1999 75hp choking at idle

[milehighboater]

I have a 1999 75hp 3 cyl 2 stroke that doesn?t like to idle around in gear that much. I can leave in running at idle in neutral for hours but when it is in gear ie. when I am in a no wake or trolling it will bog down and die. It will run for about two minuites in gear before it bogs down and I can bring it back momentarily if I hit the key in to choke it but if I don't throttle up it will die. The bulb goes soft but never flat and the motor will start up without much problem with a bit of throttle. I have recently replaced the fuel filter, coupling and bulb. It is on a tracker 175 with a permanent tank so there is no fitting there, and the tank has a breather line going to the fuel fill that doesn't appear to be blocked by anything either way there is no change when I run it with the gas cap off (I was checking for a vacuum). The last thing I was going to replace was the fuel pump diaphragm but wanted to see if I missed anything. I brought the boat up from Missouri about 6 years ago had it re-jetted and I don't think the guy did a very good job tuning the idle mixture, any good procedures for that? I think the carbs are good and clean, there is no leaks I can see and I have winterized/decarbed it about once a year. After it gets above about 2000 RPM she runs like a champ, like I said earlier it will start quick and idle in neutral for hours. Anyone that would like to throw around some ideas would be much appreciated. Thanks.

 

[Bondo]

Re: 1999 75hp choking at idle

Ayuh,... It seems obvious that it's running out of fuel,...

It is on a tracker 175 with a permanent tank so there is no fitting there,

There's Still a dip-tube,+ should also be an anti-siphon valve there...

The last thing I was going to replace was the fuel pump diaphragm but wanted to see if I missed anything

I'd guess that it Could be the fuel pump, or the Carb...

 

[bball75]

Re: 1999 75hp choking at idle

I had my 2001 Tracker 175 75HP Mercury on the water today with the exact same problem. Will idle fine but when in gear bogs down and stalls. will stay running in gear only if I continually press the choke.The Carburetors were rebuilt 4 mo ago by repair shop any ideas!! fuel pump?
Thanks

 

[milehighboater]

Re: 1999 75hp choking at idle

I think I am going to do the fuel pump. The kits are fairly cheap < 20 dollars and it looks like there is just 4 screws holding the cover on. Does anyone have any tips on the fuel pump rebuild? I would like to keep this post going, there seems to be a few people with this simular engine and problem. I will do the pump and post all results but any tips are always appreciated, Thanks.

 

[milehighboater]

Re: 1999 75hp choking at idle

I just ordered the fuel pump diaphram kit from Iboats. It should be here by April 5th. I will post my results. Still though if anyone has any tips on the rebuild please let me know.

 

[Barnacle_Bill]

Re: 1999 75hp choking at idle

If it is the square type fuel pump be sure to replace the check valves with the new style. They should be included in the kit.

 

[milehighboater]

Re: 1999 75hp choking at idle

Will I know which way to put the valves into place when I see them if I take the old valves out carefully or is it a one way only part? It is the square type.

 

[Barnacle_Bill]

Re: 1999 75hp choking at idle

If you get the kit from Mercury it comes with instructions. Don't know about Sierra.

 

[milehighboater]

Re: 1999 75hp choking at idle

I just got the new fuel pump from Iboats and it is a Serria, no instructions though. Any tips would be helpful there is a few little parts in this kit I can only guess they are the check valves. I will be doing the work on Saturday and I will try to get it on the water by Sunday and will let everyone know how it goes.

 

[Silvertip]

Re: 1999 75hp choking at idle

Have you adjusted the idle mixture and idle speed? If the engine runs fine at faster speeds it is highly unlikely the fuel pump is the problem. The carbs may also be due for a thorough cleaning and rebuild.

 

[lostinboat]

Re: 1999 75hp choking at idle

my manual says to start the engine and allow to warm up. make sure engine is in water not on muffs. place engine into forward gear at idle, always start with top carb first then middle carb then bottom carb. seat the idle screws and turn them out 1 1/8 turns.slowly turn idle screws 1/8 turn counterclockwise pausing at least 10 seconds between turns, until engine becomes rough.note the position of the screw slot. then slowly turn idle screws clockwise 1/8 turns pausing 10 seconds between turns until the engine becomes smooth.cont.this step until engine slows and or misfires.note the position of the screw slot. now turn the screw to the middle of the two positions. hope this helps

 

[milehighboater]

Re: 1999 75hp choking at idle

Thanks for the setting tips. On sunday when I test the new pump kit I will run around for a bit and then get it back on the trailer and do the carbs and see how it does, thanks for all the help guys. I will make sure to keep the post updated with the results.

 

[4JawChuck]

Re: 1999 75hp choking at idle

Make sure your carb sync is on the money and your base timing is correct, the three cylinders are sensitive to those and the idle mixture. You need a helper to hold the throttle plates closed to sync the carbs properly, i found it impossible to get it perfect by myself.

