My engine wont idle

[Samurai_Dave]

I've got a Yamaha 50D two stroke outboard (1990 model) I've had a lot of work done to it to get it into a running condition as it was previously unloved. I've had seven trips to sea with it since its restoration but a new problem is becoming a serious nuisance. The engine starts straight away but even when warm it wont tick over without some extra throttle. When on the water putting it into gear makes it conk out 80% of the time which isn't ideal when launching in a busy river. The carbs have previously been stripped and cleaned and I'm using fresh petrol. When its going the engine is great, it runs very happily. I've put on a new fuel line as the old primer bulb had an air leak but I've still got this problem.

Is there a simple fix to this?

Is there a liquid carb cleaner I can add to the petrol to keep the carb gum free?

Thanks.

 

[Lakesailor]

Sounds like the slow running jet on a carb is blocked. Does pulling the choke slightly before opening the throttle or dropping into gear improve matters?

But there are other things like float-level and partially blocked fuel filters which could affect tickover but not be apparent at higher revs. Motors tend to over-fuel a bit when revving, and the fuel pump will be running faster so a partially blocked fuel filter could be "overcome" by the higher pressure.

It can be an annoying and fiddly thing to sort.

 

[misterg]

All the above, plus: Have you synchronised/balanced the carbs? It will idle like a dog otherwise if similar engines are anything to go by.

 

[Uricanejack]

I've got a Yamaha 50D two stroke outboard (1990 model) I've had a lot of work done to it to get it into a running condition as it was previously unloved. I've had seven trips to sea with it since its restoration but a new problem is becoming a serious nuisance. The engine starts straight away but even when warm it wont tick over without some extra throttle. When on the water putting it into gear makes it conk out 80% of the time which isn't ideal when launching in a busy river. The carbs have previously been stripped and cleaned and I'm using fresh petrol. When its going the engine is great, it runs very happily. I've put on a new fuel line as the old primer bulb had an air leak but I've still got this problem.

Is there a simple fix to this?

Is there a liquid carb cleaner I can add to the petrol to keep the carb gum free?

Thanks.

Had a 55 Yamaha. Carbs and fuel allways an issue. I would suspect there is a bit of build up in the idle jets they are a bu@#$ to clean. and get blocke easy. even fresh fuel if you use a tank which had a little old fuel in it prior to filling can still be a problem.

 

[Samurai_Dave]

Sounds like the slow running jet on a carb is blocked. Does pulling the choke slightly before opening the throttle or dropping into gear improve matters?

But there are other things like float-level and partially blocked fuel filters which could affect tickover but not be apparent at higher revs. Motors tend to over-fuel a bit when revving, and the fuel pump will be running faster so a partially blocked fuel filter could be "overcome" by the higher pressure.

It can be an annoying and fiddly thing to sort.

The choke is activated by pushing the key in when starting so I dont know how I can test this.
Annoying? Most definiately!

 

[Lakesailor]

Ah That will be a solenoid which fires a charge of fuel into the carbs. I had an Johnson with that. If you look under the cover there will be a (red?) lever which allows you to engage the enrichening device.

Misterg has a point about balancing the carbs. If you dismantled the linkage, it's a must.

If your fuel pressure is low the top carb may not fill it's float chamber properly.


See that red lever? On the black solenoid. That's the choke control.

 

[Samurai_Dave]

Ah That will be a solonoid which fires a charge of fuel into the carbs. I had an Johnson with that. If you look under the cover there will be a (red?) lever which allows you to engage the enrichening device.

Misterg has a point about balancing the carbs. If you dismantled the linkage, it's a must.

If your fuel pressure is low the top carb may not fill it's float chamber properly.


See that red lever? On the black solenoid. That's the choke control.

Thanks for the tip.
I'm hesitant to even take the carbs off to clean them as my mechanical skills are somewhat lacking (although improving) I've no idea how I'd balalnce the carbs if thats the solution.

 

[seadog30]

Hi

Could be carb or electrical.

When you have tried to start the engine from cold and have failed pull a sparkplug out, if it is wet and smells of fuel it more likely to be electrical.

Check the condition of the spark plugs if they are not clean change them. If they are clean attach to the plug lead and wedge the hex part against a bit of clean metal i.e. head bolt ? and crank the engine, can you see a nice fat spark ? if not check all of the HT leads.

Otherwise for carb problems as sugested by others check the slow running jet.

Also is the slow running stop set to slow, an outboard will not tick over as slowly as the boats main engine or a car engine.

Good luck

 

[Lakesailor]

His engine starts no problem. It doesn't tickover very well.

