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post #1 of 13 (permalink) Old 04-28-2018, 09:03 AM Thread Starter
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Weber idle jet question

Pulled the old webers off, 40dcoe's, one weber was very inconsistent, cylinders 3 and 4 never fired right no mater what, turning in mixture screw etc. Once off it seems the gas was spraying against the back of the butterfly and not into the chamber like the other weber, put a new set on and the car came to life, I know "rebuild the webers" but they're 50 years old, already rebuilt once, its my daily driver and somehow new seemed better.

Running 40 151 webers now, With some fantastic cams from Richard J.

Question: Running 55F8 idle jets, at 1000- 1500 rpms a hesitation on take of, once where up to 2500rpms we're fine. So must be the idle jets, now do I go up to 60F8's to correct or down to 50's?

Also: After the car sits for 2 days its hard to start, like theres no fuel in the carbs, lots of cranking, pumping on the gas pedal, once it fires its great. Is this "float level"?

thanks guys!
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post #2 of 13 (permalink) Old 04-28-2018, 01:05 PM
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Check your ignition timing before you do anything else.
Then, check float height, then accelerator pump jets, for a blockage. Even if one is blocked you'll get the symptoms.
With a standard engine, and 55 F8's you should have no bog on progression, (unless they've been drilled incorrectly (not so uncommon !) 60 F8's are way too big for a 2 liitre, and will mask another problem.
You may need 55 F8's with RJ's cams.
I have 151's on my engine (warm 2 litre), and run 50 F8's with no bog, with 55 F8's i use more fuel can't get the right coloured plug.
Presume you're running the standard mech pump if it's taking a long time to start ?
I have a Mitsuba electric pump fitted.
I turn the key, let the pump fill the carbs, in cold weather, three dabs on the throttle, and it starts instantly. No long cranking periods, no throttle pumping.
The jetting spec I am running is :-

32mm chokes
130 Mains
200 A/Correctors
F16 Em Tubes
50 F8 Idles
35 Accelerator Pumps
Hope that helps

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post #3 of 13 (permalink) Old 04-29-2018, 08:38 AM Thread Starter
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I've got new 40 / 151's on there now, running the same jetting as before, Its a 2 Liter with cams, 2 piece header.

Our set ups are very similar:

32mm chokes
135 mains
180 A/Correctors
F16 Em Tubes
55F8 Idle jets, these are the ones that I'll drop to 50F8 to clear the hesitation on take off around 1500 rpms, at least thats what I think needs to be done.
40 Accel pump

I'm getting used to the new carbs, I have an electric fuel pump, I just need to let the pump run and stab the pedal a few times
The old Italian 40 dcoes never needed a choke, so I wonder if the Spanish webers were any different.

This is a great article too on weber set up, takes some of the mystery out of it : Tuning_weber
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post #4 of 13 (permalink) Old 04-29-2018, 09:22 AM
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Quote:
Originally Posted by AlfaEvan View Post
The old Italian 40 dcoes never needed a choke, so I wonder if the Spanish webers were any different.

Tuning_weber
No, you don't need the choke connecting on 151's either, in that regard, they're just the same as the old ones.

Steve

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post #5 of 13 (permalink) Old 04-30-2018, 08:03 AM
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Jetting

I think the 55F8 idle jets are a bit too big. 50 F 8s should be a better choice.

If you are using a mechanical fuel pump a low pressure elec one will solve the start problem. But check the bottom plate under the carbs to insure that the 4 screws on each are tight so fuel can`t "weep" out.

A wide-band O2 meter is the only way to get jetting "right-on".

Richard Jemison
RJR Racing

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post #6 of 13 (permalink) Old 04-30-2018, 08:14 AM Thread Starter
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Thanks Richard, The cams are fantastic, thank you. The cars a little screamer now.

I'll dial the carbs in with the 50 f8's, its still a learning process. I'm using an electric fuel pump, I'll check for weeping, we checked the carbs for loose screws before mounting them though.

I'll have to get too a shop, or friend... with an O2 meter. Take care!!
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post #7 of 13 (permalink) Old 05-02-2018, 01:56 PM
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Quote:
Originally Posted by AlfaEvan View Post

Also: After the car sits for 2 days its hard to start, like theres no fuel in the carbs, lots of cranking, pumping on the gas pedal, once it fires its great. Is this "float level"?
I recognise that behaviour on mine. I am thinking of trying out an electrical pump, such as this - mounted near the tank

12v Universal Fuel Pump 2.5-4.5 PSI - Webcon UK Ltd

1975 GT Junior with 2 litre lump
2006 Subaru Impreza WRX
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post #8 of 13 (permalink) Old 05-02-2018, 03:32 PM
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I recognise that behaviour on mine. I am thinking of trying out an electrical pump, such as this - mounted near the tank

