Weber 48 ida help

Hi,
Im on a freshly rebuilt 351w with afr heads 10.5:1 compression and comp cam.
My carbs are currently running
37mm chokes
F14 emulsion tubes
Main jet 175
Air correction 160.
I've never ran the car on the road but just occasional starting and get on and off the trailer it seems very fuely. Black smoke/sooted plugs.
Is there any thing that jumps out as massively wrong.
I will get it professionally tuned but I'd like it to go there better than it is now.
I've now had lambda bosses welded in the exhaust for when that day comes.
Thanks
 
Its running very on the rich site.
Ive serviced those which came with,
40 chokes
150 mains
180 air correction
F11 emulsion tubes.

Your jets are to big for the 37 chokes.
 

Mike Pass

Supporter
First check the fuel pressure is around 2.5 - 3.0 psi. Any more will push open the float needles and cause a very rich mixture. Next check the float level. A bit of a pain on IDAs but you can find how to do it on the internet. The float level is critical for the emulsion tubes to work correctly. There are some good videos on Youtube showing the effect of fuel float level on emulsion tube function. I will have a look for the setup from some 48IDAs from a 351 that I did some work on a while back.
Cheers
Mike
 

Mike Pass

Supporter
Here are a few 48IDA settings from various carbs for 351ci. These may help after you have set the above items, if you still have rich running issues. Because you need to buy 8 of everything it can get expensive to guess too much so a rolling road session with someone who knows the carbs and has a big box of jets etc, is the only way to get them right as there are so many combinations of cams and heads.
I have some bits of info on Weber 48IDA rebuild setup and tuning. Drop me a PM via this forum with your email if you would like a copy.
Cheers
Mike

Weber 48 IDA SettingsWeber FactoryNB 351My Carbs 351Redline recommendedMB
347ci (302 stroker
Street
Main venturi37?404037
Aux venturi4.54.54.54.54.5
Main jet135140165170165
Emulsion tubeF7F7F5F7F5
Air corrector120120175170120 but drilled
Idle jet70F10F104.5F1065F1070F10
Idle jet holder10060
Pump jet5050
 

Rune

Supporter
I think the most important is to get the float level correct before you proceed, And I would recomend to start with main 180 and idle 70f10.
 
Thanks for your helpful replies. My carbs were bought from webcon uk and I'm assured the floats were set when the kit was built up. But who knows and if the problem persists I'll look into that.
Just searching these pages and google and it seems no one tends to be running an f14 emulsion tube like mine are or is that not important? 5,6,7,8 seem to be the popular ones.
Is it correct that the idle jets do all the fuelling upto 2-3000rpm? Mines barley ever got to that and I have these issues. Could I also have a problem there?
Thanks
Tom
 

Mike Pass

Supporter
Have you checked the fuel pressure?
What idle jets are fitted?
The emulsion tubes basically alter the fuelling slope. Richer to leaner or leaner to richer. The numbers do not have a logical order to them.
Another way to work this out is to fit an air/fuel gauge. This will need a sensor to be fitted into the exhaust.
e.g.

Cheers
Mike
 

Brian Kissel

Staff member
Moderator
Lifetime Supporter
This is a sticky thread in the engine section. If you haven’t already seen it.

Regards Brian
 
This is a sticky thread in the engine section. If you haven’t already seen it.

Regards Brian
Hi Brian, thanks and yes I have read the thread and watch the videos.just struggling to get my head around it and thought peoples past experiences and knowledge could help me out
 
Have you checked the fuel pressure?
What idle jets are fitted?
The emulsion tubes basically alter the fuelling slope. Richer to leaner or leaner to richer. The numbers do not have a logical order to them.
Another way to work this out is to fit an air/fuel gauge. This will need a sensor to be fitted into the exhaust.
e.g.

Cheers
Mike
Hi Mike,
I haven't checked but will tomorrow re the idle jets. Supplier said 70f10.
Fuel pressure is 2.5psi at present.
Thanks for the info on the emulsion tubes.
 
