Pred. 212 missfire on pull start

[JimN]

A couple of days ago I started experiencing a missfire when pull starting. Typical for me is to turn gas on, full choke, pull start, as soon as I hear rpm's start to drop from full choke I turn choke off and ride off.
When the problem started I'd pull start, nothing, 2nd pull, Pow, 3rd pull, start up and ride off. I wasn't at home when it started. Made another stop before I went home and the same thing happened. Next day would not start at all.
Unless I'm riding fence lines around my property, right now, the majority of my rides are here to there affairs lasting 10 mins. or less
Approx. elevation 340' above sea level
180 lb bike/180 rider. 19" tires. 420 chain
100% stock predator 212, only throttle screw backed out.
Chinese tav2 8/72 gears. 2500 stall.
4000 max rpm. About 2000 idle rpm.
Approx. 15 hrs. run time. On 4th oil change. 5w30 Quaker State full synthetic.
.016 coil gap. Coil was slightly cockeyed from factory. top of coil at .016, bottom a little wider. I reset gap evenly at .016. No effect.
.003 int/ex valve lash. As found. I did not set lash. It is the same as checked after motor break in.
Flywheel inspected. No sign of any slippage. Stock timing (whatever that is ).
Carb cleaned and inspected. Gaskets from intake to ex. look good. No sign of leaks. No effect.

Bpr6es plug. 3 to 4 hours of run time on it. Changed from factory plug after 11 to 12 hrs. of run time. Gap .030.
Broke porcelain pic is my fault. Got in a hurry to take the plug threads off.



I put a new Bpr6es plug gapped at .029 and engine fired right up. Rode around for about 30 min. No problems but I have doubts.
I have ordered a full gasket set because I plan to pull the head and side cover and see if anything doesn't look right. Will probably lap the valves while I'm there. Not really a motor guy but I think I can handle that. Also check rod bolt torque while I'm poking around.

Anyway here is my question. It is my understanding that stock predators have a resistor in the plug boot.

Is it possible, by using a resistor plug with a resistor boot on a stock coil with a stock flywheel and stock timing that the spark is marginal at best, and after a little run time that is what caused the problem ?

I also ordered some bp6es plugs to have on hand. Any opinions are appreciated. Now I have to go pull weeds out of the garden.

 

[BrownStainRacing]

A couple of days ago I started experiencing a missfire when pull starting. Typical for me is to turn gas on, full choke, pull start, as soon as I hear rpm's start to drop from full choke I turn choke off and ride off.
When the problem started I'd pull start, nothing, 2nd pull, Pow, 3rd pull, start up and ride off. I wasn't at home when it started. Made another stop before I went home and the same thing happened. Next day would not start at all.
Unless I'm riding fence lines around my property, right now, the majority of my rides are here to there affairs lasting 10 mins. or less
Approx. elevation 340' above sea level
180 lb bike/180 rider. 19" tires. 420 chain
100% stock predator 212, only throttle screw backed out.
Chinese tav2 8/72 gears. 2500 stall.
4000 max rpm. About 2000 idle rpm.
Approx. 15 hrs. run time. On 4th oil change. 5w30 Quaker State full synthetic.
.016 coil gap. Coil was slightly cockeyed from factory. top of coil at .016, bottom a little wider. I reset gap evenly at .016. No effect.
.003 int/ex valve lash. As found. I did not set lash. It is the same as checked after motor break in.
Flywheel inspected. No sign of any slippage. Stock timing (whatever that is ).
Carb cleaned and inspected. Gaskets from intake to ex. look good. No sign of leaks. No effect.

Bpr6es plug. 3 to 4 hours of run time on it. Changed from factory plug after 11 to 12 hrs. of run time. Gap .030.
Broke porcelain pic is my fault. Got in a hurry to take the plug threads off.

