SpartyGW

I'm about to give up. Symptom: cold start and hot start is perfect. Problem is "warm" start. I can duplicate reliably by driving the car, then letting it sit for 45 minutes and starting it back up.

First acceleration from stop the engine bogs down like it is flooded.


What I've done:


1. Rechecked and verified float levels to factory spec

2. Increased vapor vent clearance as much as possible

3. Messed around repeatedly with choke, which I think is set perfectly

4. Changed fuel to highest octane I can buy at the pump

5. Wired open exhaust heat riser

6. Verified that the carb float bowls are nowhere near the 140* that I've read is typical with percolation (front carb does get in the low 130s right by the water neck but everything else is in the 110 range)


I've run out of ideas. If there were percolation, wouldn't I see fuel dribbling down the throttle bores when looking with the engine off or would I need to open the throttle to see it?

66jack

Check your accelorater pump diaphram...could be cracked...

Frankie the Fink

I had a similar experience just last week with my restored dual quads....acting much like percolation but the bowl temperatures didn't support that diagnosis.

Turned out to be a bad ignition coil....failing once it got hot; usually after sitting on a non-running, hot engine for a time (heat soak)...

SpartyGW

Frank, tell me more... Did it run fine otherwise? Engine revs great, and this issue clears up in a minute or two after bogging.

I'm stumped.

Jack, this is wcfb. No diaphragm per se like on a Holley. The accelerator pump has a leather or rubber seal, which is new from Daytona.

I can't recall when this started, but it is recent.

66jack

Shows you how much i know about carbs...

John S 1961

How do you start it when this happens?

For me, I expect it to crank a couple of times and fire right up, it doesn't. It spins, then I pump it a few times and hold open the throttle, fires after a bit.

These Old used cars are funny like that, they do things

jimgessner

WARD GAPPA (602) 810-2039 and MARK SCALPON (480) 922-2480 both in Scottsdale and understand vintage Corvettes.

SpartyGW

Exactly.

Cold start, I pump once about half throttle (to not hit the front carb) and it starts up on fast idle.

Hot start, I don't touch the throttle - turn the key and it fires up.

This warm start issue...turn the key and it will crank crank crank. Pump gas a tad...crank crank crank. HOld throttle slightly open and it starts.

What do you say, John? You've solved a similar issue?

rich5962

I seriously don't think you will ever correct a warm start after sitting 10 or more minutes with these carbs. My '59 has had at least 3 rebuilds of my 2x4 WCFB's since I've owned it for 29 years, and your condition, exactly as described, is exactly my condition and that of many.

Heat soak, extreme temperature and old carburetor technology all attribute to the condition. My car always did it even before ethanol. Add boiling ethanol molecules to the situation and it's worse.

I think you're going to have to succumb to ......."That's the way it is."

You may be aware of this, but for others reading ......

Just don't ever hold the pedal to the floor on hot restart, because as you know, you will flood the front carb throttle plates with fuel because the accelerator pump will squirt a full flow. The unspent fuel sitting there on restart will drain out the throttle shafts and could ignite on a hot manifold.

My 2x4's hot restart is always only half throttle or less, slowly, as to not give the squirters a full flow.

Except that one time 25 years ago when on a 10 minute restart from hot, I stupidly gave it a floored pedal, it started, and bogged leaving a downhill parking lot in 90* summer, backfired, and had a major engine fire from the leaky fuel. Thankfully I salvaged the moment with a Halon blast.

Rich

rich5962

Exactly, precisely, definitely........CORRECT! Exactly what I've done for 29 years......
Except that ONE time when the fire started.

Frankie the Fink

That may be "life as we know it with these carbs". I'm with Rich on this .... both my clones and now 'real deal' 270hp carbs require finessing after a hot run and sitting for a while. Doesn't necessarily indicate an abnormal condition

My "hot soak" ignition coil problem was a rough start after sitting after a hot run for 20 minutes or so; then it felt like an "over-rich" stumble on take off that cleared up at WOT.....very perplexing and I fought it for a couple of weeks thinking it was perc. It was a d@mn FlameThrower coil I had put on the '61 when I moved my MSD Blaster to the '63. Meant to change it but forgot all about it

Rich - you quoted something I deleted cuz I was reworking my post, but yes that works (I won't bother reposting it since you nailed it)...that paragraph comes from "The Carburetor Shop" web site...

rich5962

Frank, You and I and others with 2x4 experience know well the idiosyncrasies about this old technology and hot restarts. Original Owner's Manuals describe starting a hot engine and most always say to "floor it" (to open the throttle plates for more air) on a heat soaked and rich restart. In reality, those quotes are not intended for 2x4's, only for single 4's, and I believe it to be just a misprint and/or carryover from previous manuals. There are many errors in those manuals.

