I tried to install my spark arrestor on my DMC Dual and noticed that its creating too much back pressure for my carb to keep up. It seems to be sputtering right off of launch at around 2000rpm and then it settles off (coughing and sputtering) as it passes around 4000rpm. I took the spark arrestor back off and it ran fine. It's also making my Warrior flood easier if I give it too much gas while cranking it over.

Which needles do I have to adjust to get the thing to run right? I'm knowledgable with carbs only to the fact that I know what everything is on it, I just dont know which adjustments will give me the best output. Any help would be appreciated and please dont be afraid to include some details.

 

on the top of your carb you have what is called (needle) you need to raise the clip setting on that .witch in turn lowers your needle witch inturn leans out your mid rpm range ....by restrickting your exsaust you are causing your engine to run rich ..

 

So would turning the needle out be making it richer and turning it in make it more lean? And are you talking about the pilot needle?

 

Biggy is talking about the needle. It does not screw in or out. Like he said, it is in the top of carb (part of the slide assembly). It has notches with a c-clip on it that you move to raise or lower the needle. I believe you are refering to the air screw that is on the bottom of the carb that you access without disassembling the carb. Turning the airscrew clockwise (in) leans out the engine. Turning it counter clockwise (out) richens up the engine. From the symptoms you describe, you may need to adjust both. First turn in your air screw 1/2 turn and see what happens. This will affect the engine off idle to about 1/4 throttle. See how it runs then. If that helps down low, but the midrange still blubbers, then raise the c-clip on the needle one notch (lowers needle, leans out midrange). Always adjust one thing at a time so you know whether or not you went the right way. Also, how does the top end run? I would think the spark arrestor would affect the top end more than down low? If it blubbers up top, you may need to change the main jet. If that is the case, go down one step at a time.

 

Hey thanks CBUS660R, that info really helps a lot. I already have the main jetted to 155, but I wont rule that out if things dont shape up. The top end seemed smooth, but with it sputtering through low-mid, I didnt really want to take it all the way to the top of the powerband, so there may still be issues up there I just haven't seen yet. I think I'll start adjusting the settings this weekend and see what happens.

 

If I may just add a little, in maybe a more basic way!
The air/fuel mixture screw controls 0 to 25%......your needle controls 25 to 70%........yor main controls 75 to 100% throttle.
Now knowing this, lets establish a base line.
Turn your air/fuel mixture screw all the way in, then screw it out 2 1/2 turns.
Then insure your needle c-clip is on the third slot from the top. You get to your needle by removing the top cover off your carb, pull out the slide, and thier it is.
Leave your main alone for now.
Start your bike, let it warm up good, hows the idle?......Give it a couple quick pops, any delays, any blubbering,bogging.......if no leave it.
Now give it another quick couple of pops, may not be graet, but rideable.
Now ride it around, for ten minutes, check your plug, if it's black go down on your main.......If it's white go up on your main. Try to get it brown, but more than likely it will be black looking almost like it wants to turn brown, you may even think one more main change out you'll have it, STOP, don't change the main.
Start over again, hows your idle, do you have any back firing coming off throttle, if you rap on your throttle does the engine cost back to idle instead of rite back to idle, if either or both of these happen, take another 1/2 turn out on your air/fuel mixture screw.
Now how snappy is it, not very, try lifting your c-clip on your needle, this will lean it out, snappy yet,no, now try putting your needle back on the third slot and lower your main.

I know this sounds like alot of back and forth, but this is what it takes and more to get a perfect jetting combo.
A lot of poeple don't realize that if your riding at full throttle, your riding on your main rite, well what about the needle, and the air/fuel mixture.....do you think these two just shut off 200 yards back....NO!!!
Thats why you establish a base line, install stock settings, and then see what you have to do, work the carb from the bottom to the top and then from the top back to the bottom.
You may not want to make changes for weeks at a time after you get it running ok, but just stay with it and sooner or later it will start first start, it will idle perfect, the throttle will be so responsive to your every movement, it will just RIPPPPP!!!!!!!!!!!!

 

Gaff, what's wrong with using his current settings and adjusting from there? We already have a baseline that it runs good w/o the spark arrestor, rich with it. By adjusting from his current settings, he already knows which way to go (leaner). As for checking the plug, unless you do a plug chop from WOT in 4th-5th, you will not get an accurate reading on your main jet. I agree with the percentages for circuits vs. throttle position and that the needle and main work together on the midrange. After all, the needle acts as control for valve for the main. If you change the main, you will need to re-evaluate the needle.

 

I'm sorry I didn't explain!
The settings I gave should bring him close if not exact to stock.

A plug evaluation is an obsolete way of tuning, due to the quality of fuels and such. But it still is a graet way for the novice tuners.
My opinionated way has brought poeple to better under stand thier individual bikes.
As I work on all types and makes, I realy encourage poeple to learn thier own jetting.
How often (exspecialy on here) do we hier of poeple bringing thier mods to a shop and bam, why this and why that.
I don't want to say I know better than you or any one on this forum, but what I do know if we get this guy to stock settings and steer him in the rite direction, he will be back and let us all know his findings.

And his statement doesn't give enough info, but the 2000 and 4000 statements let me believe he will be chasing his tail with main change outs if he doesn't clean up the bottom.

And yes he will have to re-evaluate all ranges after any changes.

I personaly after many many years still re-evaluate my jeeting many times even if every thing looks and feels ok.

I find this forum to be awsome, I know you get that one smart a$$ from now and then, but for the most part you must agree, Lots of good info, and you will learn some thing every day.