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Discussion Starter #1
I have a all-original(that is, no modifications or "modern" upgrades anywhere on the car) 1967 Duetto 1600. It was running near-perfectly until 6 months ago, when the idle became low/rough/erratic. It normalized when the car was fully warmed up and never actually stalled or left me stranded, so I just lived with it. Just a couple weeks ago, it suddenly became worse, with the car actually stalling on occasion, but easy to restart and go. Finally it started doing it all the time, losing power before the stall with restarts very difficult with lots of backfiring. I have some mechanical ability, so did some of my own troubleshooting. Checked the Weber 40DCOEs to my ability limit-that is, pulled/examined all the jets and floats, all good there. Fuel pump/filter OK. In the distributor, did note the rotor was quite rough, tho the points/gap were OK. So put new rotor in with new distributor cap and changed the points/condenser for good measure. I put new spark plugs in 2 years ago, pulled them and checked them, seemed OK and equal/normal in carbon buildup. Did have one bad spark plug wire via multimeter testing, so bought a new set and replaced all the wires. The result of all this did help quite a bit-car starts normally, still same issue with rough cold idle but no losing power/stalling under throttle and revs to 5000+rpm with no issues. The only remaining problem is the car will not hold idle, even when fully warmed up now. Coming off throttle to idle, its all good at about 1000rpm, but only for about 3-5 seconds, then the engine stalls. Restarts easily.
Just wondering if anyone out there has any ideas/suggestions about anything else I should check. I'm beginning to think it may be a deeper/more complex issue with the Webers, which would be outside of my Alfa mechanic skill set. Wanted to get any advice/opinions from the Board first(as many members here have expert-level Alfa knowledge and mechanical ability)before I surrender and take the car to my Alfa mechanic(he is great and sure he could diagnose/fix the issue quickly, but I still like to do my own work as much as possible)
 

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Junk on your tank fuel pickup line.
Is your fuel pump delivering 3 pounds of pressure to your carbs all the time? Easy to put a gauge in the line and check.
 

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I'm beginning to think it may be a deeper/more complex issue with the Webers,
My best guess is that your idle jets, or idle circuit in one or more barrels is blocked. Probably Dr.G is on the right track with the "junk in the tank" (e.g., rust flakes) suggestion. How does the fuel filter in the regulator-filter look?

How well are your carbs synched?
 
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Discussion Starter #4
The fuel in the filter looked clean, but I did not check the fuel pickup line-sounds like it should be easy enough to do that. Not sure about carb sync. I have had the car 4 years now and never have touched the carbs-until my basic check as I described above. I do have a flowmeter on way from Amazon, my next step was going to be synching and adjusting the carbs. Never tried to mess with Webers before as I always thought tuning them properly was more art than science. But so many videos on YouTube that explain and demonstrate the process nowadays that I think I can give it a shot
 

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Pull the fuel cap on both Weber’s and check the little filter mesh in there, could be tiny particulates clogging it up.

Also worth taking out all the jets and cleaning them, one could have a clog. It’s even possible one has started to unscrew or something.
If it had been running fine, I doubt the carbs have fallen out of sync. Check the jetting before you try syncing them, because if you have a clogged jet the flow meter will read like one cyl is off sync, when in reality it’s not firing at all.
 

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Discussion Starter #6
Ah, did not check the filters in the Webers themselves, need to do that for sure. I pulled all the jets and they looked fine-all clean/open to the naked eye. I was wondering if it would be worthwhile open up then Webers again and clean them with carb cleaner. Lots of talk of "varnish" build up over time in carbs on this forum and others I have checked. I have always thought carb cleaner was kind of a scam, kind of like those additives for fuel that claim to "clean" your carbs/injectors/etc, like a liquid "tune-up". However, after taking the Webers apart for the initial inspection, it was obvious they had not been serviced in some time and was rethinking my opinion of varnish and carb cleaners. Do you think it's worth a try to clean the carbs and the jets with carb cleaner?
 

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I was wondering if you are running a mechanical or electric fuel pump. With a mechanical, maybe it isn't supplying enough pressure anymore at low revs. On my outboards as an analogy, the rubber vanes keep pumping out water to the engine, but the pressure output starts to decreases as the rubber vanes weaken, so the engine, in an opposite way, overheats at high output, fine at low revs.
 

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I'm going to go with air leaks on the rubber carburator mounts. Easy to check by
spray a little lubricant (in this case WD40, probably the only use for this stuff) ;)
while the engine is running.
A lot of smoke out the exhaust will show up if the mounts are cracked and leaking.
 
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I like AaronsSpider's idea about the filter baskets inside the Webers, as well as samakijoe's about the flex mounts. Both possibilities.

AlfaMRC said:
I pulled all the jets and they looked fine-all clean/open to the naked eye.

I was wondering if it would be worthwhile open up then Webers again and clean them with carb cleaner. Lots of talk of "varnish" build up over time in carbs on this forum and others I have checked. I have always thought carb cleaner was kind of a scam
"Varnish build up" in carburetors usually happens when a car is "put away wet" and the old fuel evaporates. If you are using a car regularly, varnish is seldom a problem.

However, older cars do get rust flakes in their gas tanks, which can get past the filters and clog the fine passages in the carbs and jets. A can of aerosol carb cleaner with a wand is a good tool to check how open these passages are. If you remove a jet and can spray cleaner through it, then it's probably OK. This is a better test than just inspecting the jet visually.
 

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Does this symptom have anything to do with the brakes? For instance, does it make a difference whether you have your foot on or off the brakes?
 

