2000 Johnson 50 HP Wont stay running at low idle

[qcarlson]

I have a 2000 Johnson 50HP model J50PLSSM it dies at idle, if you use the high idle start it will start and stay running @ 2000 RPMs occasionally running away to 5000+ RPMS, but at low idle it dies every time.

Carbs cleaned and rebuilt( intermediate orifice was found in the bottom cowling prompting the rebuild)
New VRO PUMP installed (was pumping very aerated fuel)
New pulse limiter
all lines have been inspected and replaced as needed
Sync and Link performed
Compression is 120 on both cyls
Good spark jumps 7/16" gap and is bright blue
new plug wires
Engine de-carbed

where to go from here?

 

[Daviet]

Re: 2000 Johnson 50 HP Wont stay running at low idle

What is your idle set at, 700-750 in the water in gear?

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

I cant get idle set it wont idle below about 12-1500 at one point I had it down around 1000 but darn thing keeps dying out. how ever 1000 out of water would be close to idle in the water.

 

[Daviet]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Have you tried adjusting the low speed needle valves on the carbs?

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Yes initial setting in the book is 3.5 turns out / I have also tried 1.5 and 1.75 does not seem to make a difference. if I partially cover the carb throat to restrict air, this seems to help but I still cant find a happy medium to get it to run consistently.

 

[Daviet]

Re: 2000 Johnson 50 HP Wont stay running at low idle

If adjusting the low speed needles in and out does not have any effect on the running of the engine, you still have a carb problem.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

If adjusting the low speed needles in and out does not have any effect on the running of the engine, you still have a carb problem.

I am wondering if anyone knows the size of the intermediate and high speed orifice's?

if I turn the needle out 4.5 turns it will idle at 1000-1100 RPMs it will only run for about 45 seconds then dies again. if I put the engine in gear its responsive enough but it should not keep dying like this. I can say for certain there is no obstruction in either carb ( I have pulled them apart three times) I felt the same as you that there is still a carb problem. it certainly does not act like it is running lean(no miss or pop). I am kinda at a loss here.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Well 5 1/4 turns seems to be the ticket that seems like I am compensating for something else but it is running steady now at 900 rpms on muffs?????

 

[Daviet]

Re: 2000 Johnson 50 HP Wont stay running at low idle

You have a good starting point, but you need to adjust the carbs with the boat in the water and in gear, the settings will be a little different with backpressure on the engine.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

I understand that back pressure on the exhaust will lower the idle RPM's but my concern is that seems to be quite a ways out to set the air fuel mixture. for example it seems that there is an air leak or an abundance of air that should not be there and I am compensating for that instead of getting to the root of the problem. maybe I am just over thinking this?

 

[Daviet]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Look on top of the carbs at the plastic top real close, I have seen some that would develop very small cracks.
I would put the boat in the water and make all final adjustments, if it runs properly, use it and forget it.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Well no cracks but on the top carb the intermediate orifice had vibrated/fallen/blown out and was laying in the cowling( clinically OCD) cant run it and forget about it. thanks for your input by the way, its much appreciated.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Well now that I have this in the water it wont stay running again, i have adjusted the low speed needles across a range of settings, seems to have very little impact, I have cleaned these carbs 3 times and they were not very dirty to begain with. Any ideas as to what culprit to test next would be great?

 

[clanton]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Did you check the pulse hose to the VRO pump? The part behind the starter.

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

What would I be checking for? I replaced the pulse limiter. Hose seemed ok no apparent cracks or air leaks.

 

[clanton]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Starter will rub a hole in the hose, close to the limiter.

 

[clanton]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Can you verify the idle timing, should be 1 degree ATDC +- 1 degree. I`m thinging you still have some engine problem.
You can disconnect throttle control rod, item C in photo 1 page 1-41 OEM manual. Butterflys in carb should be closed, engine should idle on flusher. If it will not idle, timing off, or engine problem.

 

[1outboard]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Did you ever find a solution to this problem? I have a 2000 40hp, recently purchased, doing the same thing. The carbs are clean. Idle jets have no effect on the tuning. Anything below 1500 RPM it dies. Compression, spark, timing and fuel supply are good. I am beginning to think the plastic covers on the top of the carbs are warped and are not sealing good. To me they look poorly designed, easily over tightened, to be used with soft gaskets. Anyone know of an alternative to the plastic covers?

 

[qcarlson]

Re: 2000 Johnson 50 HP Wont stay running at low idle

No I was not able to figure it out yet. I wish to god I could seems like a fuel issue. But carbs are clean and new VRO installed. I did have a orifice blow out of the plastic top so I too thought that might be suspect?

 

[1outboard]

Re: 2000 Johnson 50 HP Wont stay running at low idle

Still have not been able to get mine to Idle below 1200RPM. I made some plates to go on top of the plastic covers. My Idle screws now affect tuning. It will idle with the timing advanced to about 15 degrees BTDC around 1200 rpm. If you back the timing down and it drops below 1200 it will starve for fuel in just a couple seconds. I have put mine up for sale for $1800 to see if I can just get rid of the headache. I am beginning to think it may be crank shaft seals. I am sure there is a simple solution I just have not been able to find it.