BDA Weber tuning

[Miniliteman]

Hi,

HELP ... I am at the end of my knowledge ...

Engine: BDG with one-off pistons/rods/valves etc. and twin 55's with 48mm venturis, long 4-2-1 manifold. Been testing/dyno-ing it every evening since last Saturday and it now runs very well.
Problem is the mixture is within the acceptable range upto 9200 rpm then it becomes very rich.
Torque/power drops after that. Did a last run with fuel tank emptying (Facet pump keeps ticking) and the power went up after 9200 rpm but we shut it down quickly as the fuel ran out.

How can we lean out the mixture after 9200 rpm?
Tried most of the emulsion-tubes and jets and ignition timing ...

[Graham]

my guess is the 48 chokes are too big and dont really work properly until 9200, try reducing the choke and main jet size

[Miniliteman]

my guess is the 48 chokes are too big and dont really work properly until 9200, try reducing the choke and main jet size

Graham, we discussed that too last week but the torque is very good from 3000 - 9000 rpm which suggest the 48 chokes are working.
Any idea what camtiming would do?
Could it be that the cams should be timed "closer"?

[Graham]

i cant see cam timing making that much difference to the fuel slope,

3-9 is one hell of a wide rev range very difficult if not impossible to get right throughout the rev range on carbs, you need management and throttle bodies!

have you tried going up in air corrector size? its likely that due to the massive chokes to get the enough fuel in the engine low-mid to midrange your running very big main jets and they are simply working too well at the top end try going up a size on the mains and up a couple of sizes on the airs

[Miniliteman]

Yes we went up and down on air-correctorjets.
After yesterdays first event, most commented that the screeching "jet-fighter" noise of the engine on the dyno wasn't there.
And driver commented on lack of power especially after 8000 rpm.
On the dyno there is a long exhaust-pipe (about 10 cm dia) fitted that muffles the exhaust and ends outside somwhere.
Could it be that with less backpressure without that exhaustpipe the mixture becomes too rich?
Will have to get my portable widebandlambda thingy out of the box again ...

[Graham]

Could it be that with less backpressure without that exhaustpipe the mixture becomes too rich?
Will have to get my portable widebandlambda thingy out of the box again ...

could be, more likely though it would go lean, my car certainly did, we had fully mapped the engine so it was properly optomised fuel and ignitionwise, with less backpressure power went from 230 to 234 addiing more fuel gave 237 and taking out a bit of advance gave 240

[Roger Miller]

Leon,

whats happening at ram tubes up to 9K ?

Is there stand off ?

Have u just ?? put an air filter on it...after dyno ??



Ive had good results with pintos using smaller airs than mains, to ward off top end richness.

[Graham]

Ive had good results with pintos using smaller airs than mains, to ward off top end richness.

that would encourage top end richness

[Miniliteman]

Leon,

whats happening at ram tubes up to 9K ?

Is there stand off ?

Have u just ?? put an air filter on it...after dyno ??

Ive had good results with pintos using smaller airs than mains, to ward off top end richness.

Hi Roger,

on almost every run we used a new air filter.
At first we fitted the std (long) rampipes but found these needed shortening.
So we cut the long ones and rolled on a new 90 degree radius (effective length approx. 2 cm).
This, with a revised jetting improved power by about 25 bhp on topend.
There's no standoff.

Or could it be that the carbs frooze? It was 0 degrees Celcius saturdayevening.

PS: here a photo of the carb you asked for (somewhere else)

[Group4_Mark2]

Something which I head before and might be worth looking at is that the accelerator pump jets "pull over" at high rpm and start adding extra fuel. Could you try looking at what is happening during the power run and see if any fuel is coming from these jets as the rpms rise. Never seen this myself but worth a look.


Tom

[Graham]

carb icing would make it go lean not rich, and is unlikely to happen on very big carbs, it much more common on smaller carbs on a plenum manifold

[Miniliteman]

Thanks Graham and Tom; will have a look at the accelerator pump jet enriching the mixture at high revs.

[Roger Miller]

that would encourage top end richness

Not with corresponding emulsion tubes

[Roger Miller]

Hi Roger,



PS: here a photo of the carb you asked for (somewhere else)

Ta for that...was wondering where they would seal. !!

[Roger Miller]

2 more things .....

and yes one is that zero pump bleeds are needed

But have u got extensions on air jet holders ?

It could be vibrations aerating fuel in wells and this being sucked into air correctors.

