Bike sat for 2 months, now pops on deceleration.

Hey everyone, I'm having some issues with my 73 750. It has, unfortunately, sat for 2 months and I just started it up again today. First thing I noticed is it took way longer than it normally does to tickle. It also normally starts on the first kick where I had some trouble getting it started today. After it warmed up a bit I took it around the neighborhood and it ran just fine. Came back home and it sat for an hour. I went on a second ride and, out of nowhere, it started making popping noises on deceleration. It has never done this since I've owned it. It also felt like it was lacking a little power on acceleration. Is two months enough time for the fuel to gum up the carbs? The carbs are new Amal premiers that I put on less than a year ago. Ever since I put them on I've been having issues with them and haven't been able to get them tuned right. Idle is too low and if I don't give it gas when I come to a stop it'll stall. Any suggestions?

msh,
check for air leaks. the cross over tube may have popped off. use a propane torch unlit but gas on while engine is running and go around the manifolds. If the engine increases then there is where the leak is. If that all checks out then get into the carbs and look into the idle circuit for blockage. verify your float level with gasoline and a fuel level tube kit like this: https://andover-norton.co.uk/en/shop-de ... al-mk1-mk2
check that you didn't drop a needle.
Hard to diagnose from a distance. let us know your progress.

Cheers,
Thomas

Popping on the "down throttle" is classic for an exhaust port air leak. The pulse of exhaust gas still has some unburnt fuel content, so as it exits the port on the exhaust stroke it causes a vacuum effect on the unsealed exhaust port which sucks air into the exhaust pipe that ignites the unburnt fuel in the pipe..... POP, POP,POP...!

Renew your exhaust sealing washers. The technique to get them to reseal is usually as follows. Torque the exhaust nuts down, go for a ride to heat the bike up and then re-torque them again while the bike is hot. My commando exhaust always seals fine using that method. If it pops again somewhere within the next few rides, retighten the exhaust nut again.

There's a few other tricks to get them to seal too if just new sealing washers and good tightening technique fails, just use the search function to find the known tricks.

This was the first symptom when one of my idle jet passages blocked up. Likely to happen if sitting too long.

Russ

Loud bangs are likely to be an air leak into the exhaust.

If it's more of a "popping" effect, that may be a blocked pilot jet, or other closed-throttle mixture weakness.

If it's a well-silenced bike, there may be little difference in sound, but that's been my experience anyway.

I live on road near the bottom of a gradual slope. Every driver going past my house who is obeying the speed limit is off the gas, coasting along until the hill flattens out. After that the speed limit also increases. So,.. they coast by my house, then get back on the gas. Every Dope with a hole in their muffler goes..... POP, POP, POP.... as they drive past my house because they are OFF the throttle (on the down throttle) then the popping noise disappears when they get back on the gas after the down slope ends just past my house.

Exhaust leak popping is related to the off throttle coasting... If getting on the gas makes the popping disappear, it's an exhaust leak.

I've had an intake manifold leak that caused exhaust popping also, and that popping happened when I was on the throttle as well as off throttle, so the symptoms were slightly different for eaxh cause... but that should be helpful in determining which scenario you are experiencing... HTH.

Okay, thanks for the help everyone. I'll take some time this weekend to check everything out. The carbs have been giving me issues for awhile now anyway, so they definitely will be checked. And yes, it's more a popping noise, not a bang. And it's only when I'm off the throttle, not when I'm accelerating. I think I have some spare Commando exhaust seals hiding somewhere in my shop. Should be an easy fix.

Can't agree with the exhaust leak diagnosis. A leaky exhaust will be obvious at tickover. Popping on the over run is almost certainly a leak in the inlet side between carb and head.

My money's on clogged idle jet. Living in Boston where bikes tend to get stored for winter, I am very, very familiar with this phenomenon.


(Torontonian -- you are most correct. I am speaking of my salad days, before I discovered the joys of additives....well, these additives anyway.)

From the frozen north and long storage times you might use Stabil and clean out those pilot jets.

Strange, ive had the same problems with my new amal premiers for about a year now. If the bike isn't run for over a week, it will pop and bang around the 2000- 2500 rpm mark. This indicates a blocked pilot jet. My fuel tank and pipes are spotless but it still does it. After getting fed up with removing one carb to clear the idle jets, I remove the air mixture jet from both and blast them out with a compressor, this works.
Its very annoying.
Ive had it in a garage and paid to have them set up correctly, only for it to appear again if the bike is not run every week.
The other remedy ive used is to keep it above 3000rpm for 30 secs this usually clears it. Once the motor is hot there is no misfire.
I wont be buying amals anymore.
PS, the tank is clean and ive even borrowed a friends to try, but still the same.
Could be the electronic ignition, ive got boyer mk3 and boyer micro digital, still the same.
Good luck

blacklav said:

Strange, ive had the same problems with my new amal premiers for about a year now. If the bike isn't run for over a week, it will pop and bang around the 2000- 2500 rpm mark. This indicates a blocked pilot jet. My fuel tank and pipes are spotless but it still does it. After getting fed up with removing one carb to clear the idle jets, I remove the air mixture jet from both and blast them out with a compressor, this works.
Its very annoying.
Ive had it in a garage and paid to have them set up correctly, only for it to appear again if the bike is not run every week.
The other remedy ive used is to keep it above 3000rpm for 30 secs this usually clears it. Once the motor is hot there is no misfire.
I wont be buying amals anymore.
PS, the tank is clean and ive even borrowed a friends to try, but still the same.
Could be the electronic ignition, ive got boyer mk3 and boyer micro digital, still the same.
Good luck

Click to expand...

Turn of your petcocks a couple blocks before you get home to run down the fuel bowl and see if it still happens the next run.

Yep, it was the pilot jet. I did as Blacklav said, removed the air/mixture screw shot some carb cleaner in there then blasted it with compressed air. It worked! No more popping noise and it's idling much better than before. I just hope this doesn't become a weekly problem with mine as well. These Amals are definitely trying my patience. Thanks for the help everyone!

A little Stabil (the marine formula is twice as expensive and four times as good as regular; just sayin'...), Seafoam, Techron, or (my favorite) BG 44K in each tank will keep the bogeyman away....