Technical Chevy 235 struggling at high rpms

Currently out driving a block or two, stopping, and turning the screw in about a 1/2 turn at a time. I think I’m about a turn and a half in so far. Rpms are hovering in the more normal range at idle. Still bogging down at higher rpms, but the amount of rpms she can take before he stumbles seems to be getting more and more

 

Another possibility to add to the list. Had a '53 Ford that I had just got running and shut down on me, found a bad ignition wire and thought it was fixed. Stalled out on me driving again and after tearing into it found fine rust particles clogging the fuel pump that got past a defective filter. Finally ended up pretty reliable but always stumbled on the freeway and one time I saw black smoke in the mirror as it did it. New pump built too much pressure with RPM and needed a regulator. Otherwise ran fine. Have you checked fuel pressure yet? New pump?

 

I did put in a new pump about 6 months ago, old one took a shit. It’s all seemed ok, but I could test it to be sure it’s putting out what it needs to. Currently it’s dying in neutral after a minute or two of ideling. Starting to feel fuel related

 

Also, if it sat for a long period of time not running, gas could have gummed up some carb passages or air bleeds.

 

that plug looks like its getting way too much gas to me.

 

Turning the idle mixture screw will help nothing but the idle mixture. Use a vacuum gauge to set to highest reading , retard timing a bit . I think the timing curve is off a bit .

 

is the choke stuck on?

 

That's exactly correct. It may not be "the problem" here as such, but the jetting or cruise circuit as such, is way, way off. Spark plugs should burn very clean, even in a vintage engine, with modern gas. That plug looks like it's approaching the "rich burn" limit.

First make sure the power circuit isn't defective and adding fuel when it shouldn't.

 

Next, make sure you've a good HOT spark, the Ignition is squared away.

It could be, at least part of the problem with the plug fouling is that the ignition itself is weak. Use standard heat range plugs, don't try "hotter plugs" to clean up the fouling - standard plugs, a good strong spark, and the and the timing curve is straight all the way up and down the RPM range + the correct fuel curve, jetting and the rest of it and they should run very clean.

The big thing generally is people try to troubleshoot "backwards", the carburetor is the very last thing to adjust. Ignition, and ignition timing has to be straight, or the carburetor won't seem to run right no matter what. Then make sure things like the fuel tank & fuel lines aren't obstructed, fuel pump pressure output isn't excessive, and the carb float height or fuel bowl height is within spec.

I bet it starts easy in below zero temperature at least. No choke required, amiright? LOL Too bad ya need a fuel tanker to follow you around ...

 

I’m now heading in that direction as I bounce it all around in my head too. Vacuum reads at a pretty steady 18-20. But I’m getting the feeling it’s not carb related at all. The day before I put the HEI in it ran quite well with the carb that’s on there currently. It has to be a timing issue. But my question is are my symptoms sounding like they’re related to timing. Major hesitation at higher rpms, high idle, and occasionally stalling after ideling for a minute or two? Unfortunately per langdons Instructions it seems the factory specs of timing go out the window. Which is why using an advanced light I timed it to about 16 degrees advanced (like he suggested) and it’s in the state it is now. Do I continue on with advancing? Do I retard it? Do sell my kidney and drop a 350/350 in the ol’ Chevy what the hell do I do?

 

Choke is not, but that was my first thought. It sure as hell acts like it is

 

Did you change the plugs to the extended tip ACs? You can't be using the same plug as with the points distributor. The new plugs use a much wider gap. I don't remember what they are but a trip down to the garage and a look under my hood will tell me. You may be over thinking this. I find doing things the old fashioned way got me a better running engine than following timing lights and degrees advanced etc. I just timed it by ear and it's been fine for years now.

 

I did. When I bought the distributor from Langdon I also got a set of plugs and wires he sells which he says are tailored to the set up. The gap of the current plugs is .050

 

That sounds about right. How did you adjust your air fuel mixture on the carb? Those plugs look like they're drowning in fuel.

 

First step was gently snugged it in until I felt resistance, not seating it too much because I know you can damage the seat, then backed it out two turns. Fired it up, hooked the vac gauge up, and gave it small turns until I reached 20 on the gauge and it idled smooth. Today I took it to an empty lot and ran it through all three gears at the rpm range it starts to buck, then pulled over and sunk it in about a half turn recreating process twice. I thought it was starting to help with the issue, but it didn’t make much difference at all

 

One thing at a time. Take your time. It will ultimately save time.

Modern gasoline is different than the old days. Those old color spark plug charts, they don't really apply anymore with the modern unleaded boutique "clean air" gasoline + the ethanol. If they are running black like that, it's running at about a 10 AFR just cruising down the highway.

Use your vacuum gauge to measure the fuel pump pressure output. Just a static test is fine. Takes about 30 seconds. There's enough fuel in the bowl for engine to idle, or just disable the ignition and crank the engine over. 4 to 5 psi is plenty for most carburetors. More is not better. Many defective new fuel pumps from you know where are being sold these days.

THEN, if that's within spec, set the carb "wet" fuel height. Not the float height, that's just a bench setting that gets you close. Once a carburetor is installed on the engine the fuel height has to be checked. It's easy on some carbs, others not so much. It is a critical setting.