O...and how many ccs is this thing ?

[Miniliteman]

2 more things .....

and yes one is that zero pump bleeds are needed

But have u got extensions on air jet holders ?

It could be vibrations aerating fuel in wells and this being sucked into air correctors.

O...and how many ccs is this thing ?

Hi Roger, thing is just under 2000cc.
We tried pump-spill-valves of 100 (std), 50 (recommended by someone), pumpjets of 45 and 50 but went back to valves of 100 and jets of 35 in the end.
Extensions on the airjetholders is a good tip!
Used some on a twin IDF engine many moons ago and it cured some erractic behaviour on the top end.
Thanks, Leon.

[Roger Miller]

Try some zero bleeds.



did u see this plug reader ?

[Group4_Mark2]

Any update on this?. Another suggestion, not sure if it has already been mentioned is to look at the vibration of the carb at such high RPMs.

[Miniliteman]

Next dyno-session is probably Sunday, engine is being re-assembled at the moment.

[Jalu]

Hello
Sometimes when tuning Weber carbs has to be take the emulsion tubes to the lathe and take od diameter 0,5-1,0mm smaller but thats when it gomes lean upper rew range ( more fuel on tubewell or fuel can go easier up to the tubewell).So what happening when you drill inside diameter little larger. Hard to say i havent try it never, but will emulsion tube mix more air on to fuel or will vacuum on the tube dropp little so it doesnt aspirate so much fuel on upper rew range. I dont know but if everything else is done that is what can try.

Jari

[Miniliteman]

Hello
Sometimes when tuning Weber carbs has to be take the emulsion tubes to the lathe and take od diameter 0,5-1,0mm smaller but thats when it gomes lean upper rew range ( more fuel on tubewell or fuel can go easier up to the tubewell).So what happening when you drill inside diameter little larger. Hard to say i havent try it never, but will emulsion tube mix more air on to fuel or will vacuum on the tube dropp little so it doesnt aspirate so much fuel on upper rew range. I dont know but if everything else is done that is what can try.

Jari

Hello Jari,

we started with F9 tubes but fueldelivery was too small. So changed to F2's which is a F9 with a smaller outside diametre.
Maybe an F3 tube is the answer (a few xtra airholes at topend) but I have got most of the Weber tubes just no F3 ...

[Group4_Mark2]

The following is a possible answer to the question about running rich at High RPM from another Forum.

back to the 9200 rpm BDG problem. I was fortunate to get to work with a team that had the same problem on a DOHC Cosworth with dual 50DCO sidedrafts. That particular engine was buzzed to 11,500 max, and would go 'pig-rich' @ about 9600 rpm. The team owner had some $$ available, so he spent $145 PER SPARK PLUG, for (4) of them, and had chamber pressure transducers installed/manufactured into the steel shells of NGK Racing plugs used in the engine. We put the engine on a dyno and he rented an ECA (Engine Cycle Analysis) software/hardware system for a single weekend. The ECA is capable of monitoring the pressure transducer in the plugs and recording the cylinder pressure for every sequential plug firing. What we found with the Cosworth? At 9600 rpm, the engine began to experience moderate to serious 'cyclic variation' in cylinder pressures. That is, the cylinder pressures would often drop to the point that the cylinder would not fire at all, or the pressure was so low that the chamber flame-front was seriously affected. And the wide-band O2 sensor in the header system immediately recorded a relatively rich condition. And the weirdest thing of all? We could NOT detect/hear any cylinder mis-fire in the acoustic note of the header system! Everything 'sounded' just fine! The problem? Intake valve springs @ very high rpm. New springs were originally installed @ 65# of seat pressure. We went to PAC beehive's @ 80# on the seat. Problem solved! What was happening with the original springs? The intake valves were bouncing so badly at the seat, upon intake closing, that the 'trapping efficiency' within the cylinder was crap & cylinder pressures were all over the place, as monitored/recorded with the ECA system. Bottom line? Never get the idea that your race engine isn't mis-firing just because you can't 'hear' it in the exhaust system! And if the engine suddenly goes 'rich' at high rpm, immediately suspect the valve springs may not be controlling the intake valves ONTO THE SEATS.

[racing escort]

Interesting Mark, hope this helps to solve the problems ... could become one off the fastest escort mk2's on the continent

[Miniliteman]

The following is a possible answer to the question about running rich at High RPM from another Forum.

