Troubleshoot/confirm idle issue

[LandOfRath]

Picked up a lightly used 03 Smoker craft with a 75hp 4 stroke motor.. went through everything and got it running pretty good after it sat a few years. Occasionally after it's really warmed up it will die when put into nuetral and can be a pain to restart. I changed all the plugs and it seemed like it was better.
Yesterday I took it out to the Columbia River and drove about 60 miles just exploring and cruising to get a good feel for the boat with no issues.. got back to the dock, put it into neutral and it died. Could not get it to run without upping the throttle and died before I could get it into gear. So I went ahead and pulled it on the trailer and took it back home well this morning put the hose on it, fired right up..

My gut is telling me it's the IAC valve, is there any way to test the valve or do you have something else I should check before I blow over $100 on a new one.

Thanks

 

[QBhoy]

Is there a shift switch on that age of 4 stroke ? If your cables are tight, that can result in an issue with that. It certainly does on the newer merc anyway. Could be the IAC too, you’re right. But I think it would run fast idle or iratic idle as a tell tale.

 

[LandOfRath]

Is there a shift switch on that age of 4 stroke ? If your cables are tight, that can result in an issue with that. It certainly does on the newer merc anyway. Could be the IAC too, you’re right. But I think it would run fast idle or iratic idle as a tell tale.

Not sure on shift switch.. it start and idles perfect when cold... Zero issues when I'm driving it it's just after it warms up putting it neutral

 

[QBhoy]

Not sure on shift switch.. it start and idles perfect when cold... Zero issues when I'm driving it it's just after it warms up putting it neutral

Got you. To be honest, I’m not too up on this early era of engines…but if it has a throttle position sensor, could be related to that. Or even a temperature sensor can have an effect on the way these run. So if it thinks it’s cold…it can run a richer fuel mix. Maybe your temp sensor is having issues and over fuelling or the equivalent of choking the thing ?

 

[LandOfRath]

Im looking for the service manual atm.. I cant even find the IAC valve on the motor.. Feeling dumb lol

 

[QBhoy]

Just realised you didn’t say the age of the engine. Just the boat. I presume it’s the same age ?
I have a 2016 merc 4 stroke 115 that’s the same basic engine as the 75-115, if it’s as new as mine. If it is, the IAC is on the starboard side of the engine nearer the top end of it all. Wee plug goes into it. If it is the same or similar to mine…there is also a fuel strainer filter type thing in the end of the fuel rail, that often gets missed from maintenance actions. Every 300hours I think it should be looked at. And even if it’s older than mine…but still fuel injected…you likely have one too…as well as a VST that may have a strainer in it for the fuel pump.

 

[LandOfRath]

The sticker on the motor says NOV 2004.. I When I search the part I cant find a part that look like that..

 

[QBhoy]

The sticker on the motor says NOV 2004.. I When I search the part I cant find a part that look like that..

Think that also says it conforms to 2005 regs too. Must be ahead of it’s time, haha. Is it fuel injected or carb ? Any serial number info ? It’s defo older model than the newer ones from 2014 onwards. Given it’s CC displacement there. I’d imagine you may have an IAC. Could well be that causing this. Think that age of engine might be the same thing underneath as the Yamaha engine. If it helps.

 

[LandOfRath]

It looks like it has 4 carbs

Model# 1F75412D3
Serial #1E000024

 

[LandOfRath]

I originally thought it was injected for some reason, but its clearly not.. But I still don't think its a carb issue since it starts and idles just fine when not fully heated up..

 

[LandOfRath]

Could this be a vapor lock issue? I ran that motor around 4k rpm for a long period to get back to the dock. then lower rpms for a few minutes then it died soon as it went into neutral and became hard to start.

 

[QBhoy]

So maybe I am looking for an idle speed control valve since not fuel injected

Could this be a vapor lock issue? I ran that motor around 4k rpm for a long period to get back to the dock. then lower rpms for a few minutes then it died soon as it went into neutral and became hard to start.

Not impossible…but unlikely Perhaps. Hate to be the voice of doom…but if it’s not ran right since then…you should maybe do a compression test on her.

 

[LandOfRath]

Not impossible…but unlikely Perhaps. Hate to be the voice of doom…but if it’s not ran right since then…you should maybe do a compression test on her.

No it fires up and sounds great right now, only acts up when the motors hot.
Like starts within a crank or 2. I am going to pull the new plugs and see how they look.

 

[QBhoy]

Should maybe check the fuel pressure too.

No it fires up and sounds great right now, only acts up when the motors hot.
Like starts within a crank or 2. I am going to pull the new plugs and see how they look.

good idea. Might be an idea to check the low pressure fuel lift pump too. Make sure it’s ok once warmed up and idling

 

[QBhoy]

Should maybe check the fuel pressure too.

No it fires up and sounds great right now, only acts up when the motors hot.
Like starts within a crank or 2. I am going to pull the new plugs and see how they look.

good idea. Might be an idea to check the low pressure fuel lift pump too. Make sure it’s ok once warmed up and id

 

[LandOfRath]

Plugs look great, noticed oil was a bit over filled not a lot but I just corrected that. Oil itself looks perfect..

I am currently looking for a pdf of the repair manual for this motor

 

[LandOfRath]

More and more thinking this is a dirty carb issue. The low speed jets probably need cleaned.. When its cold I think the enrichening system is compensating for the dirty jet, but when warmed up that closes off and starves out the engine. At least that is where my brain is leaning.

 

[flyingscott]

You need to be looking at those carbs. Get a factory. manual

 

[LandOfRath]

You need to be looking at those carbs. Get a factory. manual

Already got one, and that is what I said I think the problem is.

 

[flyingscott]

The early 4 strk carbed motors were notorious for carb problems. Most of it was because they were so lean at an idle.