Up on 1 to save on tyre costs
Hey guys! I have a new carb on the way for my FXR. It's apparently identical ish to the CB250 carb that everyone uses on their FXR's (I think it's the CB250RS carb). So... what kind of jets are you fellas running? I will update what carb I am getting for mine soon, forgotten the model of it for the moment. I have a friend helping me out. Cheers!
No8 Wire Extraordinaire
You are hoping for a "Jam a 360 in it" type suggestion then forget it. Unless you are running the same motor with same inlet & exhaust & no other mods & someone else has put on the same crab with the same needle jet, airjet then there is too many variables. You can only go try it & try some other jets & record how it goes. No real shortcuts. Try small steps. See if you can borrow some jets but you need to know what type they are. Have a look on sudco or 'show&go' website or similar to identify.
Don't you look at my accountant.
He's the only one I've got.
Up on 1 to save on tyre costs
Yeah sure I'll try that. I was told to ask about what jetting is used for the CB carb on an FXR to get a starting point that might turn out to be pretty damn close. Just going off advice I have been given by the guy who is sorting my carb for me. He asked me to post on here and see what others are doing and then I can go from there with my testing. Cheers Dave
Race it don't store it !
135 main is a good starting point
Up on 1 to save on tyre costs
Awesome thanks mate
Forum whore
Did some google on the carb. Looks like a 30mm pumper. Could be a good option but a little big. But probably better than your current setup. I would put it on and see what happens. If it runs ok then do some plug chops and see where you are. The thing to remember is to get an accurate reading on the main jet is you need to be on full throttle for around 20 to 30 seconds. Bring it along on Sunday.Originally Posted by hmurphy
Up on 1 to save on tyre costs
Ok so I have a few jets now. The jet that was in the carb originally was a 165. I have a 135 in it now and a 140, 155 and a 160 to test with. The bike runs ok with the new carb just idling, but likes lots of choke (even when warm I think). It can run with no choke but I have to be careful with the throttle or it stalls when trying to rev. Basically I can't wind the throttle really quickly or it bogs/stalls.
So.... am I ready for a plug chop test? Where should I go from here? I will need to use a home made airbox of some sort to fit the carb. Does anybody know websites that have really helped them? (Just so I don't keep posting here with questions that are already answered elsewhere). I have had a look at some websites but I have heard slightly different things from other people who have done this testing with their FXR's so I figure it's best to ask the pros.
Cheers guys, I will update any progress and let you know if this carb goes well with the FXR.
Who You Calling a Pig
mate have a read through this thread that I put up recently as I was going through a simular excercise and this was my first time doing such a thing.
http://www.kiwibiker.co.nz/forums/sh...ss-on-a-FXR150
Biggest advice I can give is mark up your throttle so you can easily identify where in the circuit you are having issues, have a read of some of the links in the thread I linked.
For the record Qkkid was in my bed, not the other way round
Long Haired Yobbo
It is probably the same carb as Hells has.
If so its on the big side but should go OK.
It sound like you need to fiddle with the screw on the engine side under the float bowl, Hels bike was quite boggy and crap until I got that adjusted better.
Not sure in the super technical stuff but that seems to affect the mixture just off idle.
I played with the pumper but have left it disconnected as once set up it seems to run alright without it, maybe lots of fiddling would see some gains but so far it has worked better without pumper.
We have leaner main jet than 135 at the moment, but standard exhaust and a filter etc, Ricks advice sounds on the money.
The problem we have had is a real heavy throttle, would be a good idea to make up another cable to convert it to push/pull and run fuck all spring. (Daves brains there, not mine)
Heinz Varieties
Up on 1 to save on tyre costs
Just took it out for a quick spin with the new carb (it's my day off). It went ok I guess. It haaates quick throttle movements. If the revs are low and I pin it, it just bogs and eventually seems to sort itself out then revs like mad. I think it's pretty good up top to be honest. Seems to want to keep going up to the rev limiter (stock carb doesn't like rev limiter, no power near it), but that could just be me not getting a good chance to ride it properly. Didn't need any choke. Home made air box that only allows static air to be sucked into the carb has been fitted. 135 jet and needle was on highest setting and is now on lowest setting.
So:
-What would be the best thing to play with to eliminate how unhappy it is with quick throttle movements (from mostly anywhere in the revs)?
-The pumper isn't on yet so that might help I guess? (Should still work reeeasonably well without it though right?)
-Plug chop time?
Cheers
No8 Wire Extraordinaire
Yes pumper should come into play when you open throttle. Ideally you should have it so that it is lean enough for best power on constant throttle, but likely too lean for acceleration. Whether the pumper is sophisticated enough to compensate is the sticking point. If it isn't then you may need to richen it either in the transition (raise or change needle) or main. Experimentation.
Don't you look at my accountant.
He's the only one I've got.
Who You Calling a Pig
My guess without hearing it and based on my own limited experience is that the pilot jet is rich or lean.
While stationary (only because I cant think of a way of doing it when running) get a bit of card limit the amount of air getting to your pilot air jet. Rev it, if it is better you need a richer pilot jet, if it is worse you need a leaner jet. It should make any difference above 1/4 throttle.
Up on 1 to save on tyre costs
Ok.... carb is very close to being all sorted! Up to 3/4 throttle I am getting a really decent throttle response and quite a fair bit of power. It's actually really similar power to the stock carb and I'm not even full throttle yet. The throttle response is absolutely immediate (well, definitely compared to the stock carb!) but the main jet definitely needs some work because 3/4 throttle to full throttle is not very good.
The 135 jet that I was trying was pretty terrible. It would just splutter and surge and jump around. According to a bunch of sites I was looking at (I have done a fair amount of research on setting up carbs now) I was running the bike too lean. So I chucked in a 140 jet and wow the difference was really noticeable! It was spluttering less but still far from perfect. I thought I would try chucking in the 165 jet I have and seeing what would happen then, but sadly a van swerved off the road and smashed my carb bowl and tools that were sitting just off the road.
That's not the end of the story haha. I now have a new carb bowl so I can start the testing again.
I was wondering if anyone would be so kind as to lend me a few jets of theirs to test with? I will return all jets and even pay for the one I need. If you aren't willing to sell me any, I would really appreciate the chance to borrow jets and then go out and buy the one I need (or buy the replacement for the person who lent me theirs so they can have the new one).
1 other thing, spark plugs are cheap for FXR 150s right? To do more accurate plug chop tests (once the bike is running ok) I guess I will need a new spark plug.
The pumper on my carb will be one of the very last things I will bother playing with but I can see how it might be very valuable. Although the throttle response is really good and it hardly bogs at all down low, I think it might be running a bit lean near the pilot circuit or when the needle is reasonably low. An extra squirt of gas might make things more interesting!
Cheers guys!! Any help is muuuuch appreciated!
No8 Wire Extraordinaire
you will need to tell people what types of jets you are after, ie Keihin & Mikuni both have a couple of options. Find a pic on a website & post it.
Plug chop on a 4 stroke on unleaded might not tell you too much unless you are running it for ages. New plug will be harder to read.
Don't you look at my accountant.
He's the only one I've got.
Up on 1 to save on tyre costs
It's a Mikuni carb and the main jet looks like this: (Part number MI-4/042)
http://cycletreads.retail.sprint3.co...rceCode=21.752
Yeah I have been given advice about the plug chop test. Apparently I need to have it full pin in top gear for at least 20 seconds to get a decent reading. I will be able to do this, although it's gonna make a hell of a noise.
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