Thanks Tom!!
Who wrote that and where?
Is the "9200 rpm BDG problem" our problem?

[Group4_Mark2]

Yes, THe BDA problem is yours. I posted on anther forum (oval track high RPM specialists). I hope you don't mind. The forum is at http://4m.net/showthread.php?t=160403

The person who responed is very knowledgable in all aspects of engine building and tuning.

Regards
Tom

[Graham]

now tom has posted that, i recall my own car developed a high rpm problem, that too appeared to be a mixture issue and turned out to be valve springs that had "gone off"

[Miniliteman]

Yes, THe BDA problem is yours. I posted on anther forum (oval track high RPM specialists). I hope you don't mind. The forum is at http://4m.net/showthread.php?t=160403

The person who responed is very knowledgable in all aspects of engine building and tuning.

Regards
Tom

No problem posting it elsewhere, thanks for your effort.
Interesting read that ... must get registered on that forum!

The car hasn't been on the dyno today, probably tuesday now.
The engine has been build with the rotating/reciprocating (spelling?) mass kept as low as possible.
As the valves are very light the double-springs are also very light with not a lot of pressure.
So they might be too soft for 10000 rpm.

I know how to tune Webers (well I think I do ...) and used F7-tubes for several other (Pinto-) engines with big carbs which is similar to the F8 mentioned by someone on the other forum. Will keep you uptodate on any progess we make.

Leon.

[Jalu]

No problem posting it elsewhere, thanks for your effort.
Interesting read that ... must get registered on that forum!

The car hasn't been on the dyno today, probably tuesday now.
The engine has been build with the rotating/reciprocating (spelling?) mass kept as low as possible.
As the valves are very light the double-springs are also very light with not a lot of pressure.
So they might be too soft for 10000 rpm.

I know how to tune Webers (well I think I do ...) and used F7-tubes for several other (Pinto-) engines with big carbs which is similar to the F8 mentioned by someone on the other forum. Will keep you uptodate on any progess we make.

Leon.

Hello

Here is one choise for seatpressure.

COSWORTH FORD FVA 1969 ENGINE SPECIFICATION SHEET

Valve springs: Double springs, variable-pitch wound outer. Rate 260lb / in.
Free length 1.65”, fitted length 1.30 / 1.31” (both measured
on outer). Close coils to be fitted at head end.

What gives you those sprin rates 91lb seatpressure.
I know that bda/bdg free lenght and fittet lenght are different but that gives you idea where they shoul be for working over 9000rpm.

Jari

[Group4_Mark2]

Any updates from the Dyno?

[Miniliteman]

Any updates from the Dyno?

Sort of ... took engine apart after the first rally and bolted the lot together again after checking everything.
Went to the dyno yesterday-evening and started from scratch (we had all the previous runs to compare to).
Results:
- idle speed is too low even with some more advance: probably need to drill butterflies otherwise they already clear the first progressionholes when idling (@ 1800 rpm).
- pump back bleeds need to be closed (sorry to whoever said this and I doubted it ...)
- main venturis are probably too big (48mm); looking to make or buy 45mm ones.
- engine now runs to the 9500 rpm limit; earlier problem @ 9200 rpm was overrichness due to us over-compensating lean area at 7000 rpm with larger main jet or smaller air jet.

With the next event next weekend we settled for a compromise (a bit lower bhp then hoped for).
We found that a good reading on the dyno and a good drivable engine is not necesseraly the same thing.
On the dyno you go in one gear from 3 - 10k rpm for a powerreading whereas in reallife you buzz uo and down the gears quickly.

Grtz, Leon.

[Jalu]

We found that a good reading on the dyno and a good drivable engine is not necesseraly the same thing.
On the dyno you go in one gear from 3 - 10k rpm for a powerreading whereas in reallife you buzz uo and down the gears quickly.

AAhh. Only clock matters. When you probelly tune engine on the dyno and you go to drive it first time on to the nature there is always made some chancing at the jets and sparking advance that you can put it "speak" good and loud.
Regards Jari

[Miniliteman]

Today's update ...
Made some 44mm venturis and tested the engine again yesterday-evening with the things.
Not good; big loss in power across the rev-range and the richness still is there at 4000 rpm and the lean-ness is still there at 7500-8000 rpm.
Switched back to the last "sort-of-good" setting we had on the 48mm venturis, and changed the ignition-timing a bit to avoid detonation.
Engine now has 260 bhp / 270 Nm with a hesitation at 7500-8000 rpm.

