Why does a 1985 140 Looper idle best without idle air bleeds?

[roger3645]

I have a 1985 140 Looper, model J140TLCOS, with original carbs body 393571, with jets , Idle Air Bleed 14, intermediate 40, and HS 59D.

These carbs are very clean

Compression is 120 psi on all 4 and has a good crisp blue spark at 7/16.

The motor is new to me and the first year running it. It had sat for years in climate controlled storage.

The issue is I could never get the motor to run with these carbs, would not idle and when I got to idle it would immediately die when put in gear.

So I purchased a set of carb bodies off ebay. They were supposed to off a 1993 140 looper *(later found out they most likely came off a 120hp as that’s how it was jetted 30, 37, and 63D). Using these bodies and the jets from the 1985 carbs the motor will run. I did not change the throttle bodies.

I feel I am not getting the performance I should from a 140hp.

Running a 23 pitch Michigan Wheel SS prop the 17’ Ranger Sport r70, ran 48mph (GPS) at 5200 rpm.

So I dropped down to a 19 pitch and the boat will almost hit 6000 rpm, at 46mph without touching the trim. I trimmed it up to 6300 but didn’t push it any further than that, Hole shot is awesome.

I also tried a 22 pitch Raker and it ran about the same as the 23 pitch.

Believing I am not getting the full potential from the motor, I reinstalled the original 1985 carb bodies and jets.

Got the motor to run on the muffs but it will not idle, checked for air leaks and can’t find any. The motor will only run with the warm up level advanced a bit. Adjusting the idle timing doesn’t make any difference.

So, just to try, I put the idle air bleeds #30,from the 1993 carbs into the 1985 carbs. The motor will idle and responds to idle timing adjustments, but still idles a bit ruff. So I took the idle air bleeds completely out and the motor idles great on muffs. Haven’t put it in the water yet.

Questions

Can I run the motor without idle air bleeds?

Why does it run best without them?

Was the motor performing at it’s full potential with the 1993 carbs

Are the 1993 carb bodies for a big bore 140?

Thanks

 

[roger3645]

Just for an update. Took the boat to the lake and it would not idle below 2000rpm. Took it home replaced the carbs with the 1993 bodies and 1985 jets and went fishing.

 

[jimmbo]

The carbs for a 120 might have a smaller Venturi bore than the carbs for a 140, and that would restrict breathing. Mix and Matching Carb Bodies and Jets/Air Bleeds rarely improves things

There is not supposed to be an 'Idle' Timing adjustment, Retardation of the Spark Timing is what determines the Idle speed. You were probably adjusting what is called Pickup timing. That is a Specific Timing Spec where the carbs behind to move from a Fully Closed Position. There is also a Max Timing Advance Spec. Since you were messing where you should have been messing, you will now have to perform a complete Timing Check/Adjustment and Primary Pickup Check/Adjustment, known as a Link and Sync.
As to why the carbs worked better without the Air Bleeds... well you were messing in other areas, so the entire calibration is off

You actually have the Small Bore version of the Looper 140, a few years down the road, OMC increased the bore, so the 93 120 is actually a bigger engine. Maybe the carbs the same Venturi bore...

Get a Factory Service Manual, specific for that engine.