Hi,
so yes idle jets 70f10.
Quick question.
If the emulsion tubes have been changed do the float levels need to be reset?
Thanks
Tom
 
Good morning,
So since my last message I have now had a rolling road session and yesterday did my first 160 mile round trip road test. Overfueling was cured by lowering the main jet to 160 and the car pulls like a train.
I now have an issue with coughing and spluttering around 2 to 3000 RPM and then it clears and pulls great.
The tuner has explained to me me that to overcome this I need to lower my chokes to 34mm and although this may cost me some Power it would cure coughing and spluttering. Is the other option to drill the third progression hole? If so is there anyone at take this on as a job as I understand this is quite a precise piece of drilling required? It would be great to hear your opinions on this.
thanks Tom
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
In my limited experience, coughing and sputtering are signs of lean conditions. Progression holes drilled into throttle plates basically allow more airflow and thus more vacuum signal past the throttle plate at closed or low throttle settings - all resulting in tricking the main metering system into feeding more fuel.
My own system responded well on the dyno with simply enriching the idle fuel mixture screws.
 
In my limited experience, coughing and sputtering are signs of lean conditions. Progression holes drilled into throttle plates basically allow more airflow and thus more vacuum signal past the throttle plate at closed or low throttle settings -
Yes and no.
Coughing & spluttering is lean condition.
Progression holes, are just above the throttle blades and suply "extra" fuel from the idle circuit, when the throttle blades are opening.
The idle circuit playes a big role in 1/3th of the rpm range till main jets take over (2/3th of the rpm range).

Idle circuit contains two circuits, under & above throttle blades. Under is for idle when throttle blades are closed. Above is progression circuit and suplies aditional fuel when throttle blades are opening. If bigger idle jets do not have enough enrichment in the progession range (2000+ rpm) you have to concider a 3th progession hole to alow more fuel into this rpm range.

To complete carb basics. Aircorrection jets do the trick at 3/3th of the rpm range.
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
Yes and no.
Coughing & spluttering is lean condition.
Progression holes, are just above the throttle blades and suply "extra" fuel from the idle circuit, when the throttle blades are opening.
The idle circuit playes a big role in 1/3th of the rpm range till main jets take over (2/3th of the rpm range).

Idle circuit contains two circuits, under & above throttle blades. Under is for idle when throttle blades are closed. Above is progression circuit and suplies aditional fuel when throttle blades are opening. If bigger idle jets do not have enough enrichment in the progession range (2000+ rpm) you have to concider a 3th progession hole to alow more fuel into this rpm range.

To complete carb basics. Aircorrection jets do the trick at 3/3th of the rpm range.
You are correct. I was speaking about these holes being drilled into the throttle plates themselves to increase airflow and vacuum signal..
As I uderstand it, the later IDAs have the third progression hole but making that permanent change is something I would tend to forgo until a last resort if the other tuning methods offered by Weber do not pan out.
 
progression hole but making that permanent change is something I would tend to forgo until a last resort if the other tuning methods offered by Weber do not pan out.
You'r right, I am a carb specialist (weekly base) but agree a thirth hole conversion (drilling that 3th hole) on the older IDA's is a last resort.
48IDA carb's had one purpose back in the day's, Racing. Never ment to do cruising at 2000-3000 rpm. They suppose to run 6000-8000 rpm.

Weber IDF's are more suited for cruising rpm's
 

Mike Pass

Supporter
From the rolling road session there should be a graph of the fuel/air ratio. What is the fuel/air ratio at the problem 2 - 3,000rpm range ?
Weber IDAs do not like a lot of cam overlap as this can give a weak "signal" to the carbs. This may be the reason the rolling road guy has suggested the smaller venturis as the smaller venturi will improve the vacuum signal seen by the carbs. Carbs are reactive devices that respond to the vacuum signal created by the air flow. Maybe a look at your cam specs may help. If the mixture is weak in the problem range then a third progression hole placed above the current top hole will help to feed more fuel in the problem range. There is info online of how and where to drill the hole. Start very small and test before enlarging. The progression holes are very small but you can buy sets of very very small drills. Use them in a collet chuck on a Dremel or similar.
Cheers
Mike
 
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