Changed the plugs because they’re cheap and my 175 HP OX66 two stroke was starting hard. To my surprise, one of the plugs looked super clean, and the other 5 showed normal 2 stroke coloring. What the heck? Scary thing is that I last changed the plugs a while ago and have been running like this for who knows how long. I attached a tool that shows spark for each cylinder…and spark is present. So that’s what’s confusing. Maybe not strong enough spark. Or maybe a fuel issue. Anyone have any experience with this. Engine always seems to require reving the throttle when cold start. Is that normal? I hate racing a cold engine like I’m starting a chainsaw. Thanks
One clean spark plug, 5 dirty. Why?
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Jacktrop99
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I’m not an expert by any means but usually a clean plug means you are burning water which steam cleans the cylinder/plug, the only other stuff would be oil/ gas which would dirty it, I’ve heard of some of these older ox66 motors like I have getting a leak in the head gasket but maybe other people know more.
X2 on a head gasket/water intrusion.
No, you shouldn't have to open the throttle on an ox66 to start it unless something is way off.
There are a litany of other checks to perform when an ox66 isn't behaving correctly. A little searching will help you find those.
Mr Seasick should be here shortly. He is a wealth of knowledge on the small displacement ox66s.
No, you shouldn't have to open the throttle on an ox66 to start it unless something is way off.
There are a litany of other checks to perform when an ox66 isn't behaving correctly. A little searching will help you find those.
Mr Seasick should be here shortly. He is a wealth of knowledge on the small displacement ox66s.
Ok. Thanks for the info. A head gasket does make some sense. Water seeps in a steam clean explodes the cylinder. Uggghh. This boat has never left me stranded, but at 30 years old, more stuff is starting to go.
The need to pump the throttle on a cold start still puzzles me.
The need to pump the throttle on a cold start still puzzles me.
Ditto on the water thing. Head gaskets aren't too bad of a job, though. Chalk it up to a good "maintenance" thing to do, anyways - and do both sides. It'll give you a chance to inspect the cooling passages and clean them, as well.
Correct - shouldn't have to pump the throttle since you have fuel injection. Start with easy things like cleaning out the VST tank and filter - also, for good measure, the fuel pressure reg screen.
How does your fuel look? Look at the on-engine fuel/water sep and also drain some fuel into a clear jar from the VST tank.
When's the last time you cleaned the O2 sensor? And also changed the on-engine FWS filter?
Inspect all of the fuel hoses for cracks/leaks.
Another good PM thing... send the injectors out to be cleaned/rebuilt (it's relatively cheap to do this).
Correct - shouldn't have to pump the throttle since you have fuel injection. Start with easy things like cleaning out the VST tank and filter - also, for good measure, the fuel pressure reg screen.
How does your fuel look? Look at the on-engine fuel/water sep and also drain some fuel into a clear jar from the VST tank.
When's the last time you cleaned the O2 sensor? And also changed the on-engine FWS filter?
Inspect all of the fuel hoses for cracks/leaks.
Another good PM thing... send the injectors out to be cleaned/rebuilt (it's relatively cheap to do this).
If you have water in the gas/air mixture, I would expect to see steam coming out of the exhaust. That would result in a white exhaust color.
Which plugs looked like what. What plug had the clean spark plug?
Is this motor an SX fuel injected model? For a fuel injected motor, you should not have to open the throttle or pump it to start the motor. For carbureted motors, a problem with the choke mike require you to open the throttle and or pump it.
I am not sure that the cold start issues are related to the clean plug.
Which plugs looked like what. What plug had the clean spark plug?
Is this motor an SX fuel injected model? For a fuel injected motor, you should not have to open the throttle or pump it to start the motor. For carbureted motors, a problem with the choke mike require you to open the throttle and or pump it.
I am not sure that the cold start issues are related to the clean plug.
Great info. Thanks. Head gaskets look like one of those things that are easy 99% and a nightmare 1%. I’ll start there
I apologize if I was unclear or confused about outboard model. This is a 2 stroke 1995 175 hp saltwater 6 cylinder. Model 175TXRT. Yamaha of course.
I suspect I could have a fuel pressure issue related to hard cold start. I replaced the check valve on the fuel line right off the fuel tank pick up. That made an immediate difference. Presumably since it was cracked and clearly leaking air. I thought that was the problem all along. But the issue has returned.
