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By Tim Quinn - 6 Years Ago
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There is a big temperature difference from the left bank at +400 degrees to the right bank at 297 degrees. The measurement was taken with the '56 Ford 312 warmed up and running.
I pointed the infrared thermometer at the very end of the exhaust header, closest to the fire wall, on both banks and got the imbalanced readings of +400 degrees left and 297 to 300 degrees right bank.
Why is this happening or is it normal ????
Let me know what you think,
Thanks,
Tim Quinn
Florida
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By Robs36Ford - 6 Years Ago
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Some left cylinders running a bit lean ?
Same Spark plugs all around? Same gap?
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By Tim Quinn - 6 Years Ago
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All spark plugs are E3's and the whole left bank is hotter that the right bank.
Idle is a 700 rpm, temperature gauge (after market ) sits a 180 all day.
One thing, have a Summit 600 cfm and have the two idle screws closed, can't get the car to run well with the idle circuit screws open. Have to advance the throttle advance screw to keep engine from stalling when the idle circuit screws a opened two turns. So I close them and the engine runs smooth but hot on the right bank.
Why is it running lean on only one bank?
Let me know what you think,
Tim
Hot 'n Humid, Florida 33706
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By Dave C - 6 Years Ago
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If you have to close the idle mixture screws to keep the engine running, then I think you may have a carb issue. Maybe a blown power valve, or float to high. Retarded timing will cause high EGT's
A lean mixture can cause a low EGT, and a rich mixture can cause a high EGT. Also a collapsed exhaust can cause high EGT's. I've seen collapsed exhaust systems glow red.
Some things to look at or consider.
Dave
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By Tim Quinn - 6 Years Ago
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Dave ,
Thanks for your evaluation. I'll check the power valve.
Tim
Florida.
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By charliemccraney - 6 Years Ago
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The engine should stall with only one idle screw turned in. If the engine still idles with both idle screws turned in, then you do have a fuel problem. In addition to the power valve and floats, having the throttle open too far at idle will cause fuel to be pulled from the boosters, in addition to or possibly instead of the idle circuit. You can check this by looking down the carburetor with a mirror while the engine is running. It could also be too much pressure from the fuel pump. 700rpm is a high idle for a stock and even more mildly modified engines. If your cam does not require that, then it could be a clue to the problem. A vacuum leak or retarded timing will require the throttle to be farther open in an attempt to compensate. If the cam is large enough that 700rpm is justified, then then you may need to close the primaries and open the secondaries in order to achieve the correct idle speed while ensuring that the idle circuit functions correctly.
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By Tim Quinn - 6 Years Ago
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Charlie,
All good info, but, why is only one bank hotter ?
Also, the throttle screw is back as far as it can go, it is not engaged at all.
What if I open the idle screws 2.5 turns to let more fuel flow.
Because it is LEAN, that means it needs more fuel...right ?
Now with the idle screws open, I have to turn the throttle screw in
to prevent the engine from stalling and this gives more fuel
What are you thoughts ?
Tim
Florida
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By charliemccraney - 6 Years Ago
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I don't know why one bank is hotter.
If the throttle speed adjust screw is backed all the way off and it still idles at 700rpm, then some possibilities are:
The throttle is hanging open, maybe caught on the gasket, maybe stuck in the throttle bores of the intake or spacer.
The secondary throttle is adjusted too far open.
Vacuum port without a cap
Vacuum leak.
Some other means of getting air into the intake.
Since the engine runs with the mixture screws all the way in, you need to fix that. Anything else will be only a bandaid on the problem, which could lead to far more expensive problems, fuel washing the cylinder walls, oil dilution, etc.
Fix the idle speed problem and idle mixture problem and then move on. Maybe they are the actual issue, too.
Another thing is that your '56 312 requires a '57 or newer distributor to work with the Summit carburetor. I don't think that would cause the hot bank issue, though and it would not cause the idle speed and mixture problem.
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By Tim Quinn - 6 Years Ago
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Thanks,
I have a modern electronic distributor and coil to go with the Summit carb.
I'll work on the problems at had and get back to you later on.
Again,
BIG THANKS FROM HOT 'N HUMID TIM IN FLORIDA
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By Tim Quinn - 6 Years Ago
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Hey Charlie,
About vacuum leaks..........i have a PCV hooked up to the exhaust tube and connected to the back port on the carb. That would be a vacuum leak into the crank case...RIGHT ?
Could the PCV be installed backwards ?
Tim, Florida
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By charliemccraney - 6 Years Ago
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Some PCV Valves can be installed backwards. A PCV valve can be thought of as a controlled vacuum leak and since most PCV valves used are not application specific to our engines, it can be too much of a leak for the combo. The best you can do for an off-the-shelf valve is to use a pcv valve from a similar size and power engine. There is an adjustable, rebuildable valve on the market but it is more expensive than most seem to want to spend. http://mewagner.com/
However, the way you describe yours, I'm either not understanding or it is installed totally incorrectly. When you say exhaust tube, do you mean the exhaust pipe? The valve should be between the crankcase and carburetor
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By Tim Quinn - 6 Years Ago
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Charlie,
The tube I'm taking about is the old crankcase tube that sucked the fumes out of the crankcase.
It hung over the back of the engine and the fumes escaped under the car. Drag tube ?
Any how, I opened up the idle circuit screws to 2.5 turns, hooked up the vacuum gauge and closed the idle screws one turn and got between 19 and 20 inches of vacuum. Also adjusted the throttle screw and the idle is now 650 rpm.
