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TR6 1973 TR-6 Unbalanced Intake

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ericol222

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Any ideas why the first three cylinders draft significantly less than the rear three cylinders. Stromberg Carbs have been rebuilt, mixture needles are even but the rear carb I have to adjust to zero draft to balance with the forward carb that has to be significantly increased. Currently the idle is stable but this is obviously not right. The Vacuum Gauge indication is in the green and the timing is correct. These carburetors are very old and may not be rebuild-able.
Frustrating!
 
73 carbs, in that case it could be the mechanism that transitions the float chamber vent is not operating properly.
If there is one characteristic of the 73 carbs that sets it apart from every other year, it's that.
 
There might be more wear in the throttle shafts and/or housing in the rear carb then the front carb allowing more air to leak past the throttle plate. The carb housings can be bushed and new shafts are available if the wear is excessive.
 
Might it be a problem with the shaft interconnecting linkage? Maybe check with the carbs operating independently from each other? Just guessing. PB is the expert here.

Cheers
Tush
 
Yeah, that's certainly possible, Tush.
I have even "de synchronized" carbs in the act of tightening one of the spring couplings.
 
I installed new shafts and throttle plates, new everything I could think of. I'm sure the interconnecting linkage is "free" of each carb when I adjust.
The Float chamber transition; I will look into that once I understand what it is. I'm guessing an opening at the top of the float chamber?
Thanks for the great suggestions!
 

This is a illustration of the mechanism that is responsible for the transition of the float chamber vents (aka emission valve)
It wasn't a very good design. It lasted only 1 year (1973) and in 74 it was changed to a more robust design that prevailed thru the end of the TR6 production.
If you find there is a difference between the 2 carbs as far as balance, compare the action and movement of this mechanism between the 2 carbs, when you manually manipulate the carbs' linkage from idle to open throttle and ease back into idle.
Of course the engine need not be running when making these observations.
In the process of rebuilding a few 73 carbs, I've found this version of the vent transition to often be troublesome and understand why it lasted but one year in production.
 
Well it did not take long to see what the problem is thanks to poolboy's help. The offending carburettor (front) has the vent lever missing! I did not notice that before. Of course that lever is not available for sale at Moss but I will keep looking. I'm sure it is the problem. In the interim I will try to make something that works using the rear lever as a guide.
Thanks again poolboy for your expert advice!
 
I have levers. One way I cure the problem associated with the 73's is to remove the levers, thereby making the 73's perform like the pre-73's, those years that did not have the Anti Run-on Valve.
If it were me, I'd take the other lever off, making sure the plunger that the lever controls is extended once the lever is removed, but if you want to reinstall the lever and try to get it adjusted properly, send me a PM with your address and I'll send you the components.."gratis".
 
The only drawback is that you lose the function of the Anti Run-on Valve...but it's probably not needed. I've been without one for 10 years.
If you do experience run on, try a higher octane.
 
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