float level settings weber 40 dcnf

martijn

martijn

X addicted
i've trouble tuning my dcnfs

The troubles:
- it idles very rough and idle is hard to adjust (low vaccuum but equal on all barrels)
- engine falls dead at 6000 rpm.

specs: 30 mm chokes, 50 idles, 125 main, 185 aircorrector.

It ran fine on 36 dcnf's so it's carb related.

I think it runs to rich at idle and to lean on 6000 rpm. I want to check floatlevels settings, but the weber booklet says: 50-58,5 mm float
The ferrari 308 tutorial says:"48-58,5 mm floattravel.

what are your opinions?
 
Martijn,

40DCNF6 , 12 and 22 (Fiat Dino) is 50 / 58.5 to the bottom of the float from the underside of the cover without gasket fitted.

40DCN14 (Fiat Dino) 48 / 57.

40DCN18 (Ferrari 275GTB) 50 / 58.5

40DCN21 (Ferrari 365/GTB4) 51 / 59.5

40DCNF13 (Ferrari 206 Dino) 52 / 58.5

40DCNF35 , 36 , 37 and 38 (Ferrari Dino 308GT4) 48 / 58.5

Which is all the different models of DCN / DCNF variants I have listed in my Weber bible, so you can see it's rather model specific....

What jettings did you have in your 36's?

What emulsion tubes are you using?

SteveC
 
I don't have the numbers of my dcnf at hand but i know there from an MG maestro.

I used all the jets from my 36 dcnf as a starter in this carb, but the 36 had 29 mm choketubes.
 
Source some F24 emulsion tubes, these are the stock tube for a 40DCNF12, and seem to work the best for the sohc...

Unfortunately I can't tell you what jetting and tubes the MG Maestro carbs came with, my factory weber bible only has Italian cars in it :)

E tube function is complex and simple, but one thing to note is the numbering sytem is not linear... ie a higher number isn't necessarily a richer E tube...

F24's are quite slim and displaces very little volume so it allows more fuel in the jet well, weber part number is 61450.224... that would be one of my starting points.

The rest of the jetting looks pretty close...but check your e tubes, aux venturi numbers and needle and seat sizing... as these can certainly make a difference.

SteveC
 
hi steve

i use and used F36 emulsiontubes (recomendation from mike richmond and PBS). The needles are 175.

The MG used 145 mains so the were a lot richer. I can put these in to but seemed very rich to me
 
Stock factory settings for 40DCNF12, which is probably the most common DCNF...

Choke 32mm
aux venturi 4.5
main 1.25
air corrector 220
E tube F24
idle jet 50
needle valve 1.75
pump jet .45

If you having difficulty setting idle mixture, check that the idle mixture and air bypass screws aren't bent or damaged on the pointy tips...and check that you have the O'rings on the mixture screws...

If you have low vacuum, then check that your base gaskets are sealing, the carb bases aren't warped and your phenolic spacers aren't cracked...

F36 is definitely a fatter tube (5.9 od / 3.5id ) than an F24 (5.0 od / 3.0 id) which will displace more fuel out of the jetwell... It also has much smaller emulsifying holes and less of them than the F24... so the F36 tube will be richer at low rpm and slight throttle openings due to the lack of / less holes towards the top of the tube...and leaner towards the top end due to the extra volume it displaces...

SteveC
 
ok, i will look into it. I do think it strange that the MG, which is a 1600, has carbs with a 30 mm venturi and a 145 main with 220 aircorrector. Seems very big but it;s stock
 
Martijn,

well you are already quite rich... air corrector sizing works out to roughly three steps (i.e. 3 x 0.05mm) down in air corrector is like going up one step (0.05mm) in main jet size... although this affects top end richness more. Your already down 7 steps from a 220 at 185, so that's sort of like having 135 mains in there.

It all depends how the engine "pulls" air too, and the sohc (even a 1300) can create quite a lot of depression due to it's long rod ratio and high cycling speed... the MG (if it's a typically english engine) will be a long stroke / small bore /lower rod ratio and slower revving... so it's air requirements are different.

Check your aux venturi sizing (the diffuser where the fuel issues from) this affects (mainly) how quickly the carb transitions onto the main circuit ... 4.5's are the size for a sohc with duals... pretty easy to see, there's a number cast into the side... the maestro carbs might have 3.5's.

SteveC
 
hi steve,

The aux venturi's happened to be a 2,5 ! I also found out dat with the elektric fuelpump switched on and the engine is not running 1 of the carbs is pouring fuel directly into the venturi trough the aux venturi. The other one doesnt. I didn't had this problem before on my 36 dcnf so it must be the carb. float is a little of 50-58 mm but that can cause flooding i think. Also a 35 pumpjet was fitted, which is quite small according to your specs. I have some spare parts so i made a new basesetting with the parts i have and the i want to finetune it.

the webers are 40DCNF99 and 100.

Choke 30mm
aux venturi 3.5 (don't have 4,5 at hand)
main 1.25 (also have 120 or 130)
air corrector 210 (also have 185)
E tube F36
idle jet 47 (also have 45 or 50)
needle valve 1.75
pump jet .35 (also have a 40)

I'm glad to hear your recomandations, based on the parts i have.
 
