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Discussion Starter · #1 · (Edited)
I have a just a few questions.

Could the sound being made in the attached video be an indication that I'm burning a valve or doing something else that might be causing damage to my engine if I drive it as-is?

Has anyone ever successfully adapted a pair of Weber carbs a stock US intake manifold that was originally set up for Spica injection and gotten correct results without changing other parts?

Is there any difference in setting up the timing advance for the 2L Alfa with Spica versus the 2L Alfa with Webers?

Can anybody explain what I'm actually hearing--what is happening to cause that popping sound at high RPMs?

Thanks,

Tim
 

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sounds like the idle air screws are in too far
 

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Back in the day, we used a dollar bill held up to the exhaust pipe to quickly determine if there might be a burnt valve. With a burnt valve, the dollar will flutter as it is sucked in and blown out.
 

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Pull the cam cover and check the valve clearances if you think that you have a burnt valve. When I had one the symptom was serious loss of low end torque but decent top end.
 

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Discussion Starter · #6 ·
Ed, the burnt valve idea came from the mechanic. I couldn't quite ride with that because there was no indication before the recent tune-up. I'm kind of a "cause and effect" guy so I wanted to get opinions from the people who know these engines before letting somebody run me deeper into the engine chasing mysterious causes.

I really don't have any loss of low-end torque. :)
 

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Discussion Starter · #7 ·
And the man from Alabama gets a prize!

I decided to open up the air screws one full turn on all. The engine is running remarkably better, the idle is still fine. There were a few spits on the way home tonight, but it was more like every couple minutes rather than ever couple of seconds. This was a remarkable improvement, and while not perfect, sure moved things much closer.

I'm not uber-confident in my own understanding of engines, and I'm inclined to seek out the opinions of professional mechanics, but it seems the mechanics I talk to are at a disadvantage because they don't have the collective insights of this community of Alfisti.

Thank you again, all. It's remarkable what can be learned here.
 

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just my opinion but spitting like I heard on your video is common on webers that are not tuned correctly. find the threads on tuning--starting with checking timing, clean plugs, be sure the floats are set correctly, make sure the throttle plates are syncronized, setting idle at 800 to 900 rpm and dialing in the idle air screws. The jets could be wrong--but I would walk through the tuning sequence first. Are they older webers or the newer webers? the type (tipo) will tell you that. On the older webers the air adjusters sweet spot is out 3/4 to 1 turn--the new ones adjust out more--
 

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Discussion Starter · #9 ·
The Webers are 40DCOE 26/27 pair from a GTV All jets are spec for 2L. I went through the carbs completely last year with rebuild kit, cleaned everything, checked floats, reassembled. Plugs are new as of last week. Timing was set to Spica specs, and I don't know if that's right.

25 year professional mechanic did a tune-up. Not that I asked for it, but my buddy owns the shop, the mechanic is a new hire, it was a slow day, and he wanted to give the engine his best shot. He really did some good stuff, new points, had the dizzy out and checked for slop, made sure the advance worked correctly.

I'm way past that sweet spot right now, Frank. What does that make you think?
 

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Tim
sounds like your close but several little things can be a little off. a quick search found this thread with very good technique from Gordon. http://www.alfabb.com/bb/forums/carburetors-fuel-injection/147485-i-rebuilt-40-dcoe-27-now-what.html

I suspect your throttle plates are not exactly synched--and then you need to fine tune the air adjusters but I can't find a good thread on setting them up. A needle used in the throttle observation port to insure the throttle plates are in exactly the same position will help get the throttles synch'ed and appears to work a as well as listening to a hose on the intake of the throttle bore plus is less subjective. somewhere on the bb is a really good writeup but I can't quickly find it-- the timing at 5k should probably be a little less than what the orignal specs (drop down to 33/34 degrees) say due to piss-poor gas now days. All the info you need is on the bb if you can find it:D
 

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I played around quite a bit with timing and advance curves and I settled on 38 degrees. Retarding the ignition is unlikely to do you any good unless your engine is pinging.
 

