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[gwa84the2nd]

nice job craig  as a side note what paint have you used inside your boat as it looks nice a neat all the same collor without resin and glass showing 

[craig dickson]

Hi Folks
Thank you for your further interesting replies. Just to pick up on what was said recently:

tmbc - Mark are you racing in the A-Class this year? If so I may need to do modification 2 and reinforce the sides of my hull! You said you thought that float chambers should be as low as possible in the hull. That not being so with my installation, what effect do you think I might suffer?
You also asked why not remove the pressure pipe and have the main tank vented? My reasoning is that with the float chamber as shown pressure will be essential to ensure fuel supply to the top nipple of the chamber. If not using a float chamber, I could run the main tank vented as you suggested. But that still leaves the issue of the fuel mixture leaning out as the tank empties.

vnkwi Your take on float chambers made a lot of sense to me. Thank you very much for the logical explanation.

gw84the2nd In answer to your question: When the boat was built last year I applied two coats of polyester resin with yellow pigment added. As well as making the inside look a lot neater it gives the big advantage of sealing all those fibres which otherwise trap oil and muck. Not only does it make it easier to wipe clean inside, it more importantly allows easy preparation of the surface should extra components need glassing in. The float alloy chamber mount was fixed in with fibreglass paste and yellow pigment added. Once set I applied a coat of clear resin to seal the fibres.

Out of interest, there is in my opinion one factor that will be critical as to whether this installation is successful or not. And that is the main tank maintaining at all times sufficient pressure to make the fuel flow into the top of the chamber. This boat/engine has to date never stalled. If the engine does stop during slow running then this may be the issue.

Cheers
Craig

[tmbc]

that would be telling !!!! 
 

[craig dickson]

that would be telling !!!! 
 

Don't be shy Mark........>

It is okay to say, "I don't know"

 

 

[tmbc]

i heard it on the grape vine !

i was just told to mount a float chamber as low as possible on the right hand side of a challenger i had ! didnt bother took it out and ran with out it !

[Danny]

Hi Craig
I wish you luck with your float chamber.  I tried one many years ago, but didn't get on with it, as it kept jamming and flooding - but that was an earlier version, so yours may perform faultlessly!

Unless you are using a very large bore carb (for all out speed), a standard carb usually has enough suction at the venturi to allow the fuel to be drawn from quite a distance. I have found with the smaller engines I have used, that there is no need to have a float chamber.
 
One of the reasons I would use a float chamber, is to minimise the movements of a heavy mass of fuel in a big tank.  When accelerating, the fuel is pushed back towards the pick up (at the rear of the tank) and vice-versa when cornering.  As can be imagined,  with a 90 engine halfway through the race, the fuel sloshing about (technical term in the tank can vary the amount provided at the carb enough to make the mixture "unpredictabe".

However, if you are going to use one, then the best setup is:
1. mount it so that the fuel level in the chamber, (ie. the height of the fuel when the valve cuts it off) is the same height as the carb spraybar, (as has already been mentioned).
2. mount it as close to the carb as possible and keep the delivery tube length short (fuel filter BEFORE the chamber to pick up muck before it jams the float valve)
3. If possible, use an anti-vibration mount to minimise frothing.
4. mount it absolutely vertical to the normal running angle of the hull.

If you are running a pressurised system (another thing I never found reliable), you may find that it runs rich when the tank is full, and leans off when getting empty (the air in the tank compresses more easily than the fuel), so you may still need a third channel for mixture control.

Another thing I see from your photo, is that you are using the standard carb throttle arm (similar to an OS arm).  This is a piece of thin steel with a Z bend in it.  The bends are a weak point and will snap, especially if used with a solid rod from servo to carb.  Make yourself a replacement out of 1.5mm brass sheet, silver soldered to a brass boss (with grub screw).  This will last forever!

Finally - now you've got it all set up .... take the engine back out and put the starter belt in! 

Best wishes

Danny

[craig dickson]

Hi Danny

Thank you very much for your exceptionally helpful contribution. You made a very sensible point about the position of the fuel filter and I will be doing as you suggested. The fuel level in my float chamber will be about same height as the carb spray bar, so I ticked that box correctly!

The only one thing I would question is where you mentioned that with pressure the engine will lean out as the tank empties. It certainly did with no float chamber. However bearing in mind that the actual float chamber has a pin hole air vent at its top, the fuel once in the float chamber is not pressurised from the main tank. Therefore I would expect hardly any change in fuel pressure to the carb irrespective of how much fuel is in the main tank.

You have a keen eye for detail Danny. The starter belt can be put in without removing the engine as it just slips in between the coupling and prop tube housing if the shaft is slid out.

Cheers
Craig

[Danny]

Hi Craig
Just goes to show - I'm never too old to learn!  I didn't realise that there was a vent in the top of the float chamber!  That makes it much clearer (I eventually gave up trying to work out the principles of a totally sealed system - doh!)
In that case you are correct and should have no problems with changing mixture.  All the pressurised bit does is to deliver the fuel from the tank as far as the float chamber, after that its a pure suction feed to the carb, so should be nice and even all the time.
Don't know how true it is, but I was told that the oil in glow fuel "sticks" to the sides of silicon tube thus reducing its effective internal diameter. I always used to use one size bigger ID tube than I needed - just in case it was true!     
Cheers
Danny

[Brigadair]

Great thread this! Yes good idea on filter prior to float chamber Danny. Also bottom of float chamber (ie fuel exit) should be level ideally with carb needle, Venturi.
Key thing to remember is that the float chamber is vented in the lid, so a pressure tank will keep it full.


