What is the easiest way to test a carb.

[cmuman]

I just picked up a 1984 70hp evinrude. I bought the boat with little back history. I managed to get the motor started and running pretty well. A buddy warned me that 2 cylinders might be running well and the third just going along for the ride becuase the boat might have sat for a while. Is there a good way to test to make sure all three carbs are functioning properly without tearing the whole thing?

 

[HighTrim]

Re: What is the easiest way to test a carb.

Just to start, I would test the spark and compression on your new motor. The spark should jump the 7/16 of an inch gap with a bright blue ZAP!! and the compression should be even on all cylinders (within 10 percent) and around 100psi. Also, being that the motor is new to you, I would bath and rebuild the carbs, as well as rebuild the water pump.

That being said, in regards to your question, you could 'read' the plugs for one. A few of the 'reads' are listed below.

• Dry and powdery, and gray or coffee-colored: good.
• White: too-hot plug.
• Black: too-cold plug, or low compression.
• Wet and carbon: mix too rich, too-cold plug, bad fuel-oil mixture, bad oil, worn rings, bad ground on ignition.
• Water: water in fuel, blown gasket.
• Eroded: overheating, too-hot plug, bad timing, bad water pump, clogged water intake, overloaded.
• Carbonized and worn electrode: worn plug (replace it).
• White or grey insulator, maybe blistered: overheating, maybe from loose plug, lean fuel, wrong heat range, bad timing.
• Black with heavy fuel and oil deposits: seized piston rings.
• Dry or wet fouling: too rich mixture, too much slow-speed use, choke overuse, electrical trouble, too cold plug heat range.
• Black with soot: restricted air flow, too-rich fuel mixture.
• Molten metal on plug: detonated piston (need rebuild).

 

[wavrider]

Re: What is the easiest way to test a carb.

Run it

I always rebuild carbs on engines just acquired, making sure all orfices and passageways are clean.

the rebuild kits are not to expensive and it is great peace of mind knowing you are not running one on the lean side due to dirty carbs.

Rebuilding carbs is a lot less expensive than rebuilding a power head due to running lean.

 

[samo_ott]

Re: What is the easiest way to test a carb.

If you think one of the carbs is not working correctly then don't run the engine. As lack of fuel to a cylinder is also lack of lubrication and can fry the powerhead.

 

[cmuman]

Re: What is the easiest way to test a carb.

I've worked with rebuilding small engine carbs and carbs for cars. Is this a similar job? Do I have to readjust all my linkages when I put it all back together? What is a recommended site for carb rebuild kit? How much does it cost to have a carb rebuilt and new impellor put in at a shop?

 

[iwombat]

Re: What is the easiest way to test a carb.

If you've ever rebuilt a car carb, then you'll find rebuilding an outboard carb a walk in the park by comparison. You can get the carb kits right here on iboats, or go to your dealer for an oem kit. You'll want to get a proper manual for your outboard though.

Wanna know what's even easier than rebuilding a carb?

Replacing an impeller.


Get a manual and dust off your wrenches. These are two very easy jobs.

 

[ezeke]

Re: What is the easiest way to test a carb.

Warm the motor. Take the cover off the carburetors and start the engine. Put two fingers in the throat of the carburetors, one carburetor at a time, and wait a few seconds for the change to register. That should cause the engine too slow down each time as the carburetor runs rich and gives you a better feeling of what is going on.

If the engine picks up, that carburetor is probably running lean and should be looked at.

If nothing happens on a carburetor or if it is noticeably different from the others, that one should be looked at.