What replacement spark plugs do you use? (chinese 2-stroke)

[gone_fishin]

i think, a lot of opinion but also based on observations of about a dozen HT's...

the longevity i refer to is the lack of good oiling to the underside of the piston, usually resulting in top con-rod bushing/bearing failure.

we run the "stock spec" b6hs's for the most part, but we purposely keep the pre-mix on the gooey side (some guys never go less than 25:1 for the duration)...this does make the thread area of the plug look pretty sooty, but it's an oily soot...and the electrode itself still has the light chocolate color we want. it gets smokey during choke and warm-up, but mostly clears up after that.

so, as i said, based on all that and this topic: i have no problem recommending to the new builder who's more interested in consistency than top-speed that they go with an ngk b7hs as a good compromise.

 

[Pablo]

1) how will a 'cooler' plug result in greater engine longevity?.......Second question: is the B6HS equivalent to 'chinese stock heat range', or is it 'a bit on the colder side' referenced to the Chinese plug(s)? Is a B7HS too cold?

Your logic is sound. Basically match the plug to the engine and usage. When in doubt always start at the manufacturer's recommendation. The supplied plug is supposedly in the same range as the NGK B4HS. I haven't found one yet, but I didn't call around to small engine shops. All I could find was the B6HS. And I was using this while monkeying with my carb. I needed a hotter plug! I do think going to B5HS for winter cruising will be a bit better.....faster plug warm up and less chance of cold temp fouling. I also think a B7HS may be too cold for a non-race set up, especially in a cool climate/winter. Your mileage may vary!

 

[prism]

poor longevity of wrist pin (bearings/bushings)

Sounds like some finger ports are needed, with holes drilled in the piston. (no, no reed valves)

I hope to have a happy-time engine to examine shortly (the rack-mount is still in the parts-gathering stage, though I am cutting metal for tooling currently) so as to learn if the cylinder has enough meat to permit adding two finger ports. If it does, then I shall add them, so as to permit mixture 'flow' under the piston crown and douse that overworked wrist-pin bearing with fresh fuel-oil mixture. (As per Bell and others I've read.)

Either that, or get a cylinder w/ a steel liner. Those will have enough metal thickness, no doubt.

On the other hand, given the 'stock' Chinese plug is ~ comparable to a B4HS, then using a B6/7/8/ will most likely *want* a fine-wire electrode to prevent fouling.

 

[gone_fishin]

our maximum size for a .jpg is 1024X768/2m...so, if you can find a way to get a larger image, we can host it

 

[chrisnbush]

Huh, I took out my stock LD Z4C, and the gap is slightly over .04 inches ? Thats too much right ?

I never gapped it, just thought it would have been right from the factory. Does anyone ever shorten a gap ? I can widen the gap with the gap tool, thats all I know. I have never tried to narrow a gap.

Any help would be appreciated

cb

 

[Pablo]

There is small slotted tool to bend an electrode back in that comes on some parts store gap checkers. Or you can use a very small pair of needle nose. Or you can very gently tap it on a piece of hardwood.

0.040" that is huge. Bring it down to .022-.024"

 

[eljefino]

I got the champion recommended but it's way too short.

In a fiddling mood I unscrewed the nipple off a junk car spark plug and screwed it onto the stock chinese. Then took a practically new (was given wrong part #) plug wire, cut it to length.

It is rarely explained clearly on this site, perhaps b/c it's as simple as sharpening a pencil, but the retainer for the stock wire is a little woodscrew in the middle of the CDI. It forces a hole in the middle of a 7mm plug wire, by the carbon conductor liner, and bites into the inside of the silicone jacket. Lefty loosey, righty tightey.

Though both sides of my (saturn 1.9 liter DOHC) plug wire clicked onto the plug, the coil side looks cleaner. So I cut it with an inch to spare to form a nice loop away from the cooling fins and put it in. All ya gotta do is cut it flush. Again, this has been explained before but not clearly, or rather, it is hard to believe how easy/crude it is.

Haven't yet run an NGK plug or anything other than stock, but there is a sure improvement in upgrading the wire. Or placebo? LOL.

 

[Pablo]

Excellent post Jefe!

Good description on the simple first mod and yes it does make a difference!

Most seek out a copper core wire, buy it makes little difference IMHO. I just think the wire and the insulation in the stock set up is weak. See if you can get an NGK plug, though.

 

[sparky]

It is rarely explained clearly on this site, perhaps b/c it's as simple as sharpening a pencil, but the retainer for the stock wire is a little woodscrew in the middle of the CDI. It forces a hole in the middle of a 7mm plug wire, by the carbon conductor liner, and bites into the inside of the silicone jacket. Lefty loosey, righty tightey.

Though both sides of my (saturn 1.9 liter DOHC) plug wire clicked onto the plug, the coil side looks cleaner. So I cut it with an inch to spare to form a nice loop away from the cooling fins and put it in. All ya gotta do is cut it flush. Again, this has been explained before but not clearly, or rather, it is hard to believe how easy/crude it is.

This still isn't clear enough for me. I'm retarded. I understand how the stock Chinese plug wire is weak, but I don't understand why cutting your Saturn's wire is "so easy/crude"? Where are you cutting?

 

[eljefino]

Just guillotine it to length. Chop it like the swedish chef from muppets. Any make of wire will do that has a female crimp inside a boot, I have a nice 90 degree boot on the "coil end" of mine. As my wireset had four wires of various lengths I chose an appropriate length one and cut it down to about 7 inches in length, which fit how and where I had my CDI. I only mention it's from a saturn in case someone wants to blow $25 on new wires not knowing the crimp style... got mine from a junk bin.

I had a resistance to unscrewing from the CDI based on not really having a mental picture of how it goes together. Didn't want to disturb the stock setting. Rest assured if one does unscrew the wire they can figure out how to put it back together. It's a catch 22 that you can't see how it works until it's apart.