L20B Timing; Miss down low, Raped ape up high.

[JWJohnson]

Okay, so I have just done a complete gasket set and top end on the motor, I had a thread in the 720 section full of pics showing multiple corrosion holes in a cylinder head that I had on the motor when I bought the truck. I get everything back together (new head of course), I finally get the oil pump dizzy drive shaft toothed correctly at TDC, (in line with the mounting holes or '11:28' as some say) Long night that was. I got the truck up and running with a serious miss. It idles with miss, like the cylinders are cutting out, or firing retarded or advance I'm not quite sure. But if I keep it right on the money at 10* BTDC, no vacuum advance at idle, and drive it, it cuts out very hard and has a serious miss with very bad hesitation. Ones the RPM's pick up to around 2k-3k+, then it runs like a top. So I figure I'll advance the idle timing a hair, it gets better but not the best. So I advance it all the way, get it pinging, then pull it back a ways, pinged around 45* brought it back to like 30* and it ran, still a small miss, but acceleration was good, but when I shut it down, it started running in reverse. 

 

I have since gotten it dialed in to about 15* BTDC and it runs decently, but still has the hesitation a miss in the low RPM. So I am thinking I have a small vacuum leak somewhere, that when I open the throttle plate at a low RPM, I lose a good amount of the vacuum and that it isn't advancing the timing as it is supposed to, but once the RPM's pick up the vacuum increases, and the timing advances accordingly so that it runs pretty good. What are your thoughts, I deleted the EGR, I made a small plate and bolted it to the manifold, I am thinking that is the source of the leak, I will use a small amount of High temp Permatex and see if that helps seal it off any better. 

 

Sorry for the long rant but I am in need of some guidance. 

[racerx]

Did you spray carb cleaner around carb area and intake?

[izzo]

Also, PICS! lol

[KlassicMotion]

I notice a lot of people on here recommend using carb cleaner to check for vacuum leaks, which works, but if you use brake cleaner, it won't eat the paint off your engine or other painted parts around where your spraying.

 

Was the engine running before hand?  Was the timing set at 10* before hand?  Are you using the same carb? Are you using the same distributor?  If yes to those questions, then I would set the timing back to 10* and look for vacuum leaks. 

[metalmonkey47]

I notice a lot of people on here recommend using carb cleaner to check for vacuum leaks, which works, but if you use brake cleaner, it won't eat the paint off your engine or other painted parts around where your spraying.

 

I thought the same thing until it ate the paint off of my block. 

 

 

If anything, the non-chlorinated stuff is the one to use.

[JWJohnson]

Everything is the same new cap rotor plugs and wires too, coil tested good as well. As for the previous timing, I'm not 100% where it was at before. When I started to do the head gasket one thing led to another which led to replacing the entire top of the motor... So I didn't check timing before hand. I have never used any kind of cleaner to look for a vacuum leak. Just start it, spray it and look to see if I gets sucked up or the RPM's change? Does it sound like I am on the right track?

 

Also, PICS! lol

What would you like pics of? I have an Internet full of them. Lol

[Tristin]

I thought the same thing until it ate the paint off of my block. 

 

 

If anything, the non-chlorinated stuff is the one to use.

I use an unlit propane mini torch. No residue, no corrosion, and the engine will stumble when it finds the leak.

 

What would you like pics of? I have an Internet full of them. Lol

All of it... I want to see one Internets worth of photos please. We love photos here.

[JWJohnson]

So with the torch, unlit of course would this stumble sound more like the miss that is already there or would it be something noticeably different immediately?

 

 

Pretty this is the Internet in a nutshell, is this what you were looking for? Lol

[Tristin]

So with the torch, unlit of course would this stumble sound more like the miss that is already there or would it be something noticeably different immediately?

It would be very prominent like you were cutting out the entire air supply. Also very similar to heavy dieseling.

[racerx]

Everything is the same new cap rotor plugs and wires too, coil tested good as well. As for the previous timing, I'm not 100% where it was at before. When I started to do the head gasket one thing led to another which led to replacing the entire top of the motor... So I didn't check timing before hand. I have never used any kind of cleaner to look for a vacuum leak. Just start it, spray it and look to see if I gets sucked up or the RPM's change? Does it sound like I am on the right track?

