[tiraeth]

Hi,

First of all, I wanted to say hi as this is my first post on this forum!

I own a CRF 250R from 2008 using stock FCR carb that I'm 99% sure wasn't swapped with one from other bike. I've done complete top rebuild (have a HC 13.9:1 Wossner piston on D selection) including new valves. Re-shimmed them and they seem to be fine now (0.12-0.13mm intake & 0.28-0.29mm exhaust). I am struggling with my carb having problems with jetting it properly.

I was running NGK spark and Denso spark. When I took off Denso (after 2 hours of riding) it was black and a bit wet. I replaced with NGK because I had issues with Denso giving me backfire when de-throttling.

It's now 60-80°F (20-28°C) and I live between just 100 and 200 metres above sea level (Europe, Poland).

My current configuration for FCR is following:

- Aftermarket pilot screw (I checked for all parts including o-ring to be on it) set to various positions between 1 and 3 turn-outs
- Fuel float level set to 6mm (I did touch the float but I think I set it to 6mm now properly)
- Idle screw set so that the throttle disc burn marks match the body
- AP spout the fuel right after the throttle disc goes up, no o-ring mod
- I think my TPS is ok (checked resistance, mounting point prior to the cleaning — screw marks)
- Checked the carb / intake boots for any air leaks and couldn't find any
- NMGU needle with 3rd clip
- Main Jet #188
- Pilot Jet (Slow Jet) #42
- Starter Jet #68
- Leak Jet #65

My bike starts reasonably fine with 1-2 kicks. When I don't start it for couple of days, it can be like 3-6 kicks and if I won't start it with first few kicks then I have to use a Hot Start to do it.

After I finally start the bike, warm it up on choke and do a quick ride, it idles fine. But it hangs in like 3 of 5 cases where I use the throttle. The slower I use the throttle the more likely it will hang. If I kill the bike with kill-button, I can start it with 1 kick. No need to use Hot Start, no need to use AP. I can start - kill - start many times, no problems here.

But as soon as I kill the bike on a gear (ie. i brake with 2nd gear or lock my wheel in sand), I can't start it back easily. Usually Hot Start with 1-2 kicks is enough but if I don't start it with these 2 kicks, I can spend next 10 minutes kicking it. Randomly pulling Hot Start, turning out pilot screw 1/4 turn-outs etc...

So, when it finally runs and I turn-in the pilot screw I can turn it up to 0.25-0.5 turnouts and it doesn't die. I also don't see much difference between 3 and 1 turn outs... It dies as soon as I fully close the screw (sic!). When I get the pilot screw to be adjusted on 1.5 turnouts and adjust idle screw turning it out by 1/4 turn, it works better, the hanging idle happens less but... as soon as I kill it (even with kill-button) it doesn't want to start, I have to revert the changes on pilot screw and idle screw and… use Hot Start.

I've spent three weeks now figuring out what's going on with my FCR. I initially bought the bike with NMTT needle, #175 MJ, #45 PJ, #68 SJ and #65 LJ. Replaced with stock set for 2008 after doing top-end rebuild (and because I couldn't start the bike in the first place when I bought it — thought it was the carb that needed cleaning due to long no-run time).

Would appreciate any help, if it helps I can post some videos of the bike starting up. I'm honestly exhausted with this carb. I'm 100% sure it's the carb that is generating the problems because random "setups" on the AF-ratio makes it run better/worse...

[Leardriver]

That carb has a plethora of fiddling done to it with different jets. It will run great with the stock jets.
Try a 45 pilot, stock needle, 172 main. Without ruling out goofy jetting, it is hard to pinpoint any other driveability problems.

[tiraeth]

Thanks for the response.

According to Service Manual, stock 2008 CRF should have NMGU needle (3rd clip for my area), #188 main, #42 pilot. That's what I have.

When I bought the bike it had #175 MJ, NMTT needle (3rd clip) and #45 pilot installed. I also have NKBT needle that I got with 2007 carb repair kit (along with #175 MJ and #42 PJ) that I can use. Last time I tried (probably with 8mm fuel float level) it was painful to start the bike. Either hot or cold.

[Leardriver]

Ok, you are closer than I thought. Those bikes like a 45 pilot with the fuel screw at around 1.75 to 2.0 turns out. The main jet and needle won't have any effect on starting and idling.

[tiraeth]

I'll put #45 pilot and adjust the fuel screw on Monday.

Currently (on the jetting from 1st post and fuel screw 2 turns out) my bike starts cold in like 3-5 kicks + AP, has good idle (but hangs when closing the throttle). When it gets hot (or after I first start it) I can kick it in 1 kick. But still if I shut it down by choking it (holding brake, releasing clutch on gear) I have to use hot start to get it up and running (1 kick with hot start is needed) — if I try to start it without hot start and kick it 2-3 times, spark gets flooded and then I have to wait (and use hot start) or kick it for like 10 minutes. Randomly pulling hot start out. I wonder if this is a normal behavior because I heard that hot start shouldn't be used for any other reason than to start the bike if you crash it and it gets flooded with gravity.

[tiraeth]

I've made a progress...

Current setup is MJ #175, Slow/Pilot #45 and NMGU needle on 3rd clip. I screwed out the pilot screw to be 2 1/4.

Bike starts within 1-2 kicks, no accelerator pump needed. After a week I could simply pull out the choke, turn the petcock on and it cranked with second kick. I can shut it off and it will start within a single kick.

Problem is after intensive ride when carb is using mostly MJ and needle. When I shut it off while riding and throttle opened, it's impossible to start with with few kicks even with hot start. I have to wait few minutes, kick it several times with petcock off and hot start and maybe few minutes later it will start. If I leave it running for a minute and shut it down with kill switch, I can start it with 1-2 kicks.

I have NGK R0409B-8 spark plug.