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T

tomgt6

Jedi Warrior
Offline
I have a 1300cc spitfire engine that I am tuning.

I put new needles in the car last night. I had needles in the SU carbs for a 1147 and wanted to change them to the right needles.

After changing the needles I was getting no power out of the back carb and the power was down on the front carb.

So I know I have to redial in the jets.

I played around with them and tried to do it by sound and feel and got close but the back carb still just seemed weak. So I reset the carbs to 12 flats from stop and started the lift the piston trick. Here is what I found

The front carb would die if I started to lift the piston. So that means it is to lean (I think) and I need to go anti clockwise (this I remember for sure) with the nut.

I turned that carb anticlockwise about 15 flats I bet or more and I am sure I was at the end of the nut and still it wanted to die when I lifted the piston.

So the question is what is causing this? The carb has a new rebuild on it with about 300 miles.

The next question is why does the back carb not seem to sound the same. I put the air meter on both carbs and got them air flowing at the same rate.

I can't seem to get this carb to lean out. It just seems like it is always dogging when I rev it.

I do plan on taking the colortune out tonight and working with the carbs again but hope you guys have some good suggestions as to what may be going on.
 
There is no vacuum line on the front SU. Now I will retest the carb to the manifold and make sure there isn't another vacuum leak anywhere else. Where else would you look?
 
I will make sure the hose is clear to the back carb. Good point.
 
OK, did some work on the carbs and I keep forgetting what car I am working on. I forgot the front carb has the vacuum advance port on this car.

Here is what I found. The back carb had a issue with the hose to the jet. It would get kinked. So I cut it down a bit and things started to work better for that carb. The front carb I just kept playing with it until I was able to get it to stop dieing every time I lifted the piston. I did have on the colortune at one point then ran into issues so I took it off.

I will tomorrow put the color tune back on and see how I did by ear and feel. Thanks all for the help.

So who was right. All of you. I still have some sorting to do but it runs better and will idle smoothly. So something got done. I guess I will have to come up with a new question for all tomorrow.
 
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