L16 out, L20b in

[Dimebag]

I decided I don't want to mess with swapping jets around and generally escalating my chances to end up with both carbs fubar. I went back to see Dan at the Z Shop and bought a rebuilt identical replacement for the L20B ($150), so I'll try to get that on tonight and see how it goes. He says he has all kinds of rebuilt carbs for Datsun/Nissan, Toyota, Mazda, etc.

I still have to yank the rad and replace the water pump, but that shouldn't take too long.

[bertvorgon]

regardless, if it needs jetting, glad to give you a hand, just in case it is too lean..or whatever. Only main fuel(s) need to be changed anyhow, not any air correctors.

[Dimebag]

ok, thanks Keith - I appreciate the offer.

I got the water pump changed out and the new carb installed. Had to remove cable-throttle bits from new carb and replace with linkage-throttle bits from L16 carb - man am I glad so much of this stuff is interchangeable.

Cranked the motor and it pretty much fired right up. I had to adjust the idle screw a full turn down so it would idle. I have no idea about tuning a carburetor. Is there a base-line adjustment as starting point? I didn't touch the mixture, and the accelerator pump arm has three different leverage position holes to choose from. Maybe I should take it to a shop and get it tuned with an engine analyzer?

[bertvorgon]

If it fired right up like that, you are in the zone!

The holes for the accelerator pump let you adjust the amount of fuel squirted, when you step on it. Once you get everything running ok, and motor up to temp, a drive will tell you if the pump stroke needs adjustment. Only if you have a bit of a stumble on opening the throttle quickly, will you possible need to increase the stroke. The longer squirt covers the sudden opening of the throttle when the engine leans for a fraction of a second.

If it is idling at the engine speed you want, say 800 rpm or so, and you can just tip into the throttle, without it stuttering at all, the idle mixture is likely ok. Basically, if you turn the screw OUT, that will of course richen the idle mixture. When you EASE into the throttle, the idea is to do it kinda gently... enough that the progression to the main circuit is not hugely covered by the accelerator shot. This gets the idle mixture set up quite well. Better to be a touch on the richer side, as our 510's tend to respond to that.

You can play with the idle screw no problem, just to get a "feel" for it. Screw it in slowly, and, as soon as it starts to stumble...STOP...then..screw it out till it starts to stumble....STOP! This is your range of adjustment. You
basically want it out, just enough to give a smooth idle, AND..enough that when you just tip into the throttle, the engine RPM picks up cleanly, as it transitions to the main circuit.

[Dimebag]

That sounds like a really good instructional, Keith! Much more comprehendible than any of the manuals I've read so far. I also did some homework on vacuum gauge diagnostics, so Ron Slychuk and I will tinker with it this evening and see how it goes.

[Dimebag]

Yesterday after work while I was grilling some steaks for dinner, I couldn't resist firing up the wagon so I did - and almost crapped myself. The engine bay sword fighting had returned with a vengeance and I thought the whole thing would self-destruct! I quickly shut down and became instantly depressed at the idea of pulling the motor again to try to figure out what was going on. I thought I had cured that problem by replacing the water pump and fan, because after that I didn't hear the sound anymore. Other than that, the only difference was the car was now on the ground, not on jack stands.

After dinner, Ron came over and I gave a quick demonstration - such a terrible tinny echoing clashing noise. We pondered it and looked around, and then I jacked up the front of the car to observe the flywheel/flexplate while the engine was running. We started up and had a look, except now there was no clashing. WTF. Ron says, 'There may be something loose.' Sure enough - I had run in the bellhouse mating bolts hand tight and had forgotten to go back and tighten them up to the block. Wow. We set about tightening them all up, put the car back on the ground and have not heard that sound since.

I didn't have a timing light but I got out the vacuum gauge and we did a little adjusting here and there and called it a night with a pretty decent starting, running, sounding setup. Gotta get through AirScare and then she'll be back on the road full time again!

Thanks to Ron and Keith for the quality help - very much appreciated!

