Edelbrock tuning question


5 replies to this topic
  • 309

Posted July 24, 2004 - 07:03 AM

#1

Howdy folx,

I'm having a bit of trouble with the Qwiksilver on my WR426, I know lots of you guys run these, so I figured I'd ask here..

Background: The bike is a supermoto race bike built for TT owner Steve Claus by Rob Barnum. It was tuned for sea level. I am in Colorado at 5400 feet, so I would think it would be running rich, but....

I had no problems with starting or running, but had a lot of popping on decel. By email, Rob suggested I adjust the needle richer. This got rid of the popping, but made for some stutter at part throttle, and reduced throttle response in general. Leaning it back out a couple of clicks gets rid of the stutter but brings back the popping. Seems the leaner I go, the better the bike runs, but the popping gets worse.

On a more conventional carb, I would adjust the air/fuel or try a different pilot jet, but on this one I have no clue. Do I need to adjust the pumper screw thing, try a different needle, or what?

Thanks for your help :thumbsup:

  • mikekay

Posted July 24, 2004 - 10:37 AM

#2

After years of jets and air screws the Edelbrock can be a bit confusing. The thing to remember is: Its super super super simple.

As you know there are three things to consider when tuning it--needle placement (the screw on top), pump amount (screw on bottom right) and then there is the needle size itself.

Assuming everything else is ok--no leaks in the manifolds, airbox, proper adjustment of the valves, etc., etc.----
Then you are correct to click the needle adjuster a bit richer or leaner. Ideally you want to be right at the point where it might-once in awhile-pop on extreme deceleration.
However--you mention issues with throttle response. That indicates both the needle adjustment--and especially the pump adjustment.
On the XR650 the pump is usually about 3 1/2 turns out from full in. Not sure on your bike, but point is this--
Try getting things as dialed in as you can with the needle (red button on top) and then try to work on the throttle response with the pump adjuster screw.

If all this isnt getting you to where you need to be:
1) you might have a sticking 'pellet' in the pump system, or you might have a sticking inlet valve (its just inside the fuel line entry point). Be carefull that you dont loose the free floating pellet if you open it up for a cleaning.
2) you might want to play around with different needles. For you bike at your altidude (freudian slip) few TTers will have much info--you might want to just call Rob Barnum and ask him what needle to try. As you have found out he's a nice and very approachable guy. He is also a consultent to Edelbrock for the QS carb...

Play around a bit with the wonderfully externally adjustable Edelbrock carb. Usually its easier to dial in than the clickers on your forks.

:thumbsup:

  • qadsan

Posted July 24, 2004 - 01:12 PM

#3

The only thing I have to add is if you do adjust the accelerator pump, do it in 1/4 turn increments. As Mike said, first get the needle clicker adjuster on top adjusted so you get good WOT throttle response. If you're needle clicker is close to being maxed out at one end, then you probably need a different needle. A little popping is normal and perfectly acceptible, but if its popping a lot, then changes are likely needed. The off idle throttle response should be very quick when the accelerator pump is correctly adjusted. If the throttle response feels lazy off the bottom, then adjust the pump screw in 1/4 turn increments until it improves and note where it's at. Then keep adjusting it in the same direction until it gets lazy again. Now work within that range where it feels good in 1/8 turn increments until its as good as it gets.

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  • 309

Posted July 24, 2004 - 05:05 PM

#4

I spent a good deal of time screwing with it this afternoon, and got it running great. Throttle response is great, no more stutter or bog. However, this was again done by leaning it out to the point where I got quite a bit of popping on decel. I've owned four stroke thumpers before, and can accept that they pop some, but this is too much. The setting that is working so well is 14 clicks from full rich, which from what I've read is right on spec, the pumper screw is 3 turns out, which seems about right as well....

Here's what I'm wondering....

Will a leaner needle allow for a leaner condition at the same setting? So I can run it at say 10 clicks out (where the popping stops) and be getting a similar mixture to what I have now with it 14 clicks out? In my walnut-sized brain this seems to make sense, but the whole walnut-sized thing has lead me to distrust my brain.

Rob Barnum's email is full, and I hate bugging people at work with questions like this.

  • qadsan

Posted July 24, 2004 - 05:40 PM

#5

Will a leaner needle allow for a leaner condition at the same setting? So I can run it at say 10 clicks out (where the popping stops) and be getting a similar mixture to what I have now with it 14 clicks out?


Now it's time for my walnut sized brain to take a dump, but here's what I'm thinking at this moment. 10 clicks out is richer than 14 clicks out. 14 clicks out gives you the best top end performance, right? But...you want things enriched a bit more down below to minimize the popping. So...if you went with a one step richer needle, then you may end up at 18 to 20 clicks out to get similar top performance, but the bottom end would be enriched a bit more. There's a good deal of overlap with these needles from what I recall, but I don't know the specifics anymore. Let me ponder this a bit more because I just don't have my thinking cap on tonight (did too much roofing work today :thumbsup: ).

  • mikekay

Posted July 25, 2004 - 07:53 AM

#6

Are you sure you arent getting to much pump?
To much pump would cause what you are explaining...the bogging at low end. Of course no pump at all would do the same--but you seem to be able to acheive that crisp hit at times-so presumably the pump is working.

have you taken it out of the manifolds and whicked the throttle to watch the pump amount? you want a (very roughly)teaspoon or so of fuel to sort of 'ejaculate' up. Not sure of a better way to describe it. Not a geyser, not a mist, not a slow forming puddle either.





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