If you are blessed with something called a carburetor sitting on your engine, chances are that you know your way around a device that most wouldn’t know any better than some obscure Etruscan artifact. It also means that from time to time, you find yourself called to diagnose a power plant malady of one kind or another, be it a stock or aftermarket carb. Should you have multiple carburetors attached to your engine, you are a saint and have my deepest sympathies.
When it’s time to diagnose a carb problem, these tips always seem to help.
Don’t Rush to Judgement
The engine starts running poorly. You see a drop in economy. The power seems diminished. You get around to popping the hood and there it is staring at you, but why does it top your list of suspects? Just because your carb is the most mysterious and complicated part of your engine is no reason to profile it. For goodness sake, don’t take it into custody just because it was sitting there waiting for you.
Remember, it can’t go anywhere. There is a laundry list of possible suspects that deserve some attention before grilling (or rebuilding) your petrol passer.
You use quality gasoline. The tank, pump, and lines are clear and clean. Your filters (fuel, air, and for good measure oil too) are clean. Spark is strong. Timing is properly set. The right fuel pressure gets to the carburetor. Your parking brake has been released (or is at least on probation.) With any luck the rest of the drivetrain continues to be affixed to the engine and chassis. Right?
Are you 100% confident about these and other obvious issues? If not, conduct a closer investigation of those suspicious culprits.
Collect the Evidence
Look at the ignition components. Are your plugs clean and correctly gapped, producing a strong spark? Glad to hear that. Are the ignition wires in good shape? Given a healthy spark, break out one of those fancy tools (yes, the timing light would be best) and make sure that spark shows up on time. A little fine tuning of the advance, or retard, of the timing will make your particular gasoline work best.
What about fuel? You are sure it is free-flowing and clean. Is there enough? Is there too much? Time for another tool of sorts. Put a pressure gauge on it and look for a pressure of about 5.25 psi (plus or minus a quarter psi). You might also pay attention to when you fill your tank. When the gas station’s storage tanks are filled, sediment in their tank gets stirred up. Wait a day or so to prevent their debris from becoming yours. The combustion equation relies on air too. Not to worry, you have a clean filter ahead of the carb; or do you?
Interrogate the Suspects
We all enjoy solving the hidden problem, but don’t overlook the obvious in your eagerness to be clever. Are your brakes dragging? Your tires have not gone flat but have you fully inflated them? What about that potato in your tail pipe? Of course there are no vegetables in your exhaust system but a clogged cat, blocked muffler, or even a well kinked pipe kills performance. Vacuum leak? I sure hope you have compression in all the cylinders. What about that trailer you are towing? Did you forget about that?
Get a Warrant
If everything else checks out, then green light the assault on the carb. Saving the mechanical marvel perched on the pedestal we call an intake manifold until last will save you untold headaches. You’ll need to save those for the bodywork.
A self-described “car nerd,” Jason is a automotive columnist who has written for the eBay Motors blog, Motor Car Digest, as well as his own sites TundraHeadquarters.com and AccurateAutoAdvice. With an engineering degree, a full-time job in the automotive parts industry, and a decade of experience working in auto dealerships, Jason brings an interesting perspective on all things automotive.