Backfiring/smoke through carbs with ITG filter

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by Jdeks, Oct 28, 2013.

  1. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Two in the one day!

    So I've recently ditched the airbox for one of the foam filter intakes. Running jetting as per the recommendations most others are following:

    168/170 mains
    45 idles
    FactoryPro Needles, 3rd clip
    4mm floats
    1.25/1.5 IMS
    All stock air jets

    Once it's warm, it runs smooth, good and bloody strong everywhere. Idles fine, sarts when warm instantly.

    But even in 20 deg C weather, it struggles to start from 'cold' without the choke. Taking off on sudden throttle when cold, it hesitates coming off idle. Idling cold, if you give it sharp, sudden throttle, it falters briefly, and half the time it goes *coughclack!* and dies.

    More alarmingly, it's usually accompanied by smoke wafting out from the intakes, usually mostly the front one. Additionally, the hose at the bottom of the oil reservoir seems to pressurize and spurt oil out! :eek1

    Put the choke on, or let it warm up, it stops happening.

    My theory was lean mixture detonating prematurely and causing kickback, but with 45 pilots it seems unlikely it would be lean. Adjusting IMS either way hasn't helped.

    Valves are in spec, carb boots are seated properly.

    Can anyone suggest what's causing this backfire/carb smoke?
    #1
  2. Sumi

    Sumi Long timer

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    Carb sync, vac. leak are the most likely causes.
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  3. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Yep, I've considered that.