Today was the 2nd rallysprint of the year; it started this afternoon with a light drizzle and ended up with torrential rain!
Not good for a 2WD car against EVO/WRX-opposition.
My mate Jarno and navigator Peter got of to a good start on SS1-3; 4th overall and a podium was within reach.
Even with an engine that sometimes wouldn't rev beyond 7,5.
In service, sparkplugs were changed and one snapped off :-(
It was rectified but the crew was OTL by 30s.

Looked at some other BD-engined cars at the service area and all have F9 emulsion tubes in their carbs (45's).
If I look at the lambda-reading of all the powerplots we did, they all sort of stay the same regardless of venturi-size etc.
What we mostly used were F11, F9 and F2 emulsion tubes.
These are all of similar shape; an F2 is an F9 just a smaller tube.

What do you think of:
the richness at 4000 rpm indicate the emulsion tube will need some more holes toward the top.
the lean-ness at 7500 rpm indicate the engine is not fully on song and the emulsion tube will need less holes in the middle.
top end richness (9500 rpm+) indicate the emulsion tube will need some more low-end holes.

Anyone has experience in what a certain emulsion tube will do exactly?

[Roger Miller]

Whats the dyno curve look like ?

[Miniliteman]

Whats the dyno curve look like ?

Shit ...

There is a dip in torque at about 4-4500 rpm due to overrichness then it goes up again until 7500 rpm when there's another dip due to a lean mixture then it goes up again to 9200 rpm.
At the moment it seems to me that the emulsion tubes need some holes at the top to get rid of the richness at 4000 rpm. Then it will need less holes at midrange (there are 8 holes in the middle of an F9) so it will not leanout at 7500 plus it will need some holes at the bottom of the tube to combat top-end richness.
Almost everything on the engine is a one-off, so why not make a set of one-off emulsion tubes???
To test if I am thinking in the correct direction I will take another set of F9's and close up 4 of the 8 holes in the middle.
Any idea how go about that? Solder them? Put some kind of glue in them?

[exboyracer]

PErsonally I would solder them, I've done this in the past and it works well as long as you are good with a soldering iron.

[Graham]

soldler, its a piece of piss to solder brass

[Group4_Mark2]

Shit ...

There is a dip in torque at about 4-4500 rpm due to overrichness then it goes up again until 7500 rpm when there's another dip due to a lean mixture then it goes up again to 9200 rpm.
At the moment it seems to me that the emulsion tubes need some holes at the top to get rid of the richness at 4000 rpm. Then it will need less holes at midrange (there are 8 holes in the middle of an F9) so it will not leanout at 7500 plus it will need some holes at the bottom of the tube to combat top-end richness.
Almost everything on the engine is a one-off, so why not make a set of one-off emulsion tubes???
To test if I am thinking in the correct direction I will take another set of F9's and close up 4 of the 8 holes in the middle.
Any idea how go about that? Solder them? Put some kind of glue in them?

Sounds like you have got a handle on the problem and a plan to get it sorted. Soldering the emulsion tube is easy. Make sure you use a soldering iron with enough power and leave the metal heat up enough that the solder flows and wets the metal properly. Biggest mistake when soldering electronics is not giving it enough heat and ending up with dry joints. Metal soldering is much the same.

[Roger Miller]

Leon,

Are they 4 into one pipes u made earlier ?

[Jalu]

Shit ...

There is a dip in torque at about 4-4500 rpm due to overrichness then it goes up again until 7500 rpm when there's another dip due to a lean mixture then it goes up again to 9200 rpm.
At the moment it seems to me that the emulsion tubes need some holes at the top to get rid of the richness at 4000 rpm. Then it will need less holes at midrange (there are 8 holes in the middle of an F9) so it will not leanout at 7500 plus it will need some holes at the bottom of the tube to combat top-end richness.
Almost everything on the engine is a one-off, so why not make a set of one-off emulsion tubes???
To test if I am thinking in the correct direction I will take another set of F9's and close up 4 of the 8 holes in the middle.
Any idea how go about that? Solder them? Put some kind of glue in them?

Do you have any other ex manifold what you can try or tune on the rolling road? I think that 4-4500 rpm overrichness come on because of camming and can be solve on right ex manifold.

Jari

[Graham]

the simple truth is carbs are a compromise you cannt on an engine with wild cams get the mixture right everywhere without electronic fuel injection