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FCR 41 MX Pilot circuit problems

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Hi all

I've got a brand new FCR 41 MX i've recently fitted to my bored and stroked DRZ sm , to cut a long story short its got a flat spot/ bog from around 1/2 to 3/4 throttle, as it came from Eddie already setup i've been in contact with him directly and thought i had the issue nailed down to the AP pump timing , adjusting this did improve the problem but not completely, i didnt use the bike for a few weeks and now i have the issue is still there , i will no doubt speak to Eddie but have decided to put it on here too as i wont get a chance to work on the bike in the week and i know he's not at the shop until tues .

As the carb was already setup i didnt fiddle with anything else but decided to confirm the pilot circuit , i set a low idle and then turned the screw in (bike fully warmed up) this raised the revs right up so i thought i must need a smaller jet (48 is the current one and used by similar spec bikes ) i tried a 42 again i couldnt get the bike stumble or cut out with the fuel screw fully in and the revs didnt really alter until 2+ turns out , so now im a bit confused , i dont want to get it too lean as 42 seems way small compared to others jetting not really sure where to go next on this :thumbsup:

The bike :

462 cc bored and stroked

RHC 187 CAMS

RHC Valves (stock size)

MRD SSW Piper

K and N

3 x 3 mod

FCR 41 mx ( aftermarket)

main jet 175

ap linkages wired

i'm presuming pilot air jet removed

needle i dont know

current pilot 42

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48 to a 42 pilot is a huge jump. You should of tried a 45. Also, you need t have the idle speed as low as possible when setting the fuel screw to ensure you are not on the needle.

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 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 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 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 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 1,800 rpm, but go by the spec in your manual.

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Hi William cheers for the reply i do have a 45 also so i will try that again with the above procedure and report back:thumbsup:

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Hi all

........ i tried a 42 again i couldnt get the bike stumble or cut out with the fuel screw fully in and the revs didnt really alter until 2+ turns out , so now im a bit confused , i dont want to get it too lean as 42 seems way small compared to others jetting not really sure where to go next on this.......

462 cc bored and stroked

RHC 187 CAMS

RHC Valves (stock size)

MRD SSW Piper

K and N

3 x 3 mod

FCR 41 mx ( aftermarket)

main jet 175

ap linkages wired

i'm presuming pilot air jet removed

needle i dont know

current pilot 42

Sounds too rich, perhaps PAJ still installed ?

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42 pilot jet with the 100 pilot air jet installed is correct with the emr needle in a 41mm carb.

turn the idle down as low as the bike will stay running and re do the test.

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Sounds too rich, perhaps PAJ still installed ?

I had the carb off in the end to double check the PAJ was removed - it wasnt it still had the 100 PAJ in...so i've removed this now and refitted the 48 Pilot and the carb after having the mother of all fights with the airboot lol i will recheck the pilot circuit tomorrow now as its getting late

42 pilot jet with the 100 pilot air jet installed is correct with the emr needle in a 41mm carb.

turn the idle down as low as the bike will stay running and re do the test.

That would explain why it seemed to run better with the 42 pilot as it still had the 100 PAJ fitted

The needle was an EMR Clip 4

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With the 48 pilot and the PAJ now removed , the pilot circuit responds as expected (fuel screw 2 turns out) and the bike rips like never before :smirk: it'll be hitting the dyno soon for a fine tune :smirk:

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