Savage422

Fcr41 jetting

94 posts in this topic

So it seems that everyone here with a 470 is running a much smaller set of jets than I am.

I'm at sea level or within a few hundred feet.

I've been getting a lot of popping on decel with my set up and it seemed to be running a little hot. 48 pilot 178 main

Per instruction by the shop that sold me the carb, i needed a 205 main and a 52 pilot.

I installed both and the results are as follows:

Peak rpm is 3.75 turns out on the fuel screw. It's almost falling out, or is.

It dies at 1 turn in.

It doesn't pop on decel at all now, but the idle hangs a touch and it doesnt like to start easy, but stays running at least. It wouldn't stay running at 2 turns out

By my poor calculations, i need a fatter pilot??? That seems excessive 

Could it have anything to do with my muffler needing to be repacked? I'm pretty sure there are no air leaks anywhere.

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There's something way off with that carb if you need such big jets . You'll need to say what are your air jets and which needle for better help . I'm around 165 main and 40 slow jet ,  air is 100 and EMN needle ,don't remember what clip position, mixture screw is only 3/4 turn out, also a fcr41. Doing too many bikes currently to remember exact sizes the DRZ has and didn't write it down , should always write this stuff down !  I'm rich as heck yet so I can't see how yours is running . Make sure those numbers are genuine Keihin and not DJ which will be different.

 

 

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3 minutes ago, jjktmrider said:

There's something way off with that carb if you need such big jets . You'll need to say what are your air jets and which needle for better help . I'm around 165 main and 40 slow jet ,  air is 100 and EMN needle ,don't remember what clip position, mixture screw is only 3/4 turn out, also a fcr41. Doing too many bikes currently to remember exact sizes the DRZ has and didn't write it down , should always write this stuff down !  I'm rich as heck yet so I can't see how yours is running . Make sure those numbers are genuine Keihin and not DJ which will be different.

 

 

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I have no idea other than the carb was stock brand new fcr41mx and i only changed the pilot and main. I think I'll pull it apart to check all those those this weekend.

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I'm at 170 main 45 pilot and EMR needle 4th clip.

Look for an air leak. You're running an airbox right? I know you have a BB/Stroker. What are the other mods?

Sent from my XT1650 using ThumperTalk mobile app

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7 minutes ago, ohiodrz400sm said:

I'm at 170 main 45 pilot and EMR needle 4th clip.

Look for an air leak. You're running an airbox right? I know you have a BB/Stroker. What are the other mods?

Sent from my XT1650 using ThumperTalk mobile app
 

I'll start checking for air leaks now. Yes, I'm running an airbox. I've done the 3x3 and also cut the entire right side out also for extra air.

It has a full yosh exhaust 

Other than the bb/stroker, its all stock cams (i believe)

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Plug the side of the airbox back up , it's completely un-needed and probably slows flow down in this bike . I'd guess going down the road , airflow past the open side will cause a suction or low pressure zone right in front of the filter , exactly where you do not want it, fighting the intake from the motor .

 

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Yeah... 45 pilot and a 100 slow air jet. 158 or 155 main with a 200 main air jet at most. Bigger the bore, the stronger the vacuum signal, so with a stroker big bore, a 150 or i55 would be about right. You with a 41 and a slightly weaker signal at WOT,  slightly larger main. But none of that really affects the needle and definitely not the pilot (idle is idle).

Return the airbox to a true 3X3, nothing to be gained by making it larger. What cams in your beast? Ported? By whom? Oversize valves?

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43 minutes ago, William1 said:

Yeah... 45 pilot and a 100 slow air jet. 158 or 155 main with a 200 main air jet at most. Bigger the bore, the stronger the vacuum signal, so with a stroker big bore, a 150 or i55 would be about right. You with a 41 and a slightly weaker signal at WOT,  slightly larger main. But none of that really affects the needle and definitely not the pilot (idle is idle).

Return the airbox to a true 3X3, nothing to be gained by making it larger. What cams in your beast? Ported? By whom? Oversize valves?

I believe everything else other than the stroker and bb is stock.

 

I think these are stock cams correct?

20170909_142835.jpg

20170909_142828.jpg

15049929755211504847042.jpg

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Also, question.

I know you guys are well versed.  But if the extra hole was creating a low pressure area, that would be making it run fatter, not leaner, correct?

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Yes those are stock. The right side panel is pretty tight against the box. Even if you run with the door and seat off, it doesn't create enough change to warrant that large of a jetting change.

Sent from my XT1650 using ThumperTalk mobile app

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29 minutes ago, ohiodrz400sm said:

The right side panel is pretty tight against the box. Even if you run with the door and seat off, it doesn't create enough change to warrant that large of a jetting change.

Sent from my XT1650 using ThumperTalk mobile app
 

Agreed, something is funky and i need to find it.

I have checked and checked and i cant find an air leak.

As of now, with 3.5 turns out it fires up, runs decent, and doesn't pop on decel.

However, when i put the 48 pilot in last month it ran good too. But it suddenly started popping on decel again, but worse. 

Im going to get a new sleeve from the carb to the head and see if maybe it's just old and worn.

Nothing is open until Monday though, so until then I'll pull the carb off and see what all the other jets are.

Edited by Savage422

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Popping on decel could be a leak in the exhaust also.

I ended up dropping all the way to a 160. It's slightly lean now (13.5ish) but the conditions today are the coldest conditions I will typically ever ride in.

Sent from my XT1650 using ThumperTalk mobile app

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Ok, maybe a side note:

How do I tell for certain this bike has a stroker kit?

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The older kits(+5mm) required a spacer plate. Those with a 434 (94mm bore? Can't remember right now for sure) Piston made a 470. Todays Hotcranks or whatever sells a +4 that doesn't require a spacer place. That along with a 434 bigbore results in 462cc.

 

If you don't have a spacer plate you would have to remove the head and measure the stroke of the piston.

 

Sent from my XT1650 using ThumperTalk mobile app

 

 

 

 

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13 minutes ago, ohiodrz400sm said:

The older kits(+5mm) required a spacer plate. Those with a 434 (94mm bore? Can't remember right now for sure) Piston made a 470. Todays Hotcranks or whatever sells a +4 that doesn't require a spacer place. That along with a 434 bigbore results in 462cc.

 

If you don't have a spacer plate you would have to remove the head and measure the stroke of the piston.

 

Sent from my XT1650 using ThumperTalk mobile app

 

 

 

 

Copy copy...

I'll do that tonight. 

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Stock cams.

You have too much carb. Either source a 39 or install a travel longer travel restriction screw.

No way do you need the 48 pilot.

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Cams will be on order Monday. Just trying to fix whatever issue I have going on first. 

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Pulled my head apart and the exhaust valves are pretty cupped. Could that have anything to do with the jetting issue?

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Maybe. That's seems kind of soon. I have read a lot of bad things about Kibble White but I had also read that the past quality control issues with the Z valves were resolved.

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Just now, ohiodrz400sm said:

Maybe. That's seems kind of soon. I have read a lot of bad things about Kibble White but I had also read that the past quality control issues with the Z valves were resolved.
 

I honestly had not expected the piston and exhaust valves to be so cared with buildup. The exhaust valves were cupped, and although they didn't seem to be leaking at all, there was evidence of deposits starting to creep down the seat. 

I'm sending the whole thing to fastheads to have them service it with ferrea valves and springs

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