I have a 2003 model and had the same issues, my pump was fine and all it needed was some dialing in of the idle mixture, sync and timing. I also replaced the plastic connectors for the timing advance mechanism as they get loose and the timing jumps all over the place since they idle rough compared to a 4 or 6 cylinder. Squeeze some silicone grease into the connectors after they are assembled, cures the timing jumping at high rpm.

Don't forget to set the throttle cam roller afterwards since it affects idle speed once the engine goes into gear if its too close, I found 0.015" clearance perfect so you can shift into gear without the throttle advancing before you want it to. There must be clearnace there at idle out of gear or it won't work properly and will clunk going in and out of gear.

One other note, the manual list setting the upper carb idle mixture different than the lower cylinders but I found it runs better with them all the same. Its done to assist cold starting but I found it hurt more than it helped. My carbs ended up at 1 1/16 turns out on all three but I am at 800ft elevation so yours might be different.

Good luck.

 

[milehighboater]

Re: 1999 75hp choking at idle

4jawchuck, thanks for the tips. Can the timeing get out of wack if it hasn't been touched before? I know the carbs are out of wack, when the boat was brought up from missouri (I am at 6000 feet) I needed to re-jet the carbs and I have found many "small" mistakes the tech made when he did the job. The fuel line was routed so it was kinked on the throttle linkage, the air cleaner was left loose, and he never replaced the fuel which I paid him to. More than likely thats why they are now out of bussness. So how do I get the three carbs synced? Is it something I can do without any special tools? Thanks for the help.

 

[4JawChuck]

Re: 1999 75hp choking at idle

Syncing the carbs is done by closing the throttle, some one holding the plates closed (you need to remove the airbox cover to see them) and then loosening the lock screws on the throttle assy that locks the linkage together so they operate in sync, make sure you take the slack out of the linkage as you do this...hence the need for a helper to hold the plates closed while you do all of that.

When I got my motor the timing was supposed to have been done and when I checked it was close. I found the linkage ends were so loose that at rpm the timing was all over the place which made setting it accurately impossible(Yes I hung off the back of the transom at WOT while the wife drove the boat while I checked the timing with a timing light).

Once the linkage ends were replaced and packed with silicone grease the timing was steady as a rock and was 3 degrees out, the factory plastic ends are horrible and a poor design but the grease takes all the play out which makes the motor run so much better at idle and above. I reset the timing properly and then had to adjust the throttle cam roller clearance, the throttle and timing linkage are adjusted together so make sure everything is done again after the timing adjustment.

After all that is done reset the idle mixture, timing affects how the motor runs at idle and in the end I could turn the screws in an extra 1/16 of a turn. Mine runs like a top now and purrs at idle in and out of gear cold or hot. The fact it runs so well means I can idle the motor at 650 rpm which makes going in and out of gear a non event not a huge clunk.

The gods live in the fine tuning, taking the time to do it right pays off. Its too bad Merc uses such a poor linkage design, if I had the time and was going to keep this motor I would swap out the plastic ends and use professional quality heim balljoint ends in their place but this 90HP is getting swapped out for a 200HP Merc and that one is going to get the heim joint ends when I fine tune her.

 

[milehighboater]

Re: 1999 75hp choking at idle

Thanks for the timing tips, I found the linkages from merc and they only have the tower side, I'm not sure why but there is no option to buy the stater side. Right now they are packed withy grease and still feel tight. If there is a place you know I can purchase some nice brass ones let me know. I find it hard to beleve merc would make such an important part plastic, but they did. At least it is only 5 dollars. I got the fuel pump rebuilt, new impeller, changed gear oil, engine decarbed and trailer barrings packed just to realized sunday was Easter. Needless to say the wife wasn't as open to me heading to the lake when 10 inlaws were comming for dinner. I am hoping to get out on Wednesday or Friday to see if there is any inprovment. I will keep everyone posted.
Oh, I know an impeller and gear oil wouldn't fix anything but I figured I would get some PM done while I was at it.

 

[milehighboater]

Re: 1999 75hp choking at idle

I am proud to say the fuel pump fixed the low throttle, in gear, dieing problem. To narrow down the primary cause I waited to do the decarb after testing the fuel pump. The problem was solved with the pump but decarb helped smooth out the idle even more. I trolled around for 20 minuites without a problem, before I couldn't go for more than 2 or 3 minuites without it acting up. I would like the thank 4jawchuck for the syncing tips and the heads up about the timing, i will keep an eye out for that, and lostinboat for the idle mixture steps. And bball75 if read this do the pump, it only takes about 45 minuites when you are REALLY careful, and costs under 20 dollars. Just pay attention to the direction in which everything fits together. If you need a good diagram use the one of of mercury parts direct. It will help you align everything up correctly. Just remeber all the arrows on the side line up with each other. Also you might want to get the merc part, the serra set came with relief valve post that didn't want to lock into place and I ended up making the original post work by pushing the center out and reusing them. Thanks everyone!