39 fcr bog

[hotrodbelair]

i bought a 39mm fcr carb for my ex and it runs except for a bog on the low end when i try to punch it from idle, and when i punch it at quarter throttle. and also once i get toped out it starts to cut out. i was thinking about moving the clip on the needle down one notch. anything else should i try i dont have any jets i could put in there but im goin to a friends house tonight i can get jets from him.

[stalefish_132]

when you get it set up there should be zero bog, mine you punch it at idle and it just pulls hard from idle to red line.

what jets are you running right now? and what is the crab out of? there are few differant versions

[hotrodbelair]

it came off a 416 im pretty sure it was one made for the ex. not sure what jets are in it i looked at them a couple weeks ago i want to say its got a 148 main cant rember what its got for a pilot.

[Nick shupe]

I have a 39mm carb. for my 440 ex and it bogs a bite at frist when cold but wants she's warmed up watch out:eek2:

[GPracer2500]

The more information you can provide, the better and more accurate our advice can be.

-What's the current jetting (main, pilot, needle clip position, fuel screw setting)?
-What are the details of your bike (intake, exhaust, internal engine mods)?
-What was the jetting of your old carb? Did it run fine with that jetting?
-Where do you ride (typical temps and elevation)?
-When misfires or rough running occur, what throttle postion are you at? RPM is far less important than throttle postion for figuring out which carb circuit needs attention.

I'm not saying you can't get some good leads without all that info, but you never know which piece of information will turn out to be the key.

While the float bowl is off, check and see if your carb is equipt with a leak jet:

http://img238.imageshack.us/img238/2921/attachmentry2.jpg

I'm guessing it does not, as most FCRs originally set up for EXs do not. That's somewhat unfortunate because the leak jet is the primary way of tuning the Accelerator Pump. The AP is responsible for combating the "bog" that you're experiencing when wacking open the throttle quickly from idle or low rpms. A properly tuned pilot circuit and turning up the idle a little are the common alternatives to dealing with the bog if leak jet tuning is not possible. If the bog is really bad and occurs during real-world riding (wacking the throttle while sitting in the garage at idle doesn't count) then there are alternatives for tuning an AP without a leak jet but they are pretty hard to do--not something I'd recommend for the inexperienced.

ETA: Almost forgot: the Boyesen Quickshot AP cover might be worth considering if all else fails for eliminating the "bog" (or lessening it to an acceptable level). At ~$100 I'd try everything else first, though.

[Nick shupe]

I have a boyesen quickshot AP cover and it helps I just don't know if it was worth the 100 bucks

[hotrodbelair]

sorry i havent replied in a while i was gone all weekend competeing in a tough truck event. i worked on it today i bumped the main from a 148 to a 150 that took care of the sputtering on top end. then i moved the clip from the top of the needle down 2. that helped with the bog but but its still there now its just if im reving realy low and punch it like just barely off idle doesnt do it from quarter throttle. its got a 52 pilot and i couldnt find a leak jet. i just got done riding it im waiting for it to cool down before i check the plug. and for mods i have 440 11:1, ported pollished head, 1mm bigger intake valves, stroker cam, fmf header hmf silencer, k&n filter, and the 39 fcr carb. im not sure what elivation im at i live in warrens wisconsin, and the temp is usulaly around the upper 80s and lower 90s. do ya think i should go down more on the needle or should i mess with the pilot?

[GPracer2500]

Looking into your pilot circuit would be a good next step. HERE'S (http://www.exriders.com/vbb/showthread.php?s=&threadid=229923) my prefered method for setting/confiming a pilot circuit.