[bertvorgon]

I had the same sort of thing one time, when I put the 1800 in my wifes 1970. Upon starting i could hear this horrible k'nashing sound. Crap....11:00 PM and I'm still not finished. After many times tring to isolate where it is coming from, I determine that the starter motor nose, for whatever reason, plunges deeper into the auto ring gear now, and the ring gear was hiiting the start nose????? WTH! A couple of washers later...fixed. I almost took the motorback out........

[datzenmike]

Was the the engine / tranny plate left off Keith?

[bertvorgon]

No, that was the funny thing, I actually looked to see if I left something off, getting tired that late of course. I used my wifes tranny /engine plate, as her car was always an auto. Just plain weird! I put one of those thick galvanized washers between the starter and the plate, and it worked no problem with proper engagement in the ring gear.

11:00 PM on a HOT summer...Murphy at his finest............

[Dimebag]

When we hooked up the vacuum gauge, it was reading low at 15 in/mg and when we would spike the throttle we'd get a pop back through the carb. We played with timing a bit until we got 17in/mg and that also seemed to cure the throttle spike carb pop.

If it is idling at the engine speed you want, say 800 rpm or so, and you can just tip into the throttle, without it stuttering at all, the idle mixture is likely ok. Basically, if you turn the screw OUT, that will of course richen the idle mixture. When you EASE into the throttle, the idea is to do it kinda gently... enough that the progression to the main circuit is not hugely covered by the accelerator shot. This gets the idle mixture set up quite well. Better to be a touch on the richer side, as our 510's tend to respond to that.

Motor warm, we adjusted the idle to about 800 and then played with the mixture screw because I wanted to run it in and out to see how the motor would respond. I turned the screw all the way in with seemingly no effect at all. We gently eased on the throttle to transition from idle circuit to main and it was just as smooth as when the mixture screw was 2 turns out, which is where I left it.

A couple quick runs up and down the driveway revealed a slight hesitation when strong throttled was applied from stop. The accelerator pump linkage is already in the hole closest to the fulcrum/pivot point which should give the pump the longest stroke, so I'm not too sure how else to address that. I'm aiming to get to aircare on saturday - hope it passes.

[datzenmike]

No, that was the funny thing, I actually looked to see if I left something off, getting tired that late of course. I used my wifes tranny /engine plate, as her car was always an auto. Just plain weird! I put one of those thick galvanized washers between the starter and the plate, and it worked no problem with proper engagement in the ring gear.

11:00 PM on a HOT summer...Murphy at his finest............

Maybe you left the spacer off between the crank and the auto flex plate/starter ring??





These are from various L and Z automatics.

WITH:


WITHOUT:

[Dimebag]

oh man, I am really having a tough go with this.

I finally got the car all back together and tuned up ready to go. This morning I took it down to get the emissions tested - and it passed just fine, which was sweet, but as I was pulling out of the facility I started hearing a squeak-squeak-squeak from engine which followed the rpms.

I drove home and pulled the valve cover to find the cam lobes quite dry. I didn't have an oil pressure indicator, but on Byron's advice I went and got on and hooked it up - 38psi on idle, so it seems the pump is good. Great, just great. Looks like I'm pulling the head to see if I can find an obvious blockage. Guess that's the risk with used engines.

[bertvorgon]

At least the jetting was good............

Are you SURE the cam is not getting oil, before you rip the head off. If it was running dry, you better check that it has not galled both the cam and the rockers.

Mike..I suspect you may be right. The engine was given to me by a friend, so I only went on good faith that I had everything I needed. That would sure make sense as to the thickness of a washer curing the problem. That was a long time ago that my wife had her 1970.

[Dimebag]

At least the jetting was good............

Are you SURE the cam is not getting oil, before you rip the head off. If it was running dry, you better check that it has not galled both the cam and the rockers.

Oh yeah, she was dry alright and the #2 cam tower has some interior scoring. The other three are fine, and the cam shaft itself looks good. I pulled the head and thoroughly cleaned out all of it's oil passages - I'm going to borrow an oil-pump drill-driver-adapter from Byron today to make sure oil is making past the restrictor jet at the top of the block. Once I know it's clear, I'll put it all back together and change the oil.

The head gasket looks like it's in good shape, but you can see it's a bit wet with oil between cyl 2 and 3. The #3 piston looked a bit oily wet as well, but the #2 piston was dry.