carburation

[steed2]

i was wondering if anybody could give me a pointer here ..im have a problem with the carburation.....on hard decel after wide open it does a loud back fire ....lean condition...also if i run wide open for like say 10 sec in 5th gear ...the bike will want to die when i let off the gas?Im running a 180 main,68s, b53e needle 3rd pos., at sea level with an fmf power core 4,......maybe at 100mph im causeing a ventui effect on the vent hose under the bike dropping the pressure in the bowl?????

[roadrunner81]

Are we talking about a gargle upon decel or one very loud back fire?

[steed2]

one very loud backfire

[JKL]

Edelbrook carburator will fix the problem:ride:

[roadrunner81]

First of all an Edelbrock is a lazy mans caburetor, if you plan on replacing carb save your money for a TM40 or an FCR. Steed2, do you have any air box mods besides pulling the stock baffles out?

[steed2]

no i do not ....another thing maybe its the pilot adjustment i cant seem to adjust it properly??? ya just the restrictors removed ....no holes

i like the 180 main it gives a nice midrange pull

also there is a flat spot at the bottom the throttle ....common for these carbs ...and honestly i like the way the factory carbs works ...{except for the little prob.} i dont want an edelbrock carb {lose botom or top ...its either way ..lol}

thanks guys hope u can help me

[fla18c71]

try main188

needle 5 position all rich

flavio from rome italy

[Billahjack]

My bike (XR650R) always has too rich of a main jet if it stutters for a split second coming off of full throttle. I would try going down to a 178 and then a 175 and try to see if you feel a difference. As soon as you get that "Closing Throttle from wide open" bog gone, then you may have to raise your needle one clip position (move clip towards pointy end) to get some mid range back. I'm still trying to figure out how to adjust the fuel screw. This can help your idle to opening throttle response.

Here is a link for XR650R carb settings:

http://xr650r.us/jetting/

I'm guessing the backfire is loading a bit of unburned fuel (running rich) into the exhaust when you are closing the throttle from wide open.

May want to double check if your bike has been uncorked properly.

_________________________________

I'm running the same combo in my 2000 bike, Powercore4, Powerbomb header, no side panel cut-out, B53E Needle 3rd Position, 68S pilot and then a 175 Main. Works great at sea level. I get a "Wooomp" backfire when I shut off the bike though.

[steed2]

Yes its all proper i know cause i did it And actually i installed a hotcam .stage 2 on the week end and the bike is like a new machine .....{ off idle stumble is gone and this whole issue ^ is resolved soooo ......lol forget this now! thanks anyways guys

PS i recomend to anybody to try this cam .....the difference is amazing

[XHMXR]

i was wondering if anybody could give me a pointer here ..im have a problem with the carburation.....on hard decel after wide open it does a loud back fire ....lean condition...also if i run wide open for like say 10 sec in 5th gear ...the bike will want to die when i let off the gas?Im running a 180 main,68s, b53e needle 3rd pos., at sea level with an fmf power core 4,......maybe at 100mph im causeing a ventui effect on the vent hose under the bike dropping the pressure in the bowl?????

When you chop the throttle, you momentarily get higher than normal manifold vacuum. This typically causes a rich condition in the exhaust system and if you have any type of air leak in the exhaust system in front of the muffler it will backfire. Iv'e seen it completely disconnect the muffler at the joint where it meets the header pipe. With an AIS system usually it just burbbles or backfires many times a small amount because the rich condition doesnt happen because its getting air all the time. Without AIS it runs rich until it gets enough air then it will burn all the fuel in the exhaust in one loud bang. Just a thought.?