3 L Mercruser 1996 hard to start when hot

[bayliner1996blue]

Hello, new to forum. Did not find any similar post in archive. I have a 1996 4 cylinder (3 LX) mercuser in my 19' bayliner. The motor start on first crank when cold. When running no issues. Top speed reads 46 mph, which is consistant with boat manual.

My problem is when I motor shut off hot, it is very difficult to restart. The only why it will restart is white the throttle fully engaged (in neutral of course). In this position my electric chock is closed (only time observed chock is closed when hot). This conditon exists weather the motor is breifly shut off (seconds) to over an hour (engine not fully cooled).

I know I have a carb problem, and planning on rebuild it. I would like to know what mostlikely has failed within it so I can verify when taking apart.

The thing I am having trouble understanding is why when cold the engine can be started, stopped, and restarted with no issues and then when hot has problems. It must be something to due with the fuel ratio, but the engine runs well when going. Very fustrating!!!

 

[Don S]

Re: 3 L Mercruser 1996 hard to start when hot

Could be the choke doesn't work, and is always closed. Makes i5 run poor too. Or it's just adjusted way to tight.
After the engine has set overnight, open the throttle (engine NOT running) to about 1/4 or less throttle, but not full idle. Then adjust the choke so it JUST closes, then add 1 additional mark.
Start engine and watch to make sure choke opens. Then shut it down. It should stay open till the choke housing cools down.

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

I thought the chock what only used when the engine is cold. Should the chock be closed during a warm start?

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

Mine is a 1997 and has somewhat of a similar behavior. I just finished working on my choke so it operates correctly which is great, but it's the hot starts that I'm trying to improve. The engine fires up right away cold, and fires up every time when hot with a couple pumps, but I'm trying to eliminate needing that priming if I can (especially for other drivers). I've read a lot here about carb rebuilds including this thread: http://forums.iboats.com/showthread.php?t=181805 which was great reading, but I would be interested in reading additional input on potential areas to check.

The only other thing the engine experineces is a slight hesitation about 1/3 throttle. It's short, but there. Other than those two things, the engine runs great.

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

Sounds like we have similar problems. I also have the hestation at around 1/3 throttle also. I orginally was thinking one of the vent port in my carb was blocked and a rebuild carb would fix everything. Now I am not so sure. Someone else in the forum has similar problems after 2 carb rebuilds.

I am now leaning more toward the chock as the problem. On my engine, the chock only closes when hot at full trottle. I would think at monentary shut offs with a hot engine should restart without the chock on.

Hopefully someone in this forum has has a similar problem and corrected it.

 

[Schmoe]

Re: 3 L Mercruser 1996 hard to start when hot

I had those issues on mine a while back. I pretty muched adjusted the electric choke, set it to more lean position and that seemed to fix the problem. One thing I've noticed on these engines, if you run it hard for a while and then shut down without letting it idle for a few minutes, it is harder to crank and will diesel from time to time. I think it's just their nature as we are asking that little 3.0 to do a lot of work.

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

I would think at monentary shut offs with a hot engine should restart without the choke on.

Agreed. I'm replacing plugs and going to do a carb kit to see where that lands me. As for the choke, just last week, I worked on mine because it appeared it wasn't operating/closing correctly (even at cold). Even though I originally thought it was moving freely... apparently, there was another level of "moving freely". I pulled the choke shaft out, cleaned it and the housing, and reinstalled which allowed it to move freely enough to properly close. I think that helped my cold starts, but like you... would like my hot starts to fire right up (no pumps) which makes skiing more enjoyable for certain.

I read a lot about users of the 3.0 pumping/priming at starts etc., but I can't tell if that's something that just works or if this engine required that even when they came off the showroom floor. If they started right up off the showroom floor, there's hope.

I believe mine's running rich and the plugs look a little black (not wet though). More of a dry black build-up, so I'll also try to balance the idle mixture with a good idle position. Kind of ironic though... seems to running rich, but doesn't fire right up when hot.

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

I am going to through this one out there. I just talked to my buddy and he said he had something similar happon on his harley. He said it was vapor lock due to a fuel line collaping. I am not sure if a capapsed fuel line could cause this problem as my engine runs well when running. Perhaps at lower RMP a resticted fuel line could lean out my fuel and having the choke closed would increase my fuel ratio. It is possible that a warn engine would soften a fuel line comparied to a cold one.

Regarding the lean choke, my choke is set at the tap of the choke and the carb tabs even (not two advanced as the service manual states). This would already give me a lean condition. I was going to try moving it back to the two advanced spot to see what would happon.

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

Update: Today, I installed a new set of NGK spark plugs. I gapped them to .035. Before hitting the lake, I also topped off the tank (about 4 gallons) of 93 high-grade gas. I usually don't run the 93 gas. I must say... we had much better luck today and had successful hot-starts almost every time. I still have that hesitation in the throttle, but will continue to work on that. I've got a carb kit on the way, so I still plan to do that (when, depends on how it performs next time). Maybe that'll be a post-season job. One thing I noticed today after changing the plugs and adding 93 gas was that we had a higher idle immediately, so I lowered that using the idle screw. I also found here online that there was a service bulletin about the gap being changed to .045, so I may increase the plug gaps and see if the performance continues to improve.

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

Stopped by a mariena and talked to a mechanic. They were extreamly busy and thought it was a vapor lock problem. He suggested the choke and idle screew needed adjustment. He also suggested adding clothes pins to the fuel line to reduce the heat.

