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Old 01-08-2012, 09:38 PM
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Default Yamaha 300 HPDI Problems

I have read quite a few good posts on here and searched thru a lot of them before posting this.

I have a 2005 Hydra Sport 2800 CC with twin 300 HP HPDI Yamaha TXRC engines. I bought the boat used about 10 months ago. Once I bought it, I got everything serviced and checked. All filters on the engines were changed. After my first trip, I had one engine start to lose some power and would progressivly get worse as I ran. I took the boat in again and they recommended to have the high pressure fuel pumps rebuilt. I did that and the boat has ran great ever since (~50 hrs).

The symptom I am having is that I am losing some power again. Both engines used to run full throttle at ~5000 RPM. One engine is now running at 4200 RPM maximum. The other engine is down to 4800 RPM but I believe that is because it is not getting full help to push from the other engine. If I back the RPM back to 3800 RPM or so, both engines run in sync and throttles are at the same position. The engines sound good at cruising speed as of now. My concern is that this will progressivly get worse. Right now, I can run full thottle with the suspect engine at 4200 and it does not vary at all. It runs consistently at 4200 and never drops or rises higher unless I move the throttle myself.

I have replaced the Racor fuel/wtr sep filters, the element fuel filter and today after reading thru the website, I took the vapor seperator apart to check the filter there. I was hoping to find it clogged up but it looked spotless. I removed it, cleaned it anyway and still same problem. I would have replaced the filter on the top of the VST tank but didn't as the store was not open. I will replace that next unless someone suggests something else. Again, this were all changed in April. I typically replace everything in the spring to prepare for the new season.

Next, I removed the spark plugs and they appear pretty gummed up. They are very dark with visible build up on them. I am going to replace the spark plugs next but now I'm concerned with the amount of buildup on them. They were replaced ~70 hrs ago and I think this is a lot for that amount of time. With the amount of buildup on them, I can only imagine what the inside of the engine looks like.

Can spark plugs in this condition cause a loss in engine performance and not allow the engine to run at full RPM? I have had a bad sparkplug on my old truck and you know when it's bad because the engine will miss and sound horrible. However, with the outboard, each engines sounds perfect with no miss, it just does not have full RPM.

Second, I wonder what is causing this buildup on the spark plugs. I ran ring free in the tank for the first few tanks thru the boat when I got it, but since have stopped. Perhaps I should start again. I have seen some posts that Yamaha can reprogram the engines to perform better due to some problems they were seeing with the engines. I don't have the service history for the engines but all service recorded with Yamaha does not have anything like this.

I run ethenol free fuel in the boat.

Any thoughts you all might have I would greatly appreciate. I would prefer to work on the boat myself but am learning as I go along.

Thanks,
Greg
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Old 01-08-2012, 09:52 PM
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My first thought is to check running engine temps.... Is it possible that the suspect engine is running too cold?
At least all plugs look the same..... <---that's a good thing....
Are those plugs the recommended plugs for your engine(s)?

What is your boat's purpose? Allot of idle/trolling? 5k RPM at WOT seems low to me....
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Old 01-08-2012, 10:07 PM
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Default Boat

I use the boat for fishing, but don't do much trolling. I usually motor out and then drift around rigs in the gulf.The last trip I made was 280 miles and I kept the engines at 3500-4000 rpm the whole trip. When I went out again a few days later is when I noticed the lower rpm at wot. I am running the plugs recommended in the Yamaha manual, BKR6EKU (NGK).

Another thought I didn't mention is that the plugs on the other engine looked similar. They were very dark with what looked like oil and carbon buildup.
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Old 01-09-2012, 03:50 AM
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Bad fuel? If both engines started acting funny around same time. Are the tanks low? Try filling the up if they are. If not maybe run them down then change all filter again and fuel up. Sounds funny for both engines to have a problem at once. Also 5000k seems low anyway. Is she proped properly? Don't know much about that subject but a lot of guys on here do.
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Old 01-09-2012, 03:53 AM
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I run ring-free every fill up. If not, my hpdi's do the same. I would de-carb the engines, change the sparkplugs, and start using ring-free. Also, change your plugs every 75 - 100 hours; hpdi's hate trolling, especially if you slow troll with live bait. The carbon bridge on your sparkplugs are definitely cutting your rpm's. The motors also appear to be incorrectly propped. You should be around 5650 rpm, maximum rpm for a 300 hpdi per Yamaha. Good luck, once you figure the motors "personality", they are strong. I'll run mine till they pop. PM me if you want to talk.
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Old 01-09-2012, 04:16 AM
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i have the same setup, its a heavy boat and the 300s dont like to be lugged down, prop it so you can hit 6000 wot with a full load, run penzoil semi synthetic, do dunks decarb method once a year, and run it like you stole it. somtimes the vst filter can look spotless but be varnished up, change it. i get better fuel milage running at 42-5000.
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Old 01-09-2012, 05:02 AM
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Had the same problem, plug fouling asked the dealer to check oiling ratio everything fine, problem continued switched to pennzoil full synthetic from yamalube and problem went away.
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Old 01-09-2012, 05:53 AM
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Switch to Pennzoil Plus; De-carb; Run Ringfree; replace ALL filters; try lower pitch props. My 250 HPDI's are running 17 pitch props and see 5500 max RPM with trim tilt at high.
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Old 01-09-2012, 05:54 AM
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My Yamaha mechanic (one of the better ones in Miami BTW) told me a few things about the 300's when I purchased the boat;

1. "NEVER" idle the engines..... Start and go - and always be in gear.....
2. Run em hard - They like the upper end of the RPM range
3. Use Ring Free
4. Keep all the filters clean and change regularly
5. Never use Ethanol

Try that for a while and see how it goes....

