Subject: [TR] Annoying "bulb-blub-blub" sound

From: Joe DeMuth <[email-masked]>
Date: Sun, 20 Jul 2014 11:49:15 -0500

Does anybody know what causes the "bulb-blub-blub burble sound you get when
you let up on the gas, especially loud in higher gears. It sounds like muffled
explosions in the mufflers. My car (TR6) has started doing it excessively and
I really would like to get rid of it. So far I have adjusted the valves,
checked timing, checked the lean/rich mixture and all seemed fine. The next
step is to slap another set of Strombergs on to see if it goes away. I am
stumped. The sound started about 1/3 of the way back to Minnesota from the Hot
Springs British Car Week gathering in early June and has been getting worse
ever since. Other symptoms, hesitation on acceleration and some missing. The
distributor has recently been rebuilt by Jeff at Advanced Distributor so I
dont think that is the culprit.

** [email-masked] **

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From: "Randall" <[email-masked]>
Date: Sun, 20 Jul 2014 10:05:07 -0700

> explosions in the mufflers.

That's usually just what it is.  The carbs tend to go lean under deceleration,
and with the throttle fully closed and rpm high,
combustion chamber pressure is very low.  As a result, the fuel/air mixture
doesn't burn in the cylinder.  But it does burn
eventually when it gets into the exhaust system.

The hesitation and missing would also point to mixture being too weak, under
the conditions where it happens.

Probably first place I'd check would be the diaphragms in the carbs.  A split
or leak can cause the mixture to go lean.  Another
thing to check would be the bypass valves in the carbs, which exist just to
prevent this from happening.  You could also try going a
turn richer on the mixture adjustment and see what effect that has.

Sometimes, a reduction in exhaust backpressure will make the problem worse.
You might check the exhaust for leak or missing baffles
in the mufflers.

I assume you've already done an ignition tune-up.  New plugs (or at least
clean and gap), points, etc.

Randall