509 replies to this topic

[r_nally TT Newbie]

Thanks, 50 is about the largest pilot I have heard of anyone running but it might be worth a try.  What about fuel, I am just running regular unleaded?

[Baja Rambler TT Silver Member]

The pilot screw (fuel screw) bleeds fuel into the venturi at idle.  When you adjust it, does it change the idle?  If not, its passage may be plugged or it's incorrectly installed, i.e. spring, washer, o-ring.

[Baja trail Rider TT Gold Member]

To help on start up.My 42mm still has cable choke.When cold if I pull it out all the way,wont start BUT.If I pull it out 3/16 starts 2-3 kicks.So I think choke jet too big.If its hot(outside) on frist start up.No choke.BTR

[xr4fun TT Newbie]

Here's an update on my BSR42. I changed the PJ from 45 to 40 to try and get a quicker start when I dump the bike.  I bought a Tach and hooked it up and got the highest idle and best throttle responce with the pilot screw at 3.5 turns out.  It did not help the hot start, but it did make the cold starts much harder.  It does not like being cold now.  I'm going back to 45 or maybe try a 42.5 because I like to fiddle.

With the 45 pilot it was starting cold with one kick and starting hot with one kick, it just didn't like to be tipped over.

I think the trick to hot starts when dumped is to give it a little throttle.  First give it a couple kicks to clear it out and then crack the throttle a little and give it a kick.  If that doesn't work then leave the throttle alone at the beginning of the kick and give it a twist as you are finishing the kick.  That seems to work really good for me.

I also changed the MJ from 195 to 190. Now it rips at full throttle!

I just raced my first Hare Scramble ( 30 amateur) with the 40/190 jetting.  I love this carb!  It was a dead engine start straddling the rear fender.  I got a one kick start and got the hole shot against all of the usual e-start modern bikes! That was very fun. I could let the bike go all the way down to idle in 2nd or 3rd grear in a corner and then just grap a hand full of throttle and it never stumbled.  This race had a motocross track, log crossings, grass flat track, rock sections, and LOTS of woops.  The bike ran flawlessly and I was able to loft the front tire when ever I needed to. I ended up with a first place finish.  Never doubt the ability of the XR's!

[john1220 TT Member]

Bringing this thread back to life.  I just happen to have a Keihin CVK 40 carb sitting in my garage right now.  The intake boot will fit right on.  I'm pretty sure the engine side boot is going to slip on.  The length is very close to the same - about 4".  I got this off a KLR 650 that had been bored to a 685.  The main jet is a circular style keihn and is stamped with 136.  

Physical dimension- wise I think it is perfect.

What I can't figure out is if this carb is any good?  

Is it worth my time to fit it and jet it?  

What jet sizes should I start with?

Problems:

1: has a handlebar choke

2: cables mount on the other side of the carb ( I have the throttle tube and cables though)

3: Spent way too much time in the garage recently and my wife is sick of me going missing

[Trailryder42 Get Help Now]

You don't say what bike you're thinking of putting it on, but I would think that would be too much carb.

Do you also know that:
its slide is vacuum operated
Its designed to work with a vacuum operated petcock. You'd need to plug that vacuum port
It works ok for the KLR650 pig, riding street or dualsport, but hardly what you'd want on a trailbike.

Worth your time to screw with?..........I wouldn't.

john1220, on 13 April 2013 - 06:20 PM, said:

[left]  I got this off a KLR 650 that had been bored to a 685.  

Edited by Trailryder42, 13 April 2013 - 06:46 PM.

[john1220 TT Member]

Trailryder42, on 13 April 2013 - 06:46 PM, said:

You don't say what bike you're thinking of putting it on, but I would think that would be too much carb.

Do you also know that:
its slide is vacuum operated
Its designed to work with a vacuum operated petcock. You'd need to plug that vacuum port
It works ok for the KLR650 pig, riding street or dualsport, but hardly what you'd want on a trailbike.

Worth your time to screw with?..........I wouldn't.

If you read some of this thread you would see that others are using Mikuni 40 mm and 42mm carbs with good results.  The 40mm carbs are coming from dr650s - a pretty comparable bike in terms of mission to the KLR.  Do those Mikuni carbs have the vacuum operated slide too?

The carb already has one port blocked off, there is another above the fuel line, I'm not sure what I should do with that one.  It also has a dyno-jet kit installed on it.

[Spawn_X TT Newbie]

john1220, on 13 April 2013 - 06:20 PM, said:

Bringing this thread back to life.

this thread never died

I saw people having issues with DR650 carb. I used Polaris 500 carb (2003-2005) and it went right in. Motion pro twist kit and the small pull choke on the carb

Love the carb! Much happier than if I spent 400 on a pumper. Gas mileage is unchanged btw

[Trailryder42 Get Help Now]

I haven't looked at the Mikuni carbs.

On the KLR carb, the port above the gas line nipple and just to the rear of the choke port is a nipple for the overflow line. The port on the top side of the carb, just forward of the choke port is the vacuum nipple for the petcock that will need to be blocked off.

Stock, the fuel screw is not accessible. The recess it's in is covered by a metal plug that you'll need to drill a small hole thru, then thread a sheet metal screw into to grab ahold of it and pop it out. But I'm guessing if it has a dyno jet kit in it, that has already been done.

There's a vacuum hole in the bottom of the slide that KLR owners drill out to 7/64" for quicker throttle response, but I wouldn't do that for the XR until you see how the amount of vacuum the XR engine makes is able to operate the carb.

If you go for it, be sure to post your results.

[XR8ed400 TT Bronze Member]

Just got my BSR 42 today (Predator 500). Nice clean carb for $30. Only problem is the diaphragm on top of the slide is torn. That part is gonna cost me more than the carb! lol. Can't wait to get the rest of the parts together and try it out.