Why '66 fhc temp diff between headers + exhaust pipes?

(Puddinhead) #1

This morning used laser temperature Tool to measure heat on my '66 fhc. Found 600f on front head with 450f on adjacent header. While exhaust pipes were driver side 99 and low 80 on passenger side pipe ? Choke on to start and then off when engine warm. No coolant overheating. All three jets are even height and depth (when choke on).su tuning tool indicates identical idle sucking. Driver side pipe warm air to hand and even firing while passenger pipe rough firing and cold air to hand. Tach shoes idle at 1k, no spitting, revs nice. No smoke and no pipe spitting/oil.

Many thanks
'66 fhc

(Roger Benjamin) #2

have you checked the plugs after a good run.

(Puddinhead) #3

Thanks Roger, I’ll pull plugs and inspect.

'66 fhc

(Paul Wigton) #4

Handheld IR temp tools are notoriously variable, in their readings.

Id check that first, if all else is in spec.

(Puddinhead) #5

Thanks Paul

Then why warm air at exhaust driver side pipe versus cold air to hand at passenger side? Driver side pipe air flow seems more consistent and even while opposite side pipe exhibits uneven colder air exhaust and rough flow. Front header is running warmer and more even (at its exhaust pipe) than adjacent header.

'66 fhc

(Paul Wigton) #6

Spot emissivity of the measuring areas: are they the same? Exact same measuring distance?

Again, if the car runs properly, and all is in spec (an assumption, at this point), that suggests a measurement error.

(Ray Livingston) #7

If you’re saying (it’s REALLY not clear what you are saying…) exhaust coming out one tail pipe is notably hotter than the other, that typically indicates the hotter one is running very rich, which leads to raw gas burning IN the exhaust system. What’s coming out the tail pipes should be hot, but not unbearably so. You should be able to hold your hand 1-2" from the end of the pipe at idle for quite a while without serious discomfort. If not, you are definitely running very rich.

Ray L.

(Puddinhead) #8

Thanks Ray,

Yep, much warmer air felt at driver side pipe (front header) and more even firing than colder opposite pipe which runs rough. No spitting though, I’ll enrich the fire wall side SU a tad.

'66 fhc

(Paul Wigton) #9

If there’s a discrepency of temperature, something is amiss in basic settings.

(Puddinhead) #10

Thanks Paul, when I get home I’ll inspect plugs.

'66 fhc

(Ray Livingston) #11

Don’t waste time looking at plugs - with unleaded fuel, looking a plugs is a waste of time. Even with leaded fuel, without doing a “plug-cut” the reading you’ll get will be wrong. Go by how the engine runs. Turn ONE mixture screw CCW (leaner) until it runs badly. Then SLOWLY turn it richer, and listen to the engine. You’ll eventually find it runs better, then better, then better, then gets worse again. Back off just enough to get it running nicely again. That will get you very close. Now “feel” the exhaust. If very hot, go a bit leaner. If you feel/hear intermittent “puffing”, you could be rich or lean. If it occurs ONLY in the left pipe, it is the front carb. If ONLY in the right pipe, it is the rear carb. If BOTH pipes at the same time, it is the center carb. Once it seems right at idle, go for a drive. Often, correct idle setting will be WRONG for at-speed, almost always too lean, giving a slight lean surge when cruising at constant high speed, so you’ll have to go richer, in equal increments (1/4 turn or so), on all carbs until the surge goes away.

Ray L.

(Puddinhead) #12

Great info ! I’ll try that.

'66 fhc

(Puddinhead) #13

Ray, I just tried your suggestions, I can’t discriminate any changes happening. I went full turn and no changes.

'66 fhc

(Ray Livingston) #14

It may take SEVERAL turns if you’re way off. If your’e not sure where you are, set a decent starting point by adjusting the mixture screws until the jets are perfectly flush with the bridge of the carbs, then lower them 2-1/2 turns. That will get you in the ballpark.

Ray L.

(Tom D) #15

FWiW comment. It looks like this car may not have been out on the road for a good drive recently. If it has been “idling” around for a while, it may be all loaded up. I would not get too concerned until you get it out on the road, clean it out then adjust it.

(Mitchell Andrus) #16

Agree with Paul. While the IR handhelds may be consistent on the same material in the same condition, different materials can radiate at wildly different frequencies causing odd readings.

I once had to prove this to a fellow member by showing him a higher reading at the exhaust tip than at the manifold, defying logic. …Different materials.

(Liam O) #17

Just some thoughts and musings…

  1. ignition timing. retarded ignition would not explain why the temps are different, but it would help to explain what I think is your perception of high temps (if I am reading you right). Ray’s point about a rich mixture burning in the header is exacerbated by retarded ignition. A very poor throttle response and/or glowing header(s) would indicate over-rich mixture AND over-retarded ignition. I suggest you consider repeating you work at night to see if you observe a visible difference in the header colors due to heat. Maybe they won’t glow, but if they do, you may learn something. If there’s a significant fire a burnin’ in one or other header, you will see a reddish glow
  2. The possibility of correct timing, but a dead cylinder feeding the “hot” manifold unburned fuel. Pull each plug lead, in turn, and see what you find
  3. the condition of the exhaust system metal (any rust or holes in one side and not the other?) either leaking exhaust air or venturi-effect drawing in cold air that cools the discharge on one side before it gets to the tailpipe.

Just some thoughts and I don’t mean to distract

(Tom D) #18

Also, assuming your readings are correct, you could try checking the temperature at each exhaust port to possibly determine specifically which cylinder/s are the problem.

(Roger Benjamin) #19

looking at your spark plugs would tell a story also. just do it!!

(Terry Sturgeon) #20

Patrick You should be checking the temps of each individual (6) exhaust ports via the runner by the head. 2 - 5 should be 550 - 600 F at normal idle (not 1000 rpm), 1 and 6 always run a bit cooler, typically by 50 degrees (No I don’t know why, but have observed it on every car I’ve checked).
You need to first follow the manual’s directions exactly for tuning the carbs, in particular setting the mixture. Jets all at the same height sound suspicious - they are usually slightly different, the difference occurring when you check and adjust each carb for mixture.
I believe that checking each side of the exhaust system for different temps is a waste of time, you need to be
nearer the action by doing it at the head.
My experience with temp/mixture differs from Rays. At the head a higher temp on a cylinder port means it’s too lean. I’m not talking about large swings in mixture - like really rich, because you’ve tuned the carbs by the manual, and are close to perfect.
You can tell when you’re perfect by feeling the pressure of the exhaust exiting the rear at idle - when right (Ignition mixture etc) the pressure on your hands is very low, and the beat really even.

A quick edit - I don’t mean to suggest that 550 to 600 is a goal - really all you use it for is to balance the carbs to each other. 2 - 6 should be close to the same temp, as should 1 and 2