1952 215 6 cylinder heat riser questions
#16
06-12-2017, 08:08 AM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
The "open" flap is the normal configuration (engine warmed up) if we're going to define our terms here, right?
Anyway the purpose of the heat riser as I understand it, is mainly to prevent carburetor icing. Under certain atmospheric conditions - high humidity and well above freezing temp, the venturi effect can cause the carburetor throat and butterflies to ice up. I've seen this happen one time and it happens really fast.
So a hot start problem seems to me, is probably something else - vapor lock, fuel percolation etc. Modern gasoline is formulated a lot differently than it used to be, since the advent of fuel injection. When most cars had carburetors, the resistance to vapor lock was an important consideration in the fuel blends. Something called the Reid Vapor Pressure index or somesuch. They don't care about that now. On a hot day with a hot engine the fuel will be literally boiling in the fuel pump as well as the carburetor bowl. I've been meaning to measure the AFR at idle under those conditions. The fuel boiling should throw the idle AFR way off compared to just a few degrees cooler.
It may be just a summertime adjustment of the idle fuel mixture will help your issue, and/or maybe lower the float height a tad from stock spec. Try running MMO in the fuel. Old timers used to add a pint of Diesel in the gas per tank. Worth a try anyway.
Anyway the purpose of the heat riser as I understand it, is mainly to prevent carburetor icing. Under certain atmospheric conditions - high humidity and well above freezing temp, the venturi effect can cause the carburetor throat and butterflies to ice up. I've seen this happen one time and it happens really fast.
So a hot start problem seems to me, is probably something else - vapor lock, fuel percolation etc. Modern gasoline is formulated a lot differently than it used to be, since the advent of fuel injection. When most cars had carburetors, the resistance to vapor lock was an important consideration in the fuel blends. Something called the Reid Vapor Pressure index or somesuch. They don't care about that now. On a hot day with a hot engine the fuel will be literally boiling in the fuel pump as well as the carburetor bowl. I've been meaning to measure the AFR at idle under those conditions. The fuel boiling should throw the idle AFR way off compared to just a few degrees cooler.
It may be just a summertime adjustment of the idle fuel mixture will help your issue, and/or maybe lower the float height a tad from stock spec. Try running MMO in the fuel. Old timers used to add a pint of Diesel in the gas per tank. Worth a try anyway.
Nope. JB has it right. The flap in the OPEN position allows warmed air from the exhaust manifold into the intake- that's the COLD engine position, the flap in the CLOSED position -blocks the flow of warmed air into the intake manifold side- that is WARM engine position.
I am very familiar with RVP values - I actually own a test kit to determine actual gasoline RVP. I used to work for a car manufacturer and at one point we needed actual values for the engineers to create updated software for some of our cars that had cold/hot starting issues.
JB is also correct that with the flap OPEN it creates a very hot environment- boiling fuel in the carburetor after sitting with a hot engine. The flap open allows all that residual heat in the exhaust manifold to heat the bottom of the carburetor...
My quick test yesterday showed a noticeable difference with the flap CLOSED.
The other reason for the heat riser is to help in proper atomization of fuel when the engine is cold.
And I presume you're right about preventing carburetor icing as well. I have had that happen before- can be pretty exiting...
#17
06-12-2017, 08:10 AM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
#18
06-12-2017, 08:11 AM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
#19
06-12-2017, 08:34 AM
#20
06-12-2017, 09:16 AM
I have the 226, which is pretty similar in design I think in relation to the heat riser. It's really a bad system today in my opinion with today's fuels and Georgia summer heat. Hard hot starts, I still fight them today despite running pure non-ethanol 87, tuned carb, heavy duty radiator, etc.
I have found that on a hot start, like 5-15 minutes after shut off, bumping the gas at just the right time when hitting the start button is the trick. I also have developed the habit of letting it idle for a minute or two before I shut it down, getting a lot of heat out after a long run.
In the other three seasons of the year I have no problems.
I have found that on a hot start, like 5-15 minutes after shut off, bumping the gas at just the right time when hitting the start button is the trick. I also have developed the habit of letting it idle for a minute or two before I shut it down, getting a lot of heat out after a long run.
In the other three seasons of the year I have no problems.
#21
06-12-2017, 03:56 PM
Logistics Pro
.
#22
06-12-2017, 04:04 PM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
#23
06-13-2017, 08:45 AM
Logistics Pro
Heres an observation I've made with my 223 which has the same designed heat riser. After shutting the engine off the engine temp starts to rise due to no coolant circulation, that normal. But after sitting for a short period of time enough heat transfers to the intake manifold and carb to boil the fuel, I have a glass bowl Holley and I can watch it LOL. This is with California's own crap blend of fuel, I don't know what other parts of the country would do. Of course this never happened back in the leaded fuel days..
#24
06-13-2017, 09:35 AM
Heres an observation I've made with my 223 which has the same designed heat riser. After shutting the engine off the engine temp starts to rise due to no coolant circulation, that normal. But after sitting for a short period of time enough heat transfers to the intake manifold and carb to boil the fuel, I have a glass bowl Holley and I can watch it LOL. This is with California's own crap blend of fuel, I don't know what other parts of the country would do. Of course this never happened back in the leaded fuel days..
#25
06-13-2017, 05:48 PM
Logistics Pro
When I was having trouble starting my engine after it was hot, it was suggested that I try what was called a phenolic spacer. A phenolic spacer is essentially a heat barrier installed between the manifold and the carburetor. This spacer takes the place of the regular gasket. It is quite thick and keeps the gas from boiling.
Jim
Jim
#26
06-13-2017, 06:02 PM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
When I was having trouble starting my engine after it was hot, it was suggested that I try what was called a phenolic spacer. A phenolic spacer is essentially a heat barrier installed between the manifold and the carburetor. This spacer takes the place of the regular gasket. It is quite thick and keeps the gas from boiling.
Jim
Jim
I have the "gasket stack" - factory. Works fine as an insulator.
#27
06-13-2017, 06:19 PM
#28
06-13-2017, 08:36 PM
Join Date: Aug 2015
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
#29
06-13-2017, 09:05 PM
I have found that on a hot start, like 5-15 minutes after shut off, bumping the gas at just the right time when hitting the start button is the trick. I also have developed the habit of letting it idle for a minute or two before I shut it down, getting a lot of heat out after a long run.
Heres an observation I've made with my 223 which has the same designed heat riser. After shutting the engine off the engine temp starts to rise due to no coolant circulation, that normal. But after sitting for a short period of time enough heat transfers to the intake manifold and carb to boil the fuel, I have a glass bowl Holley and I can watch it LOL. This is with California's own crap blend of fuel, I don't know what other parts of the country would do. Of course this never happened back in the leaded fuel days..
#30
06-14-2017, 11:07 AM
Logistics Pro
When I was having trouble starting my engine after it was hot, it was suggested that I try what was called a phenolic spacer. A phenolic spacer is essentially a heat barrier installed between the manifold and the carburetor. This spacer takes the place of the regular gasket. It is quite thick and keeps the gas from boiling.
Jim
Jim