[T3] Loss of power at speed- could it be overheating- update

Mark Seaton Markse at mo-sys.com
Tue Nov 2 12:30:49 PDT 2010


Jim Wrote: "I'm not a carb guy, so I surprised to hear that things are 
so tight in there"

Well Jim it turns out it's not meant to be so tight-  I have a 
confession to make and I really have been very dumb :-(

When I first bought my car ~10yrs ago I did a lot of work on it to get 
it roadworthy (worth doing- it hasn't failed an MOT since :-))
Part of the work I did was to rebuild the carbs. Unfortunately the kits 
I bought didn't include the diaphragm for the vacuum release of the 
choke mechanism so I couldn't repair that. So I started collecting 
spares- lots of them. I ended up with a right mixture of carbs- most 
slightly different from one another. There seem to be 2 main varieties: 
early and late. The early ones have the main jet accessed from the side 
of the carb body, while the later ones are accessed from the end of the 
carb bowl. Here's a pic of the types:
http://www.flickr.com/photos/37269790@N00/5140677190/#/photos/37269790@N00/5140677190/lightbox/

They also have different floats! The early have longer more conical 
floats while the later have shallower floats to clear the housing for 
the main jet:
http://www.flickr.com/photos/37269790@N00/5140677186/#/photos/37269790@N00/5140677186/lightbox/

So guess what- I have the early floats in my later carbs!! :-(
And I have had them that way for many years and been 
worrying/complaining about the poor mpg I get all that time!
What an idiot.
Mark






On 02/11/2010 03:53, Jim Adney wrote:
> On 31 Oct 2010 at 23:15, Mark Seaton wrote:
>
>> The float was free to move but didn't seem to move
>> down very far before bottoming on the main jet housing in the bottom of
>> the bowl. I removed the float and noticed something I had seen but never
>> really thought about before, but this time it all added up- there was a
>> flaw in the casting of the carb body resulting in a small raised worm
>> like "flashing" on the top of the main jet housing. It probably sits 0.5
>> - 1mm above the surface, directly where the float would hit.
> I'm not a carb guy, so I surprised to hear that things are so tight
> in there, but very little motion of the float is actually needed.
> Looking at your photo, this casting flaw looks pretty trivial, but
> you're right that the float needs its full range of motion.
>
> One thing you could check would be to blow thru the gas inlet with
> the carb rightside up and upside down (with the right washer), with
> the carb assembled, but off the car. Then remove the casting flaw and
> repeat the test. That would give you a better idea of whether this
> really cured something.
>
>> I just removed the fibre washer from under the needle valve to raise
>> it a little and put the carb back together. I drove off and just got
>> back home with no further issues. In fact it drives smoother and more
>> assuredly than ever.
> Removing the washer was a really clever way to deal with this
> temporarily!
>
> It would be great if this was it. If these are OE carbs, the washer
> thickness is one of the specs in the OE setup data. You can check
> this to make sure you have the right spacing in there. Varying the
> washer thickness adjusts the depth of the fuel in the bowl, so it
> amounts to a fine adjustment on richness/leanness. It would be
> important to make sure you end up with the same thicknesses on both
> carbs.
>



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