Looking for drz470 jetting recommendations

[Atolduso]

Trying to set up my jetting on my bike.

1000ft 5-30degrees Celsius.

4mm stroker, 4mm big bore, web 540, fcr39mx, mrd with no insert, k&n filter.

The jets in it when I got it I feel are rich. It's got a 178 main, 100pj and a jd fuel screw.

What main jet would you recommend to start with? Also how do I know whether I know I have a pj I should remove or not? Thanks.

[ohiodrz400sm]

You mean 100 paj right? Yes, leave the air jet in.

Just an educated guess I would say 178 in a 39mm is WAY rich on a BB/stroker. I'm thinking more like 158 if not leaner still.

[Atolduso]

You mean 100 paj right? Yes, leave the air jet in.

Just an educated guess I would say 178 in a 39mm is WAY rich on a BB/stroker. I'm thinking more like 158 if not leaner still.

Yeah I was wondering if I even read it right but I remember it saying 178 when I had the carb out, which I agree seems really strange. I was thinking I would order a 158 and 160 to start.

[Atolduso]

Any other people with similar mods that can comment on jetting?

I know I read here going bb actually can mean smaller jets? That goes against what I would assume is this true?

[ohiodrz400sm]

https://www.google.com/amp/motocrossactionmag.com/news/mxa-wrench-tech-the-ins-and-outs-of-big-bore-engines/amp

[Atolduso]

Someone pointed out to me it might be a fcr41 considering the jetting. This didn't occur to me for some reason. The old owner said it was a 39 but didn't install it, it's very likely it's a 41. Don't really want to take the carb off to check but now I'm curious.

The 178 main and 48 pj would make a lot of sense in a 470 fcr41.

[Atolduso]

I need some help. So the carb is a fcr41. (Old owner told me it was a 39 and I believed that with which through me for a loop) I am dealing with the problem that when I'm pulling up to a light the bike dies as soon as it hits/nears idle speed. The idle is all over the place, lots of hanging and goes from 1900-2500 constantly. 

It has a 178 main and 48 pilot jet. I have a JD fuel screw and the screw can be turned all the way in with the idle set at around 1500. After 1 turn out the bike gets really close to dying, and at 2 turns out it dies. 

I need to lower the pilot jet right? I am buying individual jets so I was hoping to get recommendations on what to get. At 42 and 45? 

Is this likely why my bike is stalling? Overly rich right when it hits idle? It usually can not be restarted for a couple minutes after it dies. Pair that with the oem battery trying to start the no decomp 470 and it equals a lot of problems. I've been stranded a few times already. 

Edited April 12, 2017 by Atolduso

[William1]

178 main is way big. 158 possibly a 155 with a 3X3

45 pilot with a 100PAJ

Start jetting with the pilot, fine adjust with the fuel screw and then the needle and finally the main.

[Atolduso]

2 minutes ago, William1 said:

178 main is way big. 158 possibly a 155 with a 3X3

45 pilot with a 100PAJ

Start jetting with the pilot, fine adjust with the fuel screw and then the needle and finally the main.

Thanks a lot. In the OP I put it's a FCR39 but I since found out it's a 41. Trying to edit that but I think the post is too old? I will buy the 45 pilot tomorrow and try it out.

[William1]

Just now, Atolduso said:

Thanks a lot. In the OP I put it's a FCR39 but I since found out it's a 41. Trying to edit that but I think the post is too old? I will buy the 45 pilot tomorrow and try it out.

Bore of the carb has a minimal effect on jetting. Big bore/stroker and cams do and going big engine means a stronger 'suck' and calls for leaner jets for a needle and a main jet. It is very possible the JD needle will be too rich (even his 'summer' one) and you may want the Keihin EMP or EMR.

[Atolduso]

Just now, William1 said:

Bore of the carb has a minimal effect on jetting. Big bore/stroker and cams do and going big engine means a stronger 'suck' and calls for leaner jets for a needle and a main jet. It is very possible the JD needle will be too rich (even his 'summer' one) and you may want the Keihin EMP or EMR.

It currently has the EMR needle on the 4th clip. The only JD part on it is the fuel screw. 

[William1]

5 minutes ago, Atolduso said:

It currently has the EMR needle on the 4th clip. The only JD part on it is the fuel screw. 

Good.

