Tunning dual Weber's

Engine, Transmission and related drivetrain.
NunoTT
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Tunning dual Weber's

Post by NunoTT » 22 Oct 2019 10:56

Hi!

I've installed a set of 40 Weber DCOM's on my 510 for quite some time now, but I never got around to tune them. The car has been sitting for some months, but now I really want to drive it, so I need to tune the carbs.

Besides not being balanced/synchronized, the biggest problem I have it that they are too rich. Too rich to the point that sometimes at idle I have gasoline comming out of the ram pipes. The spark plugs are actually wet, so the mixture is really rich.

I now I need smaller jets, but what size should I get? I would like to avoid the "trial an error" method, since carb parts aren't cheap as we all know...

Engine and carb specs are as follow:

Engine: Stock SSS L16 (stock head, cams etc)
Carbs: 30mm Venturi, 150 air corrector, 120 main jet, F47 emulsion tube and 59F21 idle jet

Thanks in advance!
NunoTT

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bertvorgon
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Re: Tunning dual Weber's

Post by bertvorgon » 22 Oct 2019 12:40

While I can't specifically speak to any jetting issue...( I'm a downdraft guy )

When you say fuel coming out the "ram" pipes....what do you mean? If you mean the aux venturi and fuel pressure is ok, your float level is too high.

is your fuel pressure ok? And of course float level(s) Any tuning would be meaningless till you make sure you are good in those departments.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

yenpit
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Re: Tunning dual Weber's

Post by yenpit » 22 Oct 2019 13:33

There are NUMEROUS factors involved, so you can try to narrow it down, but in the end you will either use your "butt dyno" with trial & error, swap jets, drive, diagnose, swap jets, drive, diagnose etc etc...........that's what I did as a kid. The other option is to find a local dyno AND pay somebody with dyno AND Weber experience to help you.....or just let them do their thing!

Where are you located........sea level or altitude? What engine? What specs? What cam? What compression ratio? What ignition system? Based on some of this, most Weber manuals/books have charts with BASIC starting points for your jetting.........BASIC. Then you buy a range of jets based on this & either try your butt dyno OR pay somebody to do it.

Another way that sometimes works is to use an exhaust gas analyzer up the tailpipe OR a simple air fuel ratio GAUGE. These are a good first step & can sometimes get you really close............but running the car on a dyno with a specialist is THE way to go.
72 510 4dr
1965 Mustang GT Coupe
2003 Saturn LW300 - wow!
LOTS of 510 parts!

NunoTT
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Re: Tunning dual Weber's

Post by NunoTT » 23 Oct 2019 00:05

bertvorgon wrote:
22 Oct 2019 12:40
While I can't specifically speak to any jetting issue...( I'm a downdraft guy )

When you say fuel coming out the "ram" pipes....what do you mean? If you mean the aux venturi and fuel pressure is ok, your float level is too high.

is your fuel pressure ok? And of course float level(s) Any tuning would be meaningless till you make sure you are good in those departments.
I don't know how my fuel pressure is, but since I have fuel coming out of the ram pipes I would have to guess that it is either ok or too high. If I had low fuel pressure, this wouldn't happen, right?
If it is too high, what's the best way to solve it? Should I get a fuel pressure regulator? I'm using the stock mechanical fuel pump, so I have no way to turn the pressure down, correct?

As for the float level, the same aplies. I don't know how it is, but I would guess too high (too much fuel in the bowl)? What is the correct (or best) way to adjust the fuel level? I've seen people just bending the tabs on the floats and other lowering the "ball" where those tabs will touch (I can't remember the name of the "ball")

NunoTT
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Re: Tunning dual Weber's

Post by NunoTT » 23 Oct 2019 00:22

yenpit wrote:
22 Oct 2019 13:33
There are NUMEROUS factors involved, so you can try to narrow it down, but in the end you will either use your "butt dyno" with trial & error, swap jets, drive, diagnose, swap jets, drive, diagnose etc etc...........that's what I did as a kid. The other option is to find a local dyno AND pay somebody with dyno AND Weber experience to help you.....or just let them do their thing!

