eprovenzano
03-08-2011, 07:20 PM
1st a little background.
99 400ex purchased 4 years ago. HMF pipe with the top of the air box drilled. It always ran well, but smoked and burned oil. Over the years, the lack of prior maintenance was corrected. Last winter I decided it was time to redo the top end. The bike was still on the OEM top end. I installed a new piston, rings, and replaced the valve seals. I put it back together and it didn't want to idle right, it would surge and stall. After 4 hours, the piston seized to the rod. My son said it was as iF it got hot...
I bored out the cylinder again (2 over), new piston, rings, gaskets etc. It idled a little better, but still surged. This time it lasted 10 hours. Again it seized to the rod.
This time I split the cases, replaced the crank, main bearings, timing chain with a CRF 450 chain, and timing chain tensioner. The cylinder is being bored out 4 over (406). I was cleaning everything while I was putting the engine back together and decided to open the carb to check the jets. When I bought the quad, I was told the jets were changed when the HMF exhaust was put on. Well what I found surprised me. The main is a 152 with a 38 pilot air screw at 2 turns. hmmm I think I found the issue... I know that a worn cylinder can mask jetting issues but damn... talk about running lean... If I'm not mistaken I should be running a 160 - 165 main with a 40 - 42 pilot.
I ask the jetting Gods if I'm on the correct path with the jetting settings. I'm thinking I should be at 160+ with a 40 pilot. Since everything is apart, I am going to check the needle also. Where should the needle clip be set at?
99 400ex purchased 4 years ago. HMF pipe with the top of the air box drilled. It always ran well, but smoked and burned oil. Over the years, the lack of prior maintenance was corrected. Last winter I decided it was time to redo the top end. The bike was still on the OEM top end. I installed a new piston, rings, and replaced the valve seals. I put it back together and it didn't want to idle right, it would surge and stall. After 4 hours, the piston seized to the rod. My son said it was as iF it got hot...
I bored out the cylinder again (2 over), new piston, rings, gaskets etc. It idled a little better, but still surged. This time it lasted 10 hours. Again it seized to the rod.
This time I split the cases, replaced the crank, main bearings, timing chain with a CRF 450 chain, and timing chain tensioner. The cylinder is being bored out 4 over (406). I was cleaning everything while I was putting the engine back together and decided to open the carb to check the jets. When I bought the quad, I was told the jets were changed when the HMF exhaust was put on. Well what I found surprised me. The main is a 152 with a 38 pilot air screw at 2 turns. hmmm I think I found the issue... I know that a worn cylinder can mask jetting issues but damn... talk about running lean... If I'm not mistaken I should be running a 160 - 165 main with a 40 - 42 pilot.
I ask the jetting Gods if I'm on the correct path with the jetting settings. I'm thinking I should be at 160+ with a 40 pilot. Since everything is apart, I am going to check the needle also. Where should the needle clip be set at?