Trailryder42
Member
- Feb 6, 2000
- 295
- 0
Hey all,
I just got my XR400 engine back from having Thumper Racing put a 440 kit in it. They told me to run a cooler DPR9Z plug(NGK) in it rather than the stock DPR8Z.
This thing is not jetting out like I expected it to. I've messed with it almost a week playing with different jetting, fuel screw and needle positions. I think I have it close now but it's not as rich as I thought it was gonna have to be. I have gone up only 1 size on the pilot and 2 on the main and even had to drop the needle 1 position to get it running as well as it is now.
Before and After specs: Snorkle pulled, header flange welds ground, UNI air filter, 3 1/4" holes drilled in stock exhaust baffle end cap(Gordon Mod), elevation 3600'
Jetting before kit: 158/55, needle stock mid(3rd from top) position
After kit: so far- 162/58, needle 2nd from top.
I have 30 miles on it since the kit install. I rechecked valve clearances at 25. Exhaust was a little tight.
Was wondering if changing to a cooler plug, in general, all other things being the same, would cause a need to run slightly leaner jetting. ? I know in this case things are not the same but was wondering if it was something I should consider while trying to jet this thing. I tried TR's recommendation of 2 up on the pilot and 4 up on the main from the start and that was way rich.
Was also thinking about adding a 4th hole in the baffle end cap to accomodate the extra displacement flow of the engine, trying to make the exhaust system flow close to the same percentage for the 440 as it did for the stock 398, and then perhaps the jetting would come inline as easy as it did when it was stock bore.
Yea or Nay? Opinions/thoughts welcome/appreciated.
Derek
I just got my XR400 engine back from having Thumper Racing put a 440 kit in it. They told me to run a cooler DPR9Z plug(NGK) in it rather than the stock DPR8Z.
This thing is not jetting out like I expected it to. I've messed with it almost a week playing with different jetting, fuel screw and needle positions. I think I have it close now but it's not as rich as I thought it was gonna have to be. I have gone up only 1 size on the pilot and 2 on the main and even had to drop the needle 1 position to get it running as well as it is now.
Before and After specs: Snorkle pulled, header flange welds ground, UNI air filter, 3 1/4" holes drilled in stock exhaust baffle end cap(Gordon Mod), elevation 3600'
Jetting before kit: 158/55, needle stock mid(3rd from top) position
After kit: so far- 162/58, needle 2nd from top.
I have 30 miles on it since the kit install. I rechecked valve clearances at 25. Exhaust was a little tight.
Was wondering if changing to a cooler plug, in general, all other things being the same, would cause a need to run slightly leaner jetting. ? I know in this case things are not the same but was wondering if it was something I should consider while trying to jet this thing. I tried TR's recommendation of 2 up on the pilot and 4 up on the main from the start and that was way rich.
Was also thinking about adding a 4th hole in the baffle end cap to accomodate the extra displacement flow of the engine, trying to make the exhaust system flow close to the same percentage for the 440 as it did for the stock 398, and then perhaps the jetting would come inline as easy as it did when it was stock bore.
Yea or Nay? Opinions/thoughts welcome/appreciated.
Derek
