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06 CRF100F Backfiring on Deceleration

This is a discussion on 06 CRF100F Backfiring on Deceleration within the Bigger Minis Forum forums, part of the General Talk category; 06 CRF100F Backfiring on Deceleration I road race My 06 CRF100F..(Stock Class) My Carb Settings are: Stock Main Jet (new replaced Stock Pilot Jet(new replaced) ...

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Thread: 06 CRF100F Backfiring on Deceleration

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    06 CRF100F Backfiring on Deceleration

    06 CRF100F Backfiring on Deceleration

    I road race My 06 CRF100F..(Stock Class)


    My Carb Settings are:
    Stock Main Jet (new replaced
    Stock Pilot Jet(new replaced)
    Needle is one Notch Down..

    Carb Screw adjustments to fine tune the bike to run right..
    Fuel Mixtire screw(no air screw) is new,replaced and set to stock setting..

    Stock Carb,Stock Air Box,Stock Air Filter
    Carb Fully Cleaned.
    Stock Electronics.
    Stock Pipe.
    NGK Plug..Tried the 6,the (CR7HSA ,and the (CR8HSA ..I have the 8 in the bike now(it’s for extended high speed riding}in manual’ as I do)..All plugs do the same pop..no matter what plugs in the bike..

    Plug Color Is Black...Not Soaked Wet,No Caked Oil......but Black after Racing..
    ........
    The bike starts right up..Purrs..Great Idle,Great Throttle Response..No hiccups..
    The bike has incredible Midrange response..
    Very Strong Running Bike..

    Racing:First Fast Turn..In 5th Gear Downshifting to 4th Gear Hard Deceleration....POP..A BIG POP Backfiring on Deceleration..
    One pop only..no other popping,no small pops..
    Go around the track twice and it stops,no more Backfiring on Deceleration..

    Our races may be 25 minutes...or less...When I come into pit in neutral the bike has a blip in the throttle but the bike rides fine..
    After the bike cools the blip is gone..

    I could race the bike for an hour straight ,hard riding and I will only get the BIG POP Backfiring on Deceleration twice when first getting on the track in the same turn....


    Is this BAD?
    what should I look into..?


    Do I just live with it since the bike runs so strong?
    However I don't want to blow the motor..

    I have found that if I don’t decelerate as hard the first two turns and run 5th gear into the turn further I get no pop..
    Last edited by PocketBikeRacingTsmmr; 07-16-2013 at 02:45 PM.


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    davmo's Avatar

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    Popping on deceleration is usually a result of lean condition. Since you say the spark plug is black, you are running rich most likely. Here's my theory: when rapidly decelerating, the gas in the tank and carb bowl will move toward the front of the bike. This can temporarily steal gas from your jets or petcock. There is sometimes a plastic shroud, or built in cup that goes around the jets to keep gas there during turns, wheelies, fast starts or stops. Don't know if your particular carb has one or not, but it is surprising how many bikes I have come across with them missing. If your float setting is a hair low, the problem will be worse. Once you get going out there, your float will allow more gas in the bowl than when you are sitting still, that make it better as long as you are riding. Let the bike idle a bit, even after a ride, and I bet you can get the pop to show up again. I would start with the float setting up slightly.
    DFA GSD

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    awesome question ....one of my bikes in the garage is very similar it just does not go away ...I am going to try to set the float like davmo says, but is there a picture of this said baffle? I bet the jackass that had this engine before might have put it in the "spare parts" bin! its on hard breaking/down shift only and did not even know where to start explaining to ask

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    Quote Originally Posted by PhilRabbleCroteau View Post
    awesome question ....one of my bikes in the garage is very similar it just does not go away ...I am going to try to set the float like davmo says, but is there a picture of this said baffle?
    These are pictures of a PE24, and a Mikuni 28mm flat slide. The PE24 has a white plastic shroud, and the 28 has a brass one. Both carbs have a cup built into the bowl.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    DFA GSD

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    ya i have 22mm "mikuni" that has nothing of the sort .......

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    Item #27 looks to be the part on this Mikuni diagram. They list is as a "baffle"
    DFA GSD

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    awesome dude thank you....damn "baffles" I will buy one to try for sure I think I can find one... either way its worth a shot!

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    I have had a good run until the last couple of months ....carbs be phucking with me

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    Thank you..
    I know I have the plastic shroud in as the first time I took the carb apart to clean it's pilot jet it fell out and I was like OH NO!!.what was that..
    Now it's pinned in my head never to forget it..

    My float bowl may be to low so I will raise it a tad and report back after my next race...

    Crazy thing with this bike is: I can let it run and run,it won't pop it'll run great,idle great .....if I ride it casual never a pop...Only hard riding and rapid decelerating I get early in race a BIG POP upon heavy decelerating..

    Someone stated:

    Check to see if the valves are too tight.?

    Sounds like you have a burned exhaust valve and leaky valve seals?

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    that's the same as mine, I cant get it to do it on the stand and it got worse in the parking lot with street tires lol

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    Another thing I'm going to try as recommended by another member here..
    Is:
    Make sure to fully warm up the bike before racing it..

    Set the needle position clip back in the middle..it’s the only setting on the carb that’s different.
    I bring a second carb with slide,the needle is set in the middle so at the track instead of messing with moving the clip I just thrown in the other needle vice versa.

    Note: this is an 06 ..the carbs the vtype without the adjustable needle and fuel mixture screw so I had to buy an older XR100 carb to install those parts..

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    You may want to make sure the exhaust is well tight and leak free too. On de-cell the exhaust can pop if there is a leak, or you have large open end short pipe like an "Engines only outlaw pipe" which is just a noisy POS and not worth $20 nor the $15 I paid for a used one.

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    The XR100R carb doesn't have the baffle on the main as shown. I do agree that float height is the most likely cause (especially if different size wheels have been fitted).

    Setting float height is easier than you think.



    Level the bike front to rear and side to side, add sag weights or pull the rear down to emulate rider weight. Attach a clear hose to the drain as shown, open the drain screw and the fuel petcock. The fuel level in the clear hose should be even with the carb body (where the bowl and carb body meet). A little high - bike will run rich, a little low- bike will run lean. The float height in the pictured carb is very low (due to suspension and wheel mods).

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    ^^^that was a good tid bit of knowledge right there thank you

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    that is an awesome trick I did not know... thank u sir!!! I will be using this to check all the bikes we have from now on!!!

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