Fuel Screw/Pilot Jet
Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.
Gently turn the fuel screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle knob to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly).  Once warmed, slow the idle speed (knob) to the lowest possible speed.
*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***
Turn the fuel screw in until the idle becomes rough or the bike stalls.
if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.
If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.
Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.
If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.
If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.
If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,850 rpm

 

Main Jet
Starting with the recommended main, remove the airbox door and go for a ride (bike fully warmed up, 3rd or fourth gear, up a slight hill). Is it better or worse?
If it is better, you need a smaller main.
Go down one size, replace the airbox door, ride. Remove the airbox door and test again. Better or worse? If better, go down a size again. Keep repeating this till the test with the airbox door is worse.

If it was worse with the airbox door removed, tape over 1/3 of your airbox opening, test (airbox door on, of course).
If it is worse now with the tape and was worse with the airbox door off, your main is just right. You are done!

If it seems better, you need to go up a size in main jet. Then test it again (remove the tape). Replace the tape, test again. If with the tape on it is better, go up another size in main. Keep repeating this till having the tape on is worse than with it off.
To finish up and ensure you are set accurately, retest the bike with the tape off (airbox door on), ride it, then remove the airbox door (tape off, of course). Best performance should be with the airbox untapped, airbox door on.

Remember, the main only operates at WOT. Ideally, you want to be in 3rd or 4th gear doing the tests, hitting max revs (just shy of the limiter) for at least 10 seconds to get an accurate representation of the jet status.

[thnksno]

9 minutes ago, William1 said:

Once warmed, slow the idle speed (knob) to the lowest possible speed.

Question on this... I can get mine to idle so low that I hear metal parts banging around. As a result, I've been messing with this at an RPM slightly higher than my "lowest possible speed."

Am I missing something?

[William1]

Just now, thnksno said:

Question on this... I can get mine to idle so low that I hear metal parts banging around. As a result, I've been messing with this at an RPM slightly higher than my "lowest possible speed."

Am I missing something?

It can idle so slow that each revolution the engine slows down, then fires, accelerates and literally, it is hammering itself to death. So setting a low idle speed is only for adjusting the fuel screw, then set it to 1,850.

The point of the low idle speed is to ensure the needle is not affecting things.

[thnksno]

Just now, William1 said:

It can idle so slow that each revolution the engine slows down, then fires, accelerates and literally, it is hammering itself to death.

Yeah, I don't leave it that way. I just can't for the life of me listen to it while I goof with the fuel screw.

[Atolduso]

Installed the 45 today. Idle is definitely smoother and less all the place but I can still put the screw all the way in idling at 1500. 

Wasn't able to turn the carb enough to change the jet with the carb on the bike because of that damn oil breather box thing so I took it all the way off. 

Not looking forward to doing it again to try a 42. ?

 

 

[bumtarder]

20 hours ago, Atolduso said:

Installed the 45 today. Idle is definitely smoother and less all the place but I can still put the screw all the way in idling at 1500. 

Wasn't able to turn the carb enough to change the jet with the carb on the bike because of that damn oil breather box thing so I took it all the way off. 

Not looking forward to doing it again to try a 42. ?

Why are you trying to move the carb just to change a pj??That is completely unnecessary.Just about everything on a fcrmx is designed for quick trackside adjustments as a racing carburetor.Pj change should only take about 10min. or so.Do it this way:

Drain the carb bowl,unbolt and unplug the r/r and set aside with a small bungee,remove the bowl sump drain plug with a small 17mm box wrench.Lay a shop rag across the top of the transmission and with a 1-7/8" long 3-4 or 5/32" common driver bit reach up with your fingers and spin out the pj.The jet is tangent with the front edge of the sump opening and the main jet is located dead center and uses a 6mm deep socket to remove.A small inspection mirror works well to look up into the carb to locate the jets and inspect your work.

 

Edited April 14, 2017 by William1
Clean up for clarity

[Atolduso]

Finally got a 42 pilot so installing that tomorrow. The bike will still idle screw all the way in at a 45 so had to go down more. 

I switched to a 160 main because it was suggested a 178 was way rich on my 470, with mods listed in OP. The bike feels a lot slower at WOT, at least I'm convinced it does. Thinking about switching back and trying it again.

[ohiodrz400sm]

Are you sure it's a 39mm?

[Atolduso]

1 hour ago, ohiodrz400sm said:

Are you sure it's a 39mm?

 

Sorry, can't update the OP. A couple posts down from it I figured out the bike came with a fcr41mx. 

Edited June 9, 2017 by Atolduso