Can't help but notice that the tech talk here on carbs come from folks likely to be in their 50s and 60s and up,

And iwrock is in his early 20s.


heh

Anyone have something to say with respect to causation and correlation? \o/

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

Yes Jim. Among most of today's techs, they can draw codes, troubleshoot circuits, and analyze all the latest automotive technology. I remember in a column Jay Leno wrote, he spoke to several young techs whose worst fear was that someone would bring in a car with points and a carburetor.

As far as symptoms and causes go, they are probably too numerous to go into in any volume outside of a text book. There are only a few subsystems in the carburetor, but there are different combinations of things that can happen and possible multiple symptoms to be encountered due to certain failures of a single system.

That said, if someone understands how the different systems operate and their effect on engine operation, they should be ready to troubleshoot most commonly encountered situations.

Some common ones might be:

o An engine that idles and cruises normally, but stumbles when cruising and hitting the throttle. This would likely be the accelerator pump, but it also could be, or be exacerbated by, a generally lean condition. A generally lean condition could be any number of things such as low float level, clogged or too small main jets, non functioning power system.

o Engine not idling is not necessarily a problem with the idle system in the carburetor, it would probably more likely be a vacuum leak below the throttle plate. In an older vehicle (how many carbureted engines aren't older?) it can be worn out throttle shafts, something often overlooked.

o A lack of power. This could be any number of things certainly not limited to the carburetor. On a carbureted engine, timing problems including centrifugal and vacuum advance could seem like a carburetor problem. Never overlook the fact that problems CAN be caused by things other than the carburetor. A malfunctioning power system in the carburetor will usually result in an engine that feels like the accelerator pedal is connected to the carburetor throttle arm by a rubber band. It has no added fuel enrichment to add power when the throttle is opened significantly farther.

o Poor cold engine operation. I failed to list the choke system originally. A misadjusted choke, obviously can make for a hard starting engine that runs normally after warmed up. The opposite problem to be experienced from a misadjusted choke would be when it is adjusted such that it doesn't open when warm. This will make for sooty black spark plugs and a stop at every other corner for a tank of gasoline. It has more serious consequences if not corrected soon, because it is allowing raw fuel to wash the oil off the cylinder walls and dilute the engine oil.

o Flooding. It is not uncommon with carburetors for the needle and seat to stick open causing serious flooding. If you suspect flooding, remove the carb and invert it. You should not be able to blow into the fuel inlet. If you can, trash or something is causing the needle & seat to be open. On some older carburetors that have neoprene needles, after sitting, the needle will sometimes stick against the seat, preventing any fuel from flowing into the carburetor, which is of course the opposite of flooding, but it should be covered when thinking of needle & seat problems.


Again, to be proficient at troubleshooting carburetors, learn about the different subsystems and what they do. As the famous Physics Professor Julius Sumner Miller constantly repeated when teaching Physics; "it's what you UNDERSTAND that counts."

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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Guy I know runs gas dragsters, was grinding metal off the combustion chambers to cc the heads. I asked him how he knew how much to grind off and he said "experience, kid".