Howdie,

I have a buddie who owns a 00' 400ex. He had the Big Gun system and K&N filter/jet kit installed by "his" shop about 8 months ago. When he brought it home, it had a faint backfire (it was supposedly jetted correctly). He is no mechanic, but about 3 months back, he fiddled w/ the jets until he was satisfied but now the quad backfires worse. Its sitting in my garage right now waiting for me to fix.
His Big Gun system has also sprung a leak at the junction where the back part of the pipe slides over the front(header) pipe.

I dont know much about the 400ex or thumpers in general. What I need to know, is the run-around on what carb adjs. should be maid to get him dialed in correctly (mains,pilots,needle adjs..etc), and how to stop the leak on the headerpipe. Exactly what #NGK should he be running as well.

Sorry for the length. I hope this is understandable. Thanks for your time,

EC

 

Tell your friend to put everything back the way it was when he brought it home from the shop. Because the Big Gun is a racing exhaust, it's straight thru. As compared to the stock system. He will have a faint backfire when lets off the throttle. Tell him to run it till it blows! If it does he can take it back to the shop and kick some butt.

 

For jetting info and other carb dialings look at sparksracing.com. Look in their tech section they have some info for a 400EX with bolt on mods. The machine is more than likely jetted very rich which seems to be common with people who put bolt on products on their 400s.

I personally run the cold plug in my 400EX I dont remeber the number but from what I know their are only 2 NGK plugs for the 400EX/XR. I used to run the standard plug but I cracked the porcelain on like 3 of them. SO I switched to the cold plugs and havent had any problems since.

Adam Smith

99 400EX

 

QuadBuster,
I have the complete BG system on my 400 and I run a 165 main, 42 pilot and down one notch on the needle. Also, I have to seal up my headpipe and silencer about every two weeks to keep a good seal on it.

 

Give the guys at Big Bug a call. You can get their # at their web site, I believe it is biggunexhaust.com. They are very knowledgible and eager to help.

 

DPR8Z is what it should have, some run the slightly cooler DPR9Z, jetting is tough but mine is perfect with a 170 and no lid, even before my major engine work, the 146 and lid work great too, my dynojet jet kit instructions were dead on!The pilot jet should not have to be changed, thats just for idle, mine hasn't been touched.