Poor idle on 5.7 GL

[stant1man]

I recently installed a new 5.7 GL into my boat and it was fitted with an edelbrock performer 1409 4bbl and EST ignition which I had never worked with previously.

I have been struggling to get her to idle properly, she runs very well at cruise and will swiftly achieve WOT of 4700rpm when I let her (still running in).

I have checked the timing and if i were being podantic I would say that it is currently 10.2 degrees BTDC

I have played with the idle screws but just can't seem to get it doing what I want.... I get the impression the timing is changing at idle... thats what it seems like though...

It will idle for a while then start to hunt.... very frustrating... my engine with knackered big ends ran better than this at idle....

 

[Don S]

Re: Poor idle on 5.7 GL

Hook up a vacuum gauge to the intake manifold and see what it tells you.

As far as timing moving around, yeah, that's what it does. Set it per specs using the specs for your OLD engine and call it good if the advance works.

Did you get the valves adjusted right and absolutely positive none of them are too tight.?

 

[stant1man]

Re: Poor idle on 5.7 GL

I am looking on ebay just now for a vac gauge... hopefully find one.

I followed the lash instructions to the letter Don.. I am considering poping the rockers and turning them out 1/4 turn each to be sure. I'm also going to run a compression test and see what I get... It's just a little frustrating.

 

[Don S]

Re: Poor idle on 5.7 GL

Just one quick hint on valve adjustment that kill most people.
When all the valves are loose, and you turn the rocker nuts down until the push rod stops moving. One time, one time only. They will get loose. You keep testing and tightening and you will have tight valves.

 

[stant1man]

Re: Poor idle on 5.7 GL

Am I right in saying that I should back the rocker bolts out until I feel play then back in just until the lash is gone, then 360 and only then move to the next? I did it using the distrubuter method.. when cylinder is firing on number 1 for example I can do inlet/exhaust then move to next on dist so on and on...

Vac gauge now ordered

 

[Don S]

Re: Poor idle on 5.7 GL

Have you considered using the method stated in the service manual? I have adjusted many using the method in the manual and never had problems...........

 

[stant1man]

Re: Poor idle on 5.7 GL

Have you considered using the method stated in the service manual? I have adjusted many using the method in the manual and never had problems...........

Yes I tried that previously and for some reason ended up with ticking :-(

I think it is a distinct possibility that the valves are indeed a little tight... would it do any harm to turn out 1/4?

 

[stant1man]

Re: Poor idle on 5.7 GL

Ok, vac gauge arrived and the manual says leaking valve as it was flickering between 15-17hg when idling below 1000rpm.

I thought I could identify this from a compression test and the results were as follows -

1- 170
2-170
3 - 168
4-165
5-168
6-172
7-172
8-171

Seem pretty normal to me :-S

 

[Don S]

Re: Poor idle on 5.7 GL

1. Adjust valves per specs.
2. Put distributor into base timing mode and verify timing.
3. Adjust idle mixture and speed to specs

 

[stant1man]

Re: Poor idle on 5.7 GL

1. Adjust valves per specs.
2. Put distributor into base timing mode and verify timing.
3. Adjust idle mixture and speed to specs

Done all this and idle is still suspect. For some reason I think that their may be a sticky valve guide. I'm going to mix some 2stroke oil with the fuel to get some lubrication about the valve guides... Hopefully this will clear it up