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Discussion Starter · #12 ·
Frank, again you are right. My throttle plates are not synched. They are off by exactly one inspection hole, based on shining a flashlight into the barrel and seeing where the light reflects off the edge of the butterfly.

I went through all of this last year, adjusting the carbs myself, but failed because of a leak around the adapter plates that I couldn't get rid of.

Now that the adapter plate leak is resolved, I'll go through the balancing and adjusting procedure again.

Question: Should the timing advance be set before the carb adjustment?
 

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Discussion Starter · #13 ·
Ed, how far is 38° from the book setting?
 

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Discussion Starter · #14 ·
Well, that was fun...

I did find that my webers were a touch out of balance. I corrected it, and set everything back to the 'base' position of idle speed 3/4 turn past engagement and idle air adjusters set to 3/4 turn out from lightly seated.

Engine ran like crap. I adjusted and re-adjusted, even pulling plugs on front, then rear cylinders so that I could balance carbs individually.

I was ready to give up. I nearly admitted defeat. I started throwing tools and gaskets into the trunk and prepared to leave my car with the mechanic who didn't get it right, but got it closer than I did.

Then I remembered that when it was running fine yesterday, the idle air adjusters were out three and three-quarters turns. So I got bold.

Now the engine is running great, there is no carb spitting, the idle is smooth. The only issue is that my idle air adjusters are out about 4 to 4 and a half turns.

This suggests that I need different idle jets, correct? Will changing the ldle jets then lead me down a path of changing other jets?
 

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Great video.

Spitting from the carbys at the rpm you had (about 3000 rpm) tells that the idle circuit is lean.
As you noted,unscrewing the idle mixture screws helped.
Just a thought,,go up 1 size in the idle jet.
Hopefully the idle mixture screws will be out about 1-2 turns from the bottom.
If the idle mixture screws are out more than 4 turns,means that the idle jet is too small.
The video tells that the carby syncronisation is pretty close,so just play with the next size up= idle jet.
Tell us how this goes.
No,you dont have a burnt valve at this stage,but a compression test will tell all.
If you had an exhaust analyser,that can tell lots also,but after 30 odd years of playing with carbys,my ears tell me the most.
To get the best out of it,after you sort out the idle jets,put it on a chassis dyno,with an exhaust analyser up the exhaust to get the best out of the engine.
By the way,where is the engine breather pipe going to now ?

Robert
 

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Discussion Starter · #17 ·
Thanks, Robert. My idle jets are out more than 4 turns right now. I just took the car for a wash and a test spin, and I got very little of the spitting, occasionally when at a steady engine speed around 2,700 rpm. I can't seem to make it happen by reproducing a sequence of steps like speeding up and slowing back down to a steady 2,700.

The other thing about my current setup is that the engine has a slight stall condition when I first step on the gas. I need to pump the pedal a little to get beyond the stall so that I can let the clutch out without killing the engine. Is that also a factor of the idle jets being too small?

Thank you for the observations, all!
 

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Something is wrong if you are out 4 turns. They should be no more than about 1.5 turns on the Webers that you have. The later emissions Webers are screwed out more. You are masking some other problem by adjusting your carbs like this. What size idle jets do you have installed? Are you confident that the float level is correct? It sounds to me like you still have an air leak.
 

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The more turns out (over 2.5 )on the idle mixture screw generally means that the idle jet is too small.

The hesitation when having to pump the throttle to make it run better usually means the accelerator pump jets are not squirting.
Remember,when adjusting carbys,make sure you do it at engine operating temperature.
Or at least,make adjustments to get it to engine operating temperature,and then do all final balance,idle mixtures and idle.
It all just opinions,but we can only help with solutions with what information we have.
The video tells me that the idle jets are too small,or the idle mixture screw need turning anticlockwise.If the idle mixture screws are out too far=more than 3 turns,the idle jet is too small.

Robert
 
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