breaking down when cool

[Curl]

I have a 1992 60hp Evinrude that breaks down(but does not stall) on acceleration after the motor has cooled down.Idle appears to be a little rough at times, but does not stall. While the motor remains warm, acceleration on to the plane is smooth, but once cooled the problem returns. Dismantled carby's and checked filters, fuel lines and vents are all OK. Compression on all cylinders are OK with 8psi variation from lowest to highest.I tend to think this could be an ignition problem, but unsure how to go about checking coil and power pack. Stator has been replaced recently along with new plugs. Would appreciate any help offered.

 

[OBJ]

Re: breaking down when cool

Curl, do a spark test on all cylinders. The spark to each cylinder should jump a 1/2" gap with a strong thick lighting like spark. <br /><br />What plugs are you using and what is the gap? A Champion QL77JC4 works well set a .030.

 

[Curl]

Re: breaking down when cool

Thanks. I was using the "Champion" plugs, but installed new "Ngk" as a process of elimination which made no difference. I will do a spark test and get back to you- Thanks again.

 

[Curl]

Re: breaking down when cool

I have good constant spark on all cylinders. Because this problem appears to be linked with the temp of motor, i'm wondering if the(or one of) carby's are perhaps running to lean(eg. cold motor needs rich mixture). What would setting be on the "slow speed mixture"? Would all carby's have the same setting(eg. number or turns out) or would they be adjusted independantly?

 

[OBJ]

Re: breaking down when cool

The carbs are set independently of each other. <br /><br />Have you checked the engine temp at idle? Is it warming up sufficently? After idling a while, you should be able to lay your fingers on the flat area on top of the block just in front of the head, for several seconds before having to remove them. If the block is staying cold, this will effect the idle. May point toward a bad t-stat.<br /><br />When you cleaned the carbs, did you use new kits and blow out the passages with carb cleaner and compressed air? Soaking them out in carb cleaner is better yet.<br /><br />Do you noticed or have looked for blow back from any of the carbs or notice any mess laying in the lower pan that may indicate a fuel leak?<br /><br />While the engine is running, pull a primer line from a carb and see if it maybe is dribbling in a little fuel. There should be no fuel at all coming from any of the primer lines after the engine is started.<br /><br />There was two different carbs on this year engine, an early production model and a late production model that had a rather flat top on it with a plastic cap. If yours is the late production, check around the caps for leaks and that the caps are not cracked from over torqueing the screws.<br /><br />Check all your fuel lines are soft and plyable. A hard fuel line can lose it's grip on it's connection.<br /><br />Check your gasket areas. This can be done with a little carb cleaner in a can. Dribble the carb cleaner along the seams. If the engine picks up a little from sucking in the carb cleaner, you have a leaky gasket.<br /><br />I would also consider getting a service manual, OEM prefered. <br /><br />Keep us posted....thanks.

 

[Curl]

Re: breaking down when cool

Well...i have checked and eliminated all that's been suggested, and i appreciate all help offered. Before i surrender to the experts, i have read that using a hair dryer(or external heat source) can help determine if coils or power pack is the problem?.Any truth in this?

 

[fireman57]

Re: breaking down when cool

If you have a strong blue spark to each cylinder like you say it is not the powerpack. If it only does it when it is cold I'm with OBJ as it sounds like a fuel problem. You say you checked and eliminated all the suggestions but is the engine warming properly as OBJ suggested? Can you hold your hand on the head for at least a slow count of three? As suggested a good manual will be a great help. Sounds like a carb is not adjusted correctly or has some crud in it. I do not know if those carbs has fixed jets or not for the slow idle. I would again take the carbs apart and put a kit in each. Make sure that you blow all passages out with compressed air and they are clean.

 

[Curl]

Re: breaking down when cool

Definitely reaching operating temp OK. Before i dismantle carbs again, the carbs are TR model(no plastic cap) and do have a slow speed adjustment and appear to run best at 1 1/4 turns out. I understand that they should be at least 2 turns out, but run to eratic. Is slow speed mixture only for idle....or would it also effect acceleration??<br />I tend to think it may be FUEL as suggested.

 

[fireman57]

Re: breaking down when cool

each carb will be set indepently of the other. One might work better adjusted 1.5 turns and the other might be better at 2 turns. I do not have a manual for your motor might you might check the diaphragm in the fuel pump if it has one. If it has a slight tear or is wavy replace it. Had a small pinhole tear that was tough to see in mine and had the same problem. Get an OEM manual as suggested and do a link n sync.

 

[Curl]

Re: breaking down when cool

What would the procedure be to test the thermostat, also what RPM range does the slow speed mixture screw effect? Thanks.

 

[DHPMARINE]

Re: breaking down when cool

I'd want to look at the manual,for the mixture screw initial setting.Some of these engines are 3 to 4 1/2 turns out.<br /><br />Also would look at the primer bulb,but that's another theory<br /><br />DHP

 

[Walker]

Re: breaking down when cool

Try pumping up the bulb before each cold start. See if that helps.

 

[Curl]

Re: breaking down when cool

What about Spark Plug gap?. Currently at .040" as advised by local marine outlets, but according to the Manual it should be .030".<br />Appears to be breaking down at around 1500-2500 rpm under load when cold.How would i best determine which Plug/lead or carby is the cause while running it at that RPM?.<br />Thanks.

 

[fireman57]

Re: breaking down when cool

0.40 is a good gap if you do a lot of trolling and idling like I do fishing. Plug gap shouldn't be your problem here. Have you pumped your primer bulb or choke it a little at that rpm?

 

[Curl]

Re: breaking down when cool

Yep.....when i apply the choke the motor decreases in rpm's.

 

[fireman57]

Re: breaking down when cool

You may have missed some crud in a low speed idle jet, you may not have your low speed set correctly, you may still be sucking air from somewhere. Did you get an OEM manual yet? Did you actually replace all the gaskets and use a carb kit? Like DHP said some of these like the low speed turned out more than others. 1.5 turns is a starting point. Have you removed the idle screw (if it is removable) and checked for scoring at the tip?

 

[Curl]

Re: breaking down when cool

I have purchased a Manual and it says the slow speed mixture should be 2 turns out for TR Carby, but at this setting rpm's are way down that it won't idle and it runs too rich(smoky). I did not replace the gaskets when i dismantled the carby's because they all appeared in good condition, but i did clean out with compressed air. However i will replace them and let you know how i go. What i can't understand is that the issue appears to be temp(thermostat is ok) related.<br />Thanks again.

 

[Curl]

Re: breaking down when cool

Well.....i've had a local marine mechanic have a look and he is fairly confident that it is not fuel related.I replaced with the correct Champion plugs(Gapped at .030") and rechecked all fuel connections(replaced connection at motor also)and while the problem still exists it definetly idles better. Thermostat is operating OK. Because it only runs rough under load and when cool, it's time consuming as you can understand. I'm going to replace Spark Plug leads next and move on from there.<br />Will keep in touch, thanks for your help to date.