Ignition timing on 5.7L

[95yj]

Just got my new long block in the boat and got it started. Running the engine on muffs and set the timing by ear and engine sounded real good. Cracking the throttle sounded good. Put the timing light on and found out I was 12 deg btdc. Backed it down to 8 and it doesn't sound nearly as good. Cracking the throttle from an idle results in a pop through the carb before the engine revs. Engine is 90's version pre vortec with 2bbl and Thunderbolt IV ignition.

Anybody have any insight?

 

[bruceb58]

Re: Ignition timing on 5.7L

What condition is your carb in? Same one as before the new long block?

What else did you replace when you changed out the engine...spark plugs, wires, filters, carb gasket...etc?

 

[Haut Medoc]

Re: Ignition timing on 5.7L

Bad fuel ? (Water in fuel)?
Carb?
Lean mixture?....
Positive that wires are correct?
I would hook up a separate fuel source & eliminate bad gas.....
Did you change the fuel filter?.....

 

[95yj]

Re: Ignition timing on 5.7L

Same carb and intake as before but with a new carb gasket. Carb was running fine before. Old distributor, plugs and wires. Plugs stil look new, old motor ran fine on same ignition system.

Did not change the fuel filter as I didn't want to trash a new filter if the gas was bad. But I do have a new one lying around. Gas is 5 months old, 1/2 of a 55 gal tank. Put Stabil in it 4 months ago. Plus we don't have alcohol in our gas here to the best of my knowledge.

At 12 btdc, engine idles real smooth and continues running good at higher rpms. (Tested to about 2000) I realize there's no load on the motor, but I wouldn't think it would run smooth at all if the gas was bad.

 

[bruceb58]

Re: Ignition timing on 5.7L

haut medoc mentioned something that you really should check...Do you have the spark plug wires in the correct firing order?

 

[95yj]

Re: Ignition timing on 5.7L

Yes, the plug wires are in the correct order. Like I said, it idles really smooth at 12 deg btdc. It wouldn't run smooth if the sequence was off.

 

[John_S]

Re: Ignition timing on 5.7L

Did you redo the mixture and idle speed adjustment? I believe both need to be done prior to the timing being set. I don't have the manual in front of me, but believe the T4 requires the boat to be in gear and in the water for idle adj.

Other possibilities include a changed accelerator pump hole setting or vacuum leak. A vacuum gauge could help diagnois.

Depending on your ignition module adv curve, you may have too much total advance at high rpms if you leave it a 12BTDC at idle.

 

[95yj]

Re: Ignition timing on 5.7L

Carb was untouched between engine swaps. Only thing done was to unbolt it from the intake to help with removal. New gasket installed when it was bolted back on.

Pulled fuel filter / separator. Gas in it looked and smelled good. Put new filter on.

 

[John_S]

Re: Ignition timing on 5.7L

New gaskets do not mean no vacuum leak. Besides the carb, you also replaced the intake gasket. It can be fairly easy to miss removing the old gasket completely.

If you haven't disturbed the carb, the accel pump should still be in correct hole. I would not assume you don't have to touch the mixture or idle speed. I re-adjust mine every spring tune-up.

 

[95yj]

Re: Ignition timing on 5.7L

Mixture shouldn't need to be changed unless something else changes. I doubt there's a vacuum leak, but that's always a possibility. Intake manifold base was shiny clean when I was done with it and new motor had new heads, so there shouldn't be a manifold leak.

Idle speed setting is another story. Linkage on carb was slightly bent, so I straightened it out. I'll have to wait 'till I get the boat in the water to screw with that some more unless someone has any other ideas.

 

[bruceb58]

Re: Ignition timing on 5.7L

Yes, the plug wires are in the correct order. Like I said, it idles really smooth at 12 deg btdc. It wouldn't run smooth if the sequence was off.

Depending on which wires you cross, it will run very smooth with no load. I did this myself once and it took me days to figure out what I had done.

 

[John_S]

Re: Ignition timing on 5.7L

It is usually a re-iteritive process, adj mixture, adj idle rpm, until there are no changes. Check your manual, but most mixture adj are just turning in until it is too lean and engine stumbles, then turning it out till it stumbles (too rich). Then turning to the middle position between the two. You may find out that you can not get to the too rich condition, and may be another indication of a vac leak, or other problem. If it was me, I'd stop by the auto store and get a vacuum fitting for your intake and a vacuum gauge. Lots of info on the web can be found on interpreting the vacuum readings. It is something you can do now, and not wait to splash the boat.

