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Member
Posts: 8
Location: Brisbane Australia | Hello all, from Brisbane Australia, :-). I bought a 61 belverdere sedan from a young fella in Idaho awhile ago. From what i can gather and my mechanic agrees with me the car only has 67000 miles on the clock but i think it sat for a few years. I have changed plug leads ,spark plugs, new fuel tank etc and have done a compression check. All of the cylinders came up to around 140--155 psi but something is not right with the twin exhaust. on the passengers side there seems to be hardly any exhaust pressure from the pipe but drivers side is great, I noticed there was a block on the bottom of the passenger side manifold and if im right is this some kind of heat trap with a flap in it? i think maybe this flap could be rusted 3/4 closed? Is that possible after sitting for so long? many thanks in advance for any advice, Cheers, Ray.  |
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Regular
Posts: 79
| Ray,
Found this explanation on another mopar website - http://board.moparts.org/ubbthreads/ubbthreads.php/topics/140805/pr...
Background
==========
The heat riser, the choke, the heated air intake including the heat stove and air cleaner, are all suppose to work together to help the car start quickly when cold, warm the engine up quickly
when cold, reduce emmissions at initial startup and fast idle, and allow the car to be driven cold.
In addition, 2 very important settings on the carb are also quite critical, the 2nd step on the fast idle cam (choke postioned nearly closed, and the fast idle speed (RPM) for that setting which is set after the car is fully warmed up...
When all of these are functioning properly, and
set correctly, the car fires first time everytime
(COLD), goes immediately into fast idle, steps down twice (tap on the gas pedal) to normal idle speed within 1 minute and is driveable cold.
Except on very, very cold days ...below freezing etc. The fast idle to normal idle speed drop down time is longer, maybe up to two minutes.
Take any of those pieces out of the equation for any reason, deliberate or otherwise and the whole system is compromised... but what gets comprised is cold weather related stuff..
Meaning its either hard to start, slow to warm up, poor driveability cold etc...
If the heat riser is stuck open (or removed)the car will spend quite a bit of time in fast idle..assuming the choke closed corrrectly and the fast idle cam was set right... .it will be very slow to warm up...and probably have very hard to drive cold. You can't put it in gear until the fast idle steps down to normal idle...
This is classic scenario for an old mopar you
have to start and let warm up for 10 minutes before you can go driving it.
At least that has been my experience.
If the heat riser is stuck closed, the car may
run warm and even overheat in the summer time especially if you run factory A/C, but you will have none of the cold related issues...
Also, the carb will get so hot it will
eventually warp (Most of the old Carter 2bbl carbs suffer from this although you'll be hard pressed to have anyone admit it)
You'll lose some performance because of the back pressure increase...etc..
On a car with a heat riser stuck closed.. after the car warms up you can take a long screwdriver
and rotate the counter weight to open it. You'll
actually hear the engine idle slightly faster
when the restriction to the exhaust is removed (by opening the valve!)...
Bascially the car was designed to have the heat riser heat the base of the carb to get the fuel to atomize quickly when cold...
That's important if you want to start the car
and get of the driveway quickly in the winter time. Daily drivers of old needed this...
Today most mopar owners are'nt concerned about that. Most of us start 'em up and let them run for a few minutes... and then off we go...
SO what happens if yours doesnt work..
Well... your not alone I've NEVER felt like
they worked well at all even when rebuilt,
They are either slow to open never really seem to open all the way etc...
Given that original ones are 35+ years old.
Its hard to expect them to still work..
Replacements frequently just don't work very well..even NOS replacement rebuild kits (I've done those!) are'nt a fool proof solution.
Your best alternative...
If you remove the heat riser...
Make sure your heated air system works
and switch to an electric choke!
Electric choke conversion kits for the old carter 2 bbls are out there and they work very well...
I've done this..with almost no impact on cold weather starting, idle, or driveability...
Hope this helps. |
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Member
Posts: 8
Location: Brisbane Australia | Thanks for the info Madfins, When i say there is no exhaust pressure out of the passenger side pipe it feels as if its only running on two of the cylinders on that side, the engine runs smooth but no pressure, could it be valves? but then you would think the psi would be down? ill try adjusting with screwdriver and see what happens, Cheers,! |
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Expert 5K+
Posts: 8445
   
Location: Perth Australia | Check to see if it has a crossover pipe fitted into the exhaust system, if the muffler is clogged up, it will push all the exhaust out the other side
Without reading the book above, the heat flaps do sieze and also the heat spring that opens the flap also break, which can block off the exhaust
Being in Brissy, if that flap is stuffed, just leave it alone and get rid of the flap (cut it away with something, leaving the shaft intact)
Its only there to make the engine warm up faster ect
If you use the choke, you could wind the choke partially off so it comes completely off faster or fit a carby with an electric choke, whatever
The heat flap is more important in Victoria or Tassie, not so much here or where you are
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Member
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Location: Brisbane Australia | Cheers. Thanks for that Mick. Ill keep you posted. Nice ride you have! :- ) |
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Expert
Posts: 4070
Location: Connecticut | madfins - 2015-09-22 11:10 PM SO what happens if yours doesnt work.. Well... you're not alone I've NEVER felt like they worked well at all even when rebuilt, They are either slow to open never really seem to open all the way etc... Given that original ones are 35+ years old. Its hard to expect them to still work. Your description is very good. But if your heat riser doesn't work, it should be rebuilt so that it functions properly. Mine was frozen in the open position. Since I had the exhaust manifold off, I sprayed it with PB Blaster and worked it a little at a time until it opened and closed smoothly. Then I reinstalled the thermostatic spring and counter weight. I spray it once every few months with the correct Mopar penetrant to keep it functioning. My experience with starting and driving my 58 Plymouth: Even after sitting a few months, I close the choke by stepping on the gas pedal. Then the car starts right up after three or four cranks. I let the car run for about 15 seconds, then put it into drive and head out. No problems. So I respectfully disagree with your assessment that 'they never worked well' etc. Ron |
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Expert 5K+
Posts: 7450
Location: northern germany | madfins - 2015-09-22 11:10 PM
Well... your not alone I've NEVER felt like
they worked well at all even when rebuilt,
works for me with no problems whatsoever for 27 years, like back in the day for billions of people, if they are serviced. that means a drop of special oil on the shaft on both sides. not a big deal. i do it only once a year. actually if you drive daily they can't freeze. since i installed headers i'm using a larger 2.1/2" big block chevy heat riser. no problems at all. |
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Expert 5K+
Posts: 7207
Location: Victoria, BC, on Vancouver Island, Canada | Here is a video of the rebuild of the heat riser valve in my 1960 Chrysler, which was seized up. https://youtu.be/-oSPY-MYqvQ |
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heat flap,
