Choke spring or choke stove in intake manifold ?

[MrMarty51]

Step sons 1970 C20 pickup. SBC 350.
It has the choke mechanism like whats in the picture.

The base on that spring gets barely above skin temperature.
I am thinking that the passage through the intake manifold is plugged and not allowing the choke stove portion to get warm enough to allow the bimetal spring to fully unwind and hold the choke all the way open.
Can someone please tell me what temp that portion of the intake manifold should get up to.
Thank You
MrMarty

 

[Will L.]

You are on the right track

Way hotter than you touch. Many intake manifold gaskets are made with a steel block off plate built-in to the gasket. The purpose of the plate is to stop the heat from getting the intake manifold hot because cold intake equals more power.
Dollar to a donut says that’s your problem.

Oh, course if that engine has not been apart and has about 250,000 on it, and it could have an exhaust gases built up in there to plug it.

 

[Will L.]

Google search “350 small block, Chevy intake, manifold gasket” and clicked picture.

See the circled gasket has the hole for stock use? Notice no holes in the others? No one wants the egr heating it usually. People add a cable for choke.

 

[MrMarty51]

Compression numbers on this engine is excellent.
IDR what they are but this thing idles smoother than any SBC I have ever seen.
Another thing that I was very much surprised with is the timing.
Engine idling at 350 RPMs the timing mark on the HB is rock steady. No falter whatever and it holds steady when checking the mechanical and vacuum total advance.
On those intake manifold gaskets, I too have seen those that comes with a steel block off plate with tabs that can be added onto the intake manifold gaskets.

 

[MrMarty51]

I started to chisel and hammer the carbon away.
Yeah, manifold was plugged.
The intake manifold gaskets had a block off plate on one side. That plate had a hole in the middle of it.
Should a plate with a hole in it be added back onto the gasket. There are two in the set.


Yeah, I started hammering that Snapon screwdriver, pounding that carbon out of them ports, then,? Remembered to get a couple of pics.

 

[EWC]

That should be clear for both sides .

 

[MrMarty51]

That should be clear for both sides .

So do not install one of those plates that has about a 1/2” or 3/4” hole in it ?

 

[dbrannon79]

I think the hole on the plate is to slow the flow so not to heat the choke coil red hot, @Will L. would be the one to say yay or nay on the plate with the hole.

how hard would it be to convert the choke to an electric version?

 

[EWC]

If this is on a stock truck , I would leave it open . Basically it heats the intake manifold . Now if this is for performance , most people block it off to try and keep the intake cooler .

 

[MrMarty51]

If this is on a stock truck , I would leave it open . Basically it heats the intake manifold . Now if this is for performance , most people block it off to try and keep the intake cooler .

Thank You very much.
Yeah, this is on a stock engine application.
The intake manifold and most likely the engine too is from a later model vehicle of some sort.
Nick looked at the casting numbers and according to that it is a 1972 engine.
It has a block off plate over the EGR accessory holes. Some kind of greenish silicone goop that was sealing that plate.
It apparently is a very early EGR system as the parts store had no gasket for that.
I have a gasket from a more modern version that wirh some cutting and trimming I think will work. Holes wont align perfectly but they will be sealed away from each other.

 

[Will L.]

The heat activated choke is the only good thing from the design.
All other effects are bad: plugging manifold and then head, fuel flashing in manifold, raised egt which in gas engines burn the exhaust valves sooner, the egr system plugs the valves with carbon much worse by trying to burn it-valve guides and seals suffer more wear from it. While it helps emissions slightly when new, after 100,000 miles on engine egr makes it worse.

You have to decide if it’s worth the effort to clean out the manifold and just keep the heat activated one. Once it is clean and back together you need to adjust the setting on it. Most manuals will have instructions. Not hard, no money for parts, just time consuming.

Or, clean the gasket mounting area and block it off again with gaskets. The ones with the tiny passage holes are the worst of both worlds. That always plugs up with carbon and as you might learn- is ridiculously annoying to clean out. Once you get a few inches in each side- a chunk of metal cable in a drill can be your friend. A 3,000 psi pressure washer is better.

If ya block it off-
Electric choke can be done too, I just preferred the manual control of a cable.
Electric is a simple kit- probably $50 nowdays. Screws onto carburetor, has one wire to ground, the other is hot when key on- so I would tie into the coil power.
Then simple adjustment by rotating a disk part of it and tightening couple screws.

