TBR7 Won't start

[Megadan]

Originally Posted by Johnny_Sardine

If I got it to putter, and just very barely gave it the smallest amount of throttle, a couple times it started to rev. Then I was able to open it up. It revved and wasn't even, it backfired. The carb will also shoot gas out the intake when the choke is on.

This sounds to me like either the cam timing is off, or your valve lash was set at the wrong TDC. There are two TDC points, one at compression and one at exhaust. If you set the valve lash on the exhaust stroke, where both valves are actually being activated by the cam a little bit, then your valve lash will be enormously out of spec. The easiest way to know is to roll the motor over, and watch the rocker for the intake valve. Once it actuates, the next T mark on the flywheel will be TDC for the compression stroke. It wouldn't hurt to double check and make sure you have this right.

As far as having the throttle open and the starter having a harder time, you are trying to compress a larger volume of air than you would with the throttle closed. You can hear this on any healthy bike when you try to start it and open the throttle, it takes more power to compress a larger volume at the same ratio.


I was also having the same thought as paulsstag. Swapping carbs with the same result tells me it isn't the carbs. However, the intake to the head can be the culprit via a vacuum leak. The O ring that seals the intake to the head may be pinched or missing, or the flange was bolted down too heavily and warped the flange (it's soft aluminum), or the rubber may have a rip in it somewhere.

Another possibility. While the battery may say it is charged, it is possible that it can't supply the proper amps to run both the starter and the ignition. Having spark doesn't always mean it has good spark. Try swapping the Hawk battery over, or hooking a set of jumpers up to a car battery (without the car running!) and see what happens. My last battery was causing very similar symptoms, which is why I bring it up.