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My 65 Sprint GT with a stock 1600 motor, carbs and jets, usually sits in the garage for a couple of weeks at a time. When I first run it and while the engine is cold, the motor sputters from off-idle to about 3000rpm to the point where it's almost undriveable. If it let it warm up in the driveway for a few minutes, it does a lot better. Even when warm though it, it has a slight hesitation right at the off idle transition and one again at around 3500rpm. Other than that it idles smoothly and pulls strong through the rest of the range.

Ignition should be ok. I'm running at programmable 123 distributor with Bosch blue coil. I've played with the timing a bit but it doesn't seem to significantly improve these issues. I'm now at about 20 degrees advance at 2000rpm's and 34 at 4000.

I'm looking for ideas as to what may be causing the sputtering. I'm considering pulling the carbs to have them cleaned / rebuilt but I'd like to make sure I'm not missing anything more basic.

Vangelis
 

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If you want a hotter spark switch to a Bosch red coil. You could then open up your plug gaps to .030" or .035" That might help. If that does not fix it then you could try one step richer idle jets. Are you confident that you have no air leaks in the rubber carburetor adapters?
 

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I'm considering pulling the carbs to have them cleaned / rebuilt but I'd like to make sure I'm not missing anything more basic.
Ideas such as the ones suggested by alfaparticle would be a better way to spend your time and money. "Cleaned and rebuilt" won't solve a lot if the problem is incorrect jetting, a cracked (and leaking) softmount, or ...

One clue: A cold engine needs a richer mixture than a warm one. That's why carburetors have chokes (or on a DCOE, and enrichment device). So if your car runs poorly when cold, but better when warm, that suggests that the mixture might be too lean. But whether the cause is air leaking past defective softmounts, incorrect jetting, or something else is impossible to diagnose over the Internet.
 

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Jay did a good job of explaining the likely situation. Hesitations and dead spots at transition are usually caused by lean mixtures, so correcting this is the first action. Check for air leaks and replace the carb mounts if you see signs of cracking. I believe that there is more than one manufacturer of these and there are quality differences so don't go for the cheapest. What idle jets do you have? Rich Hanning - 65Sprint, has had similar problems and if he reads this he might chime in. In his case he has to run richer idle jets than "standard". There is a possibility that going up 5 on the main jet will help, but working first with the idle jets is the better plan.
Lean mixtures will often be ignited reliably with a hotter spark and that is why I suggested a higher energy coil. The Bosch red coil is close to the lowest impedance coil that can be used with a 123 distributor.
 

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Discussion Starter #5
Thank you all for the help! I should have mentioned that all these symptoms are relatively recent (started in the last 6 months maybe) and that's why I had ruled out incorrect jetting. However, the suggestion about switching over to a hotter coil reminded me that at the same time I installed the 123 distributor I also changed the coil from what may have been the original "black" bosch to a blue coil. I just switched them again to see if it makes any difference... Unfortunately it's raining pretty heavily outside today so I haven't been able to start the car, yet. I'll keep you posted once I fire it up.

If that doesn't work, my next step sounds like it should be to pull the carbs and check the soft mounts. Never having done that before, I'm curious what the best way is to get to the nuts at the underside of the carbs. It looks like it would take quite a bit of gymnastics to reach them. Is there a trick there?

Thanks again
 

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Measure the resistance of the primary of the coil - between the two connections. Then touch the meter probes together and get a second reading. Subtract the second from the first to get a true resistance of the coil. It must be at least one ohm or you could damage the 123 distributor.
 

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Discussion Starter #7
Measure the resistance of the primary of the coil - between the two connections. Then touch the meter probes together and get a second reading. Subtract the second from the first to get a true resistance of the coil. It must be at least one ohm or you could damage the 123 distributor.
Both the Bosch Blue and the older distributor register about 3.4Ohms of primary resistance. So they should be pretty safe.

Could adjusting the idle mixture screws help with the off-idle progression? I had them dialed in to get a nice idle but I could definitely try to back them out a bit to see if it helps.
 

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Could adjusting the idle mixture screws help with the off-idle progression? I had them dialed in to get a nice idle but I could definitely try to back them out a bit to see if it helps.
There is usually a dead band in the adjustment of 1/2 turn or so. Having the screws at the open end - more turns from closed-may help a little but mainly at off-idle rather than at the top of the progression. What idle jets are you using?
 

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my next step sounds like it should be to pull the carbs and check the soft mounts. Never having done that before, I'm curious what the best way is to get to the nuts at the underside of the carbs. It looks like it would take quite a bit of gymnastics to reach them. Is there a trick there?
One way that I have heard (but never tried) to diagnose the softmounts is to spray them with either starting ether or propane from an unlit propane torch, while the engine is idling. If they are drawing in air, the engine will speed up from the additional "fuel".