Good luck Craig, look forward to seeing you test it!
Garry

[ids987]

I always used to set mine up so that the "full" level was roughly level with the spraybar.
On the basis that it works by providing a constant head of fuel (constant height differential between fuel and spraybar), I think - while it's running, it's not that critical - as long as it's level or above (so that you're not trying to suck fuel uphill). If it's higher, it changes the baseline needle setting slightly, but the key thing is that it's consistent. But, if you set bottom / exit level with the spraybar, it will start to drain into the carb when it stops - meaning firstly flooding, and secondly you need to refill the float chamber before you re-start.
The needle setting with a float chamber is usually (in my experience at least), in the same ballpark as suction feed. Absolutes are obviously subject to a few variables.
Because of the "fluid seeks its own level" principle, the float chamber ideally needs to be close to the needle, so that if the boat pitches or lists, the height differential between the two changes as little as possible.

[craig dickson]

But, if you set bottom / exit level with the spraybar, it will start to drain into the carb when it stops - meaning firstly flooding, and secondly you need to refill the float chamber before you re-start.

That in my opinion is an excellent fine detail point and well reasoned. Thank you for that. I suspect that small details like that will make the difference between a good reliable set up and one that causes issues that could put people off the idea of a float chamber.
Craig

[craig dickson]

Hi folks


Just a quick update


Today I ran my crusader SC 46 engine with the new float chamber in situ.
The first thing I soon discovered was that it needed a good turn and a half on the main needle to keep it running on full throttle.


Once I had the  main needle dialled in, the boat ran perfectly. Two key aspects were noticed:


The main needle setting was less critical and could be a notch or three either way without affecting performance.


Importantly, from running my fuel tank from full to empty,the engine ran exactly the same with no leaning out as the tank emptied.


You folks have provided good tips for me prior to my test run today and I thank you for that.


For the record I did fit my fuel filter such that it was before the float needle valve. Thank up you danny for that tip!


Cheers
Craig

[tmbc]

hi m8
you mention you had to turn the main needle a turn and a half was that to richen or lean ? did the boat consume more or less fuel ?

[craig dickson]

Sorry I should have explained. I had to richen the needle setting. I didn't notice any difference in the amount of fuel used but I would expect it to use slightly less with the float chamber. I say that because without the chamber and using a pressurised supply, I had to set the mixture on the rich side.


Craig 

[craig dickson]

Hi Folks

For anyone interested I uploaded a short video clip of my boat running yesterday on test with the float chamber after having re-set the main mixture needle on the carb. Okay I realise that this is only a bog standard sports engine so the power is limited (so I am aiming for reliability as my main priority):

http://www.youtube.com/watch?v=SvIXRmllXH4

Craig

[derekwarner]

Craig....I have ZERO knowledge of these type of engines....but see what appears to be a light BLUE exhaust haze.....in you video

Does this create any form of oil pollution on the water?...........Derek

[craig dickson]

Hi Derek

I would suggest that all 2 stroke nitro and gasoline engines will emit some residual combustion products. I do not believe that it poses a pollution risk to the water in this instance. I would expect more oil (even if in relatively minute quantities) to enter the water via propeller shaft lubrication systems often seen on many model boats of all types of power plant. And I am not suggesting that even this is necessarily an issue.

Craig

[Brigadair]

On the pollution issue - the engine running was using castor oil lubricants, not synthetic, and the methanol used in the fuel is burnt off by the high temperature combustion process, (with no other additives). So as far as internal combustion goes, these type of engines are probably as low a polluter as you can get.


Brigadair

[craig dickson]

Hi Folks

For anyone interested I uploaded a short video clip of my boat running yesterday on test with the float chamber after having re-set the main mixture needle on the carb. Okay I realise that this is only a bog standard sports engine so the power is limited (so I am aiming for reliability as my main priority):

http://www.youtube.com/watch?v=SvIXRmllXH4

It has been said by some folks that float chambers have proved troublesome. If my set up proves reliable I would expect on say a 40 to 50 lap race to gain about 4 to 5 laps compared to running without the chamber.

However that extra component does give extra risk of a failure. If the float ball gets stuck (should the enclosure distort)....

If the float valve gets stuck...

If the pressure to the main tank fails (say an air leak?)....

The float chamber may be a curse!

Time will tell

Craig



Craig

[Brigadair]

Agreed craig. Don't forget the float chamber on my webra powered challenger let me down towards the end of last season, and cost me a place. The brass nipple at the bottom exit sheared off!


Time will tell!




Lol!

[hydrobob]

Well you can both have a good laugh at my new A class boat which has twin tanks for all sorts of not very good reasons!

Bob....from a dark workshop on a mountain.

[Danny]

I would suggest that you dismantle the valve and clean the needle and guide after each outing.  If fuel is left coating valve ... methanol evaporates, leaving neat castor.  SHOULD wash off the next use.  But if not, it could easily stick the needle causing no fuel, or flooding.  The system does not operate on a very high pressure.
Just a thought.
Cheers
Danny

[Danny]

Now what have you been up to Bob???   

[craig dickson]

Well you can both have a good laugh at my new A class boat which has twin tanks for all sorts of not very good reasons!

Bob....from a dark workshop on a mountain.

Bob.... could you upload a photo for us to see??

Craig

[craig dickson]

I would suggest that you dismantle the valve and clean the needle and guide after each outing.  If fuel is left coating valve ... methanol evaporates, leaving neat castor.  SHOULD wash off the next use.  But if not, it could easily stick the needle causing no fuel, or flooding.  The system does not operate on a very high pressure.
Just a thought.
Cheers
Danny

That sounds like good advice mate!