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Engine wont Start and is backfiring through the carbs - PMA, rephased 277, Pamco ign

Discussion in 'The Garage' started by NorthParkMC, Jul 24, 2014.

  1. NorthParkMC

    NorthParkMC XS650 Member

    Where to start. So I sent crank and cam off to Hugh in NC to rephase to 277, and they did great work. I got the Pamco ignition to go with the 277. Once I got it running realized the charging system was shot so decided to upgrade to the PMA. Had the Carbs serviced at a shop near by because I didnt want to deal with Carbs.

    Now, the Bike was running and I was breaking it in easy. Around 200 miles or so I was on the Highway going about 65-70 and blew the engine. White smoke, horrible noise, so I killed the engine. Turns out I blew a hole in the left piston. Pulled the engine, checked the cylinders and it looked like everything was fine except the small hole in the left piston. (right side still had great compression).

    Upon my searching for what caused this I found a small pin hole in the carb sync rubber cap on the left side. Seems the extra air into the left cylinder was causing it to run leaner and enough to blow a hole in my piston. The spark plug was also oily on that side.

    So last week I replaced the piston and gaskets and put the engine back together. Threw it back in the bike and hooked everything up. Set valves according to OEM. tried to time the bike. Its close to the fire mark.

    I cant get it to run. It pops and cranks and occasionally backfires through the carbs.
    I had a mechanic over and he cant seem to figure it out either. Although he has never worked with a pamco ignition. I didnt mess with any of the electrical after the piston blew out so Im not sure what happened. I was riding the bike almost every day. Some advice would be greatly appreciated. Has anyone else had this problem after a rephased/ Pamco ignition???
  2. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    My best guess would be the timing. On a 277, I can envision a little confusion setting the trigger rotor on the correct stroke on the correct cylinder...
  3. NorthParkMC

    NorthParkMC XS650 Member

    Yea my thoughts as well but I cant seem ti get it right.
  4. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    I've never fooled with those, but have read many posts on the subject. You definitely need to have your wits together. Could try disassembling the thing, and start over, following the instructions. Double-check the 3 pins and their orientation in the cam and advance shaft...
  5. NorthParkMC

    NorthParkMC XS650 Member

    There are 2 ways the rotor can go on to the advance rod shaft since there are 2 key holes that can be located on the pin on the advance rod. Im not sure if this matter.
  6. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    It does. Plus, if you're running a PMA, and the PMA rotor was removed, then set for TDC of the wrong cylinder, the error combination doubles. Worse would be if that PMA rotor shifted, which some have experienced.
  7. NorthParkMC

    NorthParkMC XS650 Member

    Well I used a stick to locate TDC on the left cyclinder, which is what Hugh said to do. The instructions say to set the timing according to OEM. Cylinder 1 at TDC. So I got the left side to TDC and made a new mark on the PMA alt rotor.
  8. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    A way to confirm camshaft timing would be to remove the plugs and valve covers, rotate the crank until the left cylinder valves are at overlap, see if the piston is at the top. Then do the same on the right cylinder. If the camshaft is out of time that'll cause problems...
  9. NorthParkMC

    NorthParkMC XS650 Member

    When you say at overlap you mean the valves are open I guess? When the left piston is at TDC there is slack on the intake and exhaust valves for the left side. This is where I used a feeler gauge to adjust the valves. Did the same for the left. Rotated the crank twice until the right side was at TDC then checked valves and adjusted.
  10. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

  11. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Uh oh. I guess you're not real familiar with 4-stroke engine theory.

    When you rotate the crank twice you're back to where you started.

    Overlap is the position when the exhaust valve is almost closed and the intake valve has just started to open. The piston will be at the top at this point, between the exhaust and intake strokes. Another 360° of crank rotation puts it at TDC of the compression (firing) stroke, which is where you set the valve lash.

    Since I don't know the specifics of your particular rephrase (crank and cam offset direction), I can only speak in terms of the crank/cam/stroke relationships. So, I'm not going to be of much help here. Not good at cookbook directions.

    But, this has come up numerous times here. So I hope that those threads will help...
  12. pamcopete

    pamcopete Ride.Enjoy.Life is Simple

    Well, it does. There are 32 different ways to install the 277 PAMCO and only one of them is correct. Pleased review the installation instructions on www.yamahaxs650.com and also the excellent instructions from HHB as well.

    You have to "walk" the crank through all four of the cycles for each cylinder to see if the timing is correct. The spark happens when the second magnet is just about to cross over the sensor for each cylinder.

    advance rod pins 2 ways (2)
    slots in rotor 2 ways (4)
    slots in slotted disk 2 ways (8)
    sensor to cylinder 2 ways (16)
    coil to cylinder 2 ways (32)

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