View Full Version : Un-Balanced Carb Symptoms

04-07-2012, 12:16 PM
I've been unsuccessful in a search, but I'm curious as to what symptoms of unbalanced carbs may be? I have HS6's on my TR6 and have them balanced perfectly at a 900 RPM idle. The carbs are in as new shape (3 years old). The engine runs very smoothly unless I boot it to about 5000 RPM when it seems to develop a very slight miss. As with the solution to most carb problems I've checked all of my ignition electricals from a newly Advanced rebuilt dizzy (Pertronix) through to the coil, leads, and spark plugs and everything seems okay.

Timing is set at 14 BTDC with no vacuum retard (or advance).

So back to my original question, could this slight high RPM miss possibly be indicative of a carb imbalance?

04-07-2012, 12:50 PM
<span style="font-size: 11pt"><span style="color: #006600">I had the same problem with my 3A HS6s.
Since I have overdrive I seldom get to 5000RPM so I decided to live with it.
Later on I had occasion to put her on a dynamo-meter. The technician shut down the test at 3400RPM...Said it was running so LEAN that any faster would do major damage. He suggested replacing the needles with a set of RH and manually re-balancing them with a slightly richer mixture.
Solved the hi-RPM miss for me altho I never did take it back for a re-test on the dyno.
Frank </span></span>

04-07-2012, 12:57 PM
IMO synchronization of the throttle plates is very unlikely to be the source of your high speed miss.

Mixture could easily be a problem (although it should show on the plugs, if you do a plug cut), or something that would affect mixture like valve clearances or a bad cam lobe.

The usual symptom of unbalanced carbs is rough idle, and even then they have to be pretty badly out to notice.

04-07-2012, 01:59 PM
I vote for an out of phase rotor..especially having the Pertronix which seems to make the distributor more vulerable. If you have the micro adjustment wheel on your dizzy, the phase can be easily corrected and still maintain your sweet spot.

Geo Hahn
04-07-2012, 04:26 PM
I always carefully balance the carbs but agree it is far from the most critical component -- for one thing there is a pretty balance tube across the manifold (on the 4 cyl anyway) that provides some forgiveness.

Usually I think first of plugs and plug wires when there is a high speed miss but I assumed your checking of connections included putting an ohm meter on the plug wires.

04-07-2012, 04:35 PM
Yes, the resistance on the Magnecor wires ranges from 1.4 on the shortest to 2.2 on the longest.