spitting through carbs - Alfa Romeo Bulletin Board & Forums

 
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post #1 of 3 (permalink) Old 05-18-2017, 03:02 AM Thread Starter
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spitting through carbs

First the particulars. 1600 Duetto. 10458 cam on intake, 10320 1750 SPICA cam on exhaust. Timed at 104/104. Cam marks are on the outside edges of the cap marks towards the fenders. 40dcoe 27 carbs with stock jetting. carbs balanced, and idle screws out 1 full turn. idles well with zero turns on the idle screw. 123 non programmable ignition, set on the 1600 advance curve, and timed at a few degrees above the static timing mark @ 1200 RPM idle. Cap, rotor, coil all fairly new. I've been trying to tune out a stumble when put under moderate load after poking along at 2500 to 3000 RPM. I can get it better, but I can't tune it all the way out. There's also a sporadic spit through the carbs between 2500 and 3000 RPM, under load or at idle. It runs good otherwise. Starts well even when cold unchoked just fiddling with the gas pedal for a minute or two. Any suggestions, or have I forgotten how 50 year old carbureted cars used to run?
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post #2 of 3 (permalink) Old 05-19-2017, 05:40 PM
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Has it run ok with those cams or is this a new to you setup? If so did it run fine before the cam swap? Is this a proven cam combination?
The motor is healthy with good compression?
I'd have to get my book out to see what jets a 27 has but right off the bat one turn out is generally a little lean. I'm assuming you've tried one and a half turns out?
It's obviously a little lean and not knowing the starting point I'd say either a little richer idle jet, yes they do affect more than just the idle. My 2L with webers will spit a little on a <40 deg morning until it warms up and no spits at all with a cold motor during the spring, summer, and fall if that helps.
I can for sure answer your last question... you haven't forgotten, set up right they should work just fine.

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post #3 of 3 (permalink) Old 05-20-2017, 05:12 AM
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"there's also a sporadic spit through the carbs between 2500 and 3000 RPM, under load or at idle".

Start with cleaning the 4 jets under the round access cover. A fine bristle from a brass brush will clear the idle jets. Idle jets clog first and cleared will resolve the "spitting".
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