Alfa 105 2000 GTV carb settings - solving hesitation problems

1295 Views 3 Replies 4 Participants Last post by alfaparticle, Aug 23, 2020

ronny_the_alien

Discussion Starter · Aug 20, 2020

All,

I've found this forum very useful for a number of areas and thought I'd share my thoughts on Weber carb set up and some problems I've fixed along the way.

1976 - 2000 GTV with twin Weber 138 and 139 no other modifications (yet..)

Idle - 55 F8
Pump Jet 40
Emulsion F11
Air Corrector 175
Main Jet 138
Starter Jet 85 F9

Alfaholics stainless exhaust system front to back.

It will now rev to 6,000RPM and has a good pull through all gears.

One recent problem I've been struggling with is hesitation when moving off from c. 1,000RPM to 3,000RPM, I've changed from F16 to F11 which helped.

However I recently noticed that the seals on the pump jet covers and the washers at the base of the pump jet didn't look right, a quick order to Emmanuel at Classic Carbs and £9.20 later the hesitation is all but gone. Shows how important every component, washer etc. is on these Webers.

I also had to rebalance the carbs by quite a bit so one of the pump jets was definitely not working properly.

Anyway hope this helps somebody out there, I'm sure the set up won't work for everybody but it seems to work well for me.

Now off for a nice drive in the sunshine here in the UK!

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Spdrcrj

· #2 · Aug 20, 2020

Thanks much for the write up. I’ve recently purchased a ‘74 GTV with dual Weber’s and carbs are a new experience for me. You information will help in quest to understand and properly maintain them. 👍🏻

2 stroke kart motors need a bit of fettling to compensate for temps, pressures, and such. Do these carbs need seasonal adjustments as well? I live in Las Vegas so the temp spread through the year is pretty wide.

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malcolm1

· #3 · Aug 22, 2020

Prompted by your post, I thought I would do the same. My O rings did look very perished. The aluminium washers took some persuasion with a fine blade to get them off the jets. I also sprayed carb cleaner through the jets and checked that the large and small holes were clear. I also sprayed carb cleaner in to wells where the pump jets sit in the carbs. My pump jets are 35. It drove well after, but it was driving well before - but worthwhile doing.

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alfaparticle

· #4 · Aug 23, 2020 (Edited)

40DCOE138/139 are emissions carbs and they require the correct emulsion tubes and idle jets. You have the ones for pre-emissions Webers installed and it is unlikely that you will ever get the car running properly with them.
Your emulsion tubes should be F34 and your idle jets should be 55F17 or 55F21

They are similar to 40DCOE72/73 in this chart https://centerlinealfa.com/sites/centerlinealfa.com/assets/files/default/weber_jet.pdf

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