Pump jet size is tied in with the pump cam profile... which there are at least a dozen of.. :-( and again not really linear in their nomeclature... there will be a number cast into the plastic of the pump cam...I would try the 40 pump jets myself

Go with 50/58.5 float setting, and make sure the carb doesn't flood when your turn the electric pump on while the engine isn't running... otherwise you might have a suspect needle valve or too high fuel pressure....have you got a fuel return line or pressure regulator installed? if all looks good and you still flood try moving the float down 1mm to 51/59.5. Do these DCNF's have a brass float (like most DCNF'S) or are they a plastic type of material... if they are spansil (plastic) then you need to weigh them to ensure you havent got a heavy float causing your flooding...1gram will make a difference! if they are brass, give it a shake ... if you can hear fuel sloshing inside then they are leaking...and need to be replaced.

Your carbs do sit level don't they ...(not sure if I've asked this before) as the 128 manifolding (or carbs tilted back) on an X19 requires a lower float level as a compromise.

2.5aux venturis would have pulled the main circuit in very early.. 2.5 is the cross section in mm2 of the orifice size, so going up to a 3.5 is definitely a good step IMO.

Also make sure your fuel pump is up to the job....what might have just been enough to keep the 36's happy might be not quite enough for the 40's... I would check and make sure your pump can deliver around 1.5litre/min ... and if your running a return line, make sure there is a 1/1.5mm orifice restricter in the line (braze up one end of the T piece and drill a 1/1.5mm hole in the end)

Try it at those settings and see what your consumption is like, what the plugs look like, and most of all what it feels like...and lets us all know how it goes.

SteveC
 
The pump is a pierburg pump which delivers 70 L/H with pressure of 0.27>0.38 bar. It has no return, but has an automatic cut-off when the pressure is too high. A lot of people use this pump in this setup, with smaller or bigger carbs, so the pump shouldn't be the problem.
IMG_9765.JPG


The carbs are somewath tilted but the manifold is x1/9. The whole engine is tilted (1500 cc in 1300 body). I'm going to fit a larger dogbone to put the engine straighter and will try to adjust the lower crossmember to get the engine more upright (but is this was the problem both carbs would flood.

So it must be the floatsetting or a not closing needle. Something i didn't mentionaed before is that this carb has a "broken arm". I fixed it temporary, not thinking it could have any effect, but maybe it does. Because of an other post a orderd jbweld and wil fix this properly. Maybe this causes the bad closing of the needle

 
Out of curiosity, which dogbone do you have in there now? The 1300 or 1500 one? If you change the angle of the engine, remember that the oil pump is set up to work with the engine at a particualr angle. If you look at the Mk 1 Uno Turbo, you've got pretty much the same engine at a different angle and had a different pump to compensate for that.
oilpumps2.jpg


For the life of me, I can't remember which is which in that pic, but one is from an Uno T and the other is from an '87 FI X. With all the great advice Steve C. is giving you to help you get the DCNF-40s going, I would hate to see something happen that could create problems down the line...

EDIT - Just wanted to note that I know this has nothing to do with an Uno Turbo, I was just using it to illustrate the point of the way the engine is angled in the X and how changing that can have an effect on the oil system...
 
The 1300 one. But since the engine is a 1500 (in a 1300 body) i think it needs a 1500 dogbone. (maybe that's why i have a low oilpressure reading on my dial)
 
pyrraxis,

the pump pickups are different to follow the different sump profiles... so having the engine tilted a little back isn't going to affect oil pickup unless the level is dangerously low anyway... Martijn is pretty fussy with his car so I doubt low oil level is ever going to be an issue.

Martijn,

well the pump should keep up, 70l/h is probably about the minimum I would use... seriously these little engines can have quite a demand... I've had 1litre/min pumps not able to keep up at full noise and had to change them out for 1.5l/min.

0.27 to 0.38 bar is actually a little high... thats roughly 3.9psi to 5.5psi... really it should be 3.5 to 4psi max....

Not sure if it's the angle of the picture, but the float tang/arm doesn't look to straight...you might have the correct float setting but not be shutting off the needle valve...hold it at the 50 level, and blow by mouth into the fuel inlet... see if it leaks... the arms do bend if roughly adjusted... and as these are secondhand carbs who knows whats been done in the past.

You might need to make up an adjustable top arm (dogbone) and set the engine level... if your bushes are still good, it's not hard to cut and shut to lengthen and shorten as required.

Another thing you want to address is some ram tubes / bell mouths / velocity stacks or whatever you want to call them... It looks like your 40's are the type with no extension cast into the top cover... this will mean your aux venturi will be sticking up in fresh air... the carbs will definitely work better with a bellmouth to direct the air into the throat.

SteveC
 
I think you're right that it needs the 1500 dogbone. If I remember, the dogbone needs to be "matched" to the engine and not the body. Something that occurred to me is that with the incorrect dogbone, you're also "twisting" the engine a bit. While not a critical item in the short term, it can put undue stress on both the snail mount and the transmission mount. Hopefully Steve C. can give some info on how the different mounts might affect the floats on the DCNFs...
 
Ahh, I stand humbly corrected! :happy: That makes more sense - about the sump versus the engine angles.

BTW, I've always loved the idea of going with dual DCNF-40s, but never had the "chutzpa" to make 'em happen! So I'm actually following this thread pretty close, knowing I'll never actually do it myself... :rolleyes:
 
DAAAAAAAMMMMMNNNNNN!!!!! That looks NICE! :headbang: And I don't see anything wierd with any of the angles in there. Ok, I'll shut up now and go back to lurking on this thread... :dunce:
 
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