Boat is so much fun. I swear that at 25 knots you can drop the hammer and she jumps. It’s a small joy, but we love running up on larger boats and showing them we have more to go.
So thankful for any experience and knowledge that keeps this destroyer running.
I apologize if I was unclear or confused about outboard model. This is a 2 stroke 1995 175 hp saltwater 6 cylinder. Model 175TXRT. Yamaha of course.
I suspect I could have a fuel pressure issue related to hard cold start. I replaced the check valve on the fuel line right off the fuel tank pick up. That made an immediate difference. Presumably since it was cracked and clearly leaking air. I thought that was the problem all along. But the issue has returned.
Boat is so much fun. I swear that at 25 knots you can drop the hammer and she jumps. It’s a small joy, but we love running up on larger boats and showing them we have more to go.
So thankful for any experience and knowledge that keeps this destroyer running.
I have recently purchased a 225Hp OX66. It is on a 208 Grady. It runs great and I am really happy with it. I have worked on two strokes for years. Mercury and OMC service technician. I am new to the OX2. There is a lot of information about theses motors online.
Here are a few suggestions that I have.
First and most important check that should be done when changing spark plugs is Compression check. This will give you a good idea if there is a compromised cylinder or head gasket. I found that the top four cylinders are slightly higher than the bottom 2 Cylinders. My engines compression was #1 120, #3 120, #5 115, #2 120, # 4, 120 #6 115.
Spark check tester. I have a pair of Stevens that I use. I set the gap at 7/16" this will load test the coils and ignition system. If it jumps with a clean spark the ignition system is in good working order.
Fuel filters. There are three fuel filters one in the boat screw on water separating, one located under the cowling that is also water separating with a water level float that will lift if water is present and one in the VST. This one if fouled will effect fuel pressure at start up. There is a drain for the VST. Loosen the drain plug with a small catch container and sample the fuel in the bottom of the VST. This will be the best indicator of fuel contamination in the fuel system causing a poor running condition do to fuel. If the fuel that is drained out of the VST is clean and has no water. This is a good indicator that the fuel system is clean.
O2 sensor- The O2 sensor should be inspected and cleaned. If it is dirty it can cause poor running conditions but mostly noticed at higher rpm. It will cause possibly a rough idle.
Low fuel pressure at the high pressure pump may cause a hard start but also poor operating at high speed rpm.
You indicated that the engine performs well at high speed. You can push the throttle and it jumps up. This indicates that it is still hitting on all cylinders.
It is hard to read plugs that have been used for many hours in my opinion. Especially when the engine does not fire on all cylinders at low rpm. The OX2 saltwater idles with cylinder #5 cut out. When the engine reaches 850 rpm to about 2000 rpm #5 and #2 are not firing. All 6 will fire at start up and warm up. If the spark plug that shows cleaner came out of #5 that may be because you do a lot of running below 2000 rpm. This may be true for # 2 also but # 5 doesn't fire from idle to 2000 rpm # 2 cuts out at 850 and up. either one may show cleaner than the rest. This would be normal. The best way to read the plugs is install new and run for a couple of hours then read the plugs.
There is no benefit to pumping the throttle. There is no accelerator pump it is fuel injected.
Hard Start could be has easy has a bad primer bulb check valve. You stated you installed a new one and it fixed he issue and now it has come back. I have found aftermarket primer bulbs suck and fail quickly. I always use OEM primer bulbs. Yamaha, Mercury..... If you used an aftermarket primer bulb replace it with a new OEM.
Low pressure fuel pumps on the Yamaha OX2 are known for failure. It is suggested by Yamaha that this is a maintenance item to to pressure checks on to confirm that the diaphragms are not leaking by. I replaced mine when I purchased the motor. I bench tested the old ones. The engine was running fine but one had a small leak and would not hold pressure. Have you replaced low pressure pumps ?
Brian
Here are a few suggestions that I have.
First and most important check that should be done when changing spark plugs is Compression check. This will give you a good idea if there is a compromised cylinder or head gasket. I found that the top four cylinders are slightly higher than the bottom 2 Cylinders. My engines compression was #1 120, #3 120, #5 115, #2 120, # 4, 120 #6 115.
