Vintage Dirt Bike Q & A

Trying to diagnose a 'running' issue.

The bike rides amazing, but it seems that the bike starts to 4-stroke and bog a lot on the high-end... I don't have a tach on my bike... but if you were looking at between 0 and 10,000 rpm as red-line, it'd happen about 7000rpm.

I have adjusted the A/F screw a TON and there seems to be no help there... also the bike 'dings' a lot... loud cracking exhaust... too much fuel, or too lean? can't tell.

Me-thinks the timing is off... any suggestions?

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I drink your milkshake!

Start with the basics: clean carb (especially the jets); clean air filter; fresh gas and new plug. Get the highest octane gas (without ethanol if possible) you can from the pump. Use quality oil.
The knocking/pinging/detonation can be caused by too low of octane, lean condition, or timing. Check the points condition and gap correctly. Worn points and incorrect gap can contribute to this problem.
After all the above, check back and let us know how it's doing and we can go from there. Good luck!!
Oh, and if you decide to replace the points, do NOT try and remove flywheel with any type of gear puller. Spend the $15 and get the correct flywheel puller. Best money you will ever spend on a specialty tool !!

This bike is BRAND NEW, completely rebuilt.

Carb is 100% gone through, air filter is brand new and oiled, new gas (mixed 32:1) 93 octane Shell, new plug....

I'm going to check points gap now, and then fiddle with the timing... I had the entire magneto off during the rebuild so I probably didn't install it back in the stock position.

I was just wondering if the pinging popping would be because of an advanced, or retarded timing issue...

_________________
I drink your milkshake!

Figured it out... it was the points... they were gaped at .05, bumped them up to .19 and they're good to go! Bike runs MUCH better, and the mix screw actually works!

_________________
I drink your milkshake!

Solid !!

Spoke too soon...

Still doing it.


Jetting or Timing... It's running an aftermarket expansion chamber, which the previous owner had... which means I have no idea.

Trying timing in the morning.

_________________
I drink your milkshake!

Well, doublechecked the float height... lowered it a bit and it got a tad bit better... but I'm running an aftermarket expansion chamber... and I just noticed the carb has the stock 122 hex jet in there... SO... I'm going to bump that up to a 130 and go from there.

_________________
I drink your milkshake!