New 200x exhaust backfire

[Scratt]

Hey guys I just picked up a new DG exhaust for my 83 200x and rejetted it to what I think is good but on the decceleration it makes a spudder and backfire. I searched a bunch of threads seeing lots of people had that with a leak in the exhaust or to rich will do that as well. It has no spark arrestor so I am just wondering if that will cause it with no back pressure or its one of the other 2. I can't see it being a leak just cause its brand new I could have did the jetting wrong what do you guys thik?

[Dirtcrasher]

You either are not rich enough or have an air leak. Try playing with the airscrew on the carb 1/4" turn at a time. And read that plug!!!!!!!!!!!

[big red hemi]

like dirtcrasher says its prolly lean. remove the airbox lid does the condition improve or worsen. if it gets worse then you know for sure its lean. when you up jetted did you adjust the needle. lowering the clip on the needle will pull it up out of the main jet and give the engine more fuel in the mid range. there is a great jetting thread in the first class help section.

good luck

[Scratt]

I checked out the jetting thread while I was doing my jets but I did not adjust that needle so thats probably it I just want to make sure its not cause there is no spark arrestor in there.

[H2Sbass]

Personally, I've found when you go to a bigger pipe the pilot jet needs to go up a size. If you think about it, it backfires when you are decellerating which means throttle is likely closed. The pilot jet is what meters fuel at 0-1/8 throttle. Hope this helps. :cool:

[Dirtcrasher]

A DG will probably need a main jet 2 or 3 or more sizes larger and a pilot one up; They flow quite a bit. Ultimately the main jet plays the largest role in all the jets. You may think your main is large enough which is why I said to read the plug. There are so many factors in jetting.

There was a good thread by Dammit on here somewhere......

[tri again]

Personally, I've found when you go to a bigger pipe the pilot jet needs to go up a size. If you think about it, it backfires when you are decellerating which means throttle is likely closed. The pilot jet is what meters fuel at 0-1/8 throttle. Hope this helps. :cool:

This may help in the general scheme of things.

[Scratt]

So I finally got to work on it and I moved the needle clip down 1 position so its on the last slot and the jet thats in there is #118. It stills backfires and pops on the decceleration and so i checked the plug and the tiny little ignitor thats in the middle of the plug is white and the rest of the plug is black but not wet. Any suggestions? I have not changed my pilot jet i believe when I did my jets i looked at it and it was a #40 I could be wrong though.

[Tri-Z Pilot]

Increase the idle air/fuel screw until it stops backfiring. If this does not help you definately need to increase the pilot jet a size or 2.
What happens is when you "chop" the trhottle you are running off the pilot circuit, and due to the increased airflow of your mods you are getting 'pre-igniton" of a high volume of air and less fuel that hits the hot combustion chamber and fires off before it is supposed to.
Richen up that pilot circuit and I guarantee your problems stop. But as all the veterans on here know you gotta due plug chops to make sure your jetting is where its supposed to be. Lean air cooled motors are the easiest to meltdown/ Blowup.
If you need help on how to do plug chops don't hesitate to ask, it's extremely simple.