Spark check tester. I have a pair of Stevens that I use. I set the gap at 7/16" this will load test the coils and ignition system. If it jumps with a clean spark the ignition system is in good working order.
Fuel filters. There are three fuel filters one in the boat screw on water separating, one located under the cowling that is also water separating with a water level float that will lift if water is present and one in the VST. This one if fouled will effect fuel pressure at start up. There is a drain for the VST. Loosen the drain plug with a small catch container and sample the fuel in the bottom of the VST. This will be the best indicator of fuel contamination in the fuel system causing a poor running condition do to fuel. If the fuel that is drained out of the VST is clean and has no water. This is a good indicator that the fuel system is clean.
O2 sensor- The O2 sensor should be inspected and cleaned. If it is dirty it can cause poor running conditions but mostly noticed at higher rpm. It will cause possibly a rough idle.
Low fuel pressure at the high pressure pump may cause a hard start but also poor operating at high speed rpm.
You indicated that the engine performs well at high speed. You can push the throttle and it jumps up. This indicates that it is still hitting on all cylinders.
It is hard to read plugs that have been used for many hours in my opinion. Especially when the engine does not fire on all cylinders at low rpm. The OX2 saltwater idles with cylinder #5 cut out. When the engine reaches 850 rpm to about 2000 rpm #5 and #2 are not firing. All 6 will fire at start up and warm up. If the spark plug that shows cleaner came out of #5 that may be because you do a lot of running below 2000 rpm. This may be true for # 2 also but # 5 doesn't fire from idle to 2000 rpm # 2 cuts out at 850 and up. either one may show cleaner than the rest. This would be normal. The best way to read the plugs is install new and run for a couple of hours then read the plugs.
There is no benefit to pumping the throttle. There is no accelerator pump it is fuel injected.
Hard Start could be has easy has a bad primer bulb check valve. You stated you installed a new one and it fixed he issue and now it has come back. I have found aftermarket primer bulbs suck and fail quickly. I always use OEM primer bulbs. Yamaha, Mercury..... If you used an aftermarket primer bulb replace it with a new OEM.
Low pressure fuel pumps on the Yamaha OX2 are known for failure. It is suggested by Yamaha that this is a maintenance item to to pressure checks on to confirm that the diaphragms are not leaking by. I replaced mine when I purchased the motor. I bench tested the old ones. The engine was running fine but one had a small leak and would not hold pressure. Have you replaced low pressure pumps ?
Brian
enfish
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A compression check is an easy thing to do before you start tearing things apart.
If it's the 175TXRT, I've got the same motor. That's not an OX66. You may want to edit your original post so you don't get a bunch of info on the OX66 if that's not what you have. Normal cold start for me is advance the throttle, close the manual choke, start the motor, open the choke, adjust throttle to let it run at 1500 RPM's for a minute or two until it comes up to temperature, then pull the throttle back to idle.
If it's the 175TXRT, I've got the same motor. That's not an OX66. You may want to edit your original post so you don't get a bunch of info on the OX66 if that's not what you have. Normal cold start for me is advance the throttle, close the manual choke, start the motor, open the choke, adjust throttle to let it run at 1500 RPM's for a minute or two until it comes up to temperature, then pull the throttle back to idle.
Noble, you didn't correct us when we're talking about your motor being fuel injected.... but... do you or don't you have FI?
If you don't have FI, then a lot of what we just wrote was all for not.
If you don't have FI, then a lot of what we just wrote was all for not.
Good info here BB Marine..
First let's verify if the motor is injected. My first thought was that the 'clean' plug is not firing. You would think that would be obvious but it usually isn't if it is one of the cylinders that shuts down at low revs. Also note that if the plug is shorted, the spark tester can still see a good spark but the plug isn't firing. Depending on how the spark tester was connected, a bad/leaky plug wire could cause the same condition, spark at the tester but not at the plug. A weak coil could also be an issue but the spark tester usually will show a weak/irregular spark.
I am familiar with cases where the throttle had to be pushed past the idle point for the engine to start when cold or to stop the sputter and stall when started cold. This condition can be caused by a bad O2 sensor, bad O2 sensor heating coil or more commonly, a dirty O2 sensor or a plugged O2 thimble.