Hello all,

I recently rebuilt my 3 screw SU carbs on my 240z with the Z therapy kit. It was a good experience.

At the same time I installed the MSA premium exhaust. I've noticed a very strong gas smell when driving the vehicle now. Is this normal with the SM needles? From my understanding they were overly rich during idle only?

My 240 is basically stock, with the 2.5" exhaust and 280zx distributor coming soon. The smell is so strong I'm thinking of switching back to stock needles because it is so bad. I forget who I spoke to on the phone at Z therapy, but I asked if they were ok for a basically stock engine and they said yes.

Secondly, when tuning them, one carb required 2.5 turns, and the other 3.5. Should I adjust the other float to make them exactly the same, or am I ok leaving it this way?

Colten

Gotta love it when helping hands reach out to one another.

Finally got around to installing my new SM needles (thanks, Bruce). Previously had modded N-27's, that seemed to still need a little more polishing for top end. I usually just use the syncrometer to get them pulling the same amount of air, and then use road tests to adjust the mix. So I checked it with the old needles and both carbs were pulling the same. Checked where I had the mix nuts, the front was down 5 1/2 turns, and the rear was down 5 turns. Had made so many adjustments I had no idea where they were set. Seems like a lot but that's what it took for my setup.

 

Cleaned up the domes, etc., put in the SM's. Set the mix 3 1/2 turns down, since the SM's are supposed to be richer. Checked it with syncrometer, both pulling the same. Tried push-pin test, seemed OK. Seemed a little rich, though, so leaned them to 3 1/4 turns down. Put the velocity stacks and K&N's back on and took a little drive to grocery store. Ran bad, felt lean. Made three stops, lowering the mix 1/8 turn each time. Still ran crappy. Was starting to think it was maybe too rich. Made another stop and lowered (richened) it another 1/4 turn. Then it started to run better. Richened it another 1/8 turn. Ran it to 4700 rpm (in first, due to speed limit / cops) and no miss at 4 1/2 turns down. So maybe OK. Not much of a test, but FWIW, seems like the SM's are a bit richer than my modded N27's, but not excessively rich, at least for my car. I like.

 

Also made a little discovery (new to me, that is) about the dashpot oil. FSM says get the oil between the marks on the stick. Easier said than done; even with good light and a magnifying glass it was hard to see the oil level. Eventually I got them both about to the upper line. I was pushing up on the pistons and noticed one was harder to push up than the other. Then I noticed that after adding some oil to the weak one, it was harder to push up. By adding or removing a few drops at a time I was able to get the resistance of both pistons the same. Didn't know that. Still don't know what the best amount of resistance is, though. Need to do more tests.