: The strange fuel pressure was caused by a bad fuel pump, at the end it sprayed gas in the engine bay...

 

[Lumpy Grits]

That Jeep was factory built with a 195* t'stat. They are not all the way open till about 210-215*(degress-NOT 'C').
You may need to check the radiator for blockage.
LG

 

[Torxhead]

A 750 rpm is a bit fast especially when you want to drive slow. Old Jeeps aquire a lot of in the cooling system so maintaining it is a good thing. You might want to pull a spark plug to check for fuel burn since you do have an aftermarket carb. With a fuel regulator, you should confirm the pressure with a gauge, I believe Webers like around 3.5 psi with the AMC 258 i6 / 4.2l . Verify your ignition timing for better control of that idle.

 

[Kai23]

What do you recommend as idling speed?
I have the 2.73 axles, so driving slow is a challenge...


Rebuilding the cooling system (hoses etc.) is the next step, they are very old ans one has already a taped leak...

Here the video of the vacuum test, looks good for me:

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[Lumpy Grits]

Axle ratio and idle speed are 2 different 'worlds'. Set idle to factory specs. About 650-700 rpm.
LG

 

[Torxhead]

Your axle gear ratio, Transmission , and tire size, is not an ideal combination. It makes a lot of work for the clutch also.