Initial timing 26 degrees advance?

[drh]

So I finally got a working timing light and checked initial timing at idle - something I've been wanting to do for a while now - and discovered it's at 26 degrees around 800 rpm. Engine is 310 carb. At first I thought I was doing something wrong so I double and triple checked and that indeed is what it is. I didn't check full advance at 3k rpm since it was late and I was already working in the dark.

The engine runs fines, idles smooth, and makes good power going off of my time with it which is about a year. The only time I've noticed any knocking is when I propped it too high and the engine would lug a bit sometimes when put in gear with no throttle. Any idea what could have caused this? Can timing wander over time or does this mean it was intentionally adjusted to cover up an underlying issue, or could the distributor be going bad? Also wondering if there is a way to set the timing without using the Delco timing tool to get into base mode. I didn't take off the connector so not sure how small the pins are and the possibility of getting a jumper wire in there.

If this makes any difference I checked the timing right after replacing the cap and rotor which did make the engine idle better.

Edited July 27, 2017 by drh

[MadMan]

I'm not sure what your distributor is doing, but if you have 26 initial, the starter would have a tough time just turning over the engine.

[Woodski]

@drh:  Reasonable timing advance guide for a SBC, 8-12 degrees BTDC at idle, full advance 32-34 deg BTDC at 3000+ RPM.  You can google the topic and get more info.  As noted, 26 deg BTDC at idle would make the starter work pretty hard.

[mcgreg]

Check yr owners manual for the  advance spec, rpm, and use of a special shunt plug. The delco hei distributor can not be timed correctly without the shunt in place.  Good luck!

[drh]

I made a jumper wire and 12v lead to serve as the shunt yesterday. When I check timing at idle without shunt in place it shows 24-26 degrees BTDC. When I plug the shunt to 12v it drops to around 16 degrees BTDC and the engine runs poorly. Per Indmar instructions, with shunt in I bumped idle up to 750-850 using idle speed screw and rotated the distributor to back advance down to 10 degrees BTDC which makes the engine run even worse. When I disconnected the 12v source the timing goes back up to 20 something degrees. I decided to play around with it and I have to back timing down to around 4 degrees BTDC (engine will barely run) with shunt plugged in in order to get 12-14 degrees BTDC after unplugging shunt. With the engine timed like this I have to open the butterflys so much to keep it idling I think I'm running on the transition circuit and rpms hunt and surge.

I am doing something wrong or looking for the wrong number at the wrong time? Should I just set it for 10 degrees with shunt plugged in and engine in "base time" mode and not worry the advance in regular run mode? Before I touched anything to do with the timing the engine would have a tendency to knock slightly when put in gear at idle speed. I thought it may have been overpropped but it did basically the same thing today with another prop - ACME 515. It runs strong once underway but I'd like to get the clunky low speed operation fixed. 

As a side note I replaced the PCV valve a couple days ago and the new one rattles at idle. I think this is one reason for the surging idle because if I pull the PCV from the valve cover and plug it with my finger, engine idle increases and steadies.

 

 

[williemon]

Most timing lights need a connection to spark plug one. Is that the case here? Is it on the right plug?

[drh]

Yes #1 cylinder. Front right

[mcgreg]

Hi Dhr, no 1 cylinder is on the left bank, closest to the passenger seat for a direct drive boat. Google it for the gm vortec. Also the indmar manual specs. 

Book sez set timing to 10 btdc with shunt in place. Thats the stated procedure.  If it is not running smooth then suspect other issues.

Fyi, mine runs smooth and timing very steady at 10 with shunt in place. When shunt is removed, timing marks become unsteady, apparently is characteristic of this delco electronic advance. Good luck! 

[drh]

@mcgreg: I have the light on #1 cylinder. I was (incorrectly) referring to the right front when looking from the front of the engine.

