Merc135v6 1988 - Sluggish start and then it's fine...Why?

[strippingguards]

When I start a day of boating, each time I begin - my engine only gets up to about 3900 rpms at full throttle - not even enough to get up on plane. Then - after about 5-10 minutes at full throttle(it varies each time) it kicks in and gives me the full 135hp and about 5000 rpms.<br />For the rest of my boating day I can immediately jump back up to the full rpms at full throttle but why does this happen consistently to me in the beginning? I do give sufficient warm up time in neutral (5-10 min)before trying to get up on plane.

 

[Hooty]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

Sounds ta me you may have a dead hole when it's cold, Doug. Sure way to find out is motor around for five or so minutes while the engine is struggling at WOT. Shut it down and pull plugs, noting what plugs came from where. Look for one or two plugs that look different from the rest. Maybe wetter or drier. If wetter, that plug is not getting fire. If drier, it's not getting fuel. Have a look and let us know.<br /><br />g'luck & c/6<br /><br />Hooty

 

[strippingguards]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

Hooty<br />Thanks for the suggestion. I will try this the next time I'm out.<br />Question: What can I do if there is a problem like the one you are describing? Is there a quick fix?<br /><br />Thanks

 

[strippingguards]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

bump

 

[Hooty]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

Probably will be relatively easy ta fix. Could be a fuel pump, dirty carb, stuck thermostat or some minor ignition problem. Nothing major though.<br /><br />c/6<br /><br />Hooty

 

[Greg22]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

Doug,<br />I had the same type of issue on my 90 model Johnson 150. I had recently noticed that one of the plug wires was broken. So I change it. After I changed it the engine would run rough until it warmed up and then run good. Trying to understand what was going on I decided to ohm out all off the plug wires and discovered that the resistance on all of the plug wires was about 2 to 3 ohms except the plug wire that I had recently changed. The resistance of the changed plug wire was 4.5K Ohms. I went to the OMC dealer and purchased a plug wire with low resistance like the others and went and ran the boat on the H2O and it ran great. I was told that Johnson engines would not support automotive high resistance plug wires until 93 and newer models. Have you recectly changed amy of the plug wires? I should mention I am not sure it the same is ture for Merc's??? Just my experince...

 

[strippingguards]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

I have not changed any of the spark plug wires (since I have owned it) but it sounds interesting to check the resistance of the wires. How can I do an ohm check like the one that you described? <br />Also - is it necessary to check the compression - if so how do I do that. Thanks - anyone answering would be helpful here.<br /><br />As an aside, this web site is fantastic. The advise that I have been getting from everyone is so helpful. I should have my motor purring like a kitten pretty soon. Thanks!

 

[Greg22]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

Doug,<br />Doing a compression check is easy if you have a compression checker. You can pick one up fairly cheap at a local auto parts store. Remove all of the plugs. You will have to push the compression checker firm against the head or screw the end of the compression checker into the head, where the plugs screw in (depending on which type you use). Crank the engine for two or three seconds and observe the pressure (PSI). Do each cylinder the pressure value should not vary more that about 5 PSI from cylinder to cylinder. <br /><br />To do an ohm check you need an ohm meter. Remove the plug wire place one lead of the ohm meter into one end of the plug wire and the other into the other end of the plug wire. Read the meter. The plug wires should all read about the same. Hope this helps.

 

[sag2]

Re: Merc135v6 1988 - Sluggish start and then it's fine...Why?

I had the same problem with my 1988 merc 135. I ended up replacing a stator and switch box. The dealer suggested that I disconnect the tach, and that seemed to make the problem go away sometimes. I still ended up replacing the parts, but left the tach unhooked.