New owner of a '07 175br - need some advice on motor issues

Deep Ghosh

New Member
Jul 14, 2019
11
Boat Info
2006 175br/ 2002 Dodge Dakota SLT 4.7l V8
Engines
2006 Mercruiser 3.0, Alpha One Gen II Drive
Hey guys,

I just purchased a '07 175br yesterday. The Mercruiser 3.0 would start and then die after 10-15 seconds when the seller showed it to me. I ordered a new fuel filter and spark plugs and installed them today, the motor started up and idled great (I left it running on the hose for a couple hours trying to burn off the old fuel in the tank). I am experiencing a few issues though:

1. When I give it some gas in neutral, maybe around 1/3 throttle, the engine runs for a few seconds then bogs down and almost stalls out, then runs very rough when I dial back the throttle and just idle. Once I turn it off and back on again it it idles fine. Could this be an anti-siphon valve issue? If so, where is that valve located and is it easy to replace?

2. After idling for a while, when I turn the motor off it shakes violently/backfires for 5-10 seconds. It doesn't sound like it's good for the motor... any thoughts as to why it's doing this?

3. The tachometer isn't accurate at all... When idling it shows 4200rpm. I know for a fact the motor is not running that fast, it sounds completely normal while idling. I looked on the back of the tach and the dial is set to 5P, is this correct? If so do I need to replace the guage or is something else causing the issue?

I'm hoping to sort out these issues before taking her out on the water for the first time. Any help or advice would be greatly appreciated.

Thanks,
 
I assume this is a carb motor not fuel injected. If so, floats in carb sound like the are not working properly. Run on after shut off (called dieseling) is very common for this motor, google it. No good fix from what I recall. Decades ago I had one, used to leave it in gear and shut it off so there was a load on engine, always worked but not the best solution. Make sure it has come down to idle and cooled down for a minute before shutting off, that usually helped also.
 
When I give it some gas in neutral, maybe around 1/3 throttle, the engine runs for a few seconds then bogs down and almost stalls out, then runs very rough when I dial back the throttle and just idle. Once I turn it off and back on again it it idles fine. Could this be an anti-siphon valve issue? If so, where is that valve located and is it easy to replace?
Definitely worth checking - I recently had to replace mine, the spring / ball in them gets corroded over time and will cause a restriction. A new one is only about $15, make sure you get the aluminum one for HP > 200. To test/verify this is the problem you can buy a straight through fitting for about $3. The valve is a fitting that screws into the fuel tank pickup on one side and a barbed fitting clamps to the fuel line on the other.

2. After idling for a while, when I turn the motor off it shakes violently/backfires for 5-10 seconds. It doesn't sound like it's good for the motor... any thoughts as to why it's doing this? As mentioned above sounds like dieseling or run on, common in these engines and the 4.3 I have. Here is a tech bulleten from Mercruiser. Basically make sure the correct spark plugs are in it and the idle and timing are set correctly.
http://www.boatfix.com/merc/bullet/97/97_17.PDF

3. The tachometer isn't accurate at all... When idling it shows 4200rpm. I know for a fact the motor is not running that fast, it sounds completely normal while idling. I looked on the back of the tach and the dial is set to 5P, is this correct? If so do I need to replace the guage or is something else causing the issue?
The dial on the back sets the tach to 4/6/8 cyl, not sure what 5P means. Sometimes the contacts get corroded, turn the dial a few times to clean the connections and then set at 4cyl.
 
When I give it some gas in neutral, maybe around 1/3 throttle, the engine runs for a few seconds then bogs down and almost stalls out, then runs very rough when I dial back the throttle and just idle. Once I turn it off and back on again it it idles fine. Could this be an anti-siphon valve issue? If so, where is that valve located and is it easy to replace?
Definitely worth checking - I recently had to replace mine, the spring / ball in them gets corroded over time and will cause a restriction. A new one is only about $15, make sure you get the aluminum one for HP > 200. To test/verify this is the problem you can buy a straight through fitting for about $3. The valve is a fitting that screws into the fuel tank pickup on one side and a barbed fitting clamps to the fuel line on the other.

2. After idling for a while, when I turn the motor off it shakes violently/backfires for 5-10 seconds. It doesn't sound like it's good for the motor... any thoughts as to why it's doing this? As mentioned above sounds like dieseling or run on, common in these engines and the 4.3 I have. Here is a tech bulleten from Mercruiser. Basically make sure the correct spark plugs are in it and the idle and timing are set correctly.
http://www.boatfix.com/merc/bullet/97/97_17.PDF

3. The tachometer isn't accurate at all... When idling it shows 4200rpm. I know for a fact the motor is not running that fast, it sounds completely normal while idling. I looked on the back of the tach and the dial is set to 5P, is this correct? If so do I need to replace the guage or is something else causing the issue?
The dial on the back sets the tach to 4/6/8 cyl, not sure what 5P means. Sometimes the contacts get corroded, turn the dial a few times to clean the connections and then set at 4cyl.

Thanks for the reply. Do you know the size of the anti-siphon valve? 3/8 NPT x 3/8 barb? or 1/4 NPT x 3/8 barb? My motor is 135hp, can I still use an aluminum valve or do I have to use brass? Also do you know where the fuel tank vent is located?
 
