Alfa Romeo Forums banner

1 - 20 of 37 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
Hi Guys,

I have installed a sport exhaust and perf camshafts to my 1974 GTV 2000. So now it needs rejetting to work properly, and I'm having issues with the progression and transition to main jets. I understand that bigger jets are needed, but it seem emulsion tub also need to be changed as then engine shutters between 1400 - 2100 rpms. From 2100 rpms, engine works very well with 138 main jets, 200 air jets, and F9 emulsion tube (with I suspect need to be changed to give more fuel earlier). The ideal solution would be a rolling road and see where I'm rich/poor, but I haven't found any specialist for the moment.

Has anybody have installed alfaholics (CatCAMs) P07 & P08 cams, and what fuel/air jets and emulsion tubes are needed? All suggestions are welcome

Cheers

Ludo
 

·
Registered
Joined
·
858 Posts
what kind of webers, wich choke size do you have? try F16, give it more fuel on the mains, like 145, and less air, 180 perhaps, if not helping try a richer idle jet
 

·
Registered
Joined
·
19 Posts
Discussion Starter #3
Hi Quadrifolio,

thanks for the quick reply

Actually the 40mm Weber are the 44/45 originally fitted on the 1600. So I'm bit worried the progression holes are different from the 76/77 fitted on the 2000. It wasn't an issue with Standard cams after rejetted with correct jets for 2000. Choke is 32mm.

I already tried F16 tubes, but F9 worked better. I also ordered F7 as the are supposed to operate at lower rpms (no holes at the top). I should get them today or tomorrow. Idle jets, I'm now on 60F8, but 55F8 seemed to work better at idle, not sure at progression

I'll try bigger main jets, as I noticed that 138 were significantly better than 130 or even 135. It might fix the issue.

I'll keep you updated on the progress

Ludo
 

·
Registered
Joined
·
858 Posts
model 44/45 is an EmCon (Emision Control) carb idd for 1.6 so you have to stick with the original E. Tube otherwise they are never going to work properly. Normal DCOE´s (No EmCon carb) use a total diferent E. Tubes, so the E. Tubes are not interchangable between EmCon carb and No EmCon carb (any number above DCOE32 is an EmCon carb)

Thinking loud you may use the E.Tubes from a Weber 76/77 a give it a try

Hoop this helps
 

·
Registered
Joined
·
19 Posts
Discussion Starter #5
I tried F34 which it the tube for 76/77 and this was undrivable. F9 tube used in DCOE32 for 1750 engine works the best for the moment. As it's already ordered, I shall try the F7 and if it's not better, I'll got back to F9, and try 140 and 145 jets.

Or I need to find a weber specialist with rolling road :)
 

·
Premium Member
Joined
·
477 Posts
Take the guesswork out and invest in a wideband O2 sensor.

https://www.wide-band.com/
Exactly what are you suggesting? The idea intrigued me - so I followed the link to the web site. They offer interesting permanent installation fuel injection controls, but nothing in the way of a temporary instrument you could check mechanical carbs with - at least that I could find.

I wouldn't be installing O2 sensors in my exhaust just to check my carb's operation.
 

·
Registered
Joined
·
1,126 Posts
Exactly what are you suggesting? The idea intrigued me - so I followed the link to the web site. They offer interesting permanent installation fuel injection controls, but nothing in the way of a temporary instrument you could check mechanical carbs with - at least that I could find.

I wouldn't be installing O2 sensors in my exhaust just to check my carb's operation.
I installed one in mine temporarily. You don't have to mount it permanently. Easily removed by disconnecting a power lead and plugging a bung in the exhaust with a fitting.

Small price to pay versus guessing with expensive jets IMHO.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #9
Exactly what are you suggesting? The idea intrigued me - so I followed the link to the web site. They offer interesting permanent installation fuel injection controls, but nothing in the way of a temporary instrument you could check mechanical carbs with - at least that I could find.

I wouldn't be installing O2 sensors in my exhaust just to check my carb's operation.
yep, same for me: I don't need installing o2 sensors as jetting the carbs properly is a one off. What's the advantage of these Wideband O2 sensors on a daily basis?
 

