Float level advice, please.

[siteunseen]

There were two different lengths of valves originally, I think the front one was longer.  Here's something I grabbed from MSA's site

" Image Note:
In the image you can see two needle valve housings. One is for the front carburetor and one is for the rear (they are different lengths). The interior valve assembly is pre-installed in one of these two. Match the housing length up to the carburetor you are rebuilding, and install the valve assembly in that housing, if not already in the correct housing. Each kit includes both housings, so one will be unused."

http://www.thezstore.com/page/TZS/PROD/11-3151

In your picture above that float should be parallel to the lid and higher in the front, opposite the valve side.  Do you have the SU DVD from Ztherapy?

[siteunseen]

here's something from rockauto.com that shows that they are different lengths.

This is the front , longer

 

[DaveR]

Got Bruce @ Ztherapy to chime in on this.  Few things that have made a lot of sense to me. Maybe others know this, but it was news to me.

First off, he said to ignore the SU DVD about setting the float level, as it is outdated. (at least in regards to the method) Ztherapy no longer uses grose jets, they use a simple needle and seat.  This means that there is no way that needle and seat could support the weight of the float when inverted. And if the float is resting on anything it would be the retaining spring which is obviously not the desired effect.

Because it cannot support the weight, you must do your adjustments upside down (like I did).  Let the needle and seat hang, lift the float up until the valve would shut off, and set that height (between float top and float housing cover bottom) to .55".

This is exactly what I did, so I should be in good shape to begin my tuning.

Also, he mentioned they only sell 1 length of needle and seat, and apparently he had only seen one version of carburetors that had different heights of the grose jets. He was unsure as to why this was, but had no comments or concerns whatsoever about the front and rear carb adjustments being anything other than exactly the same.

 

Now that said, it would appear that some of the other more robust ways to set the float level talked about in this thread would probably still be the best advice. (Backing it down 10 turns and checking for fuel level etc) I will probably employ these if I don't have good luck with my initial float setting.

Thanks all

Edited August 11, 2016 by DaveR

[siteunseen]

I was raised to respect my elders so please don't take this as my attempt at arguing, I'm just puzzled.  I've rebuilt 2 sets of 3 screw round top SUs and the front float valve is about an 1/8th of an inch longer.  To make my valves from Ztherapy work I had to add an extra aluminium washer under the front float valve.  

I've read many post about the front carb needing the extra depth for when the fuel all goes to the back of the bowl on acceleration.  Am I wrong @Blue @Jarvo2 @jonathanrussell?  It wouldn't be the first time and sure won't be the last but it is what it is.  I apologize for disagreeing with Mr Palmer, he is a very nice man and they may work without that extra washer but to keep the tang on my float from being bent almost straight down I added that extra washer.

A quick google search, https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1BOFA_enUS494US494&ion=1&espv=2&ie=UTF-8#q=240z different lenghth float valves

Picture of another set of SUs I have for parts.  You can see the difference on the float pins ears and the valves laying beside the rear float.  How could "one size fit all"?

 

[DaveR]

My float pin ears are the same front to back carb. If the ears were different then I could see why you would want different jet heights. The adjustments I had to make on mine weren't unreasonably bent. My car was very much unmolested, so I have no reason to think those aren't the original lids.

Actually my float lids are identical in all ways. I couldn't tell you which one was front or back. Even the vac line to the air filter is in the same rotational position and not mirrored. 

Looks like your floats might be slightly different from one another as well. Either way it can all be made to work after checking on the car, but it doesn't appear like every car from the factory had a different setup front versus back, but apparently some did.

Really good post here: 

Seems like regardless of setting, due to the slant of the engine, the float levels will be slightly different for ideal mixtures.... regardless of how you get there.

 

Edited August 11, 2016 by DaveR

[siteunseen]

Dave I'm so sorry! I had know idea your ears were the same. That explains everything. All mine are 3 screws. The front lid overflow bung is on the rear closet to the motor side. The rear carb that overflow is closest to the fender. I'm so sorry. I feel foolish. Sorry Mr Palmer too.

[DaveR]

No need to apologize to me, I have no idea what i am doing.  My car is 13 years older that I am, and I have yet to get it properly running.   I'm like you, read a lot and hope I can make sense of it when I get it in front of me.

Edited August 11, 2016 by DaveR

[240260280z]

To set the level to be the same on both carbs when I can't measure fuel depth, I hold the lid assembly upside down and blow into the fuel port.  While doing this I rotate the float and note where it shuts off the air flow,  I then bend the tab and repeat until the air stops when the float beam is parallel with the lid (see picture below to see the parallelism). 

