Hi, I´m helping a friend fix an issue with his bird, it´s a 92 305 TBI.

His car has a slight to moderate stumble/bog from off idle to about 2000 rpms.

Here´s a list of things which have been checked and are fine:

Cap and Rotor new, no change.
New AC Delco Spark plugs
New Spark Plug Wires
TPS voltage checked and ok
MAP working ok, tested on other cars
Good known distributor tested and no change
Timing set at 0
IAC Cleaned and working fine from good known vehicle
TBI assemble rebuilt
Cleaned and flowed injectors
New fuel pump tested on Camaro.

After all this, I asked him if he had checked his valvetrain and he said someone "adjusted" his valves, we took off the valve covers and some of the rocker arms had a little wiggle and others were extremely tight, He backed the nuts 1/2 a turn on all rockers and some became loose and others remained extremely tight.

So, he went ahead and tried to adjust them again following his Hayne´s manual procedure, he adjusted them until no movement could be found on the rocker arms, I told him some movement was ok but he would not listen, now, Im no expert, in fact its been years since I adjusted the valves on my 80 Trans Am so...

Anyway, can someone point me in the right direction so I can help him, I did some searches and some say the pushrod has to be rotated, others say it MUST NOT rotate, so we are lost.

Is the bog, stumble off idle but fine at full throttle a sign of valves too thight? How should we adjust them, is it better a little loose than a little tight?

 

Proper adjustment is with the lifter on the base circle of the camshaft. You adjust the rocker nut until it just starts to make contact with the pushrod. This is zero lash. With a hydraulic lifter, you then tighten the rocker nut an additional 1/2 to 3/4 turn. This puts preload in the lifter.

If you let it sit briefly, the rocker will feel loose again as the lifter bleeds down. This is normal. No NOT tighten the rocker any more.

There are a couple of ways to adjust the rockers. You can manually turn the engine over and do each cylinder one at a time through the firing order. You can turn the engine over multiple times and do each cylinder down one head and then the other.

A lot of people like doing the engine running way to adjust valves. It just gets a little messy with oil spray. Loosen the rockers off one at a time with the engine running until they just start to clatter. Tighten up until the clatter stops then go 1/2 to 3/4 more turns and move on to the next rocker.

I use the TDC marks on the balancer mainly because I have solid rollers and need to set lash. When #1 is at TDC, half the valves can be adjusted. Roll the engine over and #6 will be at TDC then the other half of the valves can be adjusted. You just need to know which valves are off the cam lobe to be adjusted.

Why is timing set to zero?

 

Thanks, that helps a lot!.

The base timing is set at 0 degrees as that´s how is set from the factory, the engine is TBI so the ECM takes control of timing advance.

Tomorrow I´ll try to set the valves for him and see how it goes.

 

Thanks a lot AlkyIROC, the valves were properly adjusted and the bog is gone.

 

They generally run best between 4° and 8° advance.