650 Will Not Come Close To An Idle

[1960 Starflite]

I have a 650, S/N 1543773, four cyl. believe it to be a 1963 however it is painted black, thought Mercs were white till 1965. I?ve been fighting this thing for a couple of weeks, as it just won?t come even close to an idle. Listed below are the things I have done:

Removed magneto, replaced points and condenser, checked coil and it is OK (Ohm readings as per manual), rotor, cap and wires check OK. Points set at .010?, Changed spark plugs to higher heat range (Champ J4C to J6C), gap set to .025?.

Pulled carbs, disassembled, cleaned, replaced filters, set float levels, checked fuel lines, replaced needle/seats, set idle mixtures screws from ? turn to 1 ? turns out.

Installed new fuel pump kits and check valves, replaced fuel line and ball pump from fuel tank to engine.

Pulled flywheel to check for sheared key, set total advance with dial indicator as per manual.

Compression is 115-120 on all four cylinders.

Engine will start when the warm up lever is advanced and it will rev and run well above this setting. However it just will not come close to an idle, no tach on this engine, just guessing that it will run around 1400 rpm and above, but not below that. I am not within ?? of the idle stop screw on the magneto bracket to keep it running. There is no timing index on the flywheel, just one stamped vertical line to align with the arrow on the magneto pulley at #1 TDC. I have run out of ideas on this, please help !!!!!!

 

[CharlieB]

Re: 650 Will Not Come Close To An Idle

Load a spray bottle with pre-mix fuel and spray it into the carbs when backing the speed down to see if the motor trys to keep running.

Also try spraying while cranking a warm motor to see if it tryys to fire and start without using the fast idle lever.

If so you may still have a restricted idle circuit or float settings too low.

 

[1960 Starflite]

Re: 650 Will Not Come Close To An Idle

I pulled the plugs again and they are wet with fuel. Could I have a problem with crankcase seals and sucking too much air which isn't going thru the carb airhorns which would make a rich fuel mixture?

 

[Jake.]

Re: 650 Will Not Come Close To An Idle

A faulty crankcase seal would lean the mixture by adding extra air.

 

[CharlieB]

Re: 650 Will Not Come Close To An Idle

Your link and synch may be slighlty off, it sounds as tho the throotle blades may not be fully closed.

Disconnect the throttle cable, manually move/hold the throttle in the idle position while you check the throttle pick-up cam for clearance to the actual throttle linkage on the carbs.

Search the sticky threads at the top of this forum and find the links to the service manuals posted elsewhere.

Download the manual for your motor and follow the directions to synch your carbs and link to the timing and throttle cable.

Follow the directions to the letter.

 

[1960 Starflite]

Re: 650 Will Not Come Close To An Idle

GOT IT !!!!! Pulled the magneto again to replace the plug wires. Thought what the heck, I'll put my ohm meter on it to check it out. Found 850-1450 ohm resistance on the 2000 scale between the rotor cap terminals. What the heck, shouldn't be ANYTHING there, but was. Had another magneto cap and checked it out, nothing between terminals, installed new wire set, ran magneto in vice with drill motor, spark looked great even at 1/8" gap (for a test). Reinstalled magneto and the darn thing will now idle.

The engine is on a stand and I will have to feather the carbs and total timing after putting it back on the boat. I fabed a pointer at TDC on #1 and degreed the flywheel to 40 degrees BTDC to aid in total timing. What should the total advance be running on our junk gas? (30 degrees)? I'm running Champion J4C plugs, will it run cleaner with J6C plugs?

Thanks for the replies.

 

[CharlieB]

Re: 650 Will Not Come Close To An Idle

21 to 23 degrees is more likely a safer range to prevent detonation.

On a hose with NO LOAD you could get by with a LOT of advance but once you load the motor with the prop in the water it would knock, ping and crush the pistons in seconds.