Float level advice, please.

[Stanley]

Tilt of the engine requires rear carb 2 mm higher fuel level for same fuel level in both nozzles. There's a thread with diagrams and the trig equations that illustrate it.

Touch up the sticking float with sandpaper - that cured a sticking one for me.

[siteunseen]

9 hours ago, jonathanrussell said:

@siteunseen....

So, I understand the theory behind the longer float ears and the longer needle jet but after much work trying to make it work, I gave up. I have a decent amount of spare parts so I ended up using a short ear float lid on my front 3 screw carbs, matched of course with the shorter needle jet. Then, I followed the process I described earlier to make the fuel level in the nozzles match at 10 turns down with the domes removed. What is my theory? I just think that the longer ears change was flawed. By lowering the front float 4mm in the float bowl and since it appears to me that the float bowl is tapered a bit, I believe that the rubber float gets restricted in terms of its movement / travel in the bowl (it hits the sides of the bowl) at the point where it should theoretically be in adjustment. The end result for me is that I can never get the float adjusted right.

So, to answer what I think was your question, I treat my 3 screw carbs like 4 screw carbs and adjust the front and rear the same....at the float and where the fuel hits the nozzle.

Maybe a 2 sensor wideband so I could measure while accelerating would change my mind.... 

My thinking is when you hit the gas the front float, being in an opposite position of the rear, swings up shutting off the fuel flow.  That was the reason they made them deeper.  Now if the lids were both facing forward and the float would drop when you accelerate then I could understand the same length ears and valves.  But we all think differently and that's what makes our forum the best, no hard headed know-it-alls cramming their thoughts in your head. 

[Mark Maras]

3 hours ago, siteunseen said:

My thinking is when you hit the gas the front float, being in an opposite position of the rear, swings up shutting off the fuel flow.  That was the reason they made them deeper.  Now if the lids were both facing forward and the float would drop when you accelerate then I could understand the same length ears and valves.  But we all think differently and that's what makes our forum the best, no hard headed know-it-alls cramming their thoughts in your head. 

 I've tried to figure that improvement? for years. I think you're right. The problem (if there was one) was probably directional. I've always run early 4 screw carbs with equal length tabs and never noticed a problem.

 

[siteunseen]

Thank you Mark.  I rarely hear that phrase.

[madkaw]

I fixed my ears on my front carb- pierced them with new holes. Tired of trying to set the float tang for the wrong size needle and seat. Got out the drill and punched new holes- didn't even measure - I was pissed it was taking this long to set flit levels. I have been using the "Float Sync " tool I bought but had a few issues with them too. They don't like gas in them too long I guess - but other than that- pretty handy


Sent from my iPhone using Classic Zcar Club

[Stanley]

Found this CAD drawing I did a couple years ago to help understand the tilt / fuel level issue - why different levels in the bowls are required to get equal fuel height in both nozzles. In my opinion this is why Nissan changed the ears and valve length on the front carb for the 3-screws in 1972. I've got the 72 engine manual, but it doesn't mention different settings, and as far as I know there was not technical report about it. Wonder why. Maybe it was a time-line thing, since the carbs were changed to flattops in 73.

The first time I opened the front float bowl I found a really bent-up float. Maybe some previous mechanic got mad and used the  "ignorance and brute strength" method on it. I've used that method myself, with mixed results.

 

inh

[Mark Maras]

 Ok. that makes sense but was it that big of a problem? I still don't understand why I've (anyone else?) never experienced a problem with the early ones. Drove it easy, drove it hard. All six plugs always ran light tan, both carbs 2 1/2 turns down, float levels as close as I could get them, (never checked float level at the nozzles) ATF in both. I'm beginning to think the longer tabs were another improvement?, similar to the heated carbs. I'll stop there before I go Lewis Black on the subject of improvements which, most of the time, are Extraneous B.S.

[jonathanrussell]

@Stanley I have seen your drawing before. Really cool. So, do you agree that the fuel at the nozzle should be the same for both carbs- 10 turns down?

 

In the 1973 Technical Bulletins manual, TS73-10 describes the procedure for adjusting the floats for 70, 71, an 72 240zs. For 72 it specifies a gap between the top of the float and the float bowl lid to be 11.5mm-12.5mm rear and 15.5mm to 16.5mm front. For 70 and 71, front and rear are 13.5-14.5. The TSB doesn't explain why and never mentions the fact that the lid ears and needle jet are longer in front for 72. I can scan and upload if anyone is interested.

[240260280z]

The fuel sloshes to the back of the bowl on acceleration and sloshes to the front when changing gears and braking. It sloshes side to side when turning, It is very dynamic.

 

If you are in a Hurricane chasing an ME-109E, you can't push negative G's to give chase because the floats lift and shut off fuel.

 

[Stanley]

11 hours ago, jonathanrussell said:

@Stanley I have seen your drawing before. Really cool. So, do you agree that the fuel at the nozzle should be the same for both carbs- 10 turns down?

 

In the 1973 Technical Bulletins manual, TS73-10 describes the procedure for adjusting the floats for 70, 71, an 72 240zs. For 72 it specifies a gap between the top of the float and the float bowl lid to be 11.5mm-12.5mm rear and 15.5mm to 16.5mm front. For 70 and 71, front and rear are 13.5-14.5. The TSB doesn't explain why and never mentions the fact that the lid ears and needle jet are longer in front for 72. I can scan and upload if anyone is interested.

Yes, that's the whole point: equal fuel level at the nozzles. Need to think about that ten turns down; since it's almost impossible to get fuel levels exactly where you want them, a perfectionist might want slightly different mix nut settings for each carb to get equal fuel level at the nozzles, after setting the floats as well is possible in one day. Maybe tuning with synchrometer per FSM does that anyway. Five tries, twenty tries, of resetting the floats, eventually enough is enough. Car needs to be on level surface while setting the bowls, not a steeply sloped driveway.

Besides fuel bouncing around as Blue stated, it also goes up and down a couple mm as the valves open and close. If you have sight glasses attached with the engine running you can see it.

I'd like to see that TS73-10, didn't  know it existed.

[siteunseen]

1 hour ago, Blue said:

If you are in a Hurricane chasing an ME-109E, you can't push negative G's to give chase because the floats lift and shut off fuel.

 

So that's the reason my Grandad was in Europe! 

[siteunseen]

15 minutes ago, Stanley said:

Yes, that's the whole point: equal fuel level at the nozzles. Need to think about that ten turns down; since it's almost impossible to get fuel levels exactly where you want them, a perfectionist might want slightly different mix nut settings for each carb to get equal fuel level at the nozzles, after setting the floats as well is possible in one day. Maybe tuning with synchrometer per FSM does that anyway. Five tries, twenty tries, of resetting the floats, eventually enough is enough. Car needs to be on level surface while setting the bowls, not a steeply sloped driveway.

Besides fuel bouncing around as Blue stated, it also goes up and down a couple mm as the valves open and close. If you have sight glasses attached with the engine running you can see it.

I'd like to see that TS73-10, didn't  know it existed.

That makes perfect sense now that I am looking at your CAD image.  When I disabled the rear my car would die so I turned the front further down to keep it running.  I'm thinking there's a half a turn difference between mine.

This winter I'm planning on going through all this information and get them more precise.  But it ran pretty darn good this morning.