Adjust the float up or down as required to achieve the proper fuel height. Everything inside the carb is predicated on the fuel height in the bowl.

It ain't like a toilet bowl, it's supposed to maintain a certain level at all times, or near enough. Idle mixture too rich will foul plugs but you've got to get everything baselined so you can figure out where to go next and make accurate diagnosis. You're looking at a lot more fouling than idle mixture screws can account for.

 

idle mixture is not the problem. mabe too much fuel pressure as rpm goes up.

 

Whatever happened with the stock distributor? Did you ever get a new insulated block for the distributor.

FWIW, the stock timing specs were 2° ATDC.
Running the base timing 20° advanced may be causing the engine to fight itself on compression.
Normally you would get pinging before the ignition became too advanced, but the Stovebolts do have some ugly combustion chambers, soooo....

Might want to try a vented cap, or try with the gas cap off, try and only make left turns
Non vented cap on a non-emissions vehicle can have you imploding the gas tank. Fuel pump trying to collapse the tank while sucking fuel.

If the HEI system he is selling is basically a stock(emissions) setup, which it probably is, then the timing curve is engineered for emissions setups. Those used Ported for the vacuum advance. Using Manifold vac may have the ignition advanced too much.

 

Hey mike, getting a little too used to me around here lately, aren’t ya’ I got a new insulator block for the old stock dizzy, even got a new vac pod for it. Then I just came to a conclusion that if I’m doing the work to pull that distributor out, I’m going HEI and here we are! After some more reading on other people running this same HEI set up on a few straight sixers, I’m concluding my 16 degrees of Initial timing is insanely too high. Tomorrow when the rain stops here I’m going to dial it back to 12, take it for a spin, and go from there. I won’t be surprised if I end up in the single digits, but we shall see

 

Ignition timing is a package deal. The initial or base timing isn't critical, insofar as the starter doesn't kickback. Somewhere between 10° and 20° is fine for most engines.

What you're really concerned about is what's is it doing at full throttle high RPM, where does it top out at? Where does it fall when steady cruising at highway speeds?

Ignition timing advance at idle can be in the high 20s or more, it won't hurt a thing. But if the distributor is defective, the mechanical or vacuum advance, lots of bad things happen performance wise.

 

right now, currently as soon as I hit 2000-2500 rpms it’s flat, sputters, I upshift, and it repeats. Haven’t taken it on the freeway. Before this new distributor and all that’s been going on the past week with it, cruising freeway speeds it landed at about 2800-3000 rpms, doing 60-65. Just to recap though, the distributor is brand new from langdons stovebolt, the mini HEI set up. I think I’m just struggling to get my settings straight with it and trying to see what I’m missing

 

Did you vent your gas cap?

 

OK. You can fine tune the distributor later and really dial it in if you want but for now - it's just general tuning & troubleshooting purposes - want to check and make sure that the timing is advancing and backing off as it should. You want to do this before you dive into the carburetor innards. The carburetor is "dumb" in that it expects everything else to be working as advertised. If it ain't you'll pull your hair out trying to tune it. Ignition (and ignition timing) is a big part of that.

Use a timing light. First, disconnect and plug the vacuum advance port. Forget about it for a while.

Then see to it (in neutral) that the ignition timing advances to around 34 degrees or so smoothly and back down again to base setting as you rev it up to 3000 or so and let off. Make sure it's done advancing all the way. Take it for a test drive or two (without vacuum advance connected) as you might play with the timing. Mechanical ignition timing is checked and adjusted separately, in isolation. Altitude and fuel quality plays a role but every engine always runs best with just as much advance is it can stand just short of ping or knock, at all times under all conditons. That is what the distributors' job is.

Vacuum advance is always adjusted last independent of the distributor itself. It was invented because at light loads and part throttle (like steady cruising on flat ground) there has to be a whole bunch more ignition advance, and there was just no practical way to get there with springs and weights. Retarded or "late" ignition timing makes it run hot at cruise especially and wastes gas. On the highway ignition advance can be 50° BTDC or more.

 

Sounds like a dud coil to me.

 

Try running a jumper straight to the battery and hooking up a test tach and see if it acts up. and try no air cleaner.

 

One thing I haven’t seen mentioned (unless I missed it) is plug wires and rechecking the firing order. If the engine ran to 3k before, and let’s assume the new distributor is okay might be a mistake we’ve all made.

 

See Post 53

 

Get rid of that Rochester Irrigation system and install a Carter YF 1 barrel,

or a Holley 1946 carb that came on the 80's Ford 200's [with electric choke]

 

IIRC, total centrifugal advance would be 24-28° by 3500 rpm.
Vac advance will add 17 ° with 8-12"Hg vac.
Idle should be 475rpm with base 2° ATDC.
With the HEI I would start with base 2° and then have the vac advance hooked up to a ported(if possible) vac. That would make it snappy when you crack the throttle.

With the engine warmed up, hold it steady at 3500rpm and see what the timing light shows.
You will need an adjustable timing light to verify. I wouldn't run much more total advance unless you have changed the engine from stock or the HEI system doesn't allow much total advance. Too little advance will make the engine lazy.

 

all good advice on here. now everyone go back and look at the spark plug. TOO MUCH FUEL!