Technical Edlebrock on Nailhead issues.d

I've a 58 Buick Special, with the original 364 engine, apart from the pistons being bored out to 0.40 and running it on lake pipes, everything else is stock.

Some time ago I ditched the 2bbl carb and fitted the correct 364 4bbl intake, with a brand new Edlebrock 750. It starts from cold absoloutley fine, and will tick over all day, throttle response sounds good, but as soon as its under load at part throttle, it has a bad flat spot, to the point where it will stall if you dont ease off, you can back off a bit then open it up again to try ride through it, but its tricky to do without it stalling.

The other thing is its running rich, the plugs are getting sooted up imediately within a minute, and the idle mixture screws seem to do nothing at all.

I have played with advancing and retarding the timing, and set the dwell angle correct, but its not making a lot of difference. I changed the ballast resitor as somebody suggested that. No difference.
I'm pretty sure the vaccum advance is working , i do have a replacelemt canister for it that I might try, I dont think this would cause the issue with it running rich or the mixture screws doing sweet FA though.

I'm now thinking of buying a tune up kit to change the jets and rods to try lean the mixture. Wondering if anybody has info on what combination of jets/rods works best .

 

Have you checked the coil to make sure it's not breaking down from heat?

 

You may have to pull the top off and check float level as well. First, make sure the primary metering rods are moving as they should. The idle mix screws doing nothing and the soot both likely point to a very rich condition. I would expect the standard rods and jets to work decently in your application...maybe not perfect but not act like this.
As 427 sleeper suggests, always make sure the ign system is in good order first.

 

No not yet, I changed the coil as a precaution when the engine was rebuilt around 2012, but I have the old one I could try.

 

Aah right, ok, I'll have a look at that too. Am I wrong to assume that as its a brand new Carb, the floats would have been correctly set and meetering rods would be working as they should?

The other mod I have made to the engine is I have blocked the heat cross over ports on the intake manifold, dont think this would cause any issues though?

 

It might, if the heat crossover is what supplies heat for the choke thermostat. This assumes that you're using an automatic choke with the thermostat mounted on the intake manifold. Without the heat it supplies to the choke stat, the choke will stay on too long or never completely open making it run rich.

When you remove the bowl cover, make sure to remove the metering rods and pistons first. Reinstall them after replacing the bowl cover to avoid bending the tips of the metering rods. Make sure the power pistons move up and down freely in their bores.

 

Its an Edlebrock 1411 750cfm with an electric choke. So no issues there, I could check that the choke plate is adjusted properly though and make sure its opening fully.

 

Where have you connected the electric choke too? Have you connected it to ballasted ignition? It sounds a lot like the choke isn’t coming off. It needs 12v

 

I cant remember where I wired it , but it does seem to work well, when the engine is cold, opening the throttle slightly will set the choke back into the closed positon, then after running the engine for about a minute, if you blip the throttle so the pressure is released from the choke assyembly, the choke plate opens and the tick over speed drops right down as set by the idle speed screw.

 

Heres a short video of it yesterday. You can hear where the flat spot occurs and it almost dies

https://youtube.com/shorts/zBcG59RHFIA?si=rwCNYQ3YLK9TGtMI

 

And here is one of it ticking over.

 

A couple of things I would check- Pull the valve covers and inspect the inner valve springs as it sounds like a couple might be broken and there is some valve float. Timing advance set at 12 degrees initially, and all in at 32 degrees at 2000 rpm. Although it sounds big, the 750 CFM carb is about right. What size jets are in there? Since it is a new carb, I would think the correct jets and metering rods are in there, and the book that came with it will specify. I am running an 800 on my 401.

 

Aah ok..i'll give that a check, the engine had a complete rebuild in 2012, so new valves, lifters, push rods, rockers, springs etc, but yeah I'll give it look. The timing I have always set to the workshop manual, wich I think says to set at 5 degrees before TDC , dwell angle at 30.

 

Has it been doing this the whole time since going to 4V? A couple of other thoughts- If the block VIN has an X stamped on it as the lead digit, it was originally a lower compression export motor. Depending on what was done during the rebuild, the CR could be even lower as aftermarket pistons have a lower compression height unless custom forged ones were used. Going from the stock steel shim head gasket to a composite one lowers the compression even more unless the block was decked to compensate. Which port on the carb is being used for the distributor advance-ported or manifold vacuum?
In listening to your videos, it sounds like it is breaking up even at idle and it is ignition related.

 

That sounds like it’s running on 4 cylinders. Do both manifolds feel equally hot? There’s a lot of grass moving by the left exhaust but not much by the right.

