Vintage Dirt Bike Q & A

All,

Thanks for the info. Your a great bunch of guys!

Here is what I did........

1) I broke down and got a brand new Clymer manual from the bike shop that I got the tires from. There trick regarding the use of "Hot Light" on page 45 figure 27 saved me a bunch. Especially when I realized that one of the stator windings has a pickoff for lights and that messes up the use of a ohm meter for checking when the points are open/closed. The only thing different in my setuo for the hot light is I used a battery charger instead of an actual battery for my power source. I do this allot because batteries have a cicuit breaker built in and there is no chance of overloading anything.

2) Backfiring like crazy no more

a).........we'll several things fixed this and I just dont know which one. First I took off the rotor again. Removed the stator and the points. I went to work shining all surfaces up again with some high grit sand paper. I took the points apart and made sure I had no shorts. I checked them again after I put them together and installed in the stator. Cant be too careful. For this I used a light I made from clymer manual. Open no light close light comes on.

b)I put it all back together. Ensuring the crank shaft nut that holds the rotor in place is good and tight. No need to have a rotor creep off the shaft and cause damage.

c) Again I went to the clymer manual and followed their instructions for setting the points using the "Hot Light". That was a breeze. Disconect the main power connector from main wiring harness. I inserted a small nail into the leads on the connector that had the yellow/black lead comming from the stator and connected one end of the leads from the "HOt Light" Next I connected the other end of the "Hot Light" lead to the bike chassis for a ground. I started rotating the rotor backwards until the F mark ligned up with tha timing index mark. If the light stayed out I turned the point a tad until it came on. I did this over and over until I was satisfied that when the F mark and the timimg index aligned the ligght just barely came on.

d)I checked the plug I am running a brand new stock NGK B8ES plug. Yeah its new but it was involved in some backfiring so I cleaned the contacts with a small file and then regapped it to a tight 0.24.

e) Nice blue spark I plugged the alternator wire into the wiring harnes. I doubled check the spark before putting the plug back in by grounding it to the muffler. Just what I expected a nice blue spark!

f) Carb cleaning again well I tore the whole carb down again.
1) I rigged up a hose with a small bottle and I ran water through the carb to make sure the float vavles and float were working right. Good news with light pressure the water flow stopped and when I released the float it started!
2) Next thing was to check the float postion when resting on the float plunger. Good news it didnt move and is right on at 20mm when measured from the float base to the carb flange.
3) I took out all the jets and made sure they were free from any garbage. Yes I cleaned them very good before but I may of missed something now was the time to recheck. All was good.
4) I assembled the carb and but before I did I sparayed a small amount of WD 40 on all surfaces just to absorb moisture I guess.

g) It fired first kick and no back-fireing I took my time and it all fell back in place again. I am certaing my timing was off before but who knows. I doubled checked the F mark against the timimmg mark with my timing light. It was right on @ 1500 rpm. Idle is good also. Dont know what the cause was bu I do know I took my time this time and I followed the manual.

3) Still having trouble with a sputter at high RPMs. I will take Rays advise and bore out the muffler just behind the spark arrester. Ill put a 1/2" hole in it. Next thing is to find some jets. Those also will be started at what ray has posted.

It snowed here last night 3.5 inches and I will say the knew knobbies were made for snow.

Larry,

That's great! It's good you took the time to find the problem with the ignition, it always kind of bothered me that I didn't find what was wrong with my bike.

Hopefully the exhaust drilling will fix the high-rpm sputter.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric