SU Carb piston lifter

[The Neck]

It seems to have quite a delay on the rpms decreasing after quick acceleration. I'm def no expert but I believe that could be related to the amount of oil used in the dashpot or maybe something is sticking? But again I'm also still learning. Not sure if you have the full books but they definite help with projects like this (I recommend Vol 2).

This absolutely. I got the carbs back together and the pistons are sliding freely, dashpots filled with MMO. I'll see if adjusting the air/fuel mixture will allow the engine to idle slower, but I agree the engine is idling too high and not decreasing after throttle as quickly as it should.

[spl310]

It isn't how much, but how thick...

[The Neck]

So cryptic, so mysterious. Just like this front carb!

I've determined the front carb is the issue. While before the piston was mostly stuck, I've narrowed it down to that piston not moving nearly as freely as the rear. So tonight after I get my daughter tucked in it's back to that carb. I believe it's isolated to the needle and jet as the point of resistance that's not allowing the piston to move as freely. If I remove the needle, it's perfectly fin in there, it's the needle that's causing the lack of movement.

[notoptoy]

If you rebuilt both carbs at the same time, is it possible yo mixed up the domes and pistons? Without needles they should drop smoothly with a solid "thunk". If they do without needles, then it is likely your needles are bent. There are several YouTube SU rebuild videos available on making sure that you have these correct and why you should not rebuild two SU's at once unless you are careful to keep the parts with the same carbs they started on.

[The Neck]

I did the front, then the rear for that exact issue. The front and rear were never apart at the same time. I bought the SU rebuild kit with two sets of new needles too. I'm going to see what swapping the new and old needle out looks like for operation.

I'm about 98% sure once this issue gets resolved it should be able to idle and run much smoother. The rear carb lifts and drops perfectly, so I'm happy with that one. When I throttle up and down with the rear the responsiveness is much better than the front.

[The Neck]

I've been doing some experimentation with this carb and needle and came to a couple conclusions.

First off, the needle and brass tube are not lining up. Yes, I knew this before but I took it a step further. I tightened down the dashpot and piston with the needle seated. I then d/c'd the jet, and rotated that around to find out the best way to line up the jet and the needle so the piston would just drop. I found what seemed to be the combination with the least resistance, and was getting a nice movement from the piston. I spun the needle to what seemed like the correct orientation to line up with the jet in its natural position. I moved the needle, and the resistance is still there. Would this mean the actual set screw for the needle is not lining up the needle properly? The only way I get a nice drop is if the jet is rotated about 160 degrees counterclockwise regardless of the needle position.

I'm also guessing the next step would be to purchase a new jet to match up with the new needle? It seems as if the piston and jet have to be in a specific orientation regardless of the needle position.

I hope that's making sense, I've been staring at this carburetor for the last 2 hours and I'm pretty sure the fumes are starting to get to me.

EDIT:

I put in the old needle to see if there was any difference. There wasn't, seems like the piston and nozzle are wanting to be set in a very specific orientation, about 160 degrees off.

[The Neck]

UPDATE:

I fiddled with this front carb for hours. Then a few more hours inside the house in a nice comfortable environment.

Turns out the issue I had was with the brass nozzle sleeve not seating properly, and constantly coming off center. Once I took that specific piece apart, and payed attention the the "centering" of that I got it. Piston raises and drops like a dream.

I followed the carb tuning procedures and have the car idling at a nice purr right around 750 RPM. Great throttle response, and the car fires right up!

Thanks to everyone for the help, and especially the member who sent over the lifter pin. That made tuning a very smooth operation!

[mraitch]

One of the things about owning an old car is 'stuff happens' Frustrating, annoying, but WOW, when the solution appears.

This why I love this Forum, for so many reasons, knowledge, great vendors, enthusiasm and love for our chosen vehicles.