Jump to content
Sign in to follow this  

Surging problem fix

Recommended Posts

I think I may have found the cause of the surging on my DR650. My suspicion is that at highway speeds, there is some pulsing turbulance at the top of the airbox after the modification (the top opened up). Kind of like if you open a car window and you get pulsing of air.

Using duct tape, I taped the top of the airbox (front and the sides) to the frame, so it has to pull the air primarily from the back or over the frame. I also put one strip across the air box opening (front to back). I am not sure if this last part is needed. So far it seemed to eliminate the surging.

Let me know if this works for anyone else.

Share this post


Link to post
Share on other sites

Let me know if this works for anyone else.

Good job m8ty, Ill give this ago at the weekend cause the surging is a $%&ki%g nightmare at the mo!!

Share this post


Link to post
Share on other sites

i covered up the hole i cut in the top of the airbox. took the side cover off. the surging was reduced.so i experimented but opening up the backside on top of the airbox. however, i broke off the bolts holding on the disks on my supertrapp ex. so now i am running with no disks,, surging was bad. so i retaped the hole havent tried it yet.

Share this post


Link to post
Share on other sites

i think i'm going to cover up my huge hole in the top as well to get some mileage back and run leaner jetting than presently in the bike.

Share this post


Link to post
Share on other sites

Just got an 05 DR650 and love the bike but in stock form the jetting was awful, can't believe that Suz would turn out a bike with such horrible jetting. Anyways here is what I did to fix my surging issues, removed snorkel, raised stock needle with 1 washer (about as thick as 1 clip position on an adjustable needle), stock main jet, backed out mixture screw 2 turns and that's it. I'm at 675 feet and about 70 degrees temp. I think it might pull a slightly bigger main but it runs sooo much better with no surging at all I don't think I'm gonna touch it unless I put a pipe on it. Remember "leaner is meaner"!!

Share this post


Link to post
Share on other sites

so.. i think you are onto something with the airflow.i think with the top cut out it may have too much flow. i know some will say that that is unpossible.

but.. i covered up the top (cut out earlier) took off the side cover. no changes still surged..i covered up half the side cover area. surging greatly reduced only surged at 70mph and then it was very slight. i am going to cover up some more and see.

Share this post


Link to post
Share on other sites

It seems to me that if the bike only has this problem at high RPM and small throttle openings (highway cruise), then excess airflow can't be the problem. "Too much air" is the same as saying "not enough fuel". Since the needle and main don't even come into play in this scenario, it seems that the pilot circuit is to blame. You can only affect that slightly with the pilot screw, so has anyone tried a size or two larger pilot jet? I notice that if I put the choke on slightly, the surging on my DR is reduced. I won't ride it that way because it's just plain wrong, but it tells me that something is causing a lean condition. The surge feels the same as when I hit the magic 130 mile mark and need to switch to reserve. Fuel starvation.

Could there be something going on with the vacuum slide? Maybe under high vacuum conditions, the slide is unstable or constantly oscillating? My slide isn't drilled, not sure if that would help the situation or hurt it.

Lastly, it could have something to do with (I don't know what else to call it) airbox harmonics when the side or top is removed. Maybe it's not a total flow issue as much as it's a pulse-wave thingy. I've heard of situations where the way that the air "pulses" through the airbox can actually create a sonic wave-type thing where the airflow becomes turbulent. At high RPM and small throttle openings there isn't much overall flow into the carburetor, but what flow there is would be at a high velocity....fast moving air slamming against the back of the carb slide a hundred times a second would maybe cause a problem?

I just wish someone a lot smarter than me would solve it without making me re-cover my airbox....

Share this post


Link to post
Share on other sites
I just wish someone a lot smarter than me would solve it without making me re-cover my airbox....

:crazy:

Share this post


Link to post
Share on other sites

Hi all.

Old thread revisited!! :)

How did you guys get on with the surging thing?

Im still trying to sort it out on mine (when cruising speeds)

At the mo i have duct taped the airbox topsides to the frame to stop the air

flowing over the top of the box.it helps with the surging but when the throttle is hard against the stop it feels like there isnt enough air flowing through the airbox.

I am gonna rip off the tape and start again.

:thumbsup:

Share this post


Link to post
Share on other sites

No fix so far, so I've basically just learned to live with it and I don't think about it much anymore. I've minimized it by going way out on the pilot screw - probably 3 turns or more, so a larger pilot may help but I haven't tried it yet. I'm now so rich on the bottom that I rarely use the choke anymore, but the surging is minimal, it runs well otherwise and I'm still getting 55mpg, so I guess I've thrown in the towel at this point.

Share this post


Link to post
Share on other sites

Mine surges off road on choppy terrain at minimal throttle input. Other than that, not much if any surging problems.

Share this post


Link to post
Share on other sites

I wonder about the slide sometimes too.

I did drill it and WFO air box mod. I had the tube that goes to the top side of the carb pointed down where air could blast into it. I had surges but only seemed in 5th gear....

I then repointed the tube up into the airbox using the little clampy thing, pointing toward the back of the bike. Seemed to help,,, but soon after that I put on the Q2 and 170 MJ and now all is well....

Somebody wrap their lips around that tube and blow on it see if the RPMs change any... Then try it going down the road :thumbsup:

Share this post


Link to post
Share on other sites
I wonder about the slide sometimes too.

I did drill it and WFO air box mod. I had the tube that goes to the top side of the carb pointed down where air could blast into it. I had surges but only seemed in 5th gear....

I then repointed the tube up into the airbox using the little clampy thing, pointing toward the back of the bike. Seemed to help,,, but soon after that I put on the Q2 and 170 MJ and now all is well....

Somebody wrap their lips around that tube and blow on it see if the RPMs change any... Then try it going down the road :)

You just Tee'd this up so some DR perv would take a swing at it, did'nt ya. But I am resisting.:thumbsup:

Share this post


Link to post
Share on other sites

I can't see how too much air could be an issue....the motor is still going to "pull" only the air it can use and the air box being cut is just no longer the "weak link" in the system.

Also, i have never had a surging issue.....

Share this post


Link to post
Share on other sites

Gas prices go up, jet sizes go down. Go figure! I know to some it may seem ignorant, but a lot of people are thinking it's surge when it's not at all. Be sure you're on a dead smooth stretch of road before imagining surge, because it could just as easily be uneven pavement working the suspension which feels a bunch like lean surging. I ain't making this crap up either...a mechanic friend tipped me off on this. Can't trust your ears on this one. I use my eyes for the above and then use them again after pulling a spark plug for a reliable indicator of overall engine happiness. I want my plugs to be like my women...nice and tan. No, I ain't going there.

Share this post


Link to post
Share on other sites

I think it's a slide stiction <sp> issue myself. Even with my bike set up a tad on the rich side I still see the surging issue that some have mentioned on my A/F meter. I don't really feel it but it is there with some very lean readings at times. If it is the same issue I'm seeing you will feel it on trailing throttle. It does not show up on the A/F meter during acceleration. It shows up during the transition from opening the throttle to closing or maintaining a particular throttle position. I've chased it around with different slide spring lengths but it never really goes away completely. I'm thinking of trying some graphite spray on the slide contact areas just to see it that changes the A/F meter any. I know it won't last long but it might help me confirm what I think is going on. If it is a stiction issue then is will be different on each bike based on varying levels of carb cleanliness, slide condition, etc.

Share this post


Link to post
Share on other sites

Does seem kinda rinky-dink to have a dry,plastic, slide riding up and down all day in an aluminum bore.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×