2005 400ex bogging issues

[Espo720]

Bought it in November and it ran greatin cold weather. When I ride in the warmer weather it bogs out after it gets hot. Came with a full yoshimura exhaust, uni filter and a big gun rev box. The first time it did it I changed the oil and filter, cleaned the carburetor and put a new plug in. The valves were tighter than spec so I set them to the factory setting. Still same deal, I am getting a little smoke if I start it to move out of the shed and start it back up later on.

I am leaning towards valve seals but wanted to see what others had to say. I have heard the big gun boxes can crap out too so wasn't sure if thats something to check out. It only does it when I've been riding for about 10 minutes.

[CJM]

Valve seals are likely going. Big gun rev box is crap, throw it out and buy a stock box.

As for the boggin, if its in the upper RPM your too rich. remove the airbox lid-does it improve? If so your too rich.

[Espo720]

Out of curiosity... Could the CDI crap out when it gets hot? I know in most engines if a coil is bad the engine usually craps out once its warmed up. Kinda figured the valve seals were hurting plan on rebuilding top end this winter. Hoped I could get some use out of it this summer.

[DragonGunner]

Sounds like it loading up on fuel, rich…do like CJM said and try with lid off……after 10 minutes after warm up before it starts also tells me might be a stuck choke, or your choke is on.

[Espo720]

What size jets do would you guys recommend? I am going to pop the carb off in the morning and check the numbers. Not sure what sizes are in already, like I said the previous owner did the full yoshimura exhaust, uni and rev box.

What are common sizes normally run with similar upgrades? I'm reading through the FAQ page at the moment.

[Blodg]

I have a buddy who had the same issue. He spent weeks messing with his jetting with no improvement to find out it was his CDI box. I don't know what aftermarket brand he had but went back to stock cdi and it ran great.

It still could be the carb but I would swap a cdi to check that if it was me.

[Espo720]

Ordered a stock cdi. Checked my jets running a 38 pilot and 170 main. I can't imagine a 170 main is too rich with a full exhaust and uni filter. There was some crap in the air box from a mouse. Musta made a home and I didn't think to check because I just put the filter in before winter. Ran better still popping in higher rpms from time to time. Cdi is a shot but I figure the Big Gun box adds almost 1,000 rpms and that might be the problem.

[Blodg]

If the motor is stock other than the pipe and filter then a 170 main could be too rich. When mine just had a pipe and filter it ran great with a 155 main jet.

[JOHNDOE83]

You will never be to rich, unless your not fully reving out. Check the jetting procedure in the FAQ section at jetsrus.com for main jet tunnig.