In a message dated 8/22/2005 7:34:50 PM Central Standard Time,
75TR6@tr6.danielsonfamily.org writes:
> I've developed a very infrequent (mostly when engine is cold) backfire
> through my front carb. That carb also seems to lose dashpot oil quicker then
> the back carb. Despite having rebuilt to carbs twice in the past 8 years
> they still need topping off on a weekly basis. If I go 2 weeks the front one
> looks empty and rear one looks to be about 1/2 full. Any relation between
> the two problems? How often do you top off your carbs? And where does that
> dashpot oil go? I'm using straight 50W Kendall oil. Tried lots of others and
> this seems to last the longest.
>
There could be a connection. Without the dashpot oil the piston on the front
carb may be rising too fast causing a lean condition when it needs a rich
one.
The reason the dashpots are leaking out is because the O-ring in the needle
adjuster is in need of replacement. O-rings are included with every rebuild
kit but it is not self-evident how to replace them. Infact the first time you
do so will make you cringe.
To replace the O-ring first remove the piston from the carb. Remove the
needle. If you can't remove the screw on the side of the piston retaining the
needle you will get no further. If the screw breaks it is time to send them to
Joe Curto.
With the needle gone the only thing that holds the adjuster in place is the
spring keeper in the bore of the dashpot. You need to drive the adjuster and
the keeper out through the top of the dashpot. This is best done with a wooden
dowel of the right diameter, one small enough to fit the bore at the bottom
of the piston where the needle was. Cut this dowel to a length slightly longer
than the dashpot. Insert the dowel in the bottom end of the bore and set the
piston on the workbench upside down on a shop towel to catch the adjuster and
the keeper. Using light blows with a hammer drive the dowel to drive the
adjuster out of the dashpot bore. Take care not to loose either piece.
Once the adjuster is out of the bore you will see the O-ring and can replace
it easily. I replaced the O-rings on my TR8 carbs and one was so dry it broke
into pieces. No wonder it leaked all the oil in a few days.
Reassembly is the reverse of the above.
I was highly concerned that pressing the keeper out and in would scratch the
inner bore of the dashpot and keep the O-ring from sealing but then I occurred
to me that the keeper never reaches the part of the bore where the O-ring
seals. My carbs now hold their oil for months on end. Years even.
Good luck
Dave Massey
57 TR3
71 TR6
80 TR8
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