Alfa Romeo Forums banner
1 - 20 of 23 Posts

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #1 · (Edited)
Here's what we've got:
2 Liter NORD with a fresh rebuild
10:1 Motronic pistons
Centerline Euro cams
Italian made Weber 40 DCOE 151s with recent rebuild kits
125 main jets
F9 emulsion tubes
200 air correctors
50F8 idle jets (the "8" is rubbed out on all four of them for some reason)
NGK BPR7ES plugs with electronic ignition system.

#2, #3 & #4 plugs are look good, like the on on the left.
#1 (on the right) is moist, has evidence of rich mixture and sometimes fouls on start up.
Car starts with a little choke, then idles smoothly and runs fine once it warms up.
Plenty of power with only a very minor stumble in transition.
I doubt its the float level or needle valve since the #2 plug looks fine.

I swapped the #1 & #2 idle jets and that did not make any difference.
Plug smells like petrol.
The choke lever snaps all the way close but do they leak sometimes?
Any help or suggestions on what to check?
Thanks

1694475
 

·
Super Moderator
Joined
·
12,439 Posts
Did you swap #2 and #1 plug to see if it's a plug? Maybe a plug wire?
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #3 ·
I'll try that tomorrow.
Good idea.

Also, Gordon, what are your recommendation on spark plugs for a performance build?
I've heard good things about these NGK's and Bosch Platinum plugs.
Thanks
 

·
Registered
Joined
·
1,757 Posts
NGKs over Bosch Platinums.
 
  • Like
Reactions: 1978alfa

·
Super Moderator
Joined
·
12,439 Posts
NKG seem to have a broader heat range acceptability in Alfa (and Ferrari) engines with Webers.
 
  • Like
Reactions: 1978alfa

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #6 ·
Negative on sparkplug swap and
Negative on plug wire swap.
No difference.
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #8 ·
Yes, they're synced and the engine idles very smoothly.
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #9 ·
Possible lead from an old thread.
A leaky choke mechanism.
Gordon again!

 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #11 ·
My mechanic did not inspect the chokes.
I just heard back from him.
This is from a spare carb I have sitting in my office.
Notice the white gunk on the seat.

1694631
 

·
Super Moderator
Joined
·
12,439 Posts
That will do it.
 
  • Like
Reactions: 1978alfa

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #13 ·
I pulled the carb off yesterday.
I noticed the #1 butterfly has traces of extra fuel being drawn past it.
The other 3 did not have similar stains.
Choke plungers and mechanism looked clean and moved freely.

1694935
 

·
Super Moderator
Joined
·
12,439 Posts
Not so much fuel as rich mix or poor combustion sign, like the fowled plug. Time for a leak down cylinder check as well as valve clearances.
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #15 · (Edited)
A quick compression check reveals all four cylinders reading ~180 psi.

I bought these carbs used so it is buyer beware.
I'll go through and give them a good cleaning and fresh gaskets.
Maybe something will shake out.
Wish me luck! 🍀
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #16 ·
@ Gordon. Notice the limiting pin for close position is broken off of the choke mechanism.
Would that make any difference?

1695071
 

·
Super Moderator
Joined
·
12,439 Posts
Maybe or maybe not. More common is a mechanism internal issue of the piston activation pin on the main gear broken off as below.
1695072

This can cause the 2 pistons to be in slightly different positions in the cylinder, but more common and worse is... where did the broken off tip end up?
Generally if a enrichment is sometimes used, make sure both stop pins are there, and the lever moves freely between both extremes with a pull of the "choke". Remove the 2 mechanism securing screws and be sure both gear tabs are there, and the gears are correctly indexed. Check that both pistons move up and down freely in the cylinders, and that normal spring pressure moves them to seat.
1695074

If the enrichment is never used, DO NOT block piston movement or the ports to the throats. The pistons are designed to bounce-up, very slightly, with Weber pop back, mechanism installed, to vent hot gasses out the backfire screen under the mechanism. If you wish to remove the mechanisms, use a factory Weber block off plate and gasket in place of the mechanism.
1695075

1695076

Leave springs, pistons and ports in place. Pop-back through a Weber will still vent flame or hot gasses through a small vent under the plate. Otherwise, these gasses and sometimes flame, vent over fuel and fumes in the float bowl and out the front bowl vents. This can, and sometimes does cause Weber explosions with unpleasant underhood fires.
Oddly some Lotus Weber users like to block piston movement or plug the throat ports with 8mm threaded Allen plugs, sometimes going to extremes of filling piston cylinders with epoxy or solid aluminum (tall) rod. I see this sort of planned disaster seldom With Alfa users. As a note of interest, RACE factory Ferrari V12's ALWAYS had the mechanisms in place, but no activating cable.
Ferrari seemingly had no problems with the Weber enriching mechanisms, and Weber pop-back.
My shop manager and head inspector approves all the work done here.

1695077
 
  • Like
Reactions: 1978alfa

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #18 ·
Great information to know and be aware of.
Thank you for posting and sharing your knowledge.
The remnant piece of the pin is on my work bench.
It fell out when I set the carb down and started examining it.
I'm not sure how it got broken.
Good thing I have some spare parts carbs sitting around! :)
 

·
Super Moderator
Joined
·
12,439 Posts
The "AH-HA!" Moment! No need to explore further. Install a new mechanism, adjust pull wire and no more plug fowling. Magic for sure! This sort of thing is REWARDING!!!
 

·
Moderator
Joined
·
1,803 Posts
Discussion Starter · #20 ·
It certainly is!
I hope the mechanism issue resolves it.
I'll post more when I put it all back together.
BTW: I like your personal Weber inspector in the last picture. 🦜
 
1 - 20 of 23 Posts
Top