Technical Chevy 235 struggling at high rpms

So here’s where I’m at, hoping y’all can help me equip myself with a few troubleshooting procedures. Just put on a langdons mini HEI distributor with his suggested plugs, wires, and the heavy duty square coil a few days ago on a 54’ 235. Timed to approx. 16 degrees advanced with an advanced light. Firing order correct, oil pump engagement, correct cast iron gear for the distributor, all that good stuff. Now what’s happening is the car bogs down and sputters bad once I get to 2000rpms. If I shift early it seems to run fine, but pushing her to the higher rpms it instantly doesn’t like it. Also at first fire up she idles good at 500-600 rpms. After tapping the gas a few times, or driving a bit the rpms hover around 1000 or even higher. Read the plugs after a few miles yesterday and they’re pretty roached. So I was thinking of giving it a 1/4” in turn at a time and taking a quick drive to see if the hesitation get better. Carb is new-ish also, and manifold vacuum reads a pretty steady 17-18 at idle. Any other ideas here that I can obsess over?

 

How did it run with the old setup?

 

Not like this. It had its own set of issues though. That distributor was pretty clapped out, as it was the original. I went with the HEI set up for reliability as this old girl is my only car to putt around town. But the sputtering and bogging down is new

 

"new carb"...........check the basics first
1. spray Brakleen around carb base/intake for vacuum leak.
2.Don't be 'skeered' to give the timing a good twist! Advance it and see if it clears up.
3.Hook up a vacuum gauge and adjust carb to get the highest vac. reading
4. Gas cap vented?
5.Gas tank old & rusty?
6. Fuel filter new?
6sally6

 

Make sure you don’t have a partially plugged muffler or exhaust…had a similar issue and at higher rpms a broken baffle in the muffler would move a block the exhaust enough to cause it to stumble…best test…remove the muffler.

 

What carburetor are you using?

 

Cap not vented, but it wasn’t before the swap and the car drove fine. Tank is new as of 2 years ago, with all new hard lines to the pump, and from there to the carb. Filter was installed at the same time. I’m not sure timing is my problem here, unless it’s the advance curve because it fires right up on initial start, and runs well at those lower rpm ranges

 

An adorable little Rochester B single barrel. Intake is stock

 

Another strange thing is, at idle with the vac advance hose unhooked it instantly starts to run rough, plugged back, and it smooths out

 

Take the cap off and give it a try. I assume you used the proper gauge wire when you put in the HEI.? Does the ballast resistor need to be bypassed with his unit?

 

Unhooked and not plugged?

 

Ah yes forgot that detail. Ran a new 10 gauge primary wire, and deleted ballast resistor. Vac hose unhooked and plugged with my finger over the flex hose

 

Just for a sanity check, you are timing it with vacuum advance disconnected?
Now, I always timed my 235’s as was laid out in MoToRs manuals.
Disconnect and plug line.
Idle speed approximately 500RPMs (I forget exactly).
Light on #1 and adjust timing/idle until the mark is shown on the flywheel.
Drive and put in 4th (only had manual transmissions) and accelerated moderately. If no ping, advance timing more. Reset idle.
Go again and repeat until it pings, then back off a bit.
I guess with a good dial back light you could figure out total advance, but that’s not something I ever looked at on mine.
But, maybe also try leaving the vac advance off and plugged, and take a quick spin. Not for too long as it will start to heat up in the exhaust, just around the block.

 

I’ve checked with a light on a bit of both. Vac advanced unhooked and hooked. Per langdons instructions it says you’ll land anywhere between 8-16 degrees advanced. Which lands you roughly right around the UTC and BB mark leaving the flywheel window. Which is spot on with where I’m at. I can try a quick drive without vacuum, but again it idles roughly when you disconnect it

 

Be sure to plug the vac line…golf tee works great

 

Well, you have to set base timing with no vacuum advance. I don’t recall if my 235s had vacuum at idle or not, it’s been awhile.
What is your idle RPMs when setting base timing?

 

I bought one of Tom’s complete systems also with the recommended hei coil. His recommendation, actually mandatory, said manifold vacuum. We struggle to get it to idle at 800+ rpm. Yes it’s multiple carb, 10-1 compression, a mid range cam:etc. but it just didn’t make sense. I finally used Venturi vacuum and 8-10* at idle with it disconnected. Idles at 550 and runs right up to 5500 if we want. Something it wouldn’t do his way. I’ve been racing GMC/Chev 6’s for over 50 years and never had one not rev if everything was good.
Yours sound like it’s running out of fuel but it was good before I would look to something on the ignition.

 

Keep giving it more timing snd see what happens.

try ported vacuum

when you say the olds distributor had its own issues what where they ?

those Rochester B carbs are good little carbs easy to build and plentiful.

but do leak fuel and air around the throttle shafts and the castings can warp and leak fuel and vacuum as well.

the fact it runs like crap at idle with the vacuum advance disconnected is strange.

make sure your timed 100% correctly on number one, then advance your timing and set your carb accordingly.

sounds like your chasing a couple problems and they are overlapping causing anger and frustration!

 

Interesting, when I spoke to him he said he suggests ported vacuum, but that I could try manifold. To me manifold vacuum seems a little counter productive as vacuum drops under load, right? That would retard timing when it’s needed, but then again, I’m just a fucking kid, so I could be wrong. Yea I doubt it’s running out of fuel, because she smells rich as hell driving, and like I said I did read plugs after a few miles and they were blacked

 

Sits happy at 500-600, until you give it gas, then it jumps to 1000 and stays there pretty consistent

 

The old one was a floppy, and the vacuum advance canister had ruptured, so I figured if I’m going to go through the trouble of pulling the dizzy, I may as well give the old girl a spiffy new one

 

If the engine is stock except for the ignition 16 degrees static sounds like a lot -

 

I thought so too. But Tom suggested it, and again, my knowledge is slim on these old cars, but it doesn’t feel like it too advanced. My symptoms (I would assume) don’t point to that anyway

 

Shot in the dark here, but is it possible I’m just running way too rich? And it’s choking itself out? Or is that something that would be more consistent across all driving conditions?

 

IIRC the spark plug gap for HEI is considerably wider than a stock distributor.

 

Stock is .035” I’m running .050” currently for the HEI which was the suggested plug gap

 

Stock is 6* BTC. I’d start there. It’s checked thru a hole in the bellhousing. The triangle is TDC; the ball bearing ball is 6*. To see the triangle you need to remove the flywheel shield and clean the surface to see it. I paint it; white same with the steel ball.
Unless you added a 360* tape and a pointer off the timing cover and found true TDC you might be just guessing. Good luck.

 

Vacuum advance only advances the timing at light load for fuel economy. Yes when you "get on it" you will lose the vacuum advance. That's the way it is supposed to work.

 

Post a a clear head on picture of a spark plug or two. If they look "roached" with modern gasoline the carb is setup pretty far off the beam.