Effect of Incorrect Spark Plugs

[DennisfromDanbury]

I have an old Grady, 208 Adventure, year 2000, with a 200 HP Yamaha two stroke engine. I am trying to keep it running as long as possible, and have spent a lot on preventive maintenance and repairs over the years. So there is no reason why the engine should not be running fine.
However, for the last four years, the engine periodically hesitates, as if one pulls back on the throttle and then immediately puts it back in its original position. It hesitates for about one second and resumes original speed. This occurs more frequently at higher speeds and in turbulence, like when one bounces over a wake or wave.
I've tried many things, with no success, and the mechanics at our marina have not figured it out. I noticed, however, just a few months ago that the spark plugs installed by the marina during winterization last year were not those recommended by the Yamaha manual. They installed BR7HS-10, but specs call for BR8HS-10. BR7’s are recommended for 150HP, BR8’s for 200 HP, which is what I have.
My question is, does anyone know what impact this could have, and is it possible that they are the cause of the hesitation problem I described?
I have been told that one scenario is that a mechanic installed the wrong plugs several years ago, and each successive year the mechanic who did my winterization simply replaced my plugs with the (incorrect) ones that were in there rather than looking at the manual to determine which one to use.
Thanks!

 

[SkunkBoat]

difference is temperature range. Its easy and quick to install six BR8s and know the answer.

"However, for the last four years, the engine periodically hesitates, as if one pulls back on the throttle and then immediately puts it back in its original position. It hesitates for about one second and resumes original speed. This occurs more frequently at higher speeds and in turbulence, like when one bounces over a wake or wave."

I would suspect VST filter, pressure regulator screen filter, dirty injectors, low pressure fuel pumps
After that...coils, plug wires, bad electrical connections

 

[seasick]

Most likely Its the VST tank.. The clue is the symptom when in rougher seas. Your VST tank filter needs to be checked and probably replaced

The plugs don't explain the intermittent hesitations. > Although the 7s will wok, next change use the 8s. I can't recall if the 8s are hotter or cooler but eventually the 7s may either foul or burn up prematurely.

 

[SkunkBoat]

look at this OX66 225 "stumbling" when running over 3500 rpm

 

[Uncle Joe]

Skunk knows what he is talking about.....that sounds like it gets starved for fuel periodically.....although I would get the correct plugs in there ASAP.
I also change my plugs in the spring after I burn out all the winterization oil....why start the season with fouled plugs?

 

[DennisfromDanbury]

Skunk knows what he is talking about.....that sounds like it gets starved for fuel periodically.....although I would get the correct plugs in there ASAP.
I also change my plugs in the spring after I burn out all the winterization oil....why start the season with fouled plugs?

Thanks. I will change the plugs in the spring from now on.
On Friday I noticed that the effect can be instantaneous...we hit a wave and instantly the motor hesitated...no more than a fraction of a second after impact. And then it went right back on.

 

[DennisfromDanbury]

difference is temperature range. Its easy and quick to install six BR8s and know the answer.

"However, for the last four years, the engine periodically hesitates, as if one pulls back on the throttle and then immediately puts it back in its original position. It hesitates for about one second and resumes original speed. This occurs more frequently at higher speeds and in turbulence, like when one bounces over a wake or wave."

I would suspect VST filter, pressure regulator screen filter, dirty injectors, low pressure fuel pumps
After that...coils, plug wires, bad electrical connections

difference is temperature range. Its easy and quick to install six BR8s and know the answer.

"However, for the last four years, the engine periodically hesitates, as if one pulls back on the throttle and then immediately puts it back in its original position. It hesitates for about one second and resumes original speed. This occurs more frequently at higher speeds and in turbulence, like when one bounces over a wake or wave."

I would suspect VST filter, pressure regulator screen filter, dirty injectors, low pressure fuel pumps
After that...coils, plug wires, bad electrical connections

 

[DennisfromDanbury]

I have an old Grady, 208 Adventure, year 2000, with a 200 HP Yamaha two stroke engine. I am trying to keep it running as long as possible, and have spent a lot on preventive maintenance and repairs over the years. So there is no reason why the engine should not be running fine.
However, for the last four years, the engine periodically hesitates, as if one pulls back on the throttle and then immediately puts it back in its original position. It hesitates for about one second and resumes original speed. This occurs more frequently at higher speeds and in turbulence, like when one bounces over a wake or wave.
I've tried many things, with no success, and the mechanics at our marina have not figured it out. I noticed, however, just a few months ago that the spark plugs installed by the marina during winterization last year were not those recommended by the Yamaha manual. They installed BR7HS-10, but specs call for BR8HS-10. BR7’s are recommended for 150HP, BR8’s for 200 HP, which is what I have.
My question is, does anyone know what impact this could have, and is it possible that they are the cause of the hesitation problem I described?
I have been told that one scenario is that a mechanic installed the wrong plugs several years ago, and each successive year the mechanic who did my winterization simply replaced my plugs with the (incorrect) ones that were in there rather than looking at the manual to determine which one to use.
Thanks!

