140 1977 -rude - wont idle

[harrietnorth]

1977 140783S w/ Trim and Tilt.

She won't idle below 1500-2000 RMP, and even then- needs a little choke to help.

Tore down the carbs, inspected the needle and floats on both carbs. Removed the fixed jets to make sure they werent plugged. Verified that the correct jets were in the correct upper and lower carbs. Put pressure on the fuel bulb, no gas shoots out, which confirms that the needles are holding.

The motor will run on muffs, but as soon as it hits the lake- cant get to idle.

Doesnt make a difference if the motor is tilted all the way up, or all the way doen.

In the rare occasion I can get the boat into gear w/o the motor cutting out, and I get past 1500-2000 - the boat will jump out of the water - and top out the RPM's at 5250-5400. (18' fiberglass v-hull)

Checked compression #1 - 130, #2 128, #3 125, #4 122.
Replaced plugs.
Verified spark with a spark tester @7/16 - bright blue spark on all 4.
fresh gas
Ran a Decarb per the forum (beautiful amounts of smoke)
No fuel line leaks between tank and carbs...

What can I check next - or should I be looking for? I thought I saw milkey gas in cylinder #4 when replacing plugs after decarb in lake. Ran it again for a few minutes, went back - there was none to find.

Thought I would pull a plug wire one at a time while running, maybe one cylinder not as hot as the rest - the only thing I noticed was the jolt to my arm was far more painful on the port bank than the starboard bank (yes - the benefit of hindsight suggests that I should use longer insulated pliers next time) (powerpack failing?)


The choke-to-life part makes me think that the carbs are the problem, but I pulled them off twice - needles are good, floats are flat and level, and the will hold off the pressure of a bulb squeeze.


At wits end. Help

 

[tashasdaddy]

Re: 140 1977 -rude - wont idle

have you tried a link n sinc? have you checked your timing? http://forums.iboats.com/showthread.php?t=228183

 

[ezeke]

Re: 140 1977 -rude - wont idle

Don't mess with the timing unless you changed it yourself.

Start by making sure that the carburetors' throttle plates are moving in exact synchoronization with each other through the whole range of movement; you have to take the covers off and watch. If they are not, adjust the linkage between the carburetors until they do.

When the carburetors are perfectly synchronized, check that the cam follower is on the throttle cam top mark when the warm up lever is in the run position and the control in neutral. Make sure that the roller on the cam follower is in place and in good condition. The roller should just be making contact. Then, check that the throttle plates are closed.

 

[harrietnorth]

Re: 140 1977 -rude - wont idle

Took to a local shop. Their conclusion is that the crank seal at the bottom of the engine must have a small leak.

They verified good compression, clean and orderly carbs, hoses solid with no leaks, no electrical issues... When all else fails, they look to a seal somewhere in the block, the lower crank seal being their first guess.

Is there any way to make sure that this is the problem before I pull the power head and replace the crank seal?

Do I have to crack the block to remove the crank seal or is it 4 bolts and a little tug?

 

[harrietnorth]

Re: 140 1977 -rude - wont idle

Don't mess with the timing unless you changed it yourself.

Start by making sure that the carburetors' throttle plates are moving in exact synchoronization with each other through the whole range of movement; you have to take the covers off and watch. If they are not, adjust the linkage between the carburetors until they do.

When the carburetors are perfectly synchronized, check that the cam follower is on the throttle cam top mark when the warm up lever is in the run position and the control in neutral. Make sure that the roller on the cam follower is in place and in good condition. The roller should just be making contact. Then, check that the throttle plates are closed.

I - for grins - checked the timing - A Ok.
Verified that the carbs moved in sync perfectly.
Made sure the throttle cam was adjusted within spec (per the service manual)
- at wits end a broke down at took to local shop -

 

[emdsapmgr]

Re: 140 1977 -rude - wont idle

When at idle, the carb butterflys are closed. The only fuel to run the engine comes from the idle circuit passages in the carbs. If these get dried fuel in them, they won't flow fuel to keep it running. When you had the carbs apart, did you blow out these passages with an aerosol carb cleaner?

 

[harrietnorth]

Re: 140 1977 -rude - wont idle

Made sure that the idle circuits were clean the second time I pulled the carbs off. Carbs are clean.

1977 motors were not designed for ethanol I am told, and ethanol is very hard on rubber seals from back in the day. could it be that the seals for the crank have begun degrading, and that the engine is sucking air from the bottom of the crank, ergo not leaving enough vaccum for the engine to draw fuel at low rpm?...

This theory supports the "choke-to-life" scenario that the motor is currently running under. Choking the engine creates more negative (-) pressure on the idle circuits and compensates temporarily for the escaping pressure from the degraded bottom crank seal.

I was hoping that there would be a concensus that this is a next valid place to check, if the fuel delivery system, electrical good, compression good...

 

[tashasdaddy]

Re: 140 1977 -rude - wont idle

with motor running, try spraying carb cleaner around intake gasket. it will tell you if intake gasket is leaking.

 

[harrietnorth]

Re: 140 1977 -rude - wont idle

with motor running, try spraying carb cleaner around intake gasket. it will tell you if intake gasket is leaking.

Are you suggesting that the carb to manifold gaskets are leaking air, or are you thinking that the manifold to crankcase?

If I spray copious amounts of carb cleaner near those gaskets, I should notice a change in rpm?

would this be reeds?

 

[LiLGrady17]

Re: 140 1977 -rude - wont idle

Are you suggesting that the carb to manifold gaskets are leaking air, or are you thinking that the manifold to crankcase?

If I spray copious amounts of carb cleaner near those gaskets, I should notice a change in rpm?

would this be reeds?

For any engine, if you spray a liquid such as carb cleaner on a suspected vacuum leak area, if there is a leak present, idle should increase/smooth out as the liquid gets sucked in & seals the leak temporarily..

 

[emdsapmgr]

Re: 140 1977 -rude - wont idle

The bubbleback exhaust system can leak water into the exhaust chest cavity. If the gaskets deteriorate or if the inner cover casting has porosity, you can leak pressured water into the chest. Also, if the exhaust cover bolts were never retorqued, they can lose their torque with age and cause poor sealing. (There is one bolt for the inner cover which usually never gets tightened, since it is hidden under the outer cover.) If you have any water ingestion issues will affect idling. Any water tends to accumulate most noticeably in the bottom cyl.