[honda250xrider]

Just wanted to give you guys a look on what I had to do to the crf head to get the crf 250r angled boot onto the head to allow the carb to clear the rear shock mount.

The head is rough right now as I'm still tweaking it and this is probably the 6th time I'm tweaking a few things in the intake track. (I still need to sand roll the intake tract smooth it out etc)

You'll notice that you have to offset the head opening as the crf 250 boot makes the carb kick up and on an angle. If not you will likely have about an 1/8" or so of the head impeding air flow.

I would love to be able to get the Trx 450 head on the atv however I do not believe it will fit as it has a more centered intake track and I have to have the angle from the crf head to make the rear shock mount work without hitting the carb on it.

This motor runs very well and will pull my mildly built Ltr without a problem.

I use 14/38 gearing on the crf motor (pretty tall if you ever have ridden a crf motor the 1-2 gears are very long) and 13/38 on the Ltr

Pictures are below.

 

[shiftx450]

In doing this, you're eliminating having to cut, rework, manipulate, and weld the stock ltr rear shock mount?

 

[honda250xrider]

No you will still have to redo the rear shock mount.

The only way I could get it to work right was to use the crf 250r intake boot. You may be able to get away with using the stock crf 450r intake book however on mine it would make the intake tube hit the rear shock tube. It would still work however it would have a sharp bend.


It also varies on how you mount the engine with relation to the rear sprocket. I opted to mount the engine so the front sprocket was aligned with the rear sprocket. On mine I had to run the Walsh linkage as the rear shock will hit the kick starter case if I use the OEM linkage. (You can solve this by putting the engine in more to the right however then you have to have custom sprockets)

 

[shiftx450]

Wouldn't a custom sprocket be much more simple that what you've got going on?

 

[honda250xrider]

It depends there's always pro and cons.

When you move the engine to the right more you also will move the shift lever to the right with that. Likely 1/4" - 3/8" . You can use a trx 450r shift shaft however I opted not to due to worrying about being able to bend it easier since it sticks out of the case an inch or so more. I ended up getting a hammerhead +12mm forward extension and turning a piece of aluminum to screw into the shifter to bring the shifter out a bit more. (When you start the process you'll see what I'm talking about on being able to get positive shifts.)

I also wanted to keep the ability to replace sprockets cheaply.

Also another thing that depends on how the carb is going to be angled is the bottom frame rail motor mount. You can move this around until you find a spot that works the best.

 

[woody]

So your building a 4 stroke 250 crf mod but with a 250cr intake boot? Is it for schoolboy classes or just to be super light because it sounds more difficult than a 450 crf mod?

 

[honda250xrider]

No, I am using a crf 450 motor but due to the rear shock mount I had to use the crf 250r intake boot. It has an angled intake boot vs straight like the 450 does.

I just got done testing the new port layout and offsetting the head/intake port and it went from a 180mj to a 168 and the needle on the 2nd clip from the 3rd.


The 168mj is still rich and I will likely end up at 162-165mj. With 168 it was hovering around 12.1-12.3 wot under load.

 

[Zumbo]

This makes me search for more quads. This thread is so bad its good. Im planning a crf swap this winter. Subscribed

 

[honda250xrider]

Let me know if you need help. I can get you any pictures or tell you how I did it and what worked best for me.

 

[camden.gilstrap]

did you make your own mounts?