Good Luck
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Old 01-09-2012, 06:57 AM
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If new plugs do not correct it I would replace/rebuild the low pressure pumps. Maybe do it anyway as they do not last forever.

Here is a kit that should fit yours.

Amazon Amazon
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Old 01-09-2012, 07:09 AM
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Maybe you are not getting enough fuel to the one motor. Did you check the fuel lines and primer bulb?? I run ethynol, micron 10, ring free when i remember and penz prem plus. I agree with needing higher rpms. I turn 6k. I have never had a problem with the motor or carbon build up. I have the same set of plugs from 2008.
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Old 01-09-2012, 07:56 AM
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Mine would do that with Yamalube crap, I would start losing performance at about 100 gallons of fuel burned. Check your oil ratio. Should be in the 50:1 range or maybe even better. I was having issues with mine and after fixing a switch and it not getting better it made it's only trip to the shop... fouled plugs from the 2 cylinders never coming on due to the switch. They put new plugs in and off she went.
Plug on yamalube


Plug on Starbrite oil/West Marine oil. Pennzoil was just as good.



I idle mine a lot. I have to idle about 1.5miles of idle speed zone. I run seafoam and startron and have never spent a dime on ring free. My motors sunk a few months ago in saltwater and i relaunched yesterday. I purged the oil line did some other minor things and they fire right up.


My bet is over oiling and yamalube.
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Old 01-09-2012, 10:58 AM
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Quote:
Originally Posted by Gary999 View Post
If new plugs do not correct it I would replace/rebuild the low pressure pumps. Maybe do it anyway as they do not last forever.

Here is a kit that should fit yours.

http://www.amazon.com/Sierra-Interna.../dp/B000N9LFK2

Not worth the effort to rebuild them. Here is a tutorial on doing the Low Pressure Fuel Pumps:

http://www.thehulltruth.com/boating-...maha-hpdi.html

Its cheap insurance.
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Old 01-09-2012, 12:47 PM
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Thank you everyone for the tips. I will switch from Yamalube to Pennzoil, run ring free, and obviously change my plugs out. Hoping to get out again soon, work just keeps getting in the way. I will update again with the results. Thank you again everyone for your advice, this website is great.

If anyone else has tips, I'll be happy to keep listening.

Thanks,
Greg
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Old 01-09-2012, 01:02 PM
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Quote:
Originally Posted by RocknReeln View Post
Not worth the effort to rebuild them. Here is a tutorial on doing the Low Pressure Fuel Pumps:

http://www.thehulltruth.com/boating-...maha-hpdi.html

Its cheap insurance.
$184 more for the whole pumps vs. kit? Very easy to replace.
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Old 01-09-2012, 02:34 PM
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As stated, something is wrong with your props as 5000 rpm is not an ideal wot.

You should be at least 400-600 higher. What size props are you running?
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Old 01-09-2012, 02:58 PM
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Quote:
Originally Posted by Gary999 View Post
$184 more for the whole pumps vs. kit? Very easy to replace.
It would be $140 for twins and the problem why its not worth it is as follows:

I did replace mine as I posted above. Before I did I rebuilt one---cuz it was cheaper. Got the idea on here. As it turns out, I over-tightened the screws on one and it leaked, but only after I was heading out. Fuel squirting out the pump and onto the engine is bad.....very bad! I noticed the smell and immediately shut the motor down before anything bad happened and I limped in. Sometimes you think tightening as much as possible is a good thing.....NOT! Just my .02.
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Old 01-09-2012, 04:04 PM
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Lots of good advice on plugs, filters, lp pumps, ring free, and 2 stroke oil. I will add to be careful running when the engine drops rpms. If the injector is partially blocked or lean you can burn a piston. I had it happen and am now careful to throttle back if a motor drops rpms.
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Old 01-09-2012, 05:40 PM
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Many, many people with 300 HPDI plug fouling issues have reported that the problem either disappears or all but disappears after switching to 100% synthetic oil.

Why not try it and then report your results?
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Old 01-09-2012, 05:41 PM
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Quote:
Originally Posted by jethro1 View Post
Many, many people with 300 HPDI plug fouling issues have reported that the problem either disappears or all but disappears after switching to 100% synthetic oil.

Why not try it and then report your results?
Blend is fine as well....
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