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.

[JerryHawk250]

Originally Posted by Megadan

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.

^^^This is what I was thinking. ^^^ Air leak

[Johnny_Sardine]

Alright well I rechecked the valves finding compression like you told me and I must have had it wrong cause the exhaust valve was way too loose. Got them both to .002 and closed it back. Threw the mikuni back on, changed the plug to an ngk. Kind of doing the same thing. Checked the carb to head gasket thing and it looks fine.

Looking around for more loose stuff or anything that can cause an air leak and found a dodgy looking situation where the exhaust bolts to the engine but maybe that's normal? not all the way seated but....


So I can get it to putter still and I got it to fire up twice but shit is smoking and it's backfiring and the exhaust is heating way up... It will not start with the choke on at all so is it running super rich??? Confused. Here's a video, first part is me trying to start it and puttering, second part is the smoking mess it is when it's fired up. First time it starts it rattles cause of all the shit I have on top of it.




What would be the best way for me to check if the timing is 180 degrees off?

Thanks y'all. I really appreciate it.

[JerryHawk250]

Stopped up Cat???? Man the cat heated up quick. Disconnect the header but don't rev it up or anything just to see if it will idle.