More esoteric stuff:
Grab the top of the distributor rotor and give it a shake. If you can feel
perceptible sideways movement your distributor bushing might have worn
enough to have unpredictable run out which means your points might hardly
open at times. Of course you should see this with a timing light, but it
might not be apparent at lower RPM.
Put a pressure gauge on the outlet of the fuel pump and see what you get
at load. Sometimes you'll get a reasonable pressure if the float needle is
closed but as soon as flow starts it falls off.
Replace the coil, condenser and points. If the problem goes away, toss all
three. The progressive nature of the performance loss makes this a little
less likely, though a declining spark voltage kind of works that way
because each cylinder has slightly different pressure and plug gap. As
always, the quick check is to narrow the gap a bunch--to say .010" and see
if it helps.
Blown head gaskets cylinder to cylinder look this way sometimes, but it's
unlikely with a Triumph motor.
-----Original Message-----
From: Russ Moore [mailto:rem@CBORD.com]
Sent: Tuesday, July 29, 2003 9:06 AM
To: Richard Taylor; fot@autox.team.net
Subject: RE: barking carbs
Check on the fuel system for any restriction. Did you overheat the engine
and possibly warp anything? How low was the water when you refilled it? If
it got hot, have you done a compression and leak down test since? I assume
no water in the oil and vice versa.
Fuel, fuel delivery, fuel pump, floats and the fuel bowls should be
checked. Check to make sure the carbs are still synchronized. You can use
the fancy ass vacuum gauge with the rising ball or the old fallback of
shoving a hose in your good ear and compare the sounds from one carb to
another by placing the other end in each carb with the engine running at
idle. Then try it at a partial throttle opening. It's more accurate than
you might think. If the linkage has slipped, having the carbs out of
adjustment will cause the type of problem you describe. If you made it all
the way back, it's likely not something major, that's the good news! Also,
you might try changing the coil after checking the points and timing. A
bad coil can cause even the strongest soul to tear hair out in trying to
diagnose it. I know this first hand.
Do you have an EGT gauge in your car? That would be a great indicator of
what exactly is going on in terms of combustion and will also be a dead
giveaway when the carbs are not both doing their job.
This is kind of like the Chineese menu, choose from above. Pretty sure
it's one of the above. I don't mean to insult you if you already have done
the above. Glad to elaborate if you can give a bit more information.
Best of luck.
Russ Moore
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
Behalf Of Richard Taylor
Sent: Tuesday, July 29, 2003 10:39 AM
To: fot@autox.team.net
Subject: barking carbs
FOTers
Last weekend I competed in the VDCA event at the Barber Motorsport Park in
Birmingham, AL. Beautiful weekend and a terrific track but I came home
early with a curious motor problem.
On the track at full throttle I first lost one, then a second then a third
cylinder until the engine quit entirely. After a ten minute rest the car
restarted and struggled (ran roughly) back to the paddock. It was low on
water. I let it cool over night and started it the next morning. If I
revved the motor slowly, it would come on up to full rpms. However, if I
blip the throttle quickly, it stumbles and barks fiercely out of the
velocity stacks.
I retarded the timing but nothing changed. I checked the movement of the
carburetor pistons and they look normal. So I packed up my stuff and drove
the 150 miles back to Atlanta in OD ( 2500 rpms, +60 mph). Temp and oil
pressure was normal and there was no measurable loss of either fluid. On
uphill grades (i.e.., under load) the barking carb syndrome would return.
The internals of the motor sound normal.
Any ideas of where to start looking? I'm kinda puzzled.
Richard Taylor
TR-4 Atlanta
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