Cracked heat riser

[chuckfmtexas]

I posted in Wanted to Buy that I need a heat riser for my 1932 Series 67 sedan.  My engine started missing badly and stalling.  When we checked a number of things we found the middle four cylinders are not firing because the apparently are not getting gas.  We checked compression and all 8 cylinders had 90 lbs, there is fire to all plugs (we converted the distributor to a single set of points). The carburetor was rebuilt 250 miles ago but we have it off and will check it to see if we have blockage. I noticed yesterday that the heat riser had two vertical cracks so we are removing it to see how damaged it is.  I am thinking that those cracks are causing the lack of gas into the middle four cylinders.  We have also seen gas dripping to the floor when the engine is running, even badly and missing.  It is like there is not enough vacuum to suck the gas into the cylinders.

 

I understand the heat riser is cast iron and there are specialists that know how to weld it and perhaps seal the cracks.

 

Appreciate any advice or experience folks have had in similar situations,

 

Chuck

[Bob Engle]

The cracks you see on the outside would be on the exhaust side of the heat riser.  Most people block the exhaust from entering the heat riser as modern gas does not need a lot of heat to vaporize.  The question will be are the 2 tubes on the inside in good condition.  If these are corroded through, You will suck either exhaust or air into the intake.  If the internal tubes are good and the exhaust is blocked from entering the heat riser, there is no need to repair the outer cracks.

 

With gas dripping out of the carb, it sounds like you may have a float problem flooding the carb.  A high level in the fuel bowl will mess up the idle jets.  

 

I would suggest hooking up a vacuum gauge on the intake manifold.  This will give you a good indication of how the intake system if functioning.  Also pull some plugs and see what they look like between the center cylinders and the end cylinders.

 

Bob Engle

[27donb]

Block it off, repair, restore or replace your cracked heat riser, and reinstall it on the engine for the last time.

 

Both of my 27's have blocked heat risers with no driving issues. 

 

The exhaust heat on these old cast iron risers takes its toll, and the system is not needed with most of these classics being driven in warmer weather and on modern fuel. 

[Guest outlaw car man]

Amen. A typical issue. Classic example, put your hand on the INTAKE manifold, if it's hot you are running HOT exhaust thru it. Very common. I would address that as the above guys have said.

[chuckfmtexas]

thanks for the advice guys,