Mine does not run smoothly with shunt in place - yesterday I set timing to 10 degrees with shunt in place and it sounds like the engine is chugging and the rpms drop off. This results in about 20 degrees when I remove the shunt and the timing marks are steady and idle is smooth. Is is normal for timing to advance 10 degrees with shunt removed? 

I checked advance at 3k rpm and it shows 28 degrees. Engine seems to run well other than the fact that I've had to open the butterflys so much to enable it to start and idle at the correct RPM that I get high idle when slowing down after a run and dieseling after I shut it off (this is after reducing initial advance from 26 to 20 degrees) I think there's an underlying issue somewhere. I've checked for vacuum leaks but can't find any. I took apart the carb and cleaned earlier this spring and it looked good. I'm leaning towards replacing the coil now but it's really just a guess. Any suggestions?

[BoatFlyRide]

I'm guessing you are not looking at the right place when using the timing light. No way it would idle decent with 26 degrees of advance at idle.

[drh]

@BoatFlyRide I'm definitely looking at the correct place. I suppose the outer ring of the balancer could have slipped and now the timing marks are off. I have heard some rattling from the balancer/timing cover area twice before on cold starts. It sounds like slack in the chain hitting the inside of the cover or some type of light metal on metal rattle. This went away both times after a minute.

[mcgreg]

drh, based on what you said above, ie, 10btdc at 750 rpm shunt in place, and then 28 deg @ 3k rpm with shunt disconnected, I'd say you have it set dead on the spec and it is working properly.

fyi, is link to Indmar manuals, click on 2003 year for setting yr timing. But you already did it.

http://www.indmar.com/Service_Support/manuals.aspx

At 750 rpm, and no vac leaks, it should pull 19+ inches vacuum with a steady needle. I know you said there are no leaks, but the way you described it, sounds like a leak at idle/low rpms. if vac is low, try blocking off the pcv valve hose with thumb and any other manifold hoses while looking for chg in vac. Are the idle mixture screws properly set?

Good luck!

[drh]

@mcgreg I have the idle mixture screws at 2 turns out - this produces the highest idle although I don't have a vacuum gauge. I think there may be a vacuum leak somewhere I just haven't been able to find it.

Like I said above I noticed when I replaced the PCV valve at the same time as the cap and rotor, the new valve rattles at idle. If I pull it out of the valve cover I can see the mechanism moving inside like there's not enough vacuum to keep it fully closed. I put the old one back in and it idles higher and smoother. Not sure if the PCV is the cause or the symptom.

[Woodski]

@drh:  A spray fluid (aka:  Brakeclean / Carb Cleaner) should assist in finding a vacuum leak.  Sounds like the PCV valve is located in a high vacuum port?  Many marine engine configurations simply run an open line to the spark arrestor and don't use a PCV valve.  One item to check, distributor gear, simply see if the distributor rotor has any slack or play, that would also manifest as timing scatter not really a large discrepancy in what you are targeting.

[drh]

@WoodskiI did try the carb cleaner method and I thought I may have found one but I ran out so bought a new can and when I went back to it I couldn't find it again. Yes the PCV is located on a full manifold vacuum port. I do have the open line to the spark arrestor from the other valve cover. I'll check rotor play next time I'm at the boat. What is normal? Timing scatter seems to be small though.

[Woodski]

@drh:  a few degrees (not much), does not sound like an issue given timing scatter results.

Just a comment on timing settings, when 'adjusting' timing or just getting reasonably close (if you don't have the proper tool handy), my experience is you are pretty close when at idle you twist the distributor to where the engine purrs nicely and to hit the actual specification, you retard slightly.  Slightly advanced at idle, in my experience, tended to be a bit faster and smoother than on the spec.  Hope that helps.

Edited August 2, 2017 by Woodski

[mcgreg]

Drh, take that pcv valve back to store and try a different brand. That  behavior is not right, i think it is why it idles poorly. Get vac gage while yr there, they are pretty cheap.

Think you just found yr problem!