Where are you located........sea level or altitude? What engine? What specs? What cam? What compression ratio? What ignition system? Based on some of this, most Weber manuals/books have charts with BASIC starting points for your jetting.........BASIC. Then you buy a range of jets based on this & either try your butt dyno OR pay somebody to do it.

Another way that sometimes works is to use an exhaust gas analyzer up the tailpipe OR a simple air fuel ratio GAUGE. These are a good first step & can sometimes get you really close............but running the car on a dyno with a specialist is THE way to go.
I've been trying to find someone with Weber experience, but it's not easy (I don't know why). I could try to tune it on the dyno... I'll try to find one local to me.

I'm located at sea level amd the engine is a stock SSS L16.

I would like to buy an AFR gauge, but I haven't found any that is affordable

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bertvorgon
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Re: Tunning dual Weber's

Post by bertvorgon » 23 Oct 2019 08:09

As others have said, there are a variety of things to make sure are good BEFORE you actually start tuning. And as every situation is different, it is hard for us to diagnose here.

For sure you need to make sure your fuel pressure as about 4 PSI...not 2 like a lot of the old books say...and no more than 5 PSI.

Am I safe to assume when you say "ram pipes" that you mean the booster venturi in the center of the choke in the carb? If there is fuel dribbling out of that, at idle, you have a problem for sure...so fuel pressure FIRST...then...float level.

https://www.racetep.com/manufacturer/ca ... pumps.html

There are a ton of sites on the Net to deal with tuning your carb. Grab a fuel gauge or any small gauge that can read low values and check that pressure is in the zone. Just "T" it in close to the carbs main delivery line. Having a good regulator should be a consideration as Webers like STABLE fuel pressure. You are correct that you CANNOT turn the pressure down with the stock pump...

https://www.racetep.com/manufacturer/ca ... carbs.html

This is a good article to at least understand how your carb works....

http://240260280.com/Tech/Carbs/Weber/D ... uning.html

You can research on line as to float adjustment..this is what I found

https://www.mgexp.com/phile/1/90717/Web ... ctions.pdf

It is possible say, that if your fuel pressure is TOO HIGH...it is overriding the ability of the needle and seat to control the fuel level so you get creep in the fuel bowl.

Somewhere online I remember seeing a basic jetting set up....but...as Yenpit said...there are so many factors....as to where to start...you have a baseline now, so once fuel and pressure sorted...it is a trial...

Where are you located?
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

NunoTT
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Joined: 09 Oct 2018 06:34

Re: Tunning dual Weber's

Post by NunoTT » 24 Oct 2019 10:35

bertvorgon wrote:
23 Oct 2019 08:09
As others have said, there are a variety of things to make sure are good BEFORE you actually start tuning. And as every situation is different, it is hard for us to diagnose here.

For sure you need to make sure your fuel pressure as about 4 PSI...not 2 like a lot of the old books say...and no more than 5 PSI.

Am I safe to assume when you say "ram pipes" that you mean the booster venturi in the center of the choke in the carb? If there is fuel dribbling out of that, at idle, you have a problem for sure...so fuel pressure FIRST...then...float level.

https://www.racetep.com/manufacturer/ca ... pumps.html

There are a ton of sites on the Net to deal with tuning your carb. Grab a fuel gauge or any small gauge that can read low values and check that pressure is in the zone. Just "T" it in close to the carbs main delivery line. Having a good regulator should be a consideration as Webers like STABLE fuel pressure. You are correct that you CANNOT turn the pressure down with the stock pump...

https://www.racetep.com/manufacturer/ca ... carbs.html

This is a good article to at least understand how your carb works....

http://240260280.com/Tech/Carbs/Weber/D ... uning.html

You can research on line as to float adjustment..this is what I found

https://www.mgexp.com/phile/1/90717/Web ... ctions.pdf

It is possible say, that if your fuel pressure is TOO HIGH...it is overriding the ability of the needle and seat to control the fuel level so you get creep in the fuel bowl.