It can be a nightmare. Full power is easy but slow running can be upset by so many things. Seadog suggests the tickover is too slow. Have you tried increasing the throttle stop setting? That could be it.
The plugs may be fouling. It could be the HT leads are failing or the wrong plugs.

If it starts and runs well at speed I'd forget about balancing the carbs for the moment. You need a workshop manual and some patience.

 

[seadog30]

Hi

Laakesailor +1

I have spent many happy hours in the past trying to remember how to put the carbs back together when the problem was eventually traced to failing HT leads

Start with the simple stuff first.

Good luck

 

[Samurai_Dave]

Still doesn't idle

I've now managed to dismantle the carbs and clean them then reassemble and refit. The engine fired almost immediately but still has the same problem as before, it won't idle without some extra throttle and sounds a bit lumpy too.

I figure I can adjust the needle valves (the screws with springs on them), try cleaning out the fuel lines just to be sure they are all clear (one carb had noticeable less fuel in the bowl then the other two) and see if I can buy a new set of HT leads.

Someone mentioned balancing the carbs. How does a novice do that exactly?

Thanks.




QUOTE=seadog30;4146901]Hi

Laakesailor +1

I have spent many happy hours in the past trying to remember how to put the carbs back together when the problem was eventually traced to failing HT leads

Start with the simple stuff first.

Good luck[/QUOTE]

 

[misterg]

Someone mentioned balancing the carbs. How does a novice do that exactly?

When you balance the carbs, the aim is to get each one of your 3(?) carbs contributing equally to keeping the engine ticking over. This gives the smoothest running and the best power/pickup off idle (very noticeably).

If everything has been dismantled, it's usual to try and set things up by eye first (with the engine stopped). You can use feeler gauges, drill bit shanks, etc. to check that each throttle valve has *exactly* the same opening when throttle is on the idle stop.

Final adjustment is with the engine running:

The best way is to use a set of vacuum gauges connected between the carb and the engine to monitor the vacuum being developed in the intake to each cylinder. (There are usually blanked-off tapping points between the carbs and the cylinder block, but I don't know about your engine specifically.)

There will be some means of adjusting the throttle in each carb individually - usually somewhere in the throttle linkage on/between the carbs. If you have CV carbs (where the slide is opened by a diaphragm), the adjustment may be an air bypass screw - Ideally you would have a look at the service manual to find the correct procedure.

All you do is use the available adjustments to bring the vacuum reading on each cylinder to the same level. During the process, you would probably have to adjust the idle speed back to spec. a few times.

In the absence of vacuum gauges you can also use a 'listening tube' to hear the air whistling past each of the throttles and make adjustments until they are all the same. The engine noticeably smooths out when you get it spot on.

Example (on 2 carbs) here:

http://www.youtube.com/watch?v=xRExxNcUVt0

If you know someone who's into motorbike mechanics, they may have a set of gauges.

 

[Samurai_Dave]

Thanks for the info. I'll have to print that out and keep it.

I adjusted the needle valves and the throttle minimum position. It now idles without conking out but still needs further tuning.



QUOTE=misterg;4153761]When you balance the carbs, the aim is to get each one of your 3(?) carbs contributing equally to keeping the engine ticking over. This gives the smoothest running and the best power/pickup off idle (very noticeably).

If everything has been dismantled, it's usual to try and set things up by eye first (with the engine stopped). You can use feeler gauges, drill bit shanks, etc. to check that each throttle valve has *exactly* the same opening when throttle is on the idle stop.

Final adjustment is with the engine running:

The best way is to use a set of vacuum gauges connected between the carb and the engine to monitor the vacuum being developed in the intake to each cylinder. (There are usually blanked-off tapping points between the carbs and the cylinder block, but I don't know about your engine specifically.)

There will be some means of adjusting the throttle in each carb individually - usually somewhere in the throttle linkage on/between the carbs. If you have CV carbs (where the slide is opened by a diaphragm), the adjustment may be an air bypass screw - Ideally you would have a look at the service manual to find the correct procedure.

All you do is use the available adjustments to bring the vacuum reading on each cylinder to the same level. During the process, you would probably have to adjust the idle speed back to spec. a few times.

In the absence of vacuum gauges you can also use a 'listening tube' to hear the air whistling past each of the throttles and make adjustments until they are all the same. The engine noticeably smooths out when you get it spot on.

Example (on 2 carbs) here:

http://www.youtube.com/watch?v=xRExxNcUVt0

If you know someone who's into motorbike mechanics, they may have a set of gauges.[/QUOTE]