HPDI 200 - how smooth should it run at low RPM?

SoLucky

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Definitely check the O2 sensor and O2 Sensor Draw Tube. I have found that this is the culprit of my idle issues and cold start issues when the carbon has built up and starts to clog the air flow.
I have tried everything to reduce the carbon, but now down to each season, do a Seafoam decarb, pull the O2 sensor and clean out all the carbon, soak the parts overnight, except the O2 sensor itself, must be careful not to damage it. When put back together, starts perfectly and idles right at 700rpm like it should.

Thanks, ROBERTH and everyone else for sharing your knowledge with me. Collectively y'all have already made a world of difference in how it runs. Setting the TPS right helped a lot. I think it was running very rich at lower throttle openings (since the TPS was out of calibration) and that was causing the engine to stumble. Once the O2 sensor is clean and working properly I expect the small remaining stumble/roughness will go away. I'll pull the O2 sensor, housing, and spindle in the "draw tube" this Sunday and clean it all up. And, if I have the time, I'll splash the boat and test out the results.
 

ROBERTH

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I use Ring Free religiously and still have lots of carbon. The O2 sensor itself is always clean. It is the chamber that is clogging up not allowing the sniffing to work properly for the O2 sensor to get an accurate sniff and make the adjustments. That is my theory so far.
I just don't get the carbon buildup. I run my engines hard, but I do troll a lot. I run nearly 2 hours out and back and always go as fast as the seas allow. Was running 38mph this past weekend back from 30 miles. That is about 4600 to 4800 rpms. I usually give it a 1 mile blast on the way back to the dock.
Even then I still get carbon buildup that requires the decarb and cleaning of the chambers.
 

seasick

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I use Ring Free religiously and still have lots of carbon. The O2 sensor itself is always clean. It is the chamber that is clogging up not allowing the sniffing to work properly for the O2 sensor to get an accurate sniff and make the adjustments. That is my theory so far.
I just don't get the carbon buildup. I run my engines hard, but I do troll a lot. I run nearly 2 hours out and back and always go as fast as the seas allow. Was running 38mph this past weekend back from 30 miles. That is about 4600 to 4800 rpms. I usually give it a 1 mile blast on the way back to the dock.
Even then I still get carbon buildup that requires the decarb and cleaning of the chambers.
Have you checked the oil pump linkage adjustment? Excess oil will also cause carbon buildup. Also check that you are running the correct spark plugs.( how do they look?)
Also research the issue with that spool that connects the chamber to the O2 sensor. Some years ago, a new version was made for SX motors. The shape of that part was changed. I am nor certain if it applies to your motor
 

SoLucky

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I'm a little tardy with an update. I cleaned the O2 sensor, chamber, and the "spindle" tube (I don't know its official name). I ran the boat this past Saturday and low RPM running is somewhat improved, but still a bit rougher then I would like. I have now replaced the O2 sensor with the $30 equivalent from NTK. Splicing on the Yamaha connectors took about 10 minutes and saved $300. I haven't run it yet, but will be heading out striper trolling on Friday, which will be a good test.

Next up will be what Seasick suggests -- checking the oil pump linkage. I think mine is over oiling, as the plugs were quite damp with oil when I changed them a few weeks back and their color wasn't right. Those plugs may have been the wrong temp. New ones are from SIM Yamaha. They sent NGK BKR-6ES11-00-00 -- are those the correct hotter plugs?

Things are trending in the right direction and with a few more tweaks she should be purring properly.
 

ROBERTH

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Hi Seasick, I have adjusted the oil linkages. They were off and I am saving a lot of oil last year. So I know that is not it now. The plugs burn pretty clean, never oily. They are the recommended plugs, same as what came in it. NGK BKR7EKU. I installed the new OXYGEN SENSOR DRAW TUBES 68F-11353-00-00 because the originals looked a bit worn and not seating properly. When I serviced the O2 sensor this season, the draw tubes looked perfect, just some carbon on them but it came off easily. I have definitely improved the carbon, but nonetheless, still have the buildup. Same in both motors. I know many others with these same engines are having the same issue.
 

DennisG01

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I use Ring Free religiously and still have lots of carbon. The O2 sensor itself is always clean. It is the chamber that is clogging up not allowing the sniffing to work properly for the O2 sensor to get an accurate sniff and make the adjustments. That is my theory so far.
I just don't get the carbon buildup. I run my engines hard, but I do troll a lot. I run nearly 2 hours out and back and always go as fast as the seas allow. Was running 38mph this past weekend back from 30 miles. That is about 4600 to 4800 rpms. I usually give it a 1 mile blast on the way back to the dock.
Even then I still get carbon buildup that requires the decarb and cleaning of the chambers.
Hmmm. I wonder the difference is, then. I also use Startron (and usually more than recommended). But the last time I pulled my O2 sensor and draw tube out, they were clean. I even took the draw tube with me to the Yamaha dealer when I picked up a new gasket and the service manager took one look at the tube and said "You must be using RingFree" :)

If I get the chance, I'll pull it out again and check as it's been a couple years, now.
 

ROBERTH

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Yeah, I am in the same mode of thinking. Seems some engines have this issue and others don't. I have 2 and they both do the exact same thing.

I use Startron and Ring Free Plus together. I started switching over to the new Marine Techron to see if it helps. Hard to say right now

The only thing I can think of is the oil. I was using the Pennzoil Semi Synthetic for a few years. Switched over to Amsoil and using it now. It does a bit better with the Amsoil which is a full synthetic. I was reading an article a while back about the Yamalube 2 stroke oil has a lower ash content to control the excessive carbon. Was thinking to swith over to that for while once I burn through my Amsoil. I found it interesting the Amsoil, which I love says absolutely nothing about the ash content. So maybe this could be something......dunno..

What oil are you using?
 

georgemjr

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2X the oil. I was a religious Yamaha fanatic, ring free/yamalube, but I switched over to a synthetic oil as I found the yamalube created too much buildup and the synthetic burned cleaner.
 

ROBERTH

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Ouch Dennis! That is way more than even the Amsoil....lol. I go through 2 gallons each offshore trip. Amsoil compared with the XD100, but again, the additives would be different I am sure.

Would be great to find out if anyone has used the 2M oil and does not have carbon buildup.

Here is what I was referencing about the Yamaha 2M oil regarding the claim of less carbon buildup. Somewhere else I found some discussion about the lower ash content.


Without a doubt, Yamalube 2M is the oil to use in Yamaha HPDI engines. While it’s possible to use other brands of two stroke oil without voiding the warranty, Yamalube 2M oil is the clear choice of boat owners who want the most out of their engines. There are several subtle differences between Yamalube 2M oil and the oil of other leading competitors. One central difference is the additives in Yamalube 2M that reduce the buildup of carbon in the engine. In addition, there are other additives to reduce condensation in the gas tank, and ensure the engine continues to operate at peak performance. It’s possible to save some money purchasing a cheaper two stroke oil, but the money saved on purchasing an inferior brand of oil is far insignificant to the cost of boat ownership. Yamalube 2M oil preserves the condition of the engine, and overall the engine will require less maintenance over its lifetime.
 

ROBERTH

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