BUT !! the exhaust manifold temp on left is 544 degrees and on the right it is 491 to 480 a big difference and closer for both sides.
What would you day the exhaust temp should be at the cylinder closest to the firewall ?
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By oldcarmark - 6 Years Ago
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You have a Thunderbird Cover. That Tube should be removed and PCV plugged directly into Pushrod Cover. Is there a Reason U used it to hookup a PCV?. The PCV can allow too much Air to pass into Carb at Idle. Trying a PCV from a smaller Engine my help or try restricting the Hose from PCV to Carb. Cut down Airflow.
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By Tim Quinn - 6 Years Ago
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will give it a try, restrict air flow on the PVC
Thanks,
Tim
Waiting Room for Heaven, Fl 33706
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By oldcarmark - 6 Years Ago
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The PCV Hookup must be Airtight with the only "Air" intake being from Valley Cover. The PCV I have on mine is a Fram FV411. I plugged it in and worked very well with no further Modification. PCV Valve is Sometimes Trial and Error to get One that works for your Installation. It sounds like You have some Adjustments to make to Carb. I would suggest disconnecting and plugging PCV hookup and setup Carb without it. Once U have adjusted properly plug the PCV back in and make Mods so it works without excessive Air passing at Idle. Then You will at least know any Problem is from PCV.
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By charliemccraney - 6 Years Ago
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As a test, to find out if the pcv valve is causing the high idle, simply disconnect it from the carb and plug the port on the carb. You won't hurt a thing to run it at idle like that for a test.
I don't know what manifold temperature should be for a good running engine.
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By Tim Quinn - 6 Years Ago
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Next Step
I have a K&N air filter with a hole in the bottom of the filter base.
I'll run the PCV hose into this hole and then the oil fumes will pass
into the air filter. This way the carb is bypassed and out of the picture !
Hopefully no air leaks.
Will advise if this plan works.
Thanks for your input, it has been helpful a true learning moment.
Tim
Downtown, Florida 33706
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By oldcarmark - 6 Years Ago
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PCV stands for Positive Crankcase Ventilation. Sticking the Hose in the Air Cleaner is useless. The Valve must be hooked to Engine Vacuum to draw Fumes from the inside the Engine. As Charlie and I both suggested unplug the PCV and cap the Vacuum inlet on Carb and setup the Carb first so its working correctly and then deal with the PCV. By the sounds of what You are describing You have Vacuum leak Issues.
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By miker - 6 Years Ago
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Try it as mark and Charlie suggested. The opening on the air cleaner bottom is made to use from a sealed oil filler cap for a “closed PCV” system. The factory oil fill cap is used on an “open PCV” system. Goggle that and you’ll see the difference and how they work.
I run both my y blocks with closed systems, using this type of cap to the air cleaner. The PVC valve is in the valley cover (with a baffle under it), then to the PCV port on the carb.
The fill cap looks like this. I don’t know if this fits our oil fill tubes. 
I’ve also used this grommet as the PCV grommet in the valley cover. Again, I’m not sure this item is exactly the one you need.
https://www.summitracing.com/parts/mor-68772
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By oldcarmark - 6 Years Ago
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miker (6/14/2019)
Try it as mark and Charlie suggested. The opening on the air cleaner bottom is made to use from a sealed oil filler cap for a “closed PCV” system. The factory oil fill cap is used on an “open PCV” system. Goggle that and you’ll see the difference and how they work. I run both my y blocks with closed systems, using this type of cap to the air cleaner. The PVC valve is in the valley cover (with a baffle under it), then to the PCV port on the carb. The fill cap looks like this. I don’t know if this fits our oil fill tubes. I’ve also used this grommet as the PCV grommet in the valley cover. Again, I’m not sure this item is exactly the one you need. https://www.summitracing.com/parts/mor-68772
I used that Grommet too. Works well. You will need a smaller Grommet to hold the PCV. Grommet will fit inside the bigger Grommet. I used Super Glue to bond the 2 together otherwise the smaller One works out of the bigger one. It almost sounds like He has a Thunderbird Cover. If so you just need a Grommet to go in the Cover once U remove the existing Tube. Already has a Baffle underneath.
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By Tim Quinn - 6 Years Ago
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The vacuum leak was caused by the PVC hook up.
Thanks for your help,
Tim
Nearly Dead
or
Newly Wed,
Florida 33706
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By charliemccraney - 6 Years Ago
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Do the idle screws stall the engine now and are the manifold temps better?
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By Tim Quinn - 6 Years Ago
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Idle screws open two turns, perfect idle and curb idle is set a 626 rpm.
Car runs better and seems more responsive............me happy
Big time thanks for your help and time,
Tim (Hot 'n Humid) Florida
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By charliemccraney - 6 Years Ago
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But does it stall if one or the other screw is turned all the way in? Verify that it does and all is probably well with the carburetor, now.
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By Talkwrench - 6 Years Ago
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Looks like all fixed , Sounds like it was carb issues that Charlie ran you through .. Just wondering if you still had an exhaust / heater flap in one of the manifolds?
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By oldcarmark - 6 Years Ago
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Talkwrench (6/16/2019)
Looks like all fixed , Sounds like it was carb issues that Charlie ran you through .. Just wondering if you still had an exhaust / heater flap in one of the manifolds?
Heat Riser Valve. Good Point. They tend to seize up.
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