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Carb Damper Piston & Needle Piston

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Hi All,

TS14998L is back on the road. As with Jonny Lu's car it has been off the road for 35 years.Its last trip in 1982 was memorable because I drove off with the hood (bonnet) not fastened which left me with a sore head and broken windshield.

 

After several drives this week, I checked the mixture and checked the level of the fluid in the dash pots. After topping up the front carb, I noticed that the damper piston on the front carb seemed to slide into place with less resistance than the rear carb. While trying to diag the problem I noted that one damper piston was longer than the other (2.850 inch to 3.085 inch. However, switching their position (front to rear) did not cause the difference in resistance to change position. Further examination found that the tube on the needle piston( where the damper piston enters) on one carb had a consistent diameter from top down where the other had a larger diameter opening at the top which stepped down. Both needle pistons had the same part number. I believe the one with the stepped down tube was later production designed to allow the damper piston to slide into place more easily. From my supply of parts, I reassembled the system with matching parts using a short damper piston and stepped needle piston as found in most of my spare carburetors. The damper pistons now have the same resistance in both carbs. Overall, this probably has no affect on the engine operation but it kept me busy for a few hours.

 

Does anyone have any ideas as to why the damper pistons and needle pistons have these differences?

 

Dave

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Dave, Dont know the details of the SU variants. But I would suggest you do the 'drop test' on your new piston/dome assemblies. The air seal between piston and dome is critical for normal operation and they are not usually regarded as pick and mix.

Peter

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Drop Test and Time them as Peter says,it's the only way to get a Matching Set that will Work as Designed.

Any Videos of that about procedure Peter?

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