Merc 3.0 Idle Issues

[jsmaeb1215]

Picked up a 96 stingray with a merc 3.0 this spring. It is my first boat so I am doing my best to read over the forums and learn as much as possible from all you great folks.

I am having a bit of an idle issue. Cold starts are a bit rough, I typically have to apply throttle for the first minute or two until it warms up. Once it warms up it will idle "ok".

It seems the best I can get the boat to idle at once warmed up is around 900rpm, from what I have read 700 is the number I should be shooting for. All of this seems to indicate the carb needs a rebuild. I am pretty sure this is the kit I should be looking to pickup.

Carburetor Kit for Mercruiser, GLM 76086 - Sierra 18-7098-1 - iboats

One other issue I noticed, 1 of the 4 nuts holding the carb down is missing. I don't have one that fits off hand so I will have to snag one from a local store, not sure if this is really my issue. I appreciate any and all input.

 

[Bondo]

Re: Merc 3.0 Idle Issues

Picked up a 96 stingray with a merc 3.0 this spring. It is my first boat so I am doing my best to read over the forums and learn as much as possible from all you great folks.

I am having a bit of an idle issue. Cold starts are a bit rough, I typically have to apply throttle for the first minute or two until it warms up. Once it warms up it will idle "ok".

It seems the best I can get the boat to idle at once warmed up is around 900rpm, from what I have read 700 is the number I should be shooting for. All of this seems to indicate the carb needs a rebuild. I am pretty sure this is the kit I should be looking to pickup.

Carburetor Kit for Mercruiser, GLM 76086 - Sierra 18-7098-1 - iboats

One other issue I noticed, 1 of the 4 nuts holding the carb down is missing. I don't have one that fits off hand so I will have to snag one from a local store, not sure if this is really my issue. I appreciate any and all input.

Ayuh,... The missin' nut could/ will no doubt possibly cause a Lean condition,...

It also sounds like the choke might need adjustin',...
It's in the manual,...

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Ayuh,... The missin' nut could/ will no doubt possibly cause a Lean condition,...

It also sounds like the choke might need adjustin',...
It's in the manual,...

Appreciate the input, I will check out the manual. I left out a few key peices of info.

Engine SN#: 0F753377
Drive SN#: 0F721062

 

[havoc_squad]

Re: Merc 3.0 Idle Issues

There's a good video on rebuilding a standard 2bbl Mercarb, it does not cover every subject or the specifics of the model of the Mercarb you have, BUT it does give a good walkthrough.

https://www.youtube.com/watch?v=JHjjAz367Ng&list=TLbmGEWv_PBvc

Make sure you find the correct service manual instructions for that carb and compare it with the rebuild kit's info. They should be 1 = 1 in the specs. (Float height, float drop, etc.)

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Appreciate the video, that really helps out!

Today I am going to pin down a new nut to put on the carb and see how she runs. Allthough i don't have very high hopes, you just never know.

What is the best way to pin down what model carb I have? The carb has the following numbers stamped on it.

13898490
3901

 

[smassey22180]

Re: Merc 3.0 Idle Issues

I had similar issues last month with my carb. This is the kit I got. It will work for your part number also. MerCarb Marine Carburetor Repair Kit - Mercury Marine

 

[r.j.dawg]

Re: Merc 3.0 Idle Issues

Just in case you don't have it, here's the manual for your engine.
Boatinfo - Mercruiser Service Manual nr. 13 - 1990-1997 Engines GM 4 Cylinders

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

I had similar issues last month with my carb. This is the kit I got. It will work for your part number also. MerCarb Marine Carburetor Repair Kit - Mercury Marine

Interesting that kit is $15 more than the one I listed from here on iboats. Is the one I listed more of a generalized kit?

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Well I found a nut which would fit the carb. Started the boat and got her up to operating temp, went to let it idle and it just died. I set the idle screw, and air screw back to the suggested settings in the manual. Once I did that it was idling, only issue is it seems my tach has now stopped working. It definitely seems to be running different but without any rpm's I can't do much.

Any suggestions or idea on what I could use to get a solid rpm reading? I don't have a very nice timing gun with the rpm readout's.

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

I wanted to add one thing. The rpm gauge works when I rev it up, but at idle it just drops to 0, very odd as it has never done that before.

 

[Bondo]

Re: Merc 3.0 Idle Issues

I wanted to add one thing. The rpm gauge works when I rev it up, but at idle it just drops to 0, very odd as it has never done that before.

Ayuh,... Sounds like the Tach itself,... give it a Ta-pity tap,...

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Ayuh,... Sounds like the Tach itself,... give it a Ta-pity tap,...

I tap it and it just bounces up to 4-5k, then drops back to nothing. Tomorrow I am thinking I will try to check the wiring on the back of the tach. Other than that, I am thinking I need a new one?

I must say that just even on the muff's the boat feels different with the carb tightened all the way down. Even the sound has changed a bit. Overall much better.

All the input is a huge help, appreciate it!

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Pulled the dash to check out the tach. Everything looks nice and tight with no corrosion. I also gave the tach's engine selector a few spins as I have seen that suggested quite a few times.

I was quite surprised at how many wires was coming off the back of the tach. I was only expecting 4 or so.

Might just go bight the bullet and pick up a tach.

 

[sti1471]

Re: Merc 3.0 Idle Issues

trace the wires from the tach to the engine. where it connects to the engine, make sure the connections are not only tight, but clean. if you can, remove them and clean them with a wire brush and install them again. Clean all the connections on the back of the tach as well. Check all the connections on the coil as well. In the manual number 13 posted above, go to page 255. that is your wiring digram to help you trace the issue.

it could be dirty and when you rev the engine the volts are high enough for the connections to get a reading, but at idle the volts drop and the connection is not good enough to get a reading.

