View Full Version : TR6 Late TR6 ; loss of power?

09-19-2008, 07:22 PM
Re: 1976 TR6 with original twin ZS carbs

Hi again,

Second question in as many days, sunny fall weather in southern Ontario brings great TR6 weather this year....

On acceleration ( in gear) the car bogs – i.e.: in second , say 2800-3000 revs the power drops off and the engine sputters ….this is generally consistent in all gears. However when I pull the choke at this point the car goes like a rocket..conversely , when I push the choke back in (normal) the engine looses all power and bogs again…?

For reference- the engine will rev 3000+revs freely without problem in neutral…

Again, I should mention I am quite new to this having only driven 1000 miles in my just finished car…

….I was hoping to get this sorted Saturday as the big British sports car day in Bronte Creek Oakville Ontario is this Sunday….I have been going to this event for about 10 tears without a car…this was our big début!…

Comments welcome.

Thanks again fellows, Stephen

09-19-2008, 08:06 PM
The first thing I would do is check very carefully the condition of the carbs' diaphrams. Remove the damper, the 4 screws securing the cover, the air valve return spring, and then the air valve with the diaphram in place. There's about 3.5 ml of oil in the damper,so you may have to replace some after you make the inspection.
Be sure that you locate the tab on the rim of the diaphram into the slot on the carb when you reassemble.
Just a quick easy test and a good place to start.

09-20-2008, 08:27 AM
How is the fuel filter?

09-20-2008, 09:03 AM
Stephan - get back to us after you check the carb diaphragms. Make sure than when you reinstall/fit them prior to putting the tops back on that the tabs modeled into the rubber are sitting securely in the tab/notch in the metal carb body.

If that doesn't cure it we can move on to other potential causes.

Best to take this one step at a time.

09-20-2008, 08:19 PM
Carb Diap's - OK
Dashpot Oil - OK
Air filter's - OK
Fuel Filter should be good / Just flushed tank...

Thought there may be a air leak in the manifold or carb to manifold gasket - based on the increase in power when I pull the choke in... used WD40 with engine running - in those points - everything seems tight..

Also cleaned the carb pistons and carb inlets throats with spray carb cleaner while in there there...

...put all back together...started up...took for a run...same problem...

Question - Carb balance>>? one carb seems to be sucking more air ( I could feel this with the back of my hand..)

Also when I cover the intake to the back carb the engine falters but when I cover the front catb - almost no change in RPM?

..thanks for the tip on the notches...

Next check ???

09-20-2008, 08:33 PM
Is it possible that you have a blockage in the fuel line to the front carb? Needle valve in float chamber stuck closed? Linkage between carbs tight and operating both?

09-20-2008, 08:42 PM
Running horribly lean if pulling the choke makes that kinda difference. Are the pistons free in the chambers? I.O.W. with engine off can you raise 'em up with a finger and on removing finger they drop with a "clunk" when released?

09-20-2008, 09:10 PM
That's a good idea that the Dr. has. Did you notice any difference in resistance when you removed them to ckeck the diaphrams? If they pass the test with a clunk, start the engine and with the air cleaners removed give the engine a little rev with the linkage, and see if the pistons rise somewhat in unisyn.

09-20-2008, 11:22 PM
[quote=Halkett]Fuel Filter should be good / Just flushed tank...

Hmmmm... I'd take a closer look at that.

> running lean
> just flushed tank
> fuel filter "should" be good.
(maybe clogged from debris loosened in cleaning tank?)

Just a thought.


09-20-2008, 11:40 PM
If one carburetor is noticeably sucking more air, it's sucking more fuel. One of your carbs is fuel starved to a certain degree.


09-21-2008, 06:46 AM
Pistons have same-ish resistance - although they are not moving in unisyn on application of throttle.

...working the starved carb theory if i turn the front carb ajusting screw down - which brings RPM up - the carb will suck more air...

I am also going to pull the top of the front carb again thia AM..second guessing?

..thanks team , Stephen.

09-21-2008, 08:27 AM
Stephen, it may seem obvious, but as long as the 2 carb throttle shafts are joined by the accordian like spring clamp, what you adjust in terms of idle speed to one will affect the other.
If you are attempting to synchronize the carbs, at least 1 carb has to be loose from the linkage. During the process the carbs need to be independent, united again after they are synchronized.
I think it's a good idea to take a closer look for a tear in that diaphram. Sometimes it's if just a split and needs a close exam.

09-21-2008, 08:43 AM
Yup. Hold each piston/diaphragm up to a light as you ~slightly~ stretch it around its circumference. Even a PINHOLE will affect the performance.

...oh: and as you hold 'em up to the light you'll get oil drippin' down yer bib unless you empty 'em first. :wink:

Refill the dashpots with whatever you use in the crankcase.