Weber 4bbl Carb Adjustment

[egldvrbags]

1995 4.3LX, Engine sn: 0F436164, Weber 4bbl Carb, Alpha 1 Gen 2, Thunderbolt IV

Trying to figure out the correct procedure to adjust the idle/mixture for my Webber 4bbl carb.

The service manual 5C-13 step 4 is to put it in forward gear, idle position. Step 6 says to adjust the idle speed to the specified idle RPM in the "tune up specifications chart in section 1-B."

In section 1-B, the specification for idle RPM is 650, in NEUTRAL. There isn't a specification for idle RPM in forward, idle.

Also, service bulletin 97-9 has a different procedure for adjusting the idle mixture.....ie, just in neutral.

Can someone guide me to the proper procedure? And, what should the idle be in neutral AND in forward, idle?

Thanks!

Bags

 

[John_S]

Re: Weber 4bbl Carb Adjustment

Some 4.3L experts will chime in, but in the meantime.... A T4 would indicate to me that the idle speed is done in gear. Obviously, in neutral the rpm will rise some. I did look at the SB, and they refer you back to the SM for final idle speed, because they are covering all webers, all engine sizes and both T4 and T5 ignitions.

 

[mpdive]

Re: Weber 4bbl Carb Adjustment

Are you adjusting idle speed or idle mixture? Your post says mixture....AFTER you adjust the idle mixture at a point that is close to 650 rpm's, put the boat in drive with no thottle and adjust to 650. Take the boat out of drive and see if your sitting somewhwere about 650-700. Make sure when it is in neutral, that the idle speed screw is in direct contact with the throttle body before determining actual idle speed. Check to make sure the engine does not diesel at shutoff.
Oh yea...then pat yourself on the back and have a cold one...

 

[egldvrbags]

Re: Weber 4bbl Carb Adjustment

Are you adjusting idle speed or idle mixture? Your post says mixture....AFTER you adjust the idle mixture at a point that is close to 650 rpm's, put the boat in drive with no thottle and adjust to 650. Take the boat out of drive and see if your sitting somewhwere about 650-700. Make sure when it is in neutral, that the idle speed screw is in direct contact with the throttle body before determining actual idle speed. Check to make sure the engine does not diesel at shutoff.
Oh yea...then pat yourself on the back and have a cold one...

I want to adjust both the idle and mixture.

The manual on p. 5C-13 has a procedure with everything done with it in the water, forward gear, idle. But, there appears to be a different procedure in SB 97-9.....if I'm reading it correctly??

Service Bulletin 97-9 for the Weber 4bbl carb:

Adjusting Idle Mixture Screw
The initial idle mixture screw setting is 1-1/4 to 1-1/2 turns out from seat. Setting the idle mixture
screws at 2-3 turns out from the seat will cause the engine to run too rich at lower RPM.
To adjust the idle mixture screw correctly, the throttle plates must be nearly closed. Please do the
following:
NOTE: Engines with Thunderbolt V ignition systems must have the ignition module put into ?base
timing? mode before turning key to start the engine. After adjustments, shut engine off. Remove
the module grounding wire, then restart the engine to take module out of ?base timing? mode.
1. Disconnect throttle cable.
2. Set idle speed (RPM) screw so engine idles at 550-600 RPM in neutral gear.
3. Adjust idle mixture screws.
4. Reset the idle speed screw until engine idles at its recommended RPM.
5. Adjust and connect throttle cable.


Does this mean at step #3 to then do the procedure in the manual, p. 5C-13 (ie, put in forward, idle, then adjust)? Or, just do it in neutral per the SB?

Thanks!

 

[mpdive]

Re: Weber 4bbl Carb Adjustment

Do all the adjustments in the water. Don't get overly confused with too many bulletins. Turn the adjustment screws in barely finger tight and back out one and a half turns. Make sure you are at base timing. Start the engine and let it warm up to op temp. In neutral. get the rpm's to about 650 as your baseline. With a vacuum gauge or tach, set the mixture by turning the screws in and begins to falter and then slowly back out looking for the highest vacuum or rpm. This will usually be no more than an additional turn and a half. DO NOT over rich the setting. Your only looking for the peak. Anything more is rich. Then proceed to set the idle speed in gear to spec. Put it back in nuetral. Take the accelerator cable off and set your base idle to spec. Reconnect the cable. IDLE SHOULD NOT CHANGE WHEN CABLE IS INSTALLED. If so, cable needs adjusting. Put back in gear and recheck rpm's. Pull jumper.