I believe the 2x4 restart was never described properly in the manuals, and if they did, they would likely be admitting to a fire hazard. Dual fours can be dangerous if not handled properly.

If anyone ever drives my car without me, I give detailed instructions on re-starting a hot engine to never pedal it beyond half throttle. If they don't pay attention, they don't drive it!

When I first bought my '59, the linkage was not progressive, it was fixed to both carbs and both throttled together. It may have been done to avoid such restart issues. I changed it to originally designed progressive soon afterwards.

Your quote from the carb shop is based on many decades of their experience with this fuel system. They know what they're talking about.

Rich (WCFB 2x4 fire survivor)

PAmotorman

the way we fixed this back in the day was to take apart the fuel pump and drill a .015 hole thru the fuel pump valve body plate. also blocked both sides of the heat riser crossover in the intake manifold with .005 thick stainless steel shim stock

MikeM

I don't understand all the drama here. Any engine I ever had with a float bowl on the carburetor, I always opened the throttle to start the engine once it got warmed up and that included four different sets of the Chevy 2X4 carburetors.

That's what the owner's manual tells you to do and I believe it's correct.

It is true that the 2X4 carbs shouldn't be opened ALL the way due to the extra shot of gas from the front carburetor which will slightly flood the engine.

2X4 carbs are no more dangerous than any carburetor except they just hold twice as much gas that can catch fire in the event of something igniting the fuel.

"No touch" (on the gas pedal) starting didn't become the right way to start your car's engine until the advent of electronic fuel injection whether the engine was hot or cold.

SpartyGW

Well, I guess I'm sort of relieved and sort of disappointed.

This is a car I drive and that :45 minute window is something I continually run into.

Maybe my starting routine is exacerbating the problem. I'll try to always start with the throttle cracked and see if that improves things.

rich5962

Yes that helps for sure, and blocking the heat riser also, but I use my '59 year round here in Florida and want that cold start warm up help.

Mike, No drama.........I agree with what you've described, and that's true for a single four setup, floor it to restart a hot engine. But as you say not for the 2x4's......The manuals don't differentiate the hot start method for 2x4's.

Rich

rich5962

Yes, join the crowd.

A gentle foot to help avoid the accelerator pumping a giant stream will be your friend. Just feather it afterwards until the richness dissipates.

Rich

MikeM

So there's no misunderstanding of what I said, I said for a warm restart to open the throttle as you described to start. Always. On a hot restart, I found from time/time it was beneficial to open both carburetors.

If the OP is having a problem restarting a warm engine with the throttle cracked open, he has a problem other than the owner's manual instructions in my estimation.

The fact that PAMM drilled a hole in his fuel pump is some evidence of trying to prevent either raw fuel or vapors from bleeding into the engine on hot engine shutdown and flooding the engine.

To restart a flooded engine, you open the throttle to give the engine more air, just like in the owner's manual. Doesn't matter if it's a Blue Flame, a Rochester FI or something in between.

Contrary to what often gets reported, this warm/hot start deal didn't just start with E 10. It's been around longer than I can remember.

I personally never thought manipulating the throttle to start the engine under different temperature conditions was anything out of the ordinary or bothersome. It was second nature.

Even women knew how to start cars under varying conditions before Electronic FI.


PS. This statement in the OP's complaint is not normal, regardless of starting procedure and this leads me to think something is wrong with his car besides the way he tries to start it but the hard warm starting and this bogging down could be related:



"First acceleration from stop the engine bogs down like it is flooded."

SpartyGW

My assumption is that my starting routine is flooding the carb on warm restart leading to this acceleration bog.

When cold I would crack the throttle, otherwise I always tried to start just by turning the key. Sometimes it works, sometimes it doesn't.

From now on I will always crack the throttle and see if that alleviates the issue.

MOXIE62

Install a fuel injector manifold gasket. Keeps heat off the carb.