View attachment 311293 View attachment 311294 View attachment 311295 View attachment 311296 View attachment 311297 View attachment 311298

I put a new Bpr6es plug gapped at .029 and engine fired right up. Rode around for about 30 min. No problems but I have doubts.
I have ordered a full gasket set because I plan to pull the head and side cover and see if anything doesn't look right. Will probably lap the valves while I'm there. Not really a motor guy but I think I can handle that. Also check rod bolt torque while I'm poking around.

Anyway here is my question. It is my understanding that stock predators have a resistor in the plug boot.

Is it possible, by using a resistor plug with a resistor boot on a stock coil with a stock flywheel and stock timing that the spark is marginal at best, and after a little run time that is what caused the problem ?

I also ordered some bp6es plugs to have on hand. Any opinions are appreciated. Now I have to go pull weeds out of the garden.

I start ALL my lil turd motors like this,

No throttle
Ignition off
Choke on

No throttle
1 or 2 short, slow, chug chug pulls

no throttle
Ignition on
Choke off

Then give em a yank, they fire up every time.

Try that a time or 2.

You could use a lil bit more low speed jet, they very lean outta the box. Your high speed is looking good.

 

[sparkwizard]

Have you noted any difference in the way it runs with the questionable plug and the new plug?
My first instinct was to suggest a new plug.
Resistor plug and wire might reduce your voltage at the plug, but should not change timing.
I have been told many times, resistor plugs and wires are designed to reduce noise in your radio, and radios in the immediate area. No performance gain.

 

[JimN]

BSR define a "lil bit more" , like drill it out to .018 if it measures at .016.
The only time I had a problem starting before now is when I had the idle at about 13- 1400 and even then it started just fine. I just had to feather the choke for a little bit to keep it running until it warmed up just a hair. Ever since I idled it up to 1900-2000 no problems. Then again I have not tried to start in 50* or lower temperature.

Sparkwizard, can't say for sure, it was only twice that I ran it and at that just for a few minutes each time before I got back to the house. The next time I tried I couldn't start it at all. LOL, I think I would have saved myself a lot of work if I had changed the plug first. After I put the new bpr6es plug in it started right up.
I wish I had ohmed the old plug, before I hacksawed it, and compared it to the new one. May have told me something. Maybe not. I think I'll wait and see if the same thing happens again with the new bpr plug after about the same amount of run time. If so I can then put in 1 of the new bp plugs that will be here in a few days and see what happens. If it happens to both plugs I'll know where not to look.
Still want to crack the motor open and take a look see but I'll wait on that, maybe till it gets real cold around here.

 

[BrownStainRacing]

BSR define a "lil bit more" , like drill it out to .018 if it measures at .016.
The only time I had a problem starting before now is when I had the idle at about 13- 1400 and even then it started just fine. I just had to feather the choke for a little bit to keep it running until it warmed up just a hair. Ever since I idled it up to 1900-2000 no problems. Then again I have not tried to start in 50* or lower temperature.

Sparkwizard, can't say for sure, it was only twice that I ran it and at that just for a few minutes each time before I got back to the house. The next time I tried I couldn't start it at all. LOL, I think I would have saved myself a lot of work if I had changed the plug first. After I put the new bpr6es plug in it started right up.
I wish I had ohmed the old plug, before I hacksawed it, and compared it to the new one. May have told me something. Maybe not. I think I'll wait and see if the same thing happens again with the new bpr plug after about the same amount of run time. If so I can then put in 1 of the new bp plugs that will be here in a few days and see what happens. If it happens to both plugs I'll know where not to look.
Still want to crack the motor open and take a look see but I'll wait on that, maybe till it gets real cold around here.

Yea, .018" works good for a stock gov'ed engine. Don't go too far, most chinese carbs I've played with can barely go passed .020".

Don't worry much about the resistor deal for a stock engine. You're not turning enough rpm to justify a non resistor coil or plug.

Leave it stock gov'ed for now, you can tweak on other things, like another 4* degrees of ignition timing, a lil carb turning here and there, maybe a thinner head gasket down the road.

You got that big gear and stall now, you don't wanna play with the tune too much, or you'll be on you head, lol.