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Fcr39mx

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fitted the above carb to my 06 sm few day back and was having issues with it stalling and just not running right. In the end gave up partially due to work commitments and being ill and took it to local garage. They have got it running and said its reliable and runs fine with no issues but that they think the pilot air jet needs to be bigger as its all the way in. I believe it's a 100.

Now I've read a few different things suggesting the pilot air jet should just be removed. Is that correct and why would you do that and what issues leaving in would it cause?

Thanks

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Psalliss , it depends on how old your carb is . Did you buy a brand new carb or is it secondhand ? The newer ones have supposedly fixed that problem , but the older MX had to have the air jet removed . I did mine in 2010 and had to remove the jet . I am sorry but I dont know when they fixed it , do you know what size your pilot jet is ? This can cause that problem if it is too small , greg

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Yeah ..an old fcr carb could have worn components , like the throttle slide for example .

Best to make sure wear is not the issue then work on the jetting .

Does it ' pop ' when you close the throttle ? .

i was talking to him on facebook... OP has a used fcrMX with 160,45,100, emn 3rd, 3x3, yoshi rs2, oring mod,... his main complaint was that upon quick blip of the throttle with bike on a stand the bike dies,, but will stay running with smooth throttle openings..

he now took the bike to a shop, and they are telling him that the pilot air 100 jet is wrong..

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Thanks for the replies. The carb is a reconditioned one from kehlin which was bought about 6 months from the person I bought it from and has done few miles since. The pilot jet is 45. I presume it's the newer mx but I don't know

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i was talking to him on facebook... OP has a used fcrMX with 160,45,100, emn 3rd, 3x3, yoshi rs2, oring mod,... his main complaint was that upon quick blip of the throttle with bike on a stand the bike dies,, but will stay running with smooth throttle openings..

he now took the bike to a shop, and they are telling him that the pilot air 100 jet is wrong..

Further to that the bike started fine from cold the other day and after 20 sec idle died and struggled to re start. Once started seemed to run ok ish but stalled a few times at junctions when going to collect a new tyre. After getting tyre fitted it started fine but stalled shortly after. Local Honda garage was literally just round the corner so nipped into to speak to them and then wouldn't start again, so was left. Will be collecting it shortly so we will see how it runs.

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Did you adjust your idle to the specified 1800rpm? 

 

That could possibly fix your stalling issues.

Edited by DeeAreZee

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Did you adjust your idle to the specified 1800rpm? 

 

That could possibly fix your stalling issues.

No I didn't as had a brain fart and totally forgot about the idle speed. Doh.

Anyway bike is running fine now. The technician who worked on it wasn't in so the shop manager didn't know fully what was done but believes that he dropped the need to 4 and beyond that he isn't sure but suggested that it needs a bigger pilot jet.

The bike surges slightly but only done three miles on it and the revs don't drop instantly. There is a very slight hesitation I think. Also the bike sounds more rattly but that could be down to the chain tensioner. Had the automatic off when putting the carb on so could be that. Have put a manual on know and think I've set it right, going to take it to a local dyne guy next week. Had hayabusa and ducatis there and he's excellent and more so with carbs so I reckon it should be perfect then.

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Well thought it was better. Started yesterday first Time but then stalled on idle with choke out after about 30 seconds whilst locking garage. Started again without issue but kept stalling en route to work with quite a bit of surging at around 40mph in 4th gear.

Before setting off home turned the idle up a bit which seems to have stopped the stalling but still surging. Feels much like when you run out of fuel but not quite as severe. I'm hoping that dyno guy can get me in this weekend.

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The surging could be a situation with the bike not getting enough fuel. 

 

Are you at sea level? If so, did the shop check the jetting in the carb to make sure it was the correct one for that elevation?

 

Also, another possibility could be that your fuel screw is slightly off. 

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It does seem like there's not enough fuel. Yes at sea level and the jetting is all correct for my elevation. I'm not sure to be honest. My knowledge is basic when it comes to carbs. I'm sure it's just some minor adjustments and maybe jetting changes and local dyno place will sort it. Hoping to get in Saturday.