Getting at the four nuts on the underside of the carbs isn't that hard. Be sure to disconnect the battery first, because the starter "+" terminal is right there. I just reach my left arm behind the rear carb, right arm around the front, and work on the fasteners by braille. If your 8mm nuts take a 13mm wrench, try to find nuts with 12mm across the flats - makes it easier to get a box wrench on them.
 

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They should be good for a 1600 motor with no modifications or problems. 50F8 is one step richer.
 

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Your problem sounds the same or very similar to mine. I was running 50 F9 idle jets to avoid spit back. I recently switched back to 50 F11s, convinced that the richer jets were covering up other problems. The spitting came back from just off idle through progression. Additionally, there was a roughness and hesitation revving the engine under no load. Using carb cleaner sprayed at the mounts, I found substantial vacuum leaks. Also, one pump jet was clogged, which Gordon Raymond advised could cause spit back and contribute to the hesitation. Four evenly spraying accelerator pumps, new soft mounts, and a little ultra gray on the gaskets on both sides of the mounts have eliminated the spitting/hesitation and the leaks. Both Ed and Gordon Raymond provided invaluable guidance during this project. HTH.
 

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We have a '64 Porsche SC in the fleet with a similar issue, I have worked at it for a few years now (the hesitation is not real bad) and no improvement. Is it possible the fuel quality we get at the pump these days is not what it was 50 years ago?
 

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Sounds like I need to take a closer look at the mounts! Speaking of which, has anyone tried solid mounts like these from Alfaholics:

Alfaholics aluminium carburettor mounts - Classic Alfa Romeo spare parts

65Sprint, how did you determine that the accelerator pump jet was clogged?

Thanks again for all the thoughful feedback.
Many, many people have bought the solid mounts from both Classic Alfa and other sources, me included on three occasions.
For me this is a no-brainer, gets rid of the poor quality soft mounts available today, and pretty much fit and forget.
This is a highly emotive point amongst us Alfa fans, there are many thread conversations on the subject, but for me they have been 100% reliable. You have to fit them correctly using thackeray spiral spring washers, or the Cosworth type soft "bobbin" mounts, and not tighten them fully, but once done, they are superb.
You'll need the short ones if you're going to keep using the standard air cleaner.

Steve
 

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Speaking of which, has anyone tried solid mounts like these from Alfaholics:
I would not touch them with a long pole.
 

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See, I told you the subject was emotive !
O ring seals and spring washers that are used on these solid adapters are also used on Weber conversions for SPICA manifolds and I would suggest that a lot more of them have been installed in the USA than in the UK. They gave Weber conversions a bad name because of the difficulty in keeping them leak free. I bought two cars with this conversion and I swapped them out for Euro manifolds and rubber adapters. There is no way that I would go back to those things.
 

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O ring seals and spring washers that are used on these solid adapters are also used on Weber conversions for SPICA manifolds and I would suggest that a lot more of them have been installed in the USA than in the UK. They gave Weber conversions a bad name because of the difficulty in keeping them leak free. I bought two cars with this conversion and I swapped them out for Euro manifolds and rubber adapters. There is no way that I would go back to those things.
ED, if you are talking about Alfa's only, I would probably agree with your numbers.
But , this system has been used since the 1960's when Weber DCOE carburettors became "de rigeur" for the modification of hundreds of different engines.
Every OE and aftermarket inlet manifold I've ever seen for the whole range of BMC A & B series, BMC six cylinders, all the tens of different Ford engines, from the pre-crossflow Kent, through XFlow, Pinto, right up to modern Zetec and Duratec engines, Opel & Vauxhall, Triumph four and sixes, Datsun, Lotus, Aston, BMW, Rootes Group, Jaguar, Mercedes, MG, Renault, Toyota, Volvo, all had this system of mounting DCOE's.
In effect, hundreds of thousands of OE cars, and millions of aftermarket conversions.
I believe, only Alfa & Lancia were the exception.
My view is that early o'ring failure was and is down to incorrect assembly.
The amount of carb / inlet assemblies that I get in for refurb / resale, (mostly Ford / BMC / Opel Vauxhall), with incorrectly fitted joints is about 5%. Admittedly lots of these are old units never touched for 20 years or more, but that's when it got a bad name.
With the advent of the Misab plate, and the Cosworth type "bobbin" instead of the thackeray washer, the propensity for failure is all but eliminated, although there are still some ham-fisted home mechs out there that think every nut should be tightened to death.

When I have been hunting for an Alfa for myself, (I've probably looked at 50 cars over the last 25 years), about half of them have had leaking OE soft mounts.

When I sell assemblies, I use both the older thackeray washer and twin O ring plates, and other times use the Misab plates and Cosworth type bobbins. These are mainly on MGB single 45 DCOE conversions, Ford Crossflow / Pinto / Zetec, Volvo, BMW and Triumph fours / sixes. I have never had one complaint about the life of these components.

Just think of all the Historic Racers and Rally cars, (huge in Europe), and the many hundreds of thousands more classic cars fitted with them, with no issues.
In my opinion, they really are not a problem, and an extremely worthwhile modification to an Alfa.

Steve
 
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