Race Engine Forum UK

Need to know what jetting you all are running on your DCOE 45s. Looking for only base line data as a starting point and to help diagnose a very rich condition. I attached a picture of the setup for reference. 5.2 liters, 10:1 compression, .475" lift and 230 I+E duration at @ .050 tappet lift, 1.5 ratio rocker arms, 110 LC. Fixed timing magneto dead timed at 25* for now. Carbs synced very close. Idle speed screws in from contact 1/2 (rough) turn.

Existing jetting
Mains: 145 (1.45mm drilled out? should measure)
Air correctors: 170
Idle jets: 40f6

Basically it will idle down well considering cam and idle screws like to be at between 1/4-1/2 turn out. Great throttle response off of idle. Seems ok on the pilots but as soon as it sees the main circuit it goes blowing black rich. The jetting seems close numericaly but you all can let me know if that is correct. From my form searches the range is wide as far as what people are running.

I have verified float levels at 8.5mm and fuel pressure is at 4 psi.fuel inlet valves close off well and it can hold the pump pressure with the engine off. Cold start valves are shutting off well.

What emulsion tubes and primary choke size?

G

Guy Croft wrote:What emulsion tubes and primary choke size?

G

I'll get those as soon as I can.

Tks
Robert

Chokes are 40mm
Emulsion tubes are F2

Are you running without headers?

G

No, it was run with headers. 1 3/4" full length pr1maries into 1 3" collector, no mufflers

It could well be the emulsion tubes, F2 is not one I've ever used and their characteristics from the Weber manual are markedly different from any tube I've ever used. For starters I would try F16 and see what influence they have.

These are item 13 on the drawing at this link (forthose who don't know their way around DCOE carbs):

http://www.webcon.co.uk/weber/40dcoe.htm

I have no exp of this engine as-such but I wonder if the fixed 25 deg ignition advance might be contributing to the problem.

GC

Thank you for your advice.

Will look at ordering a set of f16 ET's Hope They will allow me to try them and return them if the results are not good.

The fixed mag timing is common in drag racing and usually has no ill effects. I still need to move it up to 34*. Maybe that will help. I dead timed it at 25* for cam breakin.

Robert

Worth mentioning that you will never get on the main circuit 'off-load', even at progression off-load you could rev it 'off the clock.

It is common for DCOE to go very rich at prorgression off-load, 7% CO or more.

To check the main circuit you have to physically drive or dyno - forgive me if you know this.

GC

Thanks I did not know DCOE's have that tendency to go rich in the pilots and unloaded.

When I referenced the black raw fuel laden exhaust when in the mains I visually see main nozzle discharge and this in at 1/2 throttle and rapid engine acceleration.

To update my post I did gauge the main jets and while they are marked 145 1.45 mm(.057") and they gauge to a 165 - 1.65mm ( .065") . They appear to have been drilled.
I have 8 X 130 and 8 X 140 MJ arriving today so I can try that tonight. Now I suspect all jets may have been drilled including pilots possibly. So more gauging tonight.

Robert

I would not even look at small mains, with your huge cylinder size on 40 chokes I'd expect to have 145 (1.45mm dia) mains - or bigger.

I would imagine the initial a/c (air corr) size would be OK.

G

So I gauged all of the other jets and only the main fuel jets were opened up. I installed the 140's because that is what I had and it now seems OK.
Still need to drive it but so far it has cleaned up. 3/4 throttle raps off of idle are crisp with only a slight puff of fuel at the hit (probably pumps).

I will be mindful of your warning on the small 140 jets. Once it is driving I will do a comprehensive plug read.

140 main on 40 chokes is an odd combo on an engine with 650cc cylinders Rob.

It suggests to me that the chokes are too big really and that the velocity thru the carb is low. EG: I use 145 mains on many 500cc cylinder applications.

G

I suppose the proof will lie in the pudding.

Currently will take instant full throttle and has some black so at least in that regime it is not yet lean. Depending on how tight the converter is it could as you recommend need larger jets.

1800# and 400+ hp will limit time on WOT for sure.

Thanks for the insight,
Robert