Once you are done with all of it- you now know that engine is carboned up.
Disconnect the exhaust pipe before it goes into any muffler or trap system.
Do the water down the carb/intake de-carboning process. Disconnecting and reconnecting exhaust is the hardest part. Doing it parked next to any greta thornburg neighbors is always funny, and is almost always done before the cops get there.
then even if they have video - you can show the officer it is now “fixed” and you were just working on the car trying to make sure to not contribute to global warming. Haha

You can do it without disconnecting exhaust but that carbon can plug up mufflers, cats, etc. so I generally disconnect.

 

[ak diesel driver]

The warmer the engine the better

 

[MrMarty51]

It is done, mostly.
The temp on the choke coil spring mounting surface, previous, was as hot as 115* F.
After getting it back together and checking the choke stove portion of the intake manifold several times the temp was at 275* F and I imagine it was rising.
The choke coil spring had unwound far enough to hold the choke firmly open and the fast idle cam totally released to the curb idle speed.
I think the linkage adjustments too is spot on.
Funniest was the ignition timing.
I did remove the distributor. Before pulling it I showed Nick to turn the engine so rotor points to the no. 1 position. Turn the crank until the HB mark aligns with the 8* mark, mark and scribe the distributor to the block.
After installing the intake and all components. I give the throttle a kick, choke snaps shut. Nick cranks over the engine, whut, no start. Look over, coil wire, plug in the coil wire.
Nick twists the key and boom. Instant fire up. I honestly think it started on the first piston that went to TDC.
Fast idled just fine. Choke went to full open and fast idle dropped with a blip of the throttle.
Vacuum booster disconnected and plugged, timing light turned to flash, Nick check this out. Timing was exactly and perfectly on 8* BTDC.
Nice too that there is absolutely no waver in the timing. It is spot and dead on each fire cycle. I have never seen a points ignition that steady.

 

[MrMarty51]

Oh yes. The rubber hose on the fuel system is of the high pressure fuel injection variety. It is mighty tough getting it on over the filter and fittings but not much of it becoming dislodged or bursting.

 

[dbrannon79]

It is done, mostly.
The temp on the choke coil spring mounting surface, previous, was as hot as 115* F.
After getting it back together and checking the choke stove portion of the intake manifold several times the temp was at 275* F and I imagine it was rising.
The choke coil spring had unwound far enough to hold the choke firmly open and the fast idle cam totally released to the curb idle speed.
I think the linkage adjustments too is spot on.
Funniest was the ignition timing.
I did remove the distributor. Before pulling it I showed Nick to turn the engine so rotor points to the no. 1 position. Turn the crank until the HB mark aligns with the 8* mark, mark and scribe the distributor to the block.
After installing the intake and all components. I give the throttle a kick, choke snaps shut. Nick cranks over the engine, whut, no start. Look over, coil wire, plug in the coil wire.
Nick twists the key and boom. Instant fire up. I honestly think it started on the first piston that went to TDC.
Fast idled just fine. Choke went to full open and fast idle dropped with a blip of the throttle.
Vacuum booster disconnected and plugged, timing light turned to flash, Nick check this out. Timing was exactly and perfectly on 8* BTDC.
Nice too that there is absolutely no waver in the timing. It is spot and dead on each fire cycle. I have never seen a points ignition that steady.
View attachment 85414

I see the location of your oil fill. you can swap the valve covers left to right and have the oil fill in the front on the passenger side and have the pcv grommet in the front left as that is if you want. pull the carb or bag cover it and give the engine a craigslist rebuild (rattle can paint job) after a good power washing too if ya want to spiffy thing up under the power barn LOL

 

[MrMarty51]

I see the location of your oil fill. you can swap the valve covers left to right and have the oil fill in the front on the passenger side and have the pcv grommet in the front left as that is if you want. pull the carb or bag cover it and give the engine a craigslist rebuild (rattle can paint job) after a good power washing too if ya want to spiffy thing up under the power barn LOL

I like old crusty, scraped and bad paint. IDK about Nick though. He might find that intriguing.
Maybe I should surprize Him. Get some of that Rustoleum color shift paint and do a number on it.
I will pass along the info to Nick in case He does want to freshen it some.

 

[Will L.]

Love mouse motors. Like them more than I do the 6.5 for sure, especially without a ton of accessories. Power steering depends on the rig if needed, alternator and ac compressor now that I’m old and whiney. Everything is so simple to do.

That fuel line all needs to be the sae30r9 also because of the corn juice.