I assume this is a carb motor not fuel injected. If so, floats in carb sound like the are not working properly. Run on after shut off (called dieseling) is very common for this motor, google it. No good fix from what I recall. Decades ago I had one, used to leave it in gear and shut it off so there was a load on engine, always worked but not the best solution. Make sure it has come down to idle and cooled down for a minute before shutting off, that usually helped also.

Thanks, if the anti-siphon valve doesn't solve the issue I will inspect the carb
 
Thanks for the reply. Do you know the size of the anti-siphon valve? 3/8 NPT x 3/8 barb? or 1/4 NPT x 3/8 barb? My motor is 135hp, can I still use an aluminum valve or do I have to use brass? Also do you know where the fuel tank vent is located?
Sorry, aluminum is for engines < 200hp, so use aluminum for yours - 1/4" npt and 3/8" barb https://www.wholesalemarine.com/moeller-marine-aluminum-anti-siphon-barb.html. Fuel tank vent on yours is likely the Perko with the vent built in - if you look inside engine room you will see the large fill hose and beside it a 3/8" vent line. You can verify the vent is not the issue by leaving the cap off for a test. Make sure vent line does not have a dip in it where it can hold fuel, should be all downhill to the tank.

Another, couple of things to look at:
1. Buy some carb cleaner and clean the heck out of it, spray it all inside the throat butterfly valves and choke valves and into the float champer.
2. Make sure your choke is opening all the way, it should be wide open within 2min of startup.
3. Check all the fuel line clamps, make sure they are tight, if you are sucking some air it will cause the types of problems you are seeing.
 
Last edited:
Sorry, aluminum is for engines < 200hp, so use aluminum for yours - 1/4" npt and 3/8" barb https://www.wholesalemarine.com/moeller-marine-aluminum-anti-siphon-barb.html. Fuel tank vent on yours is likely the Perko with the vent built in - if you look inside engine room you will see the large fill hose and beside it a 3/8" vent line. You can verify the vent is not the issue by leaving the cap off for a test. Make sure vent line does not have a dip in it where it can hold fuel, should be all downhill to the tank.

Another, couple of things to look at:
1. Buy some carb cleaner and clean the heck out of it, spray it all inside the throat butterfly valves and choke valves and into the float champer.
2. Make sure your choke is opening all the way, it should be wide open within 2min of startup.
3. Check all the fuel line clamps, make sure they are tight, if you are sucking some air it will cause the types of problems you are seeing.

Thank you so much for the info. Do I use any sealant or tape where the anti-siphon valve meets the fuel tank?

Do I need to remove the carb to spray it down or can I just remove the flame arrestor and spray it down there? Do I just let it air dry for a while before trying to start motor?

I'll make sure the choke opens up and that all fuel line clamps are tight.

Thanks again for your help!
 
1. No telflon tape or sealant on the anti-siphon valve, just tighten and it should seal fine. A general rule is never use teflon tape on fuel fittings, tape doesn't hold up to the fuel solvent and eventually some of it ends up in the fuel system - not good.

2. Leave carb on, engine cold, spray liberally in throat and linkage, spray into the vent hole so it gets into the bowl.

3. Put flame arrestor back on - crank engine. Engine will run rough and may smoke some while it burns off the carb clean and gunk it cleaned off.

4. Take it out and give it a good hard run - don't over do it, but engines like to be "aired out" once in awhile.
 
Just an update on my issues... turned out to be the carb. Rebuilt it and boat seems to be running fine on the muffs now, hopefully I can take her out this weekend!
 
Still having issues with the tachometer though... going to compare the boat's tach with a shop tach to see how off it is. It's better than it was after I turned the dial on the back a few times but it still doesn't seem accurate. Does anyone know where I can find a replacement tach for my 175?
 
I have a 1994 searay with a 3.0 mercruiser in it and I am having the same problem boat runs good some times then others as it starts to plain off it bogs down and almost shuts down I have replaced the plugs, plug wires, distributor, rotor button, pick up in the distributor, fuel pump, carbrator and I am at loss on what the problem may be any suggestions would be great
 
James, have you tried running by using a portable tank hooked directly to the engine? This would tell you if there was an issue in fuel delivery, upstream of the engine such as a clogged vent (could also try with fuel cap off), clogged AS valve, failing pick-up tube or failing/old fuel hose.
 
James, have you tried running by using a portable tank hooked directly to the engine? This would tell you if there was an issue in fuel delivery, upstream of the engine such as a clogged vent (could also try with fuel cap off), clogged AS valve, failing pick-up tube or failing/old fuel hose.
I have tried a portable tank also had the problem with that I have also tried running it with the fuel cap off same issue
 
Still having issues with the tachometer though... going to compare the boat's tach with a shop tach to see how off it is. It's better than it was after I turned the dial on the back a few times but it still doesn't seem accurate. Does anyone know where I can find a replacement tach for my 175?
Most OEM tachs are Faria. If so, for a 4 cyl I/O the setting should be 2P. At idle you should see 650 +- rpm.
 

Forum statistics

Threads
112,943
Messages
1,422,707
Members
60,927
Latest member
Jaguar65
Back
Top