Stock bore 10.8-1 piston + XR400 Cam?

[Crowdog]

Anyone here drop in just a higher compression piston & XR400 Cam with a port & polish? Did you modify your carb?

Or is it a better idea to go with a 416 Piston?

Crowdog

[James70214]

A port and polish aint gonna do much unles you get a bigger carb. As for modding your carb they remove the choke and can bore it to 37.5mm. You should just get the 4166 piston you will be happier.

[Crowdog]

Does modifying the carb require removal of the choke?

Crowdog

I put a WB all-around cam in mine with the piston (almost identical to the xr cam). It made a big differance but most important is the total package. I put a pipe on (great), airbox mod w/filter (better), pocket ported the head (better), advance key (better), put comp core in exhaust silencer (better).

I didn't remove the choke because I think I need it for very cold riding in winter. I didn't use the xr head gasket and did use the stock base gasket. Going to change that in a couple of months for more psi.

My quad feels like a 50% power increase although I know it's not near that much. If I was to do it again I probably would go 416 because the cost is virtually the same but a bit more powerful. :D

[400exRacerX]

I just purchase a je 10.8:1 stock bore piston, with a xr400 cam, and viton valve seals. i'll let you know how it is when I am finished. As for the port and polish, you will only notice it with a bigger carb and oversized head pipes.

[shook]

I did every thing you spoke of and Im satisfied but if I had to do it over I would probably go with a bigger cam may the GT Thunder cam or the W/B track cam theres not alot of size difference in the stock cam and the xr400 cam.It is larger but not by much

I have the same mods your talking about and I'm pretty satisified. I have more low end and it really hits it in third gear. I also modified my airbox, but you'll want to do that with a different cam. I also ride mostly tight woods and cross country, so I didn't want just a top end cam. After I talked with Terry at Marcums he said the xr cam is as good as any drop in cam. Plus the xr cam is only 120. If I had it to do over again I would consider the 416, because it doesn't really cost any more other than the cost of the bore. I haven't raced a 416 to tell if there is that much of a difference. I did race a 440 when my bike just had its pipe and it did not pull away from me, matter of fact I did beat it. I can't imagine there is a whole lot of difference between a 416 and stock bore with the xr cam. I like the idea of being able to punch it out to a 416 when it comes time to rebuild.

[tinner]

I'm happy with mine, I probably will get an FCR carb though.

[Dave400ex]

Mbiigamber, that is a Good Thing about staying at the Stock Bore. When you go to Rebuild it, you can just buy a 416 Piston. Then a 425 Piston.

I would still go with a 416 Piston though. I`m sure it adds More Power than a Stock Bore Piston. If anything would ever happen to the 416 you can still Bore it to a 425.

[Leo]

The stock bore JE piston is 10.5-1, and that's only if your using an XR headgasket..

I'll have a full report on mine (10.5-1 JE stock bore piston, XR cam, and XR headgasket) if I ever find time to slap it in :D

Leo

[knighttime]

Hey man, u gotta install that stuff. After you do you will be kickin' yourself for waiting so long. I would return the piston u have and get the 416 though. I modded mine myself (see below) and it rides so much better than stock that I would never own or ride a stock 400ex.:cool: