Ran into a problem last week while riding 2 up, uphill. Under throttle, I'm losing power and hear some maybe? knocking sound. It's the same sound that an engine makes when the clutch is released at too low of an RPM to take off. Or at least that's where I've heard it before (In cars primarily)... That clunky struggle sound.

Anyway, I thought maybe I needed to retard the timing. Did that, it got worse. Then I changed the points/condenser (blue streak), and plugs... No change.

I let the engine cool down overnight. When I started it the next morning, everything sounded great, until I got up to temp. Maybe 2-3 miles down the road,the same sound and loss of power. Returned home...

Tonight, unless someone here has better advise, I'm going to adjust the valves. They are OEM hydraulic lifters, which I thought were self adjusting? And, at this point, I'm not even sure I'm headed in the right direction. Could my auto advance springs be too tight (Rivera)? That was the last thing I replaced... Maybe a month ago.

What am I missing? Thanks for the help... again

'75 shovel

 

The mechanical advance unit behind the breaker plate might be worn or sticking. It's worth a look and relatively cheap to replace.

 

Did you put in old gas, or like I did one time (that I know of) or did you inadvertently hit the 87 octane button like you might be used to with your car/truck. Sounds like detonation with could be from low octane gas. it is most likely to act up in a hot engine. The gas is com-busting too early.

 

I'm liking the low octane gas idea... I could have messed up and put the wrong fuel in. I'll stop by AutoZone on the way home and puck up some octane booster. At the very least, its a much easier trouble shoot than adjusting the valves. I'll let you know how it goes.

Thanks

 

Bike smoking any or blowing more oil than usual ? With the old stock 74's gas grade isn't a issue unless it's the 15% ethanol crap then you get a lot pinging and they run hot. Flyweights maybe but that usually manifests as starting issues unless the units completely hashed and the Rivera's rarely do that.

Knocking/ clunking under the conditions you describe I'd be checking the primary chain tension and the rear chain adjustment and wear. Do these before you go off into the engine to far, symtoms can act like the little woman just gained 200lbs suddenly.

One last thing watch the octane booster stuff that **** eats rubber and swells orings & seals, do not over add it.

 

The reason I went with the bad gas idea is this...

I always fill it with highest grade gas from the same (Shell) gas station. At least I try. Magnut1 jolted my memory and I realized my last fill up was from a gas station I've never been to before. Last night I noticed I was low enough on gas that I could just go back to my usual and fill up. Instant change in performance. Today it's running like it was all just a bad dream.

I was shocked that something so simple would be the fix. Thanks for the help. Just to be on the safe side, I'll check the chain tension at my next oil change.

Thanks again. You guys are awesome. My bike would not be running without this forum. Thank You!!

 

Yeah I can see that , had some bad gas from a few noname places before but the bike would cut out and stutter verses losing power , played hell getting all the water out of the tank.

 

Update

Okay... It was the auto advance. It was getting stuck. The hotter the bike got the more the advance would stick, the more the advance stuck, the hotter the bike. I guess the shaft that the cam slides on was expanding too much?? I replaced it with an OEM today... Viola!! Bike is cool and running like a champ in 90+ degree weather. I have all of my power back. I might have had bad gas also... but ultimately the auto advance was the source of the problem.

Wanted to update this in case anyone else has the same problem.