If this fails to work, then it sounds like the tach needs to be swapped out.

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

trace the wires from the tach to the engine. where it connects to the engine, make sure the connections are not only tight, but clean. if you can, remove them and clean them with a wire brush and install them again. Clean all the connections on the back of the tach as well. Check all the connections on the coil as well. In the manual number 13 posted above, go to page 255. that is your wiring digram to help you trace the issue.

it could be dirty and when you rev the engine the volts are high enough for the connections to get a reading, but at idle the volts drop and the connection is not good enough to get a reading.

If this fails to work, then it sounds like the tach needs to be swapped out.

Went and snagged a new tach from Bass Pro. Installed, and now the boat won't start. I am pretty sure the tach is working, when I turn the key on it resets to 0 and while turning the motor over the needle is jumping with the turns of the motor.

My plugs are quite soaked in fuel, so I don't think fuel is the issue. I am thinking spark, could the tach prevent the boat from starting in anyway?

I had a single grey wire, 4 blacks, and 4 purples. The purples are going to the post labeled sensor, the blacks are going to the post labeled grn, and the grey is going to post engine.

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

Yep sure enough, when I took the old tach out I just looked at what wires were hooked up to what post. I never thought to compare the actual speedo's themselves, the sender post and ignition post were switched. I went ahead and made the change so now the gray wire is on the sender and the purple's are on the ignition. She still isn't firing. All I smell is fuel, so I am thinking she is just real flooded. Going to give it a try tomarrow and if need be replace the plugs. I guess its not my day, one step forward and 3 back! Appreciate the help guys.

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

I just keep striking out and making things worse. Went to mess with the boat a bit this afternoon to see if it was no longer flooded. Hooked it up to the muffs and started to turn her over, as I was doing this I heard a click and all went dead. Peaked my head under the dash at the fuses and my 10a ignition fuse was blown. Put a new one in, soon as I turn the key, blows the fuse. Obviously this is some type of short, I looked over the rpm gauge again and all seemed well.

I am stumped and frustrated at this point. Maybe I should try removing the new rpm gauge and putting the old one in place. I amm 99.9% positive I have the gauge hooked up right. Purple being the ignition, grey being the sender and black being ground. When I had the send and ignition wire's crossed last night could that have killed the gauge, and now that I have it hooked up right, its shorting out?

If I understand things correctly, it is going to be a number of things.

1. Gauges
2. Coil
3. Alternator
4. Choke

I feel this diagram confirms that I have the guage hooked up correctly.

http://stingrayboats.com/products/pdf/wiring/180RS_wiring.pdf

I did attempt to disconnect the choke already without any luck. Does this sound like the correct direction to go in?

 

[oldjeep]

Re: Merc 3.0 Idle Issues

Maybe I should try removing the new rpm gauge and putting the old one in place.

That would be the first thing I'd do.

 

[sti1471]

Re: Merc 3.0 Idle Issues

What is the make and model of the new gauge you bought?

if your plugs are "soaked" with fuel, then I am guessing it is getting flooded for some reason. especially if you are smelling fuel.

put the old gauge back on and see if the boat starts up. if it does, then there might be some type of wiring in that gauge that is not compatible with your wiring.

One thing you can do is take the #1 cylinder spark plug out of the engine. Plug the spark plug into the spark plug wire and turn the key. you should clearly see a good spark and hear the clicking sound of the spark. If there is not spark, remove the new gauge and install the old gauge and turn the key again. Does it spark with the old gauge installed? If not then take the coil spark wire off the distributor cap and put it next to a ground or insert a spark plug in the end of the wire and turn the key and check for spark.

Also, my 3.0L engine has a red button back in the engine bay and it says "push to reset". try to push that and see if that breaker just flipped and needs to be reset.

 

[jsmaeb1215]

Re: Merc 3.0 Idle Issues

What is the make and model of the new gauge you bought?

if your plugs are "soaked" with fuel, then I am guessing it is getting flooded for some reason. especially if you are smelling fuel.

put the old gauge back on and see if the boat starts up. if it does, then there might be some type of wiring in that gauge that is not compatible with your wiring.

One thing you can do is take the #1 cylinder spark plug out of the engine. Plug the spark plug into the spark plug wire and turn the key. you should clearly see a good spark and hear the clicking sound of the spark. If there is not spark, remove the new gauge and install the old gauge and turn the key again. Does it spark with the old gauge installed? If not then take the coil spark wire off the distributor cap and put it next to a ground or insert a spark plug in the end of the wire and turn the key and check for spark.

Also, my 3.0L engine has a red button back in the engine bay and it says "push to reset". try to push that and see if that breaker just flipped and needs to be reset.

Here is what I have done so far.

1. Disconnect all wiring from tach and test turning key to on
- The 10a ignition fuse no longer blows

2. Returned "New" tach for another new tach
- Still same issue, blow 10a ignition fuse

3. Installed original tach
- Still same issue, blow 10a ignition fuse

4. Attempted to start with tach disconnected
- Wouldn't fire, plugs soaked

At this point I am stumped, how I managed to install a gauge and really mess something up.

I am not sure if it will even work, but I tried turning it over with the gauge disconnected and it wouldn't start either. I checked my breaker but I am unable to push it, should I be able to push it even if it doesn't need a reset?



UPDATE

Just tested for spark. I don't see any spark with the gauge disconnected, or just the sender/ground wires connected.