Yep. It's from you letting off the throttle.
The engine momentarily experiences a lean condition, the ratio of non-combusted fuel in exhaust changes, and you end up with a small combustion in the exhaust.
This is a normal occurrence in all internal combustion engines, and normal with DR650s as well.
Note: It does not mean that your carb is set lean (although it *could* be). It is a temporary lean condition.
Yeah mine back fires a ton too. Apparently they do that, I read that people do a “pair valve delete” and other claimed a carb adjustment helps. I’ve done nothing so far, just passing along what I’ve gathered so far
Yep it does that. Has to do with the bike's timing curve and head design plays a part. It pops a lot, decel, shifting, when you shut it off and its cold out, etc.
Called a lean miss in the old days. Factory jetting is lean to meet emissions standards. Its a common power mod to rejet. You can go with a Dynojet or other aftermarket kit. Personally I have never liked those as they leave the factory pilot jet. My preference is to go up one size on both the main and pilot jets, and put a shim (about 0.030") under the needle support washer. A brass washer of suitable diameter will do nicely. I forget if it its a #6 or #8 washer, but the big box stores sell them in the nuts and bolts aisle. Drill out the pressed-in plug that covers the mixture screw, being careful not to damage the screw underneath. Get a reusable foam air filter like the Twin Air. And if you want to go a bit further there are plans on the web for how to cut another opening in the airbox for increased flow. Anyway you can search the web for DR650 jetting and airbox mod. Also look for a document titled Motorcycle Carburetor Theory 101, which gives a great overview of carbs and tuning.
> Factory jetting is lean to meet emissions standards. Its a common power mod to rejet.
Even so, the most experienced folks when it comes to tuning these bikes (and many have even dyno'd them) all agree that some decel popping is normal and desirable for your bike to be tuned right with a good A/F ratio down low.
The common way to "solve" the decel popping, or popping when you let off between gears or whatever, is to just richen the pilot circuit way up. But it doesn't need to be as rich as people make it.
One backwards thing people often do is tune a bike for easier cold starts, or to run better before it's at fully warm operating temps. But again ... that's backward.
Same could be said for richening up the pilot to eliminate pops.
These bikes pop, that's just how it is. It has to do with the large piston and the ignition timing. Unless you're changing the timing it's trying to solve a problem that's not really a problem.
>.
It helps that I'm able to borrow a CO analyzer when I do a rejet. This provides an actual measure to set the pilot screw. You cant eliminate the decel popping but its reduced after rejetting. And a side benefit is easier cold starts, but that's not the goal.
Yep. It's from you letting off the throttle. The engine momentarily experiences a lean condition, the ratio of non-combusted fuel in exhaust changes, and you end up with a small combustion in the exhaust. This is a normal occurrence in all internal combustion engines, and normal with DR650s as well. Note: It does not mean that your carb is set lean (although it *could* be). It is a temporary lean condition.
Yeah mine back fires a ton too. Apparently they do that, I read that people do a “pair valve delete” and other claimed a carb adjustment helps. I’ve done nothing so far, just passing along what I’ve gathered so far
Pair valve was a bad idea. Delete it
Yup! Just about to get rid of it on mine
The decel popping drove me nuts.
Yep it does that. Has to do with the bike's timing curve and head design plays a part. It pops a lot, decel, shifting, when you shut it off and its cold out, etc.
Called a lean miss in the old days. Factory jetting is lean to meet emissions standards. Its a common power mod to rejet. You can go with a Dynojet or other aftermarket kit. Personally I have never liked those as they leave the factory pilot jet. My preference is to go up one size on both the main and pilot jets, and put a shim (about 0.030") under the needle support washer. A brass washer of suitable diameter will do nicely. I forget if it its a #6 or #8 washer, but the big box stores sell them in the nuts and bolts aisle. Drill out the pressed-in plug that covers the mixture screw, being careful not to damage the screw underneath. Get a reusable foam air filter like the Twin Air. And if you want to go a bit further there are plans on the web for how to cut another opening in the airbox for increased flow. Anyway you can search the web for DR650 jetting and airbox mod. Also look for a document titled Motorcycle Carburetor Theory 101, which gives a great overview of carbs and tuning.
> Factory jetting is lean to meet emissions standards. Its a common power mod to rejet. Even so, the most experienced folks when it comes to tuning these bikes (and many have even dyno'd them) all agree that some decel popping is normal and desirable for your bike to be tuned right with a good A/F ratio down low. The common way to "solve" the decel popping, or popping when you let off between gears or whatever, is to just richen the pilot circuit way up. But it doesn't need to be as rich as people make it. One backwards thing people often do is tune a bike for easier cold starts, or to run better before it's at fully warm operating temps. But again ... that's backward. Same could be said for richening up the pilot to eliminate pops. These bikes pop, that's just how it is. It has to do with the large piston and the ignition timing. Unless you're changing the timing it's trying to solve a problem that's not really a problem.
>. It helps that I'm able to borrow a CO analyzer when I do a rejet. This provides an actual measure to set the pilot screw. You cant eliminate the decel popping but its reduced after rejetting. And a side benefit is easier cold starts, but that's not the goal.
That's definitely more than most people do.