 

I'll check the block for the X.
Vaccum is going to passenger side, so above the throttle blades.
Pistons were standard as far as I remember.
The book says my Edlebrock 1411 has Main Jet primary .110"
Main Jet Secondary .107"
metering Rod ( primary only) .075" x .047"
set up spring - Orange 5"
accelerator pump nozzle diamater .035"

Originally the car came from California, it was imported into the U.K in 1988.

It was running fine for a good while after the re build, with a 2bbl carb. I then put the lake pipes on, still with 2 bbl, and thought it just didnt feel super responsive. It was also really loud, so I made some baffles and fitted those. I am now realising that the problems with it miss firing and running badly started after that, I hadn't realised this was causing issues until I took those baffles out yesterday and it now running ten times better. It was undriveable before. But because it was backfiring, I assumed this was timing related, so have been playing around with that, then I had trouble with it it starting from cold, and thought maybe the 2 barrel was at fault, so tried another one. These are all old used carbs btw. So then I got the idea into my head that a 4bbl would be better. I aquired the correct 4 barrel intake for the 364, and got an old rochester 4 jet, i believe came from a 59/60 Buick. This again ran ok while stationary, but was still missfiring and I think needed a rebuild. I decided to buy a nice new shiney Eddlebrock 750 instead. And this again seemed to run ok, but was undriveable due to it stalling under load. So fast foward to yesterday and I remove those baffles, and the back firing has stopped and the car will at least now drive much better, but still tries to stall if pushed. The thing being, that since I hadnt thought the exhaust was causing issue, I have beeen messing with the timing and set up of the carb.

I am now thinking that I have probably screwed the idle tick over screw in too far, to stop it from stalling, due to the timing being off, which has opened the throttle blades too far thus bypassing the idle circuit, which would explain why its running rich and the mixture screws do nothing.

I guess I need to wind that back out, adjust my home made throttle linkage so its not holding the blades open, and then re set the timing to increase tick over that way. Then adjust the mixture screws with a vaccum gauge on it. If all else fails I can put a 2 barrel back on and standard exhaust. Its just finding a decent new 2 barrel that will bolt straight on. I am guessing Stromberg 97's are way too small in the CFM dept?

 

They are both throwin out plenty of exhaust gas both sides. Also all 8 plugs are sooted up.

 

That really sounds like an accelerator pump problem. Have you checked to see that you are getting a full, steady squirt from the accelerator pump? It should deliver fuel through the full stroke.

 

Aah yeah, this was the other thing I was wondering about. I was thinking maybe I should change the linkage position to the top hole on the pump lever, its fitted to the middle hole at the moment.

 

Nailhead motors, if set up properly, like a lot of carb and the Stromberg will be too small. I will need to check my book, but .110 jets sound a little fat.

 

Aah thanks, that would be great.

The Edlebrock book shows the 600 CFM to have .098 and .101 jets. I guess that would be the next set down to go for?

 

The .110/.107 jets are correct for that carb. Pump should be in the top hole, not the middle hole. Something else you should check- is the damper valve still in the exhaust manifold and could it be stuck partially closed?

 

No, don't do that. The tuning kit will come with a booklet and a chart that shows jet and rod change steps for your particular carb. That's the way to tune the carb. The next leaner step will be much less of a change than the 600 carb jetting setup.

 

often it is the distributor not advancing or advancing too fast or slow, look under the points plate for missing or broken advance springs or something dragging on the bottom or outside edge of it. had the same problem on my 425 Nailhead distributor.

 

The damper valve? Do you mean the plate that's controlled by a thermodtatic coil that sends the exhaust heat back across the intake when its starting cold?

If so I removed that. It was stuck closed after the rebuild, so overheated a couple of times before I realised.

Runs at normal temp now, i fitted an electric temp gauge, and it warms up at the right speed and stays at around 80 on the gauge, ( in the middle ) oil pressure is good too.

 

Oh ok..brilliant, thats good to know

 

Oh really? Ok, I'll have another look..I have an electronic ignition kit I bought from Rock Auto last month , that I was planning on installing, but figured I'd get the car running better first. One thing at a time . I might pull the distributor out at the weekend and give it a look over and take some pics.

 

Also check the wire that’s attached at the breaker plate that goes to the - at the coil. After many years of breaker plate moving back and forth acting upon the wire can cause internal strans of wire to break one by one. Much like bending a coat hanger over and over until it breaks.

 

Aah yes, those old LT wires were pretty flimsy. When I first had the engine rebuilt, I gave the distributor an overhaul, replaceling those wires, along with the points, condenser, cap and rotor. I will check vaccum advance though , and see if thats opperating and moving. Like you said something could be broke. The mechanical advance with the little springs all seems to be moving freely.

 

Yep, that valve. If removed cross that off the list. Which distributor do you have? The early ones have the advance springs below the breaker plate, the late ones have the springs on top. I prefer the late one, even on the earlier 364.