Problems! PLEASE HELP ME!

[Jimbo45]

Ok.  I am getting frustrated.  I am getting an '86 going, that I acquired with a worn out top end.  It was the first top end it had, since a complete rebuild, that the previous owner had done.

I fitted a new PWK 38 airstiker, and the rest of the setup is listed in my signature.

I also fitted a known to be good OEM coil, and have checked all electrical connections and wiring.

I am pretty sure I had my jetting nailed pretty close, in the testing I have been doing the past few weeks as time allows, in winter temps, about 20-35 degrees F.

Fresh 32:1 93 octane gas.

Keep in mind, I have yet to do an extended riding session, only quick jaunts in the empty lot, as I make repairs and changes.

I did a little riding today, to verify the jetting, and see how it is running.

Keep in mind, it was a bit cooler today, only 6 degrees (I had previous taken a short ride in 25 degree weather).  I fired it up, let it warm up, and fine tuned the air screw.  Gave it a few revs, and off I went.  When I got to the empty field by my house, I let her rip, and went full throttle through 1-5 gears.  It ran great, for the first pass up through the gears, not missing a beat, and pulling great.  I turned around to come back for another run through the gears, and it bogged out, lost power, like it was not getting fuel, or the ignition was failing.  Really loosing power, and I had to slow down, feather and pulse the throttle, and keep the rpms and throttle low, to get it back to the house.  Once back in the garage, is seemed to then rev out fine, when I hit the gas full throttle, a few times (which it woudn't do when it was having the problem out in the field).

What is going on, and what can I check/test/replace next???  I am reasonably sure their is not an air leak since the idle is so rock solid and it is so easy to start.  The reeds, a Boyesen carbon fiber rad valve, look great.  I tested the new to me OEM coil and it is solid.  

Could it be as simple as a fouled plug? (I will put a new plug in tomorrow)  Could this be a bad CDI or stator?  Could it just have been running super lean, since it was only 6 degrees out?  

Its weird that it runs great for a few minutes, then flames out and almost won't run.  Please give me a direction to go from here.  I am going to put a new plug in, and it is suppose to be warmer (35 degrees) tomorrow, and I am going to try it again and see what happens.

[FerrinMotorsports]

Do you have good fuel flow to the carb??...

[Jimbo45]

Do you have good fuel flow to the carb??...

That was my first thought also.  I do have an inline filter (hi flow) but, I pulled the fuel line off the carb, and turned on the valve, and it ran out in a good stream, so I think that is good to go.

[rk88r]

6 degrees is cold, my guess is a lean bog. Note your throttle position relative to rpm prior to and during the bog. My guess is that when you came around to make another pass you had chopped the throttle (reducing the flow of fuel) while the rpms were still up. I would guess the cold temps in conjunction with a lean pilot circuit caused the bog.

[2ndmoto]

Typically "bogging" is associated with a lean condition. You stated it was fine the first run. This leads me to believe you are sucking the float bowl dry or you have an air leak. I would try the exact same thing you did today, but try putting the fuel valve on reserve.

When you checked the fuel flow did you pull line off the carb or the petcock?
Is the carb clean? Plugged main or pilot?
Have you done a leak down yet recently?
Have you checked spark? Nice fat and blue?
Have you checked timing?
Verified the float is not binding?
Is this a ported cylinder? That carb is big for a non ported...might work well in the cold though.

Best regards
-Jason

[Jimbo45]

6 degrees is cold, my guess is a lean bog. Note your throttle position relative to rpm prior to and during the bog. My guess is that when you came around to make another pass you had chopped the throttle (reducing the flow of fuel) while the rpms were still up. I would guess the cold temps in conjunction with a lean pilot circuit caused the bog.

This is my hope as well.  It is supposed to be 30 degrees warmer tomorrow.....I will try again with a new plug and see what it does.

[Jimbo45]

Typically "bogging" is associated with a lean condition. You stated it was fine the first run. This leads me to believe you are sucking the float bowl dry or you have an air leak. I would try the exact same thing you did today, but try putting the fuel valve on reserve. Will do, and add more gas to the tank, there was about a gallon in it today.

When you checked the fuel flow did you pull line off the carb or the petcock? disconnected from the carb
Is the carb clean? Plugged main or pilot?  Brand new carb, no jets plugged
Have you done a leak down yet recently? Nope, hoping that isn't the problem
Have you checked spark? Nice fat and blue?  Spark looks OK, but hard to kick it over fast enough to tell
Have you checked timing?  No
Verified the float is not binding?  Float level good and not binding that I can tell
Is this a ported cylinder? That carb is big for a non ported...might work well in the cold though. Mild porting.  Carb seems to work good  for the first few minutes for some reason.

Best regards
-Jason

I probably need to add, there was some popping when it was bogging out too.  Not popping out of the exhaust, but it seemed maybe to pop back through the carb maybe.  Not sure, it happened like once or twice only.  This makes me suspect electrical issues....

[2ndmoto]

Check your stator, pickup coil and flywheel. Popping through the carb sounds like ignition timing.


Best regards
-Jason

[Usmoneylover]

Detonation from lean main jet is my guess...162 seems small to me try a 170-175...I'm running a 172 in mine right now.

[Skeans1]

What about your tank vent and fuel cap nothing pulled or stuck? And is the vent just a hose? Also since you've had a back fire you may want to re check your reeds and make sure they are still good.

[Jimbo45]

Detonation from lean main jet is my guess...162 seems small to me try a 170-175...I'm running a 172 in mine right now.

Could be.  I would think it would recover quickly, in the lower throttle ranges, though, if that were the case.  It seemed to run like crap in at all levels of throttle, once the bogging started.  It had a rich bog with the 162 in a bit warmer weather, so I wouldn't think it could be terribly lean now.  But, I will see what happens tomorrow when its warmer......

[Jimbo45]

Check your stator, pickup coil and flywheel. Popping through the carb sounds like ignition timing.


Best regards
-Jason

Yep, after the test tomorrow with a few changes, if no luck, I will be testing those with the multimeter.  I wonder how definite those tests are though?

[Jimbo45]

What about your tank vent and fuel cap nothing pulled or stuck? And is the vent just a hose? Also since you've had a back fire you may want to re check your reeds and make sure they are still good.

Oooooo.....I hadn't thought of that.  It has one of those short 3" vent lines with an aluminum vent cap on top.  Good thinking, I will check that out tomorrow, and make sure it is venting, and then put on a regular vent hose.  

Thanks for all the help guys!  The more input the better!  I want to try everything, before I start buying pricey electronics and changing parts, just to see if it fixes it.

[Usmoneylover]

Was the throttle pinned wide open when it was popping?

[Skeans1]

Also pull the cap and shake it to make sure the ball isn't stuck as well.


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