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Inline spark testers

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Is there an inline spark tester that works with motorcycles?  Each one I've purchased is only for the bigger stud or screw-on terminals, not the smaller threaded terminals that comes on my XR.

https://www.sparkplugs.com/Data/uploads/ThreadedTerminalStud.jpg

vs

https://www.sparkplugs.com/Data/uploads/terminal.jpg

 

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Not needed (or wanted) with a CDI engine. They were a useful tool back in the day to check a rotor/points/condenser system. If the spark gap in the tester becomes to great, it can possibly damage the CDI.

With a CDI, you test the coil, the stator and connections with a meter  and diagnose from there. Your service manual will cover this.

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Thanks will do that. It's a 94 xr, but has CDI.  Trying to diagnose why the engine cuts out past 3/4 throttle in the first 1-3 gears, but not 4-6.  I've been suspecting ignition related.

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Could be a fuel issue.  I'd lean toward that.  The engine is loaded differently in higher gears and revs more slowly.  If it were ignition related I'd expect misfiring in the high gears not the low ones.

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I've tried two mains already - 128 and 135 (stock's 125).  Both were clean...  It also doesn't matter how fastly or slowly I roll past 3/4 throttle.  the second i twist past 3/4 it cuts out until i return it back to 3/4 throttle.

The bike violently runs out of power the second I go past 3/4 throttle in 1-3 gears - if I wasn't paying attention I'd be going over the bars.  In 4th-6th, throttle response is smooth from 3/4 to WOT.

Isn't jetting solely based solely on throttle position?  So 3/4 throttle in 3rd vs 5th doesn't matter?

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94 XR250R, bored out to 280.  Pilot #42 (40 stock), fuel screw 3 turns out, needle is a J7Sβ-3.

Issue occurs just the same at WOT.  Throttle response is great from idle to 3/4 throttle..

Fuel flow rate - hose is in decent shape.  I have an inline filter as well.  Just double checked the flow arrow is pointing down to the carb.  I have some spare hose i can probably use to replace it.

Checking the ignition coil, the resistance between the two coils is 3-4 Ohms, spec is 0.1 to 0.3 Ohm.  It's an old bike, so I could live with that, but I'm not seeing any continuity between the spark plug lead and terminals (should be 7-12 kOhms)...

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@jamesm113 When you say "cuts out" does the engine actually lose power (as in no spark) or does it "bog" and wont accelerate any further? Do you have the stock intake or did you put on a secondary intake filter or a "pod" from emgo or UNI?

 

What kind of inline filter do you have? Paper filters are fine with gravity fed systems but any of the sintered metal ones are made for pressurized systems with a fuel pump of some sorts and will restrict flow in WOT applications.

 

Being that its smooth in the upper gears where the load on the engine (lower gears) is less and requires less HP to get up there in the RPM range I suspect that you have a fuel starvation issue. Try upping your main jet to a 142 or a 145 (especially since you bored out 12% more than stock). 112% * 125jet = 140jet just based on simple math.

Edited by ThumperCurtis
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5 hours ago, Trailryder42 said:

Make sure the spark plug boot on the end of the coil wire is tight and the connection isn't corroded.

Was going to ask about that.  How is that supposed to connect?  Do I push it on?  Twist it on?  It just pulled right off and I was able to get 4 kOhm's of resistance at the end of the coil wire..  But once the boot went on, I couldn't measure any resistance.   I tried removing the spark plug cap/resistor/spring too, but I couldn't measure any resistance.  I simply just pushed it on until it wouldn't push any further.

All the other ignition related components were within the service manual specs.

 

3 hours ago, ThumperCurtis said:

@jamesm113 When you say "cuts out" does the engine actually lose power (as in no spark) or does it "bog" and wont accelerate any further? Do you have the stock intake or did you put on a secondary intake filter or a "pod" from emgo or UNI?

 

What kind of inline filter do you have? Paper filters are fine with gravity fed systems but any of the sintered metal ones are made for pressurized systems with a fuel pump of some sorts and will restrict flow in WOT applications.

 

Being that its smooth in the upper gears where the load on the engine (lower gears) is less and requires less HP to get up there in the RPM range I suspect that you have a fuel starvation issue. Try upping your main jet to a 142 or a 145 (especially since you bored out 12% more than stock). 112% * 125jet = 140jet just based on simple math.

The bike cuts out so violently that if I was really caught off balance I could go over the bars.  It feels like I hit the brakes.  I have a UNI air filter, not the stock filter.

 

As for the fuel filter, I'm pretty sure it's paper.  It's a visu-filter from the dealer.  looks like this: https://images-na.ssl-images-amazon.com/images/I/31MjN6S4oLL._SX355_.jpg  The same model filter hasn't caused any issues in my wr450f...  

 

My understanding is that you don't need to rejet for to account for bigger bore XR.  The bigger cylinder volume creates a greater vacuum, which extracts more fuel out of the jets...

 

And for what it's worth, after testing all the ignition equipment, I went on a 2-3 hour ride today, did not have it cut out on me once.  :excuseme::excuseme:

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9 hours ago, jamesm113 said:

Was going to ask about that.  How is that supposed to connect?  Do I push it on?  Twist it on?  It just pulled right off

The rubber boot goes over a metal crimp connector that's crimped to the coil wire. Make sure that crimp connector on the wire isn't loose or corroded. Over a long period of time, that connector can build up that green corrosion gunk between the wire strands and the connector, just like what happens to your car battery cables.

If you look up inside the rubber boot you should also see a screw. That holds in a resistor and spring. Make sure that resistor isn't busted or something. It's a common mod to replace that resistor with a copper slug of the same diameter and length. Copper has the lowest resistance of any metal besides gold. I made my slug from a piece of 10ga. electrical wire. A lot of folks cut a stainless steel screw to use but it's resistance is higher.

XR resistor mod.jpg

Edited by Trailryder42
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15 hours ago, Trailryder42 said:

The rubber boot goes over a metal crimp connector that's crimped to the coil wire. Make sure that crimp connector on the wire isn't loose or corroded. Over a long period of time, that connector can build up that green corrosion gunk between the wire strands and the connector, just like what happens to your car battery cables.

If you look up inside the rubber boot you should also see a screw. That holds in a resistor and spring. Make sure that resistor isn't busted or something. It's a common mod to replace that resistor with a copper slug of the same diameter and length. Copper has the lowest resistance of any metal besides gold. I made my slug from a piece of 10ga. electrical wire. A lot of folks cut a stainless steel screw to use but it's resistance is higher.

XR resistor mod.jpg

Yea, I checked the resistor and spring, they were all good.  About 4.4 kOhm for the resistor.  Thanks for the tip on the 10 gauge wire.  I'll swap that out

I did not see a metal crimp on the coil wire.  Just a hole in the insulator and I think the actual lead wire was buried up there a little bit.

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DAMMIT! LOL

I have too many bikes and have my paws in too many threads around here to keep things straight. I'm so sorry dude. I was thinking of another type spark plug boot.

Put that thing back together.

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