Johnson Bodgy Idle

[tafc010]

Hey all, got a mid 80's 70 HP Johnno that runs like a train but idles like a sh%^&*x. We can cruise at part or WOT any time and for any distance but as soon as we throttle back to idle to chuck the pick (or whatever) the engine stalls. Then it cannot restart unless you use the fast idle lever, and it splutters indicating a flooding situation before the engine clears. It is a bit of a worry when you are being blown onto rocks and the motor is not playing the game. We are currrntly running a 50-1 mix and there is no oil injection. It has tripple carbs.

Now for the fun part, it ONLY does this in the water, on the trailer flushing the motor it will idle for 20 minutes (we timed it waiting for it to shut down, got the shits real bad and turned it off, hit the key and it fired and idled again,laughing at us all the time)

Any suggestions would be most helpful. We have pulled the bowls of the carbs, checked filters etc all is clean and good.

Thanks in advance

Geoff

[SPARKY]

Don't mean to be rude but take it to your mechanic

I have 135 mercury that was doing the same thing and nearly ended on the rocks at north head.

Booked it in the next day.

I thought it was the plugs oiling up. Turns out the motor has some sort of thermostat that opens and

Closes to allow the engine to operate at a certain temperature. This was not closing so the engine was not getting up to the rite temperature to operate efficiently, so at idle it would just stop and not want to start unless you throttled up.

Turns out this part cost less than ten bucks (plus labour) to fix.

I don't know what your boat is worth but mine is worth about $35 to $40K doesn’t take much to work out what the smart thing to do is dose it.

SPARKY

[tafc010]

Don't mean to be rude but take it to your mechanic

I have 135 mercury that was doing the same thing and nearly ended on the rocks at north head.

Booked it in the next day.

I thought it was the plugs oiling up. Turns out the motor has some sort of thermostat that opens and

Closes to allow the engine to operate at a certain temperature. This was not closing so the engine was not getting up to the rite temperature to operate efficiently, so at idle it would just stop and not want to start unless you throttled up.

Turns out this part cost less than ten bucks (plus labour) to fix.

I don't know what your boat is worth but mine is worth about $35 to $40K doesn’t take much to work out what the smart thing to do is dose it.

SPARKY

Sparky, dont worry about being rude. It's just the EGO thing, the two of us that own it can build maintain and race cars no drama so this thing is hammering our fragile ego's. Plus it's pissing us off as well. You may have the answer because even though we ran it for 20 minutes on the stands the water coming out of the cylinder head is COLD. Why didn't we think of that?

Thanks heaps

Geoff

[chrisg]

tafc

It does it on the water because the back pressure on the exhaust gases is enough to stop the motor. As suggested make sure its up to temp (got a temp gauge?). Any doubts about the thermostat chuck it. I had one on the same motor that tested fine in a pan of hot water but would jam open out on the water...result....lumpy idle and more smoke than usual.

See how you go..let us know.

Cheers

Chris

[tafc010]

Chris, Thanks for that. Got some spare time Wednesday night, will post the result. Thanks again to all.

CYA

Geoff

[tafc010]

tafc

It does it on the water because the back pressure on the exhaust gases is enough to stop the motor. As suggested make sure its up to temp (got a temp gauge?). Any doubts about the thermostat chuck it. I had one on the same motor that tested fine in a pan of hot water but would jam open out on the water...result....lumpy idle and more smoke than usual.

See how you go..let us know.

Cheers

Chris

Whoever said get a mechanic to look at it go to the top of the class, did all the usual stuff, fuel pressure, water temp & thermostat, comp test, plugs and full ignition test then called***** , anyways he comes out, fires it up, takes the carb linkage off and tells me only 1 carb is working, the others have a drama with an emulsion tube sealing causing the rich idle and stall.

Coupla days later and some $$$, three recoed carbs and a boat that runs like a dream.

OUTSTANDING.

CYA

Geoff

Edited January 11, 2007 by Flightmanager

[Guest rzep]

Glad to see you had a happy outcome.

You had her out on the water yet?

[PPSGT]

I have the exact same model Johnson, and it ran all day at anything over 1/3 throttle but

stalled when docking or going slow. Was then hard to start if it stallled, blew a bit of

smoke and then ran again fine until you ran it slow.

Took it to a mechanic that works on older Johnsons - I thought it was stuffed carby or a million other

terrible and expensive things.

Turned out to be a faulty thermostat. Mid 80's johnsons have to run real hot at idle to burn off the

oil that forms on the plugs, or they stall or run rough. A lot of non-Johnson trained mechanics dont

know this and think its running to hot and remove or alter the thermo stat so it runs cooler at idle

I had a new thermo stat installed and all the temp's tested. I have gone from wanting to sell it

to first start everytime, as soon as the key is turned, no choke or warm up lever. (once out on the water)

FIrst start of the day at the ramp I now just lift the warm up lever 1/4 up push the choke as the

I turn the key - starts first go ever time

Jason