Cool running cylinders

Seems all non-carb items have been addressed.

Before any carb disassembly, would recommend testing the service fuel level in the float bowls, using the clear plastic tube method. Look for too high fuel level in carbs 1 and 2.

If fuel levels are okay, would next suspect the pilot circuits.

And, is an in-line fuel filter in place?

Good Luck!

The only filter so far is the petcock filter. Do you guys generally replace the petcock with a single outlet one, the run a filter to a splitter? The left side hose is pretty short fof an inline.

If the fuel level is too high wouldn't it flow through the overflow before it flooded the carb out?

Post edited by: Kersten, at: 2007/10/17 17:40

Would put separate in-line filter on each line between the petcock and carbs. And route a new left line with a loop to allow room for the filter.

By the time excess fuel reaches the overflow, the proper level has already been exceeded. So a too high fuel level may result in excessively rich mixture without overflowing.

Good Luck!

I just re-adjusted the floats and cleaned out the float valves and slapped them back on, to no avail.
Against my better judgment I rearranged the slides the last time I had them off (1 and 2 swapped with 3 and 4), and this time I swapped the floats out the same way. I checked all the jets,(spotless)and put them back on, again, to no avail.
1 and 2 are still running cooler, and backfiring, Particularly after shutting it off and restarting.

Patton wrote:

it is entirely possible for acceptable cold compression figures to become unacceptable as the engine reaches operating temperature.

And vice versa?

wiredgeorge wrote:

Whether the carbs are in sync or not will not affect the cylinders firing. Off base a little...

I was hypothesizing that if the throttle plates on 1 and 2 were not opening as far as the plates on 3 and 4 then the first pair might not burn as hot but I guess it wouldn't be quite so hot.

THREAD REVIVAL!!!!!! (lol)


Ok,
Compression check

---

good
Valve lash

---

good
Timing, plugs,wires----good
Fuel, filters

---

good
So, I had a friend check out the carbs again (logical right?). We put the slides back in the proper carbs, but he noticed the carbs were on the rack wrong, so we swapped them back into their rightful position. Double checked the floats, blew everything out again, did another bench synch and slapped them back on.
Zero, Zilch, Nada, NO F'n change whatsoever.
Now

---

as before, 1 and 2 are still running cool, loading up and popping, and 3 and 4 are running fine.
EVEN THOUGH we swapped the carbs around. #1 and #3 carb were in the wrong place on the rack and got swapped back.
(Here's were my head spins---->) IF it is the carbs, wouldn't #1 run fine now and #3 be running cool?

So let's look at the electrical part again --

Are original coils being used?

What is voltage measurement to coils?

What is voltage measured across battery terminals at idle speed?

What is voltage measured across battery terminals at 4000 rpm?

What is condition of battery?

What is condition of the plug wires?

What is condition of the plug wire caps?

Has spray water mist over plug wires on running engine in darkened garage been performed to check for electronic leakage?

What is condition of the spark plugs?

All of the above matters with respect to the quality of spark across the plug tips. Is it a good, fat blue spark?

The AXIOM --
correct fuel mixture,
at sufficient compression,
with properly timed adequate spark,
WILL produce cylinder firing.

So a non-firing cylinder (i.e., cool exhaust pipe) is evidence that at least one of the above axiuom conditions is failing.

With acceptance of correct compression and valve clearances, that leaves fuel mixture, ignition timing, and spark quality.

The above questions relate to spark quality.

Ok... you have compression and the valve clearances are OK... Two cylinders are cool; aka not firing. The #1 and #2 cylinders? OK... swap the #1 plug wire with the #4 and the #2 with the #3. See if the problem MOVES to the #3 and #4 cylinders. If it stays on the #1 and #2 cylinders, I think it is safe to rule out electrical but not before. Then it will be safe to assume it is a carburetor issue.

Not trying to insult anyone but have you checked the spark plug wires?

Just my .02... are you sure enough fuel is flowing to the 1 and 2 carbs? Is the petcock partially plugged and just trickling a scant amount of fuel. Sounds like there's just enough fuel for idle but then leans way out above that(hence popping and backfiring) like the fuel isn't flowing fast enough above idle (incomplete burning due to insufficient fuel). If you pull the fuel lines off the carbs and open the petcock does fuel come out the same on both fuel lines? Sorry if I'm way off base here, just maybe something to check. And please let us know when you figure it out, may help someone else here! One more thing, Can this particular petcock be taken apart(i.e. cleaning) and then be put back together wrong?

Post edited by: twinkyrider, at: 2007/10/26 12:33

twinkyrider wrote:

Just my .02... are you sure enough fuel is flowing to the 1 and 2 carbs? Is the petcock partially plugged and just trickling a scant amount of fuel. Sounds like there's just enough fuel for idle but then leans way out above that(hence popping and backfiring) like the fuel isn't flowing fast enough above idle (incomplete burning due to insufficient fuel). If you pull the fuel lines off the carbs and open the petcock does fuel come out the same on both fuel lines? Sorry if I'm way off base here, just maybe something to check. And please let us know when you figure it out, may help someone else here! One more thing, Can this particular petcock be taken apart(i.e. cleaning) and then be put back together wrong?<br><br>Post edited by: twinkyrider, at: 2007/10/26 12:33

I had this very same epiphany at work today. I have swapped the carbs around. the plugs around, the wires around and even the coils around, and it only affects 1 and 2. The common denominator is the damn petcock! I will tinker with it after my afternoon nap and repost later.