Spark Plug Recommendation - Honda ATV Forum
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post #1 of 17 (permalink) Old 04-26-2019, 09:48 AM Thread Starter
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Spark Plug Recommendation

I pulled the spark plug from a '88 TRX350D today and to my surprise it had an NGK D6EA plug in it, which isn't one of the ones listed in the service manual for the bike. It is carboned up pretty good. Which plug do you guys recommend for it? I see there are 3 NGKs (DR8ES-L, DR8ES, & DR7ES) listed as compatible in the manual. I'm thinking the fouling might get worse if I use the colder plugs.

I have a compression gauge, so I may as well check it before I put the new plug in. Any special procedures for doing that on these bikes, like hold the throttle down or etc?

Last edited by KoolBreeze; 04-26-2019 at 09:57 AM.
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post #2 of 17 (permalink) Old 04-26-2019, 10:02 AM Thread Starter
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Here is a pic of the plug.
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post #3 of 17 (permalink) Old 04-26-2019, 08:34 PM
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The spark plugs i cant really make a recomendation on since im not into utility quads. But the compression test i can help with.
1. Make sure the battery is charged 100%(i usually put my battery tender on it)
2. Turn kill switch on handlebar to off position
3. Hold throttle wide open.
4. Crank it over until the needle stops climbing. (Generally 5 to 10 turns).
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post #4 of 17 (permalink) Old 04-27-2019, 07:25 AM Thread Starter
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Quote:
Originally Posted by SlammedRanger View Post
The spark plugs i cant really make a recomendation on since im not into utility quads. But the compression test i can help with.
1. Make sure the battery is charged 100%(i usually put my battery tender on it)
2. Turn kill switch on handlebar to off position
3. Hold throttle wide open.
4. Crank it over until the needle stops climbing. (Generally 5 to 10 turns).
10-4, thanks! About the same as any other engine looks like.

I went ahead and put the DR7ES it for now. It runs fine but I will pull & check it after running it some.

I've got to check the exhaust for leaks too. Every time I ride it much at all I smell like exhaust when I get off. I've got a homemade smoke machine I made a few years ago that should be just the ticket for checking it.
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post #5 of 17 (permalink) Old 04-27-2019, 08:36 AM Thread Starter
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Compression is 150psi, which is a little low according to the manual spec. Not sure if that’s typical with a machine this age or not. I do not hear the valves ticking but I have not checked them yet. The new spark plug was already carboned up since putting it in yesterday afternoon and it wasnt riden much. Not wet with oil or anything, just a dry carbon deposit.

Smoke tested the exhaust and didn’t find a leak except at the spark arrestor clean out plate.
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post #6 of 17 (permalink) Old 04-27-2019, 08:50 AM Thread Starter
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I just came across a post by retro that says using an adapter on the compression tester can cause a low reading since it adds volume. I had to use the adapter with my OTC tester, so maybe that's the issue or at least part of it. I could wet test it. I don't have a leak down tester or I'd check that also.
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post #7 of 17 (permalink) Old 04-27-2019, 08:54 AM
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Your 1st plug pic looked like it had been running rich with a bit of oiling. So the carb/air cleaner needs some work and its probably got four leaky valve seals, minimum. It may be getting weak in the compression department too.

Someone probably put the hotter range plug in it in an attempt to sweep those problems under the rug, but higher heat range plug don't ever hide or help problems, plug just runs a bit hotter. LOL


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post #8 of 17 (permalink) Old 04-27-2019, 09:01 AM
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On an old machine like this the needle can wear the taper to a smaller diameter which will cause a slight rich condition. You can replace it and it's holder/jet or lower the needle position with the clip. Leaning the fuel screw may help as well. As previously mentioned it looks like a rich condition and a little bit of oil too. A carb overhaul and new rings may be all that's needed if you catch it in time. Running with worn rings just wears the piston and cylinder at exponential rates.
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post #9 of 17 (permalink) Old 04-27-2019, 09:05 AM
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Yep, these small displacement ATV motors are very unforgiving to swept volume losses in compression tester adapters. If yours does not have a low-pressure schrader valve in the adapter the readings you'll get with that adapter are useless. The rubber o-ring rarely provides a good seal on the head either, most times they leak pretty bad. So your 150 PSI reading might be 20-50 PSI lower through that adapter, depending on its volume. If at all possible I generally leave the o-ring off and use a common spark plug gasket on the fitting and snug them down tight.

EDIT: Another problem with adapters is most of them are short... where you have a long reach spark plug hole they rarely fill half of that hole.
@misterclean59 clearly understands motors inside an' out. Excellent post an' brain candy... :-)



Last edited by retro; 04-27-2019 at 09:28 AM.
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post #10 of 17 (permalink) Old 04-27-2019, 07:57 PM Thread Starter
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Your 1st plug pic looked like it had been running rich with a bit of oiling. So the carb/air cleaner needs some work and its probably got four leaky valve seals, minimum. It may be getting weak in the compression department too.

Someone probably put the hotter range plug in it in an attempt to sweep those problems under the rug, but higher heat range plug don't ever hide or help problems, plug just runs a bit hotter. LOL
I’m sure my dad can put whatever plug the Honda shop sold him in it. He bought a new bike 6 or 8 years ago and pretty much parked this one except for some grunt work around his place now and then.

He’s anal about not using ethanol gas and always treats his gas, but I doubt seriously the carb has ever been off of it, so it could probably use a cleaning/rebuild. I cleaned the air filter a few weeks ago.

It doesn’t use any oil and the plug was not wet, albeit black with soot/carbon. It was also only finger tight. I’ve got a scope and meant to have a look in the chamber but forgot. I’ll probably wet check the compression though, so I’ll have a look around in there then. I’ve been meaning to get a leak down tester to check my old pickup, so I may do that also.

The adapter on my compression tester does not have a valve. The end up the hose that screws into it does. The adapter is also a lot shorter than the plug. I’ll look around and see if I have another one. Use too but haven’t seen it around in a while, so it may have walked off.

Last edited by KoolBreeze; 04-27-2019 at 08:02 PM.
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