Looking forward to fueling being spot on as you can feel the difference between the mikuni and fcr

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Turned the idle up a little which seems to have stopped the stalling but need tp do but more riding to test.have also ordered a 42 and 48 pilot jet to see if it reduces the surging I'm experiencing at constant throttle at 40 mph. Can the jet be changed with the csrb on the bike?

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Following on fro this thread https://thumpertalk.com/topic/1167889-fcr39mx/#entry12860293

I'm still having issues with the hesitating. The bike has been on the dyno and they say the fueling is spot on and no issues but the bike is hesitating at small throttle openings when the throttle is Constant. It accelerates fine with no issues. The dyno and the garage think it's electrics. It's had a new plug, replacement coil from somebody else and the tps disconnected and is still doing it.

I've asked them double check if the slow air jet is in as someone suggested that that could cause the issue. Has anyone any ideas, suggestions or had the same issue. Thsnks

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What dyno is the testing being done on?

Once off idle, pilot and slow jet have next to no effect.

 

If the hesitation is at low rpm in low gears on the flat, it could be too rich on the straight diameter of the needle. I assume you have the EMN in, try the EMP or the EMR.

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What dyno is the testing being done on?

Once off idle, pilot and slow jet have next to no effect.

 

If the hesitation is at low rpm in low gears on the flat, it could be too rich on the straight diameter of the needle. I assume you have the EMN in, try the EMP or the EMR.

I'm unsure on what dyno if I'm honest. What diff would that make? I'm pretty sure it's emn. Why would other needle make a difference and why wouldn't it show on the dyno? Thanks for your help and merging threads,

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Big difference. If it were a DynoJet or other inertia drum type dyno (which is what 99% of the shops have), you could never detect the 'hesitation' you are feeling. Only real high end shops have the correct type of dyno (a 'Brake Dyno') that can apply a load irrespective of rpm.

 

I doubt it is electrical. I think you need to find a better shop. Electrical issues manifest first as a high rpm miss that gets worse and worse over time and/or under load. They also often show only once the engine is hot.

 

Idle speed should be set to appx. 1,850.

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Garage Took it o this dyno place

http://www.powertech.uk.com/motorcycle_dyno_lancashire.html

I wasn't really convinced with the electrical explanation but I'm no mechanic. Idle should be 1800 as that's what I asked them to set it at, why would the needle make a difference ?

Garage Took it o this dyno place

http://www.powertech.uk.com/motorcycle_dyno_lancashire.html

I wasn't really convinced with the electrical explanation but I'm no mechanic. Idle should be 1800 as that's what I asked them to set it at, why would the needle make a difference ?

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Needle controls operation just off of idle to just below wot. That shop should know that. Seems they do not. The last later in the needle code, identifies the diameter of the straight part of the needle, which controls fule from just off of idle to about 1/4 or less. Not rpm but actual throttle position. The P is slightly leaner than an N and an R is the next step leaner than a P. Again, if the shop really knows what they are doing, they would know this too.

 

I see too, you may have a worn out carb from the shyster at http://keihin-fcr.com/ He is not in any way, shape or form, affiliated with Keihin. He scrounges used carbs and unloads them. Sometimes people get a decent carb, some have gotten totally worn out junk.

 

Another part you should/could try replacing is the needle jet emulsion tube. They are a wear item and will cause rich running and mostly apparent at low rpms. You may find out after all the time and money you spend trying to get a used carb working it would of been cheaper to of bought new.

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The carb wasn't from that place I don't believe , it was bought from another owner who got it from kelhin. So you think a p needle maybe way to go. I'm really not convinced they know what they are doing but I know even less what I'm doing than they, that said I'm convinced it's fuelling related. Are the needle jet emulsion tubes expensive?

There is another dyno place but does mainly top end scooter modifying and are more carb oriantated. They ajve the fastest uk scooter.,at pop in on way to work and have a chat and see if they sound like they know what they are talking about.

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