Thumb Throttle

[Entomber]

I just bought a used 400 EX and it runs fine but it doesnt look like it was well maintained. Anyway... I own a DS650 and rode a Raptor the same day I was riding my EX for the first time and I noticed the stock thumb throttle is wickedly stiff. Is it me or it's that way. Perhaps there is some dirt or grime in there that makes it hard to push.

I would check your caboe to see if it is freyed or kinked at all.
you can also take the cover off above the thumb throttle.
You can shoot a little WD40 in there where the thumb throttles moves...good luck

[barbwire44]

Open up the thumb throttle cover and remove the spring on the throttle arm it will help a little bit and won't affect the return spring in the carb.

[Deathbringer]

Yeah if the throttle is that stiff then something is wrong. Two ways I would approach it. First, check your cable for kinks or bends, and if it is replace it. Second, If the cable is in good shape, I would try a cable lubber they attach to the cable at one end and shoot lube down it till it comes out the other end. Just my two cents..

[86atc250r]

No, the thumb throttle on the 400EX should feel very nice if everything's operating properly.

Just go to servicehonda.com and order a new cable, like most other parts for the 400EX, you will be pleasantly surprised at how inexpensive it is.

Also make sure the thumb throttle housing isn't full of water or grime... Also clean and grease the thumb throttle shaft that runs thru the housing.

[Entomber]

I bumped into another 400 EXer at the local track and I asked if I can push his. Mine is slightly stiffer than his. I will lube it with some WD40. It's still not as easy to push as in a Raptor or DS. Sorry if I sound like I'm slamming it.. I guess I'm spoiled by my DS. I love how this thing wheelies....(unlike my DS) it comes up and off on demand.

[86atc250r]

His was probably in need of a cable as well.... I find it (when maintained properly) more effortless than pulling two carbs on the Raptor. Not sure about the DS, because the only two DS's I've ridden had Mikuni pumpers (and one had a twist).

One reason it may be a little more firm than an OEM DS is the DS uses a BSR CV carb in which you are only operating a butterfly with your throttle, engine vacuum pulls the slide.

You'd be surprised at how much a cable will help, even if the cable itself feels like it's operating freely when removed.

As the cable wears and gets grime in it, it will bind under load making the throttle seem "stiff" yet operate freely when not under load.

For the $14 a new OEM cable costs, seems like a no brainer if you think the throttle is stiff....

[Entomber]

You know.. I know this is a Honda based forum but you have enlightened my theroy on how the heck that slide would be pulled up on my DS carb!!!

I will invest in the cable. 14 bucks is nothing. How long do you think it would take for a not so exprienced guy to replace. It's not THAT stiff (like my friends DS Stage III with the Ron Woods carb) but the Raptor did feel smoother to enage as well as a stock DS. I will invest in the cable and will report the feedback.

[86atc250r]

It's a pretty easy job - no more than an hour for a first timer. Also take this opportunity to make sure the throttle is adjusted so that when you apply full throttle at the thumb, the carb is actually opening to full throttle - many 400EX's are delivered with the throttle only opening to around 70%...

What carb is Woods using? A buddy has a couple DS's and has 41mm Mikuni pumpers on both of them, they felt pretty good, but he will need to build some sort of seat support over the carb - if you put a lot of pressure on the front of the seat it will "pop" down and will obstruct the throttle pull on the carb so that you can't open the throttle without popping the seat back up.

The EX carb appears to be a CV carb when you first look at it, but when you operate the throttle cable both the slide and butterfly are mechanically acutated. Don't know the reasoning behind it, but it will generally give better throttle response than a CV type carb and will be easier to tune....

Also, be careful, the stock EX carb has an accelerator pump, so you can easily flood the engine by operating the throttle without the engine running.