wantsabike
Well-known member
thought I changed that before, but guess I didn't save..... im not sure which carb is on it, but It says Keihin on it
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backfiring/pop/crackle
- Thread starter wantsabike
- Start date
thought I changed that before, but guess I didn't save..... im not sure which carb is on it, but It says Keihin on it
Get a JD jet kit and follow the instructions burning toast easy.
Sent from my Nexus 4 using Tapatalk
Sent from my Nexus 4 using Tapatalk
Then it's not a BST40 like on the KTM 640 Adventure. Same carb used on almost 20yrs production DR650. Doesn't get any simpler to change pilot, shim needle or adjust fuel screw. Since it's Keihin, I'm not of practical help.(altho, easy to say, should be very simple too)
wantsabike
Well-known member
I think it has had carb work done before, as there is an aftermarket fuel screw.... but no clue what was done
Ya, I can't tell from this side of the internet either. If you've eliminated exhaust leaks, repacked muffler and don't feel comfortable working on the carb you might want to look at the aircleaner/airbox setup. Is there a snorkel you could put back in? A restriction in the airbox will richen it up in theory.
If it's got the extended fuel screw you could try to get max fuel flow there, could help. Looks like you got some reading to do
wantsabike
Well-known member
Ya, I can't tell from this side of the internet either. If you've eliminated exhaust leaks, repacked muffler and don't feel comfortable working on the carb you might want to look at the aircleaner/airbox setup. Is there a snorkel you could put back in? A restriction in the airbox will richen it up in theory.
If it's got the extended fuel screw you could try to get max fuel flow there, could help. Looks like you got some reading to do
it doesn't seem to have any leaks that i can tell of, and I do think the muffler is due to be repacked as I knocked on the pipe and it sounds pretty hollow bottom to top lol... ive done carb work before on my 450 race quad, but not all units are the same either. I think I may try the duct tape idea tho, smart and easy
with these fuel screws im not 100% sure on which way they turn in order to be richer/leaner this one has numbers on 1-4 I believe.... confusing part for me is were should the number be for the setting you want on itI'm not really up to speed on the 450 race quads but there's a good chance it had the Keihin FCR39 flatslide. They are an awesome carb when set but are the most complicated. I could see how that would be intimitating without theory and setup knowledge. If your smc has that I wouldn't touch it without a manual and great understanding. You'll just grope around in the dark. If it has the typical CV type carb, shimming needle and pilot jet change is very easy. Turn the extended fuel screw clockwise to lightly seat it. Count the turns. Should be something like 1.5 to 2.5 turns(ballpark) Turn it out farther than it was. Thats more fuel.
If you ask what is a CV carb?, back away don't touch anything.
If you ask what is a CV carb?, back away don't touch anything.
wantsabike
Well-known member
actually ya my quad had a fcr on it and it took me an afternoon to get her dialed in with jetting needle and everything but man when I was done it was a monster !
wantsabike
Well-known member
well since the muffler needs to be repacked I think im going to repack it before messing around inside the carb, as the muffler is basically hollow right now lmao
So, have you figgered out what model Keihin is on your bike? I remember reading that the FCR series carbs can come with an air cut circuit which meters fuel on decel to prevent popping. That could be malfunctioning. Of course, I can't see that being emission compliant so maybe somebody retrofitted one for performance.
wantsabike
Well-known member
nope not exactly sure whats on this bike quite yet as its very hard to see, but there are numbers stamped in the lower side of the carb maybe that will help with identifying it. but ya the muffler needs to be repacked for sure, it looks like all or most of the packing is blown out
wantsabike
Well-known member
well picked up some moose racing packing for the silencer hoping that gets rid of the popping I get during deceleration lol.... hoping to get it installed this weekend but we will see as this weekend looks busy already lol
lolwithout re-jetting, try adjusting the idle mixture screw to a richer setting, if that doesnt work, youll need to up your pilot jet 1 size. any exhaust/intake mods will help the engine but in return cause it to lean out more from the factory settings. most/all bikes are pretty lean as it is with the pollution controls and mileage concerns. if this carb has never been off the bike or ever worked on, you may not have access to the mixture screw, so a jet change is easier, repacking the new slip on will do you no good, defeats the purpose of it, return the old muffler back on the bike then.
wantsabike
Well-known member
Yea, as far as I know the motor has no mods at all except a pro circut t4 slip on silencer which was just repacked last weekend. The carb does have a aftermarket mixture screw on bottom of carb, can see big handle with 1,2,3,4 labelled on it but I'm not sure which way it should be turned if ny at all. I can take a pic to show ya and see what way it should be turnt to run richer.... I've done carb work but hate it as I like to fine tune and dial it until it perfect and I don't have the tools to do that down here anymore all my tools are at my parents up north as I don't have room for stuff here
Yea, as far as I know the motor has no mods at all except a pro circut t4 slip on silencer which was just repacked last weekend. The carb does have a aftermarket mixture screw on bottom of carb, can see big handle with 1,2,3,4 labelled on it but I'm not sure which way it should be turned if ny at all. I can take a pic to show ya and see what way it should be turnt to run richer.... I've done carb work but hate it as I like to fine tune and dial it until it perfect and I don't have the tools to do that down here anymore all my tools are at my parents up north as I don't have room for stuff here
i think ktms of that year used keihins, fcr's? you would turn the mixture screw ccw, to richen. give that a try and see what happens. your adjustments should be 1/3 - 1/2 turns at a time with 20 secs between for idle changes with that carb. find the sweet spot, hopefully you wont have to re-jet
wantsabike
Well-known member
Yep have a fcr carb on it indeed... So when turning CCW is that looking at top of carb or bottom side of carb ?
Maybe I will try turning and playing with it to get rid of popping or atleast try to this weekend
Maybe I will try turning and playing with it to get rid of popping or atleast try to this weekend
wantsabike
Well-known member
Ah ok ya I will give it half a turn out and see if that helps then
A bit of crackle and pop is sometimes normal. Remember, the factory bazookas often mask that sound. Richening up the mixture to the point of completely eliminating the popping sound can cause a drop in performance (and f'ing around with carbs opens up a whole new can of worms). I would have an experienced shop inspect your plugs. If the colour is ok, I wouldn't worry about it. I also have a bit of popping on deceleration, and my plugs look fine.
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