Xr70 carb on a 50

As the title says I'm putting an xr70 carb (17mm) on my stock 50. Has anyone does this and know what intake manifold they used? I think I need one that moves the carb to the side like the big bore carbs, but I am not sure where to buy one.

As the title says I'm putting an xr70 carb (17mm) on my stock 50. Has anyone does this and know what intake manifold they used? I think I need one that moves the carb to the side like the big bore carbs, but I am not sure where to buy one.

I had the same thing happen when i put an XR70 cylinder and head on my 50.  I am also in the process of trying to find an intake and will let you know what i can come up with.  You may want to ask the folks at DrATV.com

I had the same thing happen when i put an XR70 cylinder and head on my 50. I am also in the process of trying to find an intake and will let you know what i can come up with. You may want to ask the folks at DrATV.com

I've seen a full 17mm kit for the xr50 on fast50s.com. I emailed them to see if they would just sell their intake. I'll update when I hear back.

Maybe something like this would work?

http://m.ebay.com/itm/330304544044?nav=VI&sbk=1

Edited by mjwwf5

Well, my experiment failed miserably.  I mistimed the bike and when I kicked it over, bent a valve.  So, it is back to a 50 again until I can rebuild the 70 head.  Let me know if you hear anything.  The saga continues.

I just looked at the adapter and although it may work,it defeats the purpose of the bigger carb.  You want airflow, and just adapting a 70 carb to a 50 intake won't get you what you are looking for.  

I got a reply from fast50s and they said they custom make an intake and gaskets for the 50 head. Pretty expensive at $60.

I've read in a couple forums that people used 18mm intakes from bbr or trailbikes. I think they had to drill out the bolt holes to fit though as they won't fit normally.

Interesting.  I will give the Brown Brothers a call here soon and ask about their intakes.  I think an intake that tips out the carb would work also, its just a matter of finding one that fits the bolts on the head.

As I recall, the XR/CRF70 carb bolt holes are only 45mm apart, whereas the bigger carbs (18mm Keihin, 19mm Mikuni, and the TrailBikes 20mm ShengWay) are all 48mm apart. Trailbikes makes an intake for the stock 50 head that is match ported to the opening, but those carb mounting bolt holes are also 48mm apart. 

Interesting. I will give the Brown Brothers a call here soon and ask about their intakes. I think an intake that tips out the carb would work also, its just a matter of finding one that fits the bolts on the head.

Let me know what you find. I'd like to do this right on mine and not rig it if that's possible.

Also are you porting your head? I've never tackled that before and am wondering it it is necessary.

Edited by mjwwf5

Are you doing this to support a big bore kit?  Just wondering if you are trying to piece two bikes together to get one of them running.  I have a functional stock 50 carb if you need one. 

Are you doing this to support a big bore kit?  Just wondering if you are trying to piece two bikes together to get one of them running.  I have a functional stock 50 carb if you need one. 

Nope.  Nothing like that at all.  I have an extra 70 engine with a roasted bottom end, so decided to put the top end on the 50.  Now we are just trying to figure out how to make the 70 stuff fit on the 50 frame.  

An  alternative would be to cut the 70 manifold at the base, rotate the upper part a 1/4" to the right, and reweld it, like I had done to a 50 manifold, shown below on a 70 head. I was curious to see if a stock looking small-block stroker would run with a stock carb and pipe.

 

101_0029-640_zpsa1f58cdf.jpg

Although a solution, this is something I was hoping to avoid.  Chicks dig welding skillz, but unfortunately, this is why chicks don't dig me.

 

I think BBR has something that will fit and make this work, but they have about a two ay turn around on emails.  I am in waiting mode.

Heard back from Chris Brown and the BBR manifold will not work for the 70 carb.  It is for a larger carb they sell in their kit.  So, to make it work, you would have to fashion something custom like dirtbkr did.  Damn it.  

 

Oh well, need to order a standard 50cc piston and just get the thing running as best we can for the 6 year old.

The ATC/TRX 70 intake manifold works perfectly for the Honda 50 engine using the XR70 carb.  I've used this intake on two of my 50's, both 1982 Z50R's. One of the 50's has a Powroll 75cc kit (stock 50 head) and the other has their 80cc kit (XR70 head).  Performance is very good and the power comes on smooth with no bogs.  I used the stock Honda jetting on both carbs.

The ATC/TRX 70 intake manifold works perfectly for the Honda 50 engine using the XR70 carb. I've used this intake on two of my 50's, both 1982 Z50R's. One of the 50's has a Powroll 75cc kit (stock 50 head) and the other has their 80cc kit (XR70 head). Performance is very good and the power comes on smooth with no bogs. I used the stock Honda jetting on both carbs.

Do expect the ATC/TRX 70 intake fits newer 50s as well?

I wouldn't know for sure without checking but I don't believe that the intake mounting has changed for the 50 in a long time, if ever.  I imagine that there is a difference in the intake passage diameter between the TRX 70 intake and the Z/XR/CRF 50 but I didn't do any port matching.  I used the TRX 70 intake gasket and heat isolator plate next to the carb.  Good Luck!

The intake mounting is the same, the issue is the carb top and throttle cable hitting the frame. I'm almost positive that the clearance is less on the XR/CRF50 frame than it is on the Z50 frames, and the ATC/TRX manifold stands taller than the 70 one does.

You are possibly right about the TRX manifold being taller than the CRF version.  As noted, the reason the CRF 70 manifold doesn't work on the 50  frame is that it positions the carb top so that it interferes with the frame.  The difference between the XR/CRF 70 manifold and the TRX 70 manifold is the TRX version curves out and moves the carb. away from the top rail of the frame - that is why it works.  I'm 95% confident this intake manifold will also work on the later XR/CRF 50 frames. 

Thank you both- super helpful!!

Create an account or sign in to comment

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

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now