Heat riser/ choke question

[BigBlockMopar28]

When I changed my 318 from the stock 2bbl and intake to the 4bbl 340 intake, I used the intake gasket that blocked off the heat riser for whatever reason. Saw a fb discussion about heat risers and up to this point I had no idea it was used for the choke and fast idle on it, ever since then the electric choke wants to stay in fast idle for a very long time, even on startup after being driven. That being said, is there a way to adjust fast idle and when it returns to regular idle without the use of the heat riser? Carb is a 600 holley street warrior vacuum, first carb i've owned with an electric choke minus the stock 2bbl. TIA

 

[RustyRatRod]

You're talking about the exhaust cross over, not the heat riser. The heat riser is located in the passenger's side exhaust manifold and closes on cold startup to aid in fast warm up.

The exhaust cross over IMO should be left unblocked on most street cars that are driven every day, or several times a month. The cross over helps atomize fuel and also takes a part in proper choke operation as you've already said. I am unsure if you can adjust the choke so that it will work to your satisfaction with the cross over blocked. You can certainly try.

 

[odcics2]

As stated above...
On a cold start in cold weather, the gas will condense in the intake and puddle up. And yes, some gets into the cylinders, washing the oil off the walls.
This is the very reason of a choke! You need SOME gas in a vapor state to run the engine!

Chrysler had the 5-50 warranty and their durability testing reflected the goal of parts lasting that long.
Hence, heated crossover and a heat riser to get it all warmed up as fast as possible.

 

[toolmanmike]

As far as I have seen the electric chokes on carbs nowdays can be adjusted by loosening the cover screws and turning the cover to richen or lean. The covers are usually marked. The electric choke works independently of the heat riser and crossover and you should be able to adjust it to get satisfactory results. I wouldn't adjust it any more than a notch or two at a time.

 

[toolmanmike]

Here's a great video.

 

[krazykuda]

When I changed my 318 from the stock 2bbl and intake to the 4bbl 340 intake, I used the intake gasket that blocked off the heat riser for whatever reason. Saw a fb discussion about heat risers and up to this point I had no idea it was used for the choke and fast idle on it, ever since then the electric choke wants to stay in fast idle for a very long time, even on startup after being driven. That being said, is there a way to adjust fast idle and when it returns to regular idle without the use of the heat riser? Carb is a 600 holley street warrior vacuum, first carb i've owned with an electric choke minus the stock 2bbl. TIA

As far as I have seen the electric chokes on carbs nowdays can be adjusted by loosening the cover screws and turning the cover to richen or lean. The covers are usually marked. The electric choke works independently of the heat riser and crossover and you should be able to adjust it to get satisfactory results. I wouldn't adjust it any more than a notch or two at a time.

TMM is correct, just adjust the electric choke on the carb so it will open properly... I had a 318 with a Holley 600 vac secondary with electric choke and drove it daily in below zero weather...

Once the electric choke is adjusted properly, just pump the gas twice, turn the key to start it, watch the oil pressure go to start cold pressure, then put it in gear and drive away with no stumbles... even below 20° F, it still would not stumble in gear after a fresh cold start...

 

[AJ/FormS]

Even factory 340s ran a crossover with a heat-riser valve. If you are running into the colder seasons, IMO you need that system in good working condition.
If you are running the stock 318 under that big-port intake, IMO, I highly recommend a small-port dualplane 4bbl intake; It will really wake the teener up. At least it did my 73. No contest; gobs more low-rpm/midrange torque, I thought. I even swapped down from 3.55s to 3.23s, with very little loss in seat-of-the-pants performance.I ran the big TQ, and dialed the secondaries in as fast as she'd take 'em.

Cold engines also like lotsa timing to start the fire very early,to synchronize the peak cylinder pressure where it needs to be with all the cold parts trying to kill the fire. . You just have to co-ordinate the cold timing with the hot-timing and make sure to keep the power-timing below the detonation threshold.
I use (on my 360) a two-stage timing curve, very fast up to cruise rpm (2250 for me), or a little higher. Then I slow it right down so I can burn 87E10 at WOT. It doesn't come "all-in" until 3200/3400, for my aluminum heads, which stay colder even longer.With iron heads you could probably speed it up some.

 

[Murray]

All of this is good advice. Electric choke is eliminating the need for a properly working heat riser. Just to add- beyond the electric choke thermostatic spring adjustment, there is linkage adjustment for fast idle adjustment. Sounds like the engine is not coming off the fast idle cam. Find this cam. There is an adjusting screw for curb idle and one for fast idle. Hope this helps.