As for the spark plug gap, is it supposed to be 45 not 35?

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

I'll check my own fuel line. I know it runs quite closely to the block, so it indeed could be picking up too much heat. I'm not sure if that's the original path of the line or if it's been shortened/re-routed by the previous owner. I had to do a search on the clothes pin theory and it appears to be an old trick for insulating the fuel line (probably because when it began, clothes pins were everywhere as well as easily attached). Maybe I'll see about a shielding the line a little from the block.

As for the plug gap, I believe .035 was the original spec and then was later updated to be .045 The bulletin was Service Bulletin 2006-03, but I'll have to try to relocate the link. The gap depended on serial number of the engine. I gapped mine at .035 before locating the bulletin, but may adjust.

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

I re-read your previous post on changing the plugs and octane ratio of your gas and seeing improvements. Were the plugs a different heat range?

Regarding the octane ratio, it is my understanding that the higher ratio gas only prevents predetination. I do not believe I am having this problem. My problem is fuel starvation. I think you should try the 87 gas again on your next fuel up to see if there is a difference (will save you some money at the pump).

I don;t know if you saw my last post, by my mechanic told me that my issue was mostlikely a carb tuning problem and not a rebuild problem. I believe you mensioned wanting to rebuild your carb. I thought of that too, and would be more that willing to do if it helped my problem. My mechanic didn't directly tell me, but implyed it wouldn't help (he sell the rebuild kits so it would have been in his best interest finiacially to sell me the carb kit. He as given me excellent advice in the past so that is why I am leaning on his suggestion).

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

Update, Cleaned out my carb filter (small amount of girt) and removed my choke. Messed up the choke install (basically no more choke) and the engine restarted fine with zero throttle. Suspect choke is part of my problem.

Anyone know how to test an electric choke? Is the choke electric solely for the purpous of opening sooner when cold (choke coil not heated up yet). I see no other use for the electrical aspect of this thing.

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

See response to your post in the other thread about the choke: http://forums.iboats.com/showthread.php?t=336865

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

Thanks Startwork for the break down on choke operation. Turns out I had it right after all. When I was messing around with the motor last evening, it was starting without primeing when hot. This was with the choke fully open. I would like to think I corrected the problem, but doubtfully. I had the motor cover off and it was a cool evening so if heat was causing my problems it was not present.

Watching the choke open when I put the key in the ignition (not starting motor) I saw the choke open (cold engine) in about 1 min. This leads me to believe it is possible if your engine does not fire right way, you could in attempting to start your engine several times, heat your choke coil up to a full open position making it much harder to start.

Looking at how the choke works, I have no idea how in the past I was able to have the choke close when the engine was hot at WOT? The choke coil should have pervented this from happoning. One thing I noticed was my choke tab marks were dead even . I am going to try advancing the choke 2 ticks clock wise to give a little less choke.

 

[smartwork]

Re: 3 L Mercruser 1996 hard to start when hot

This leads me to believe it is possible if your engine does not fire right way, you could in attempting to start your engine several times, heat your choke coil up to a full open position making it much harder to start.

I've not had any difficulties starting cold (which is when the choke is closed). My difficult starts were only when the engine was hot which is when the choke should already be open from the engine having been running and hot. My last trip had successful starts (hot and cold) after changing the plugs and adding the 93 gas, but I'm still going to do some additional cleaning/tuning to see how good it can get. I'll also try going down in gas octane again (like you mentioned) to help decipher what is actually solving the starts.

 

[victorc1]

Re: 3 L Mercruser 1996 hard to start when hot

Hello, Read your post and I hope you fixed the problem you have with your choke. I have a 1996 Monterey 180 SCR with a 3.0 LX Mercruiser Alpha One Gen II and my top speed is 35 MPH. I read yours does 45 and its a 19". Any tips on how to bring up the MPH's?

 

[Bilgamesh]

Re: 3 L Mercruser 1996 hard to start when hot

I had a problem with mine that is pretty much what you guys are describing. I found the carburetor was dribbling fuel after shutdown which was flooding the motor. I was told that opening the throttle introduced enough air back into the mix to get it started. Please forgive me if I have misread your problem, or FWIW, read the thread here:

http://forums.iboats.com/showthread.php?t=328127

 

[bayliner1996blue]

Re: 3 L Mercruser 1996 hard to start when hot

bilgamesh, did rebuilding your carb help with hot starts? I read somewhere were someone removed the choke altogher during warm weather.

victor, what size and pitch prop are you using. 44 mph is what is listed in the bayliner brocure for my boat. My top speed is 46 (no wind) and the trim almost all the way out. With the trim all the way in, 35 is around top speed (this is all at around 4400 rpm).

 

[Bilgamesh]

Re: 3 L Mercruser 1996 hard to start when hot

It is easy to get sidetracked down a bunch of blind alleys, and I don't want to cause you to do that. I did, and chased a phantom "ethanol fuel and vapor lock" problem. Therefore, do not dismiss any of what has been offered by others in deference to my experience. However, I can tell you with absolute certainty that I have a 3.0L with a Mercarb that was hard to start when hot. It would start if I gave it some throttle, and run fine. I looked in the carb after shutdown and saw fuel dribbling. I rebuilt the carb, and I can no longer see fuel dribbling, and the hard starting when hot problem is gone. Good Luck!