 

[Silvertip]

Re: Ignition timing on 5.7L

Not an expert by any means but if this is electronic ignition, did you put the ignition in base timing mode? If not, you may have been closer to the correct timing the first time.

 

[180shabah]

Re: Ignition timing on 5.7L

Silver, this is electronic ignition, but only the Thunderbolt V needs to be put into base timing mode before setting initial timing.

 

[95yj]

Re: Ignition timing on 5.7L

That's correct. The V does all kinds of adjustments on the fly which is why it needs to be put into base timing mode. The IV doesn't have any of those options.

I'll run out and see if it's possible to buy a vacuum gauge. The fitting I should be able to get from a hardware store, the vacuum gauge is another story. It took me a whole day of searching just to find someone selling a timing light and then it cost me the equivalent of $125. Stuff like this is hard to get on an island.

 

[95yj]

Re: Ignition timing on 5.7L

Well, there's no place on the island that sells a vacuum gauge. Now I'm trying to find someone to borrow one from. In the mean time, I have a noise coming from the motor that sounds like an exhaust manifold leak without the ticking noise that accompanies it. I would think this would be a vacuum leak, but the problem is, it seems to be coming from inside the carb.

Splashed the boat and it ran fine, but the timing was still set to 10 btdc. Tried to get timing light on it to retard it, but too much sunlight and couldn't see anything. Didn't want to idle the boat any more before break in, so I ran it around the bay. Seemed to run pretty good but I think the timing is still too far advanced.

 

[John_S]

Re: Ignition timing on 5.7L

Sometimes you can detect carb and intake manifold leaks by spraying carb cleaner around the carb base and intake/head seam. If the engine speed changes it indicates a leak. It does not find all leaks. Vacuum gauge would still be the best bet and gives you better info on how the whole engine is running. The new engine might have some issue in the valve train. Sticking, misadjusted lifter, etc. New does not always mean, no problems. Do you have a compression tester?

You mentioned break-in and rpms. If the engine has new flat style hyd lifters/cam, then the initial runtime rpms need to be high. My poor memory says around 2.5-3K, but check the documentation that came with your engine.

 

[LuckyPenny]

Re: Ignition timing on 5.7L

All of the options stated are (would be) correct if it were not for one unasked question. You stated that the carb was untouched, that you changed out the manifolds and are using all the old parts off of YOUR OLD ENGINE.

This is great, and saved you a bucket of money. Now my questions. How old (hours) did your old engine have on it? Secondly, you said that you did not change any of the settings, why? why not?

When everything was running fine on the old engine that was because you tuned it to your old engine. Now that you have a new block, you now have higher, and more equal compression. Your cam is not worn thus your valves are opening more. the timing chain does not have any slack in it.
When you put it together did you mech set the timing? #1 valves closed and the timing mark on '0'? did you replace the rotor and cap on the dirtr? RESET the CARB to factory spec's, the list goes on.

a 350 is a 350 is a 350 as long as they all have the same conditions. Yours don't. You took all the usable parts from an old engine put them on a new one and can't figure out why it won't work. Go back to the basic. Set everything to factory spec's then take it from there.

good luck

 

[Bondo]

Re: Ignition timing on 5.7L

95vi Solved this Issue,.... Over Here.......

when I got back into the marina and looked over the motor, I noticed the harmonic balancer had a distinct wobble to it.

I think this Explains your Timing Issue........

It Sounds like the Balancer Slipped...................

 

[95yj]

Re: Ignition timing on 5.7L . . . Updated

Re: Ignition timing on 5.7L . . . Updated

Well, back to square one. New balancer finally arrived; no more wobble. Incidentally, the old one was only off by 1/8 inch side to side. Timing reads exactly the same. It has to be advanced to 12 or 14 degrees BTDC for the motor to run good, and then it runs great in the driveway.

Incidentally, the old motor wasn't that old. It had just been rebuilt 30 hours prior and had a new timing chain, new cap, wires, etc. so it wasn't an old sloppy motor. And yes, when I installed the distributor, I rotated the engine till both #1 valves were closed, aligned the TDC mark and installed the distributor pointed at #1.

Still haven't acquired a vacuum or compression gauge, I have each on the way. I'm going to set the idle and mixture with the boat on the water tomorrow and then see how it goes.