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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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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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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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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 · #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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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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Discussion Starter · #23 ·
Thanks, guys. I had an opportunity to look at the carbs again this morning. The idle jets are 50F8. The idle mixture needles were visually inspected and are okay. I sprayed some carb cleaner around the base of the carbs and the adapter plates and got no acceleration. I am out 4 turns in this video.


I guess the next thing to check is my float levels?
 

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Discussion Starter · #26 ·
The weather has been a little sketchy around here of late, and I have been busy with work, but I wanted to give an update. I made a tool for checking the float levels, and they were low. I must have been measuring incorrectly when I rebuilt the carbs. The floats now sit at 6.5mm as measured with a 6.5mm rod. They are a little more than 15mm in the other direction, but it seems that shouldn't matter as much. I didn't want to completely disassemble the carb covers to bend the tabs.

The result is that I'm not getting any of the spitting now, but my idle screws are still out around 4 turns. There are no air leaks that I can discern. The engine seems to be running great, but I am only getting around 19.5 mpg in mixed conditions driving. Idle jets are 50f8.

Would there be sense at this point in following Robert's advice and going to the next larger jet? What are the trade-offs there, other than still not knowing why my idle screws are turned out so far. Fuel pressure is good and regulated. Timing perhaps? My timing marks are for Spica. I have a timing light, but is there a better way to set this?
 

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Discussion Starter · #29 ·
Robert, All opinions are welcome around here, and sometimes even the most adamant authorities can be wrong on some point. :) I was going to take the car for a drive down to Nashville this week, but it looks like the weather won't be cooperative. Round trip is around 350 miles--that would be an interesting test for the car.

I think it will be worth trying to swap out jets, but I think I'll look at timing again, first. I did think I was getting better mileage previously.

In any case, the car is improved, and so far, this is the best its run in at least a decade.
 

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Discussion Starter · #31 ·
I read the posts about your experiences, Ed, thanks! It's great info. I'm not ready to move up to an electronic distributor--the new business isn't making enough money to pay the regular bills yet, so I can't really justify Alfa upgrades right now. But next year...

We did pull the distributor and make sure it was functioning properly. The only concern I have is that the timing was set using the Spica marks, and I haven't been able to find anything that says "when you go from Spica to Webers, this is how you set the timing differently".
 

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Discussion Starter · #33 ·
Ed, how do you tell how many degrees you're at when the timing marks are M P F?
 
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