Somewhere online I remember seeing a basic jetting set up....but...as Yenpit said...there are so many factors....as to where to start...you have a baseline now, so once fuel and pressure sorted...it is a trial...

Where are you located?
When I say ram pipes I really mean the ram pipes (or trumpets as some call them). I literally have gas dripping out form the front of the carbs.
I try to get either a fuel pressure gauge or a fuel pressure regulator ASAP (I might have a friend that can borrow me one to test this). If my fuel pressure is too high I'll have to install a fuel pressure regulator, and if it is too low an electric fuel pump. Correct?

After I get the fuel pressure sorted I adjust the fuel level like you said.

Thank you very much!

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bertvorgon
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Re: Tunning dual Weber's

Post by bertvorgon » 24 Oct 2019 10:51

Yes, an electric pump WITH regulator would be the best and really only option, that way you have control over
a main part of your system.....fuel control.

If it is running out the air horns ( ram pipes) then you do have a major pressure/float issue.

No wonder the plugs are wet and you risk "washing" the cylinder walls of lubrication, which is not a good thing.
When you have the tops off the carbs, make sure the needle and seat(s) look ok too
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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bertvorgon
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Re: Tunning dual Weber's

Post by bertvorgon » 24 Oct 2019 11:06

https://www.lainefamily.com/images/Webe ... Manual.pdf

I knew I had this bookmarked in my computer.....The actual Weber book ( one of many actually)
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

Keith Law
1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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icehouse
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Re: Tunning dual Weber's

Post by icehouse » 24 Oct 2019 13:12

This is how I tune them. I find the orginal box and packing material. Box them up real nice just like they came out. Then I load the box into my car, drive down to the river and chuck them in! haha That's a Heinz joke if you guys don't remember it :)
"People don't like it when shit doesn't match their rule of thumb." Sam

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Re: Tunning dual Weber's

Post by iceD » 24 Oct 2019 21:48

This might be the longest seriously technical thread I have read where the perpetrator has not stated there location. Realm 101.

ice D

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Re: Tunning dual Weber's

Post by 510rob » 25 Oct 2019 00:57

icehouse wrote:
24 Oct 2019 13:12
This is how I tune them. I find the orginal box and packing material. Box them up real nice just like they came out. Then I load the box into my car, drive down to the river and chuck them in! haha That's a Heinz joke if you guys don't remember it :)
That is good humor. Where is H.P. these days anyway?

NunoTT
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Re: Tunning dual Weber's

Post by NunoTT » 25 Oct 2019 01:04

bertvorgon wrote:
24 Oct 2019 10:51
Yes, an electric pump WITH regulator would be the best and really only option, that way you have control over
a main part of your system.....fuel control.

If it is running out the air horns ( ram pipes) then you do have a major pressure/float issue.

No wonder the plugs are wet and you risk "washing" the cylinder walls of lubrication, which is not a good thing.
When you have the tops off the carbs, make sure the needle and seat(s) look ok too

It doesn't run out continuously. Only at idle.
I'll make sure the the needle and seats are ok when I open them. Before I installed them in the car, I took them apart and cleaned them all up, so the needle and seat should be fine. But I will double check.

NunoTT
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Re: Tunning dual Weber's

Post by NunoTT » 25 Oct 2019 01:05

bertvorgon wrote:
24 Oct 2019 11:06
https://www.lainefamily.com/images/Webe ... Manual.pdf

I knew I had this bookmarked in my computer.....The actual Weber book ( one of many actually)

Thanks! I'll give ir a good read!

NunoTT
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Joined: 09 Oct 2018 06:34

Re: Tunning dual Weber's

Post by NunoTT » 25 Oct 2019 01:07

iceD wrote:
24 Oct 2019 21:48
This might be the longest seriously technical thread I have read where the perpetrator has not stated there location. Realm 101.

ice D
By bad. I forgot to say where I'm from when bertvorgon asked me. I'm from Portugal

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