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That Dang Surge is Back

80 posts in this topic

My bike has the DJ kit per Jesse with DJ 155 main, needle in 4th groove, airbox cut out, mixture screw at about 1.5 turns. This pretty much cured the stock surge. Now I've dropped my gearing just a tad with a 16/47/520 combo and seems like the surge is back. I guess it moved me right in the lean spot of the rev range. I don't notice it at fast Interstate speeds, but I sure do here at home. I was wondering about sticking the airbox screen back in. What do you reckon? I like this gearing, by the way.

Sarah

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you could raise the needle?

I'm assuming that the surge is between 1/4 & 3/4 throttle.

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Go up a size on the main jet and raise the needle up one grove,also check the float level:excuseme:Whats the plug look like? .My FCR was surging after 6 months of all kinds of riding(trail,highway),did the above and it all went away.

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My bike has the DJ kit per Jesse with DJ 155 main, needle in 4th groove, airbox cut out, mixture screw at about 1.5 turns. This pretty much cured the stock surge. Now I've dropped my gearing just a tad with a 16/47/520 combo and seems like the surge is back. I guess it moved me right in the lean spot of the rev range. I don't notice it at fast Interstate speeds, but I sure do here at home. I was wondering about sticking the airbox screen back in. What do you reckon? I like this gearing, by the way.

Sarah

Maybe just turn the mixture screw out 1/2 turn or so. The surging may be more related to colder weather than anything else.

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OK, I'll turn the mixture screw out a tad, that'll be easy enough. I don't think it's running rich, the plug looks good and there's not even a smidge of soot in the pipe. Thanks, I'll give it a try tomorrow and holler back.

Sarah

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Maybe just turn the mixture screw out 1/2 turn or so. The surging may be more related to colder weather than anything else.

+1

surge is usually caused by a lean condition. You may try putting the screen back in as it will slightly richen things up everywhere throught the range.

Surging below but near half throttle thru midrange, shim or raise needle.

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The mixture screw didn't seem to make much difference so I set it back where it was. I may be nuts, but installing the screen felt like it moved the surge up in the rev range so that I felt it at interstate speeds. I don't know if that's possible or not but it sure seemed like it. I took it back out. I'll either live with it as is or raise the needle and see what happens. Thanks again, everybody.

Sarah

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The mixture screw didn't seem to make much difference so I set it back where it was. I may be nuts, but installing the screen felt like it moved the surge up in the rev range so that I felt it at interstate speeds. I don't know if that's possible or not but it sure seemed like it. I took it back out. I'll either live with it as is or raise the needle and see what happens. Thanks again, everybody.

Sarah

If you are anywhere near sea level, 155DJ is too lean. One size up on main should cure it.

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My DR has always had some amount of surge if it is run at a steady RPM of around 4500-5000 (especially in 4th gear). Below that RPM it doesn't have the HP to noticibly surge, above that it is winding enough to keep things stabile. My guess is that your new gearing put you in a surging range at your cruising speed. The cold weather cold also make this more noticible. To some point I think the BSR carb is ready to rip or not at that speed, so very small changes in pressure/throttle position kick you from one mode to the other and back

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Wybs-- Sounds like you hit it dead on.

bgrzdr-- I reckon we're just under 800 ft elevation. I bought my DJ kit cheap from another DR rider, just my luck the 160 main jet is missing.

Sarah

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uping the main jet would certainly be the easiest way to remove a lean surge at cruising, if not the most efficient fuel wise.

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BSR-1,

I'd sure rather go the most efficient route. Raising the needle will most likely lower fuel mileage, but not as much as going up on the main jet? Man, these finicky carbs are something. Thanks for your patience.

Sarah

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Hey Sarah,

Since we know you've put thousands of happy miles on your DR with your current jetting it doesn't make sense to me that the jetting would suddenly be wrong. I would look at everything else that might affect it before making a jetting change.

There have been reports of wind turbulence around the carb vent hoses causing some surging. I'd suggest repositioning those vent hoses to get the hose ends out of the wind. While you're at it make sure they're not kinked or plugged. Check the secondary air filter too.

Pull the float bowl and check for dirt or water in the bottom of the bowl.

If you haven't removed the tiny fuel filter in the carb fuel inlet get it out of there. It can plug up easily and cause all kind of running problems.

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Thanks again for the help. The carb inlet filter is long gone, I'll check the vent hoses. I really think it's as Wybs said, the new gearing put me just in the wrong spot.

How complicated is a pumper carb? Christmas is coming up, you know.

Sarah

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How complicated is a pumper carb? Christmas is coming up, you know.

Sarah

I got the TM40 from Jeff & it was a piece of cake to install!

highly recommended!

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So it's really swap carbs and go? Seems like I read something about tinkering with the accelerator pump and knew that was sure nuff over my head. Thanks again.

Sarah

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In most cases it is 'bolt on and go' but just like the stock carb there can be some benefit of fine tuning it for the particular bike. One advantage is that tinkering with the TM40 is easier than tinkering with the stock BST.

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