12v Universal Fuel Pump 2.5-4.5 PSI - Webcon UK Ltd
You may find this type of pump very noisy, and they run constantly with a "buzz". A much better bet would be the reciprocal type pump, such as a Facet silver top :-
https://www.ebay.co.uk/itm/Facet-476...QAAMXQVT9TDyiI,
or a Mitsuba (or Mitsuba style) pump :-
https://www.ebay.co.uk/itm/12v-Fuel-...IAAOxy4t1SlKrs
With the reciprocal pumps, they tick, and only pump when required, so once the carbs are full, you only get a tick when the fuel is being used and needs to be replaced, and you don't hear it inside the car when you're driving.
I have a pair of original Mitsubsa's, that I've owned for over 30 years, one on the car, one kept in the boot as a spare. They were the best of the best, used on many Works rally cars in the 70's and 80's.
I've never had to use the spare, and I've swapped them from car to car over that period.
Try and get an original Mitsuba if you can, but if not, I've also fitted lots of Facet cylindrical style pumps too, and they too, are reliable.
Steve

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post #9 of 13 (permalink) Old 05-02-2018, 04:20 PM Thread Starter
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Made excellent progress with the Webers. Changed the jets from 55 F8's to 50 F8's, and while we were at it, we decided to take a look at the distributor. We noticed the Marelli Plex weights only swung so far out, the springs also looked heavier. We compared to another Marelli Plex unit at the shop, hmmm, we noticed this units weights swung further, hmmm, more advance, on closer inspection we noticed a second set of groves, that was allowing the weights to swing further.

We put it all together and took it for a spin. The hesitation on take off was gone. Amazing. Step on gas and car goes, plugs look good too, nice and clean.

So, we tried putting the 55 F8's back in, nope hesitation came back. With the 50 F8's you can drive slowly in 2nd without the car lurching back and forth.
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post #10 of 13 (permalink) Old 05-04-2018, 12:15 AM
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Originally Posted by GTA R View Post
You may find this type of pump very noisy, and they run constantly with a "buzz". A much better bet would be the reciprocal type pump, such as a Facet silver top :-
https://www.ebay.co.uk/itm/Facet-476...QAAMXQVT9TDyiI,
or a Mitsuba (or Mitsuba style) pump :-
https://www.ebay.co.uk/itm/12v-Fuel-...IAAOxy4t1SlKrs
With the reciprocal pumps, they tick, and only pump when required, so once the carbs are full, you only get a tick when the fuel is being used and needs to be replaced, and you don't hear it inside the car when you're driving.
I have a pair of original Mitsubsa's, that I've owned for over 30 years, one on the car, one kept in the boot as a spare. They were the best of the best, used on many Works rally cars in the 70's and 80's.
I've never had to use the spare, and I've swapped them from car to car over that period.
Try and get an original Mitsuba if you can, but if not, I've also fitted lots of Facet cylindrical style pumps too, and they too, are reliable.
Steve
Thanks for the thoughts. Yes, I looked up "mitsuba" but saw they were no longer produced, and saw that Classic Alfa sell the "silver top" as an option. Would you fit either of these under the bonnet in a puller mode rather than by the tank in a pusher mode? I have K&N pancake filter, so there's plenty of space under the bonnet. I assume fitting one of these means removing the mechanical pump, the pump rod and fitting a blanking plate.

1975 GT Junior with 2 litre lump
2006 Subaru Impreza WRX
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post #11 of 13 (permalink) Old 05-04-2018, 01:07 AM
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I fit mine under the bonnet, on the off side inner wing, together with a Malpassi Filter King (pressure regulator / filter).
Many disgree with this,and use theirs in a pusher mode, but I've been fitting them under the bonnet for 40 years+, and have never had a problem. With a Facet reciprocal pump, I fit a non return valve in the line just before the pump to stop fuel draining back, but the Mitsuba has never needed one.
When you first fit it, you'll need to prime the pump by sucking on the fuel pipe, (carb side of the pump), until fuel at least part fills the pump. Connect the hose to the carbs and you're there.

Yes you'll need to remove the mech pump and op. rod, and use a blanking plate.

Steve
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post #12 of 13 (permalink) Old 05-04-2018, 05:49 AM
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You guys in England can get away with mounting the fuel pump up front because you live in a cool climate. Vapor lock is much more of a problem in hotter places.

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post #13 of 13 (permalink) Old 05-04-2018, 08:49 AM Thread Starter
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I've been using a "Chevy LUV" electric fuel pump. Works great and its quiet. https://www.ebay.com/itm/ACDelco-EP4...UAAOSwuzRXdKVU
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