Spark Plug for NU50 70cc Kit

After an almost year long delay due to herniating a disc and a pinching a nerve, I am back to getting parts together for my 1983 NU50 build. I already have the Polini 70cc kit (119.0030) and I am seeing a discrepancy for which spark plug to use. The manual for the Polini kit recommends using a Champion L82C, and that plug does NOT have a resistor and is NON-projected tip. The NU50 shop manual recommends NGK BPR4HS-BPR6HS plugs which have a resistor and a projected tip. I am going to use the NU50 head (I am still debating between using the stock one, or a custom cut one from Treatland) with the kit. All that being said, do I use a plug with a resistor and projected tip? Or, is there some reason that I should use the Polini recommended plug? I have been searching around for an answer and can’t seem to find what I am looking for. I appreciate any help I can get on this.

Re: Spark Plug for NU50 70cc Kit

Captain Janeway /

get a BPR7HS or BPR8HS depending on your temps. I run a DR kit and an 8 plug. . What's the shape of the piston? Pointy top or flat? My Malossi has a pointy piston and needs a non-projected tip. I'd wait for someone to give you a for sure answer.

Re: Spark Plug for NU50 70cc Kit

Here's what the piston looks like. It was hard to get a good photo of it, but it is a little rounded, or "domed," on the top. I don't know that I would say it is pointed or flat.

poliniPiston.jpg

Re: Spark Plug for NU50 70cc Kit

That^ piston has a slight dome .

Being as you're not decided on which head you'll use , I'd wait and try both type plugs in both heads . Hand turn the crank to feel for any contact with the protruded tip .

Re: Spark Plug for NU50 70cc Kit

> P D Wrote:

> -------------------------------------------------------

> That^ piston has a slight dome .

>

> Being as you're not decided on which head you'll use , I'd wait and try

> both type plugs in both heads . Hand turn the crank to feel for any

> contact with the protruded tip .

Bingo!^

I can tell you from personal experience with a Polini 70cc kit for Garelli that the Champion plug recommended by Polini is the one you should use. Why?? Because the plug needs to he shorter than stock to clear piston dome. Ask me how I know? Find an equivalent NGK that DOES NOT HAVE A PROTRUDING TIP.

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(edited)

Re: Spark Plug for NU50 70cc Kit

> live ɘvil Wrote:

> -------------------------------------------------------

> Bingo!^

>

> I can tell you from personal experience with a Polini 70cc kit for

> Garelli that the Champion plug recommended by Polini is the one you

> should use. Why?? Because the plug needs to he shorter than stock to

> clear piston dome. Ask me how I know? Find an equivalent NGK that DOES

> NOT HAVE A PROTRUDING TIP.

> >

live ɘvil - Thanks. I thought I read about someone on here using a Polini 70cc kit. Any advice on whether the kit likes a resistor vs. non-resistor plug better?

I appreciate the input on this from everyone. I kind of expected that I may have to figure out which version of the NU50 head I would be using first, and then see which plug I would need. I was just hoping that someone may have been in the same situation and could say which plug I needed so I could be ready ahead of time. The NU50 I bought came with an Autolite 4123 plug in it which has a projected tip and resistor so I should be able to test if the projected tip is a "no go."

Unless I find a reason that I shouldn't, I'll probably go with a plug with resistor whether I have to use a projected tip or non-projected tip. I am planning on adding a tach and temperature gauge and I have seen a number of complaints about erratic gauges when using a plug without a resistor.

Re: Spark Plug for NU50 70cc Kit

You can use a resistor plug or a resistor cap .

Re: Spark Plug for NU50 70cc Kit

> Colby T Wrote:

> -------------------------------------------------------

> live ɘvil - Thanks. I thought I read about someone on here using a

> Polini 70cc kit. Any advice on whether the kit likes a resistor vs.

> non-resistor plug better?

Does not matter. Resistors are radio frequency suppressors to eliminate interference with electronics. You might get a slightly stronger spark without a resistor.

> I appreciate the input on this from everyone. I kind of expected that I

> may have to figure out which version of the NU50 head I would be using

> first, and then see which plug I would need. I was just hoping that

> someone may have been in the same situation and could say which plug I

> needed so I could be ready ahead of time.

You'll need the Champion or equivalent regardless of head because of domed piston in kit. You're not gonna find a head that gives more clearance to offset the domed polini piston.

> The NU50 I bought came with an

> Autolite 4123 plug in it which has a projected tip and resistor so I

> should be able to test if the projected tip is a "no go."

Bearing in mind that the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is dissipated and the hotter a motor becomes. I dont think you're gonna have any shortages of heat running a 70cc kit with higher compression.

> Unless I find a reason that I shouldn't, I'll probably go with a plug

> with resistor whether I have to use a projected tip or non-projected

> tip. I am planning on adding a tach and temperature gauge and I have

> seen a number of complaints about erratic gauges when using a plug

> without a resistor.

I've never had any problem with non resistor plugs on my trail tech. I dont have the tachometer option though. (edited)

Re: Spark Plug for NU50 70cc Kit

> P D Wrote:

> -------------------------------------------------------

> You can use a resistor plug or a resistor cap .

But NOT both at the same time.

Re: Spark Plug for NU50 70cc Kit

> live ɘvil Wrote:

> -------------------------------------------------------

> > P D Wrote:

>

> > -------------------------------------------------------

>

> > You can use a resistor plug or a resistor cap .

>

> But NOT both at the same time.

Maybe I should have CAPITALIZED with BOLD and italicized the 'OR ' . ;)

Re: Spark Plug for NU50 70cc Kit

> P D Wrote:

> -------------------------------------------------------

> > live ɘvil Wrote:

>

> > -------------------------------------------------------

>

> > > P D Wrote:

>

> >

>

> > > -------------------------------------------------------

>

> >

>

> > > You can use a resistor plug or a resistor cap .

>

> >

>

> > But NOT both at the same time.

>

> Maybe I should have CAPITALIZED with BOLD and italicized the 'OR ' . ;)

Sure, for the o.p.

I know better

Re: Spark Plug for NU50 70cc Kit

Yup . Some folks need that little extra clarification to settle nerves and such . ;)

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