·
Registered
Joined
·
19 Posts
Discussion Starter #10
I installed one in mine temporarily. You don't have to mount it permanently. Easily removed by disconnecting a power lead and plugging a bung in the exhaust with a fitting.

Small price to pay versus guessing with expensive jets IMHO.
Ok, make sense. And how do you choose E tube once you have the richness?
 

·
Registered
Joined
·
1,126 Posts
I'm not suggesting it for daily basis.

It shows you your actual mixture in real time. Quite handy when jetting Webers that were not OEM. Real time readings.

Is that transitional bog due to a rich or lean condition?

Are the mains so lean you risk burning a piston?

Do you wanna spend a little over $100 for the tool or guess with hundreds of dollars worth of jets, tubes etc?
 

·
Registered
Joined
·
1,126 Posts
Ok, make sense. And how do you choose E tube once you have the richness?
You are in uncharted territory my friend.

There are charts for the E tubes, but you don't know whether your mains or airs are even correct. How about idle jets?

Have you cleaned your jets and verified they're the same across the board? has anyone previously drilled them?

Have you set the float levels?

If they're off, the emulsion tubes will never meter things correctly, no matter which ones you use.
 

·
Premium Member
Joined
·
13,082 Posts
The original jetting for 40DCOE44/45 is 30 mm venturi, 4.5 aux venturi, 117 main jet, 50F15 idle jet, f16 emulsion tube, 180 air corrector - for a 1600 Super.

2L cars with 32mm venturis usually need 130 or 135 main jets and F16 emulsion tubes and 50F8 idle jets. Air correctors mainly affect wide open throttle mixture.

I agree with Slowcreek that installing a wideband AFR meter will let you see exactly what is going on and eliminate the guess work.

You will find usefull information here: https://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/260689-weber-tuning-lambda-sensor.html
 

·
Premium Member
Joined
·
477 Posts
I installed one in mine temporarily. You don't have to mount it permanently. Easily removed by disconnecting a power lead and plugging a bung in the exhaust with a fitting.

Small price to pay versus guessing with expensive jets IMHO.
Now you have me thinking and doing some web research... and I have to share this
- love the 'Good Old Boy' approach.

Did you weld up a fitting on your manifold/header for a wideband O2 sensor? Or was it already there?
 

·
Registered
Joined
·
858 Posts
I tried F34 which it the tube for 76/77 and this was undrivable. F9 tube used in DCOE32 for 1750 engine works the best for the moment. As it's already ordered, I shall try the F7 and if it's not better, I'll got back to F9, and try 140 and 145 jets.

Or I need to find a weber specialist with rolling road :)
back to topic, my understanding is that with EmCon carbs you can not interchage E.Tubes like in the older ones, it doesnt work that way, like the tube has a lot more and bigger holes for the transition phase, older ones doesnt have this feature, stick with the original ones and play with the fuel and the air
 

·
Registered
Joined
·
1,126 Posts
back to topic, my understanding is that with EmCon carbs you can not interchage E.Tubes like in the older ones, it doesnt work that way, like the tube has a lot more and bigger holes for the transition phase, older ones doesnt have this feature, stick with the original ones and play with the fuel and the air

That may be. But, we have no baseline yet.

My Spanish 40DCOE 151s use standard jets though.

E tubes, or anything else, is not relevant if the float levels are off, jets are mismatched or incorrect.......
 

·
Registered
Joined
·
1,126 Posts
Now you have me thinking and doing some web research... and I have to share this YouTube - love the 'Good Old Boy' approach.

Did you weld up a fitting on your manifold/header for a wideband O2 sensor? Or was it already there?
Welded a bung in for the O2 sensor.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #18
Are you mentioning the holes in the tube, or the progression holes? F16 E tube original tube for DCOE 44/45 have very few holes, and tubes with lots of holes definitely don't work.

But I think slowcreek is right, I need to get out of the guess work, and find out where I'm rich/lean and rejet accordingly. BTW there is a very interesting explanation of how emulsion tubes are working by David Vizard:

 

·
Registered
Joined
·
1,126 Posts
I'll be sure to watch that video later.

check your float levels first.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #20
I checked the float level, and jets are new, so it must be the wrong jets and tube. But as camshafts are new and so is the exhaust, I'm starting from scratch...
 
1 - 20 of 37 Posts
Top