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Discussion Starter #11
Thanks to all so far for your input/help. Just got back from trying a few things in the garage:
1)the small mesh fuel filters in the Webers were clean/good
2)tried the WD40 trick to check the rubber carb mounts, passed that test so I think mounts are OK
3)brakes don't affect symptom at all
4)I have a mechanical fuel pump. Wondering about this now. I did get some carb cleaner today and after doing all the above, just sprayed some directly into each carb barrel with the car running. This actually did improve the idle situation. The car idled perfectly at 800rpm for several minutes. Then I shut engine off for a few minutes. Restarted easily, but idle rough and wanting to stall again unless given some throttle. The more throttle given and longer it was held, the longer the idle stayed stable, though it would drop and want to stall eventually. This is making me think the fuel pump may be the biggest issue-revving motor provides proper fuel pressure for proper running and gets the fuel in the carb bowls to proper level, but not enough pressure generated at idle to keep it there. Does that sound logical?
Since just spraying the carb cleaner into the carb barrels, I think I will proceed with plan to take the carbs apart again and clean them and all the jets thoroughly internally with carb cleaner. I don't have any kind of pressure gauge to test fuel pressure, is there any trick to testing without a gauge? If not, mechanical fuel pump is cheap($35 via Classic Alfa)and looks easy to change out, may just be simpler to go that way.
 

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Dr. G is likely on the right track. Your car probably still has a FISPA mechanical fuel pump and FISPA FRB 11 pressure regulator. NEITHER survive long with todays fuel replacing no longer available gasoline. Diaphragms harden and crack losing flexibility. So the pump no longer pumps correctly and the regulator no longer regulates to 3# pressure. The solution will be a new or rebuilt mechanical pump, and rebuilt or replaced FRB11 regulator, along with a re-set of pressure. New components are used in new or rebuilt fuel system components that are modern "fuel-proof". Low fuel level in the bowls from low pressure will cause the running issues you mention.
Now, as a general rule, DON'T mess with the Webers. They do not go out of tune the way you discuss in your initial post. Factually, 95+% of ALL Weber issues are IGNITION related, the rest are fuel related in one way or another. Fooling around with the Webers without a good idea of what your trying to accomplish, or failure to thoroughly investigate causes of running changes, particularly without considerable experience, can create more problems than it solves. Just because Webers have plenty of screws to turn and other neat parts inside, does not suggest that poor running is a Weber issue.
As usual, this is only my opinion from my own experiences over many years.
 
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If you live anywhere near a lake or a RaceTrac, you should be able to get real gas. If you have been putting ethanol in your Duetto and not using it up on a regular basis, say every month or so, I think Gordon is right. Ethanol gas has screwed up my old cars, lawn equipment, boat, etc. I now use non-ethanol Rec 90 in all that stuff.
www.pure-gas.org should have stations in your zip code.

Mark
 

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Discussion Starter #14
I certainly hope it is the fuel pump and not a Weber issue. I could not agree more with Gordon and his general rule "don't mess with Webers". I had a '74 Spider 25 years ago, great car in all respects except had the original Spica injection system which gave me no end of hassles. Finally gave up and converted it to Webers, which not only made it run well but also increased performance(and sounded great!). Only problem I ever had was trying to balance and tune them myself. This was before the days of the internet/YouTube/etc, so was winging it from the owners manual and an old Haynes manual I had. Never got it right, took it to a pro who got them set perfectly and I never had to much them again for the 6+ more years I had the car. This is why "messing with the Webers" on the Duetto was my absolute last resort! The way its running now makes me think it is indeed the fuel pump, have a new one on way from Classic Alfa, will know for sure soon.
Ironblock, thanks for that link for finding ethanol-free gas. I have heard how ethanol is bad for old cars, but have had no choice. No RaceTrac in my area, have never been able to find any ethanol free gas, hope the link will find someplace near me that is relatively convenient.
 

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I run alcohol free unleaded. Thanks President Bush. Got stranded before I figured out how much water settled in my boat tank, ouch.
I was just going to add this and I see Gordon figured that out.
100low lead is available at smaller plane airports as long as you don't live in "you can't do that" areas of the country. Put it in a 5 gallon container for race day. I run non-alcohol gas in my boat and my Alfa.
BTW, 100ll will gum up your O2 sensor and you have to heat it up to rejuvenate it. Ask me how I know.....now.
When my boat sits over winter I add TCW3 to 100ll and run that through the engine. The TCW3 coats the engine internals and the fuel does not degrade as pump gas does. Funny, my engines don't give me trouble anymore.

 

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Well, I agree with the issues of the old OE rubber anywhere with alcohol enriched fuels. But Low Lead Aviation 100 octane actually has more lead in it than 110 octane Race fuel, to deal with full power turbocharged aircraft engines. But your Duetto doesn`t have an O2 sensor, and that fuel isn`t needed for it. The Ethenol free pump gas is fine.
But I do suggest using a can of "Seafoam" Fuel Injector/carb cleaner for a couple of tanks full as it will remove varnish build up in jetting and bowls in the carbs..
It`s easy to use a spray can of ''Carb cleaner" through the idle jets and passage to see if there is blockage.
But if the engine runs OK "off idle" at RPMs under 2500 then the idle curcuit is fine. I suspect a pressure problem that is causing "flooding" into the carb throats being the issue.
 

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I've switched from 100ll and now my car runs faster on Jet A. The 100ll goes in my outboards for winter, not in the Alfa.
1650076
 

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I have to agree with the "don't touch the Webers" camp. I did a Weber conversion 25 years ago on my '71 1750 Spider Veloce and have NEVER touched them since. Any issues with performance, idle, stalling, etc. have ALL been either ignition or fuel system related. Thankfully there haven't been many issues. She runs sweet and the induction noise is the best!

1650231
 
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