Engine no wanna run :(

[LTZ C20]

Hey all. So here's my problemo, my truck doesn't wanna stay running. I have a new engine that I built and now a new transmission. A lot of you, like Capt, Bake, Rich W and some others know I have had some issues with the engine.

So know I got everything all hooked back up again. She is just about ready to drive around, just minus a exhaust pipes. Open header at the moment. When I try to start it, it either starts right up or struggles and then starts. Then it will either cough and sputter and die OR I can give it a little gas, it will pick up and run and as soon as I let off the pedal, chokes and dies.

This morning, when it was cold, I actives the choke, started it and she ran. She ran good for about 10 min at 2 grand. When at op temp, I bumped the choke to the second stage and it ran there for about 5 min, then gave it a little gas and then eased of the pedal and it went to idle and idled no problem. After that I could shut it off, start it again, run fine. Let it sit for 5 min same thing, ran fine. I left it sit for 10-15 min, it doesn't wanna run, just struggles all round.

I have taped on the screw heads for the valves in the bowls of the carb to make sure they aren't sticking. I adjust the mixture in and out 1/4 to 1/2 turn both in and out with no change, still struggles. When it was running good and the choke was off I crept the idle down to 500 or so and it idled for prob 10 min easily.

It's like it's lethargic lol. Unless it's at 3,000 rpm it don't wanna stay running. It's a Holley 600 cfm electric choke, model number 80457S. While it sat for 6 months putting the transmission in, I never adjusted anything.

I need to make this start and run every time cuz  as soon as exhaust is done and it's registered it becomes my DD again and my brother who just got his license will be Getting the Tahoe I've been doping around in for half a year. I miss the truck and I need to be able to drive it around the block to make sure the new trans is working. I haven't even been able to pull out of my driveway cuz the motor is being a poop.

[rich weyand]

What's your base timing set at?  Have you checked to see that the centrifugal advance is coming in?  How much centrifugal advance comes in when it's all in?  Are you running your vacuum advance on timed vacuum or manifold vacuum?  How much vacuum advance comes in?  Are you sure the choke is closing to the right setting?  Should be a gap between the choke plate and the bore even when the choke is all the way in, and usually, that is adjustable -- not sure about the Holley.

[LTZ C20]

Base timing is at 12-14 I believe. I have not checked the centri advance. Not sure how much comes in either. It's a brand new GM performance HEI compete distributor that went in when I built the motor. I read that vacuum advance article on here that a member posted awhile ago. It's hooked to mani vacuum. I set the choke cap to be right in the middle. I believe there was 9 or 11 marking on the cap and I set it to the middle so it wasn't too soon or too far. At choke full on there is a small gap still between the plate and bore yes.

When I was driving it before the trans went out it ran pretty darn good. Wasn't perfect but I know it has to be fine tuned for max performance and efficiency. Orient get that done before the trans quit.

[LTZ C20]

Correction on last sentence. "DIDN'T get that done before the trans quit."

[rich weyand]

Here's the curves on the distributor I think you have.
http://paceperformance.com/i-6251715-93440806-gm-performance-hei-distributor.html

Compared to the stock distributor, the centrifugal advance comes in late (mechanical advance should be all in by 3000 rpm).  Also, that's a ton of vacuum advance, 20* where I think stock is more like 8*, and that 12-238-2 cam pulls a lot of vacuum, which means it's going to come in early.

Do you still have your old distributor around?  Might be interesting to swap in a stock distributor and see what you get.

Oh, and you did check to see that the distributor is still where you set it, right?  That it didn't wander because you were too light on the clamp?

Another test would be to retard the base timing to compensate for that huge vacuum advance and see what you get.  A further test would be to connect it to ported vacuum (per the mfr recommendation for this distributor) to see how it idles with that huge vacuum advance cut off.  (BTW, I'm the guy who posted that article about ported vs. manifold vacuum, but I still think it would be interesting to see how it idles without that big vacuum advance in.)

This article is interesting.  Read forward from this point:
http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor#Ignition_advance

[LTZ C20]

Yea that looks about right. I got it from work. (Work at Chevy Dealership)

I don't know where the old distributor is. I don't know if I have it either. Might have given it to a friend, might be in the garage somewhere. But it's old, crappy, doesn't work well and it's disgusting dirty and is not getting near my new engine lol.

The vac advance use to be at ported and I moved it to mani after I read that article. Is it possible that's my problem? I might be sucking it to far advanced. Forgot to mention at high rpm with open header I'm hearing a pop every once in a while. Not sure if that's normal with open header or timing to far??? It sounds kinda like if u got to cylinders swapped on the distributor and they are firing out of order but no where near as loud and scary. Maybe I should put it back to ported vac? Should I drop my timing down??? This thing would pull hard if I jumped on it when it was running beige trans crap out. I would love to see how she runs fine tuned and with this new 700.

[rich weyand]

You could try ported vacuum, then you could try backing the timing down to maybe 4-6 degrees base timing.  That at least would tell you if timing is the problem.

A lot of "performance" products are just that: if you are going to circle-track race the vehicle, or do drags or something, then it's the part to have, but they are not really made for street use.

You know that our engines are very similar in the bottom half of the rpm range, until those high-compression, oversize valve heads you have kick in with that cam's longer duration.  I have the same torque peak at the same rpm.  I run the stock distributor, though with Accel high-voltage coil, cap, and rotor.  But I have the stock advance curves both mechanical and vacuum, and it starts and runs great.

So try ported vacuum and see how it idles.  Then try backing off the timing to about 4* BTDC and see how it runs.  If things clean up a lot, then you know that's the problem.  You will need to put a stock distributor in it to really tune it for best street performance: if the advance curves on that distributor are the problem, you will never get it to the best street performance until you change it out or rebuild the advance curves.

[LTZ C20]

Ok I will try that. Not sure how I'm gonna get the timing adjusted if it won't idle. Lol gotta try ported vac first. Could that cause poor transition throttle too? A couple times when I tried to rev it to get it to run it would hesitate for a second then catch and rev up.

[rich weyand]

Usually poor off-idle transition, if it's timing related, is from running on ported vacuum, but you have so much vac advance in that curve, you're in uncharted territory for me.  14*+22*+20* is 56* of total advance, which is too high.  That's why I think backing off base timing 10* is a good idea. 

To get it to idle, you could just loosen the disti and twist it CW a 1/4", and work from there.

[LTZ C20]

Ok. So I'm still kind of confused on how to tell which advance is working when. When is mech advance activated, when is centri activated and when is vac activated?

Also if I turn the disti Clockwise, isn't that advancing? Or am I backwards. I can never remember which way is which. I should, I've had to do it enough freakin times.... I struggle with the finer points of tuning and such. I'm no pro yet haha.

[rich weyand]

Mechanical advance and centrifugal advance are the same thing.  If you have the vacuum to the distributor disconnected, at idle what you see is "base timing".  Rev the engine up to 3000 RPM, and on most distributors the mechanical (centrifugal) advance will be "all in", and you will see what is often called "total timing", which is base timing plus mechanical advance.  Reconnect the vacuum advance to a manifold vacuum port, and what you will see at idle, when the vacuum is high, is base timing plus vacuum advance.  At cruise, at highway speeds, you will actually get base timing plus mechanical advance plus vacuum advance all in at once.  This number should not be higher than 50, some say 52.  Right now you are at about 56.

Note that when starting, the engine is not yet pulling any vacuum, and you are starting the engine on base timing.  As soon as it starts, the vacuum advance pulls in.  With that base timing and that much vacuum advance, you can't keep it running.  If you back off the base timing 10*, that will compensate for your vacuum advance being 20* instead of 10*.  So if timing is the problem, backing off to 4* BTDC for your base timing should make it idle really nice.

The rotating pole piece on the distributor shaft moves clockwise, that means if you rotate the distributor body clockwise, the rotating pole piece will line up with the stationary pole piece on the distributor body later in its rotation, giving a later spark, i.e. retard.

[LTZ C20]

Ahh ha! I see. So I first tried plugging both vac sources as run on base time, worked ok for about 1 min. Then put it to port vac, it didn't like that. So I went to adjust the disti and found the bolt was LOOSE! So I tightened it just to the point I could barely turn it with a small amout of force. Rotated it CW with no change. 1/4 inch retard and advance with no change. Went about 1/2 inch retard and it started to struggle so I went back to the middle then crept slowly CCW and it started to pick up and run better. I then tightened the disti clamp and put the vac advance back to ported vac, it was disco'd and the port vac was plugged while adjusting disti. I then revved it a few times and it's running good it seems. Idle was a little idle, small tweak, in park idle is about 550 or so and in gear idle is about 450. I thought that was slow but sat in gear for while, at 450 and it never struggled or popped or wanted to die or acted like it was starving for fuel. It just say there and idled at 450. So I shut it off. Fired right back up and ran. Then I closed my hood and slowly crept down my driveway, onto the street, went about 20 ft, turned around and came back into driveway. NO PROBLEM RUNNING OR MOVING WITH JUST OFF IDLE ACCEL!!!!

Choke seems to be working good. I don't own a timing light so I will have to borrow one and recheck but since I went to 1/2 inch or so CCW. Be running good. Now it's been sitting while I'm writing this. Gonna let it sit for prob 15-20 min total, then start her and see how she does.

My concern now is, yea I must be close, gotta check it with a light to be sure. But above 2500 rpm I think, maybe it's between 2 and 3 grand, when I hold it there, I'm stilling hearing that popping noise. Like I said when to plug wires are crossed on the disti cap. Could my CCW rotation be just a little to far causing popping from the exhuast? Is that normal for open header?

[rich weyand]

OK, so loose distributor, the rotating shaft dragged it way retarded.

Spec is 550 RPM idle in gear.  Usually about 700 in Park.

Not sure on the popping.  Quick google search says it's probably the headers.
https://www.google.com/?gws_rd=ssl#q=popping+open+headers

[LTZ C20]

Yea I figured. I know spec is 550, but at 550 in park and at 450 in gear it sounds good, runs good. 700 sounds like it's idling to high. Maybe it's the header over stating it because it's so loud?? Not sure. I just drive up to the stop sign and it really seams to like 450. No problems idling there.

I hope that's all it is. Won't know till get pipes and muffs on it.

[LTZ C20]

Any ideas how to take the slack out if the throttle cable? Seems a bit stretched in it's old age and isn't going quiet all the way to wide open.