Re: 1968 mercuiser 120 hp rochester carb
Jim, You are using Marine carbs. Yes?<br /> Just posted this in another thread.<br />Before Replacing/Re-building the Carburetor<br /><br /><br />We often blame the carburetor for: POOR PERFORMANCE and/or a POOR RUNNING ENGINE. Although this does happen, it is not the most likely reason for engine problems. The carb has very few moving and or wear related parts. If a carb has gone bad, it is usually caused by some other reason other than wear and tear.<br /><br />The following items should be checked before replacing/re-building the carburetor.<br /><br />Fuel System<br />1. Adequate fuel pressure at all operating RPM and loads.<br />2. Dirt in system - Is the fuel filter and/or water separator clear and free flowing?<br />3. Clogged, pinched, or kinked fuel lines.<br />4. Clogged fuel tank pickup and/or anti-siphon valve.<br />5. Water in the fuel.<br />6. Quality of fuel.<br /><br />WARNING:<br />Gasoline is very flammable and highly explosive under certain conditions. <br />Service a carburetor only in a well ventilated area away from lighted cigarettes, open flames, or sparks. Use care not to spill fuel.<br />Clean up any spilled fuel immediately.<br /><br />Flame Arrestor<br />1. Is the flame arrestor clean and free flowing?<br />2. Is the flame arrestor properly sized for the engine?<br />3. Is it bent or damaged?<br /><br />Engine <br />1. Does the engine need a tune up? - Points, spark plugs, condenser, plug wires, cap & rotor. <br />2. Battery, battery cables, and charging system condition.<br />3. Electrical connections.<br />4. Overall condition of cooling system.<br />5. Cylinder Compression and vacuum leaks.<br />6. Seizure and/or binding in the drive train?<br />7. Over or Under sized propeller? In good condition?<br /><br />Boat<br />1. Is the engine room ventilation clear and properly sized for this engine?<br />2. Is the boat bottom in good condition.<br />3. Can water drip onto the engine due to clogged and/or poor drainage?<br />4. Is there excessive water sloshing around in the bilge?<br /><br />Protect Your Efforts<br />MOST CARBURETORS FAIL BECAUSE OF:<br />· Dirt in the fuel system - Dirt is the #1 cause of carburetor failure.<br />· Dirt in the flame arrestor - Air flow is blocked, causing poor performance and/or rough running.<br />· Over tightening when installing.<br />· Clogged, pinched, or kinked fuel lines.<br />· Water entry from fuel tank and/or dripping onto engine from above.<br /><br />BEFORE REMOVING OLD CARB:<br />· Disconnect batteries.<br />· Shut off fuel supply<br />· Identify, tag, and disconnect all fuel lines, electrical lines, and linkage.<br />· Note carb base gasket condition and type.<br /><br />BEFORE INSTALLING:<br />· Flush fuel lines.<br />· Install a new fuel filter and fuel water separator.<br />· Compare and match the new carb base gasket to the old one.<br />· Clean the flame arrestor and housing.<br />· Service PCV valve if equipped.<br /><br />BEFORE STARTING ENGINE:<br />· Change engine oil and filter if the reason for carb service was flooding.<br />· Check for free movement of throttle linkage.<br />· Ventilate engine compartment.<br />· Connect batteries<br />· Open fuel supply.<br />· Crank engine and then check for leaks.<br /><br />AFTER STARTING ENGINE<br />· Check for leaks.<br />· Check choke operation.<br />· Re-check linkage movement.<br />· Bring engine to operating temperature.<br />· Check and adjust idle timing in neutral and in gear. **<br />· Make final mixture adjustments to carb, in gear. **<br />· Lake test unit and verify operation through out RPM range.<br /><br /><br />** If idle is electronically controlled (such as current Mercruiser, Volvo, Crusader, and other engines), install jumper to disable computer control, before attempting to adjust timing and or idle mixtures.<br /><br /><br />Note: The above information should only be used in conjunction with your owners and service manuals and should not be your only source for servicing your engine and/or it's carb. <br /><br /><br />George Van Parys,