 

[DennisfromDanbury]

I am replying to my own post because I am not sure how these threads work and I want everyone to see what I say.

Thanks to all of you for taking the time to give me this great advice. And SkunkBoat, great video and great advice. Your problem from a few years ago sounds very much like mine.

A few days ago, we hit a wave and the engine hesitated immediately...a tenth of a second or less after impact. Would a filter problem cause this to happen so quickly? (There are also times when it takes a few waves for this to happen).

About two years ago, I asked the mechanic to check the VST filter. He said it looked OK and there was no junk or water in the VST itself...I don't know whether he cleaned it or not, but he put it back in. I have since been told that the VST filter can look ok, but not actually be OK. The finger viewing tip might be the way to go, or maybe just replace the filter.

I'm wondering if the high pressure fuel pump itself, within the VST, is causing the problem. It's 20 years old, as are my two low pressure fuel pumps. If they suddenly lose an electrical connection during turbulence, there would be an instantaneous effect. The mechanic has checked external electrical connections (that is, connections outside the pumps) and not found anything loose, but maybe there's a contact inside the pumps that gets broken periodically by turbulence.

I've read somewhere that there is a float inside the VST. That seems like something that could be affected by turbulence if not working properly.

Someone told me once that it is often something simple that causes a person to give up on an outboard motor. I think there's something really simple causing this...hopefully the VST filter...but I am not sure we will ever find it.

 

[ScottyCee]

I've been into my VSTs all the way for the last two years. I replaced the filters last year, and found the new filters clogged again this year, but also that they cleaned right up. These can be cleaned by opening the VST without removing it - a little easier. There is indeed a float that needs to move freely, and there is a drain screw at the bottom that can allow you to "inspect" the contents via a far less invasive process than actually opening them up. Draining mine via that screw never did a thing with regard to cleaning them.

There's a way to find out whether any of the work of disassembly of VST is needed at all. Find a partner and have them check the pressure of the fuel rail when the motor is misbehaving. It should be constant at all time, slightly higher when motor is at high rpm. Like 35-40 psi or so, IIRC. There's a Schrader valve on the fuel rail, so you have to take off the cowling for this test. If no drop in pressure with motor struggle, then that effectively rules out lift pumps, HP pumps, etc., as your problem.

 

[Capt Bill]

I can't help you with the heat range, but what I can tell you is that as of today, I personally have witnessed 6 engines of various manufacturer, including 2 Yamaha outboards, a Honda pressure washer, a Mercury outboard, a Kohler commercial mower, a Honda outboard, with engine problems, (ran terribly.. low power, no full rpm, etc)t that turned out to be caused by the NGK spark plugs. One engine had brand new and correct NGK plugs installed a few days ago; started right up but no power; ran terrible. Replaced with Denso spark plugs (cross-referenced from the NGK number), and the engine ran perfect.

This has happened to many times, and in each case, the bad plug looked perfect. Not cracked, not fouled, properly gapped. But replaced with a set of Denso plugs and no further problems. I always though NGK plugs were the best, but I won't be buying any more.

 

[seasick]

That is news to me...

 

[SkunkBoat]

Never heard a bad word about NGK...wondering if there is a flood of counterfiet??

IMO after seeing mine.....if you own a Yamamaha 2 stroke (ox66) and you haven't touched the VST filter in years and never touched the pressure regulator screen/ injectors that you can recall, you need to do that job that I did and send out the injectors because your motor needs it. It might not be your immediate problem but it is a problem.

 

[seasick]

I currently only change my NKGs on my Yami SX about every three years. I used to swap them annually when the motor was newer. I never have had a defective plug in 15 years.

 

[ScottyCee]

AFA fuel injectors are concerned, rebuilt Bosch are about $5-6 per cylinder on eBay. I believe that they cost more to send out, but ??