Setting 72 SU float Levels - one more time

[Stanley]

I know this has been covered many times. I've done the search, watched the ZT video. Yes the front float is meant to sit lower. Thread #38660, response by Bcalvosa, 5/23/2010 seems to explain why the best (although I read a conflicting theory based on the gas sloping during acceleration), that is because the engine is tilted and different float levels equal same levels at the nozzle (relative to that carb). Bcalvosa states the gas level to be 25 mm front, 21 mm rear, measured down from the tip of the bowl including the gasket. Most other sources say 25mm front, 23 mm rear.

Which is right? I've got to install some new float valves & nozzles, then a local race mechanic is going to mod my needles. I want my settings & mix to be exactly spot on before I take it in so he won't have to mess with that; don't care if I have to spend a whole day getting it right. I think the mix needs to be set so the mix nuts are set the exactly the same, otherwise the needles won't be at the same level in the nozzle at any speed, which might matter esp at top end.

Love those Hondas, but can't let them win.

[Duffman]

I hope Bruce at Ztherapy jumps in, but I go with 23 mm for both, works great!

[Stanley]

585 fsm Fig EF-47.pdf Here's a couple of shots from the 1972 L20A, L24 Nissan (engine) Service Manual. The first one clearly shows the fuel level to be 23 mm down from the bottom of the lid, not from the top of the bowl or the gasket. The second shows the dist. 14 to 15 mm from the bottom of the lid to the metal tang on the float, slightly different than the top of the float but maybe it doesn't make much difference.

I talked to Bruce on the phone, he like other respectable sources agree the level in the nozzle being the same is what matters. The only problem is it's hard to see whats going on in the nozzle. Read about checking it from above but seems like there should be an easier way than removing the chamber, checking the level if possible, removeing the float cover and adjusting the float, putting the covers back on a getting fuel pressure up, repeat, repeat, etc.

BTW the 72 fsm shows various 3 and 4 screw models in the photos and drawings - no mention of any difference in front/rear float lids.

You could pull the nozzle out, hold it level and mark it, but when you pull it some gas runs out changing the measurement.

My plan is to use the sight glass and mark the nozzle at a equal mix nut position, 2 1/2 turns down for example.

Hope that works.

583 FSM fig EF-46.pdf