 

 

What would you like pics of? I have an Internet full of them. Lol

Yes, it will suck it in and RPM will go up...Never had a any problem with carb cleaner eating up my paint.  You are spraying around carb area...

[JWJohnson]

I will giv it a shot tomorrow, I will try my torch first, I don't have any cleaner around the house. So in theory a vacuum leak would make sense to the contributing factor?

[racerx]

you can also use a vacuum gauge to find leak..

[JWJohnson]

Yeah I was thinking about the gauge, but I don't necessarily need it just yet, if I can't isolate the leak with the mentioned methods then I will probably go get one to be sure.

[datzenmike]

Take the top off the air filter and watch the accelerator pump squirt when you work the gas. Is it  strong flow or weak and bubbly? A good strong  squirt richens a forced lean condition just above idle where the idle circuit can't supply enough gas yet the primary barrel can't either because the air flow past the venturi hasn't built up sufficiently.

 

You might want to entertain the thought that the primary jet may be part blocked and fuel flow reduced in the primary barrel. The air mixture will be slightly lean. It will lack power and may stumble. Once revved up the secondary opens and brings on the power.

 

Have you checked your cam timing? If retarded the intake closes later. This allows the piston to rise too far up on the compression stroke before it closes. Murders low RPM power but aids high.

[JWJohnson]

Found A leak, not 100% if it is the cause or not but it was leaking pretty good. I used starting fluid to look for it, tried the torch and nothing. The starting fluid did perfect I hit my EGR delete plate with a little fluid and the missing stopped for a second and then went back to normal. As for the accelerator pump, strong stream getting good fuel. Cam timing is like 5* advanced according to the timing indicator on the crank pulley. Timing is right on the nuts so now I'm pretty sure it is my EGR plate.

 

Some photos:

 

 

Looks like some air passing by

 

 

In place with some high temp Permatex for some added grip

 

 

Here's the setup, ignore the plug wires still need to get a holder for them

 

Electric fuel pump on top of a good mechanical fuel pump, bought it with it but so far I have t found a good place to mount it that I am happy with so it stays right there for the time being.

[JWJohnson]

If this doesn't seal it up good then I'm going to pull it out again and thread the recirculating pot in the middle on top and put a bolt in it too.

[racerx]

Is that normal to have mech. Fuel pump w elect. One, together, i always thought one or the other.

[JWJohnson]

The dip P.O. Put the electric on and disconnected the mechanical one, it isn't running both; you could if you wanted but it would'nt warrant any gain.

[KlassicMotion]

I tapped and plugged my ports (you can kind of see it here).  Works well.  The top port, where yours is leaking is one I tapped and threaded in my factory PCV valve.  I would recommend hooking up the PCV system.

 

I like what Mike is saying... I would look to that next, personally.

 

[JWJohnson]

I thought about just threading everything and plugging it, I like the PCV idea though. I am running the valve cover PCV right now but am just letting the crank case EGR hook up chill. I checked and confirmed good everything that Mike was saying about the carb and cam timing. Everything is good except vacuum. I started it tonight and it ran much better. I did t drive it anywhere but the idle was much better. So we will see.

[racerx]

Klassic motion...is that a fuel regulator that goes to carb inlet?  If so what type and what you think about it?  thx, RacerX

[Dat Soon]

Cam timing is retarded. Will have low manifold vacuum and want a lot of initial timing. Also sensative to any vacuum leaks. If you have a re- ground cam or aftermarket cam you can't always rely on the timing marks. Either use a degree wheel or the old redneck method of splitting the overlap.

[JWJohnson]

Same cam as before. Degrees 5 advanced.

[banzai510(hainz)]

Dat soon is asking if you line the cam sprocket back up correctly?  the  v  back of the sprocket is lined up to the dash on cam tower? at TDC. like off a tooth on timming chain.

 

5deg adv or retard? how you know? You use a degree wheel. Stock sprockts are 0, 4 and 8 deg pos 1 2 and 3 accordingly.

 

for mis also ck the valve lash correct.

[datzenmike]

 

 

This above is perfectly timed cam.

 

 

To check yours, set accurately to TDC.

 

Look through top hole on cam sprocket with flash light.

 

V notch on back of sprocket MUST be directly below the small horizontal etch mark on cam thrust plate behind it or just barely to the right for proper cam timing. If notch is to the left, block the chain and move the sprocket to the next number up.