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914World.com _ 914World Garage _ Challenging Carb Repair

Posted by: Racer Chris Sep 20 2012, 09:38 AM

We were having trouble tuning a customer's 2270 engine.
One cylinder would never idle properly but it would run at elevated rpm just fine.
When we removed the carb to inspect it, we found that the idle mixture screw had been screwed in too hard, pushing the seat through the casting.
It had been sort of repaired by glueing the seat into the hole, but the glue wasn't holding up too well and the seat was loose and misaligned.
At first we attemped a simple repair using JB Weld to hold the seat in place, like the first repair.
That worked for a little while, but the epoxy softened up from fuel and the seat came loose again.

Rather than throw an otherwise good 44IDF in the spare parts bin, we made a permanent repair by boring out the carb base and installing a custom made sleeve.
(you can see the edge of the broken out area around our 1/4" milled hole)
Attached Image

We used a short piece of 3/8" od aluminum rod found in our material storage area to turn a 1/4" od shouldered insert.
Internally we drilled a shouldered hole for the seat to press into and tapped the insert with a M5x0.8 thread for the mixture screw.

The insert was installed with green loctite.
Attached Image

In the last picture you can see the drilling for fuel to the mixture screw that goes from the bottom of the carb base into a passage cast into the carb body.
The bottom end of the hole was plugged with lead.
We drilled up through the newly installed insert, and resealed the bottom of the hole with a short aluminum plug and a little JB weld for final seal.