It is important that the beam and float  on Hitachi carbs are not  twisted (the beam and float top should also be parallel).

Doing this method is easy because the assembly is literally in front of your nose. It seems to do the job reasonably well.

 

 

[siteunseen]

Thanks Dave, I'm bad to get tunnel vision or tunnel thinking.

Blue thank you too, I adjusted mine very similar to what you're saying. The floats should be parallel to the lids. I've always set mine to.55" upside down. It's running very well now so it may be awhile but I want to try what Dave did, have them dangling down, not resting on the pin and see if there's much difference that way. But I'm not touching them until I have to. 8^)

And the floats in my last pic are the worst two of six. Those are my parts/core set.

So the moral of my hiccup or foul up, for my information is the earlier 4 screw SUs have equal depth float pin arms or ears. Learned something new today. Thanks.

[jonathanrussell]

@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.... 

[Namerow]

5 hours ago, siteunseen said:

I was raised to respect my elders so please don't take this as my attempt at arguing, I'm just puzzled.  I've rebuilt 2 sets of 3 screw round top SUs and the front float valve is about an 1/8th of an inch longer.  To make my valves from Ztherapy work I had to add an extra aluminium washer under the front float valve.  

I've read many post about the front carb needing the extra depth for when the fuel all goes to the back of the bowl on acceleration.  Am I wrong @Blue @Jarvo2 @jonathanrussell?  It wouldn't be the first time and sure won't be the last but it is what it is.  I apologize for disagreeing with Mr Palmer, he is a very nice man and they may work without that extra washer but to keep the tang on my float from being bent almost straight down I added that extra washer.

A quick google search, https://www.google.com/webhp?sourceid=chrome-instant&rlz=1C1BOFA_enUS494US494&ion=1&espv=2&ie=UTF-8#q=240z different lenghth float valves

Picture of another set of SUs I have for parts.  You can see the difference on the float pins ears and the valves laying beside the rear float.  How could "one size fit all"?

 

According to my notes, these were the changes to the carbs that occurred as of Jan. 71 production and the emergence of the so-called Series 2 cars...

Different, front vs. rear…  Front = long-ear, long-needle;   Rear = short-ear, short-needle.  Drain fittings added. 3 screws for float bowl covers. (S1 carbs used 4-screw float bowl lids, with long-ear / long-needle for both front and rear.  Bowls did not have drain fittings.) For the 72 that I no longer have, the carb re-build kits that I bought had entirely different part no's.

[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. 

 

[Mark Maras]

 True, unless your Merlin float chamber was upgraded to a "Miss Tilly's Orifice. 

Edited August 13, 2016 by Mark Maras

[siteunseen]

3 hours 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.

 

19 minutes ago, Mark Maras said:

 True, unless your Merlin float chamber was upgraded to a "Miss Tilly's Orifice. 

History lesson here?  It is for me. 

Also a spelling lesson. One T in the US and Canada, two TTs in Europe.    carburetor carburettor

According to this it was fuel starvation at first then overly rich causing them to flood out. 

The early versions of the Rolls-Royce Merlin engine came equipped with a SU carburettor. When these aeroplanes performed a negative G force manoeuvre (pitching the nose hard down), fuel was forced upwards to the top of the float chamber of the carburettor rather than into the engine, leading to loss of power. If the negative G continued, the fuel would collect in the top of the float chamber, forcing the float to the floor of the chamber. This would in turn open the needle valve to maximum, flooding the carburettor with fuel and drowning the supercharger with an over-rich mixture. This would lead to a rich mixture cut-out, which would shut down the engine completely, a serious drawback in combat.^[1]

Negative G commonly occurs when manoeuvring to fire on an enemy aircraft in a dogfight. Moving the stick forward would starve the engine of fuel, producing a sudden loss of power. This would let the enemy get away, and if continued the manoeuvre would cause the carburettor valve to open, provide far too rich a mixture and stop the engine. During the Battles of France and Britain, the German fighter aeroplanes had fuel injected engines and therefore did not suffer from this problem as the fuel injection pumps kept the fuel at a constant pressure whatever manoeuvres were made. The German pilots could exploit this by pitching steeply forward while pushing the throttle wide open, the pursuing British aircraft being left flat footed since trying to emulate the manoeuvre would result in loss of power, or fuel flooding and engine shutdown. The British countermeasure, a half roll so the aircraft would only be subjected to positive G as they followed German aircraft into a dive, could take enough time to let the enemy escape.