Jump to content
Sign in to follow this  

How big should I go?????

Recommended Posts

I have an 96 XR 400. She is gettin kind of tired. I was planning on rebuilding it but I was thinking about going bigger. My dad recently did the same thing, but left it as a 400 and now wishes he went bigger. So not wanting to make the same mistake, how much bigger should I go. I dont want to go to big (such as a 440) becuase I cant afford to replace the things the bigger engine will break. I still want my ol girl to be bullet proof but have a lil more power. If it matters any to ya I ride mostly woods trails ( two track and single tack ) mostly but jump out on the road occasionally. I am also 5'11", 160. I was think somewhere around a 420 but dunno. Let me know what you think?

Share this post


Link to post
Share on other sites

Rebuild it to stock specifications. Scrape up the cash and get a Mkuni pumper. Twist the throttle and people will see your "pearly whites" from a mile away, you'll be smiling so big. Your bike will still be bullet proof but it will feel like an entirely different machine.

Share this post


Link to post
Share on other sites

The Mikuni Pumper is a carburetor with an accelerator pump the Edelbrock Quicksilver is also an option, these will eliminate the off idle hesitation but wont increase horsepower or torque much. I went to the 440 w/Hot Cam, Kibble White Valves, Edelbrock, etc. and other than being able to power through the stock clutch have not had any reliability issues what so ever. The Hinson 8 disc clutch set-up fixed the clutch issue.

Share this post


Link to post
Share on other sites

Stock bore is 85mm. You can go up to 87 without having to re-sleeve. If you go to say an 86mm that would put you at about 407 but you could also bump the compression up to 10.5:1 This leaves plenty of room for future expansion. If you want to get really serious you could also stroke it a couple of mm. 2mm of stroke with that 86 mm piston would put you at 418 cc. The added stroke plus higher compression will increase low end torque.

(Bore squared times stroke times .7854 = ccs displacement) Make sure you're using centimeters not millimeters.

8.5 X 8.5 X 7.0 X .7854 = 397.2 cc, stock displacement.

Area of a circle is pi X r squared, but your using the diameter not the radius. pi/4 = .7854.

Share this post


Link to post
Share on other sites

gbabe, We are riding at crow canyon sunday the 27th just south of new Philly Ohio, You anywhere near there? if so come join us.

Share this post


Link to post
Share on other sites

I dont know if the pumper thing will really solve my problem, I just need more power on those technical hills where ya gotta get on it then off then get back into it. My ol girl just doesnt have the power.

Where is that place in New Phila. I live in a 30-45 min west of there. Is it trails or mx stuff.

Share this post


Link to post
Share on other sites

Have you taken out the snorkel, removed baffle or gotten aftermarket exhaust, and rejetted? If not i seriously suggest doing the gorden mods, it made my 98 into an entirely different bike. Als make sure you valves are in spec. I just went on bore over when i redid my top end and i can wheelie with no problems through 3rd gear, definitely no lack of power on hills.

Share this post


Link to post
Share on other sites

First, like someone else, make sure the valves are in spec. It makes a friggen huge difference in power.

I went to a 426cc, 11:1 compression. Couldnt be happier. I also replaced the valves with kibblewhite valves at the same time. I've adjusted them ONCE since then (couple thousand miles later). I check them every oil change, and theyre spot on.

Power gain made the bike way more fun. I've had no issues with clutch or anything else.

Share this post


Link to post
Share on other sites

I know I sound like a broken record all the time...mikuni pumper...mikuni pumper.....but I really believe that the most significant "flaw," if you will, with the XR400's engine performance, is the stock carb. The XR should absolutely have the pumper from the factory. The XR is affordable...thus the cheep stock carb and a few other items to keep costs down. Nevertheless, even if you increase displacement, I can't see the point unless your going to melt down the stock carb to make beer cans, and install a pumper. Night and day difference vs. the stock carb. All the new four strokes have pumpers for a reason - they work. When I installed the pumper on my XR, the bike felt 50 pounds lighter - super crisp throttle response, power on demand - super light front end.

Share this post


Link to post
Share on other sites

Yes I have done the gordon mods and everything is jetted right and no issue there.

What is stock compression?

Share this post


Link to post
Share on other sites
The Mikuni Pumper is a carburetor with an accelerator pump the Edelbrock Quicksilver is also an option, these will eliminate the off idle hesitation but wont increase horsepower or torque much. I went to the 440 w/Hot Cam, Kibble White Valves, Edelbrock, etc. and other than being able to power through the stock clutch have not had any reliability issues what so ever. The Hinson 8 disc clutch set-up fixed the clutch issue.

BAD ASS. :ride::applause::thumbsup:

Share this post


Link to post
Share on other sites

I only have so much money to spend. So should I rebuild my tired old girl and make her bigger, then later on down the road put a pumper on it or should I buy the pumper now and worry about rebuildong it later.

Share this post


Link to post
Share on other sites

Sounds like you need to rebuild before you consider any additional items. How big is discretionary. Personally, I always enjoyed the knowledge that the stock engine is proven to be as reliable as a hammer - just plain indestructable. That's why I never went bigger with the displacement. I always worried that the engine would lose some degree of reliability if modified in that regard. Heck - part of the reason I got that XR was becuase I knew it would never leave me stranded in the woods. That's why I went for the pumper when I wanted more performance...and it worked. So personally, I would stay stock. Some of the guys with more experience with the oversized top ends may tell you different. Sounds like quite a few have had good results with the big bore kits.

Share this post


Link to post
Share on other sites

The pumper transforms your bike!!! I got mine installed Saturday. I know it does not increase HP, but it sure feels like it. And the power is instant, right from the very bottom end. There is NO way to compare it to the stock POS they put on the XR 400.

There is a Mikuni for sale on this board or fourstrokes.com, for 275.00, but it is used. Regardless, go to XRsonly.com and check it out. You will not be disapointed.

Oh, rebuild your top end, and see how it runs, then, put on a Mikuni, and feel the difference. You WILL not be disapointed.

Also, if you google HOnda XR 400, you'll find many tech articles that talk about the Mikuni. It's unanimous.

Share this post


Link to post
Share on other sites
I only have so much money to spend. So should I rebuild my tired old girl and make her bigger, then later on down the road put a pumper on it or should I buy the pumper now and worry about rebuildong it later.

I would do a compression check before you decide.

You are on a budget like most of us then I would make sure you have lost compression before you spend the cash on a big bore kit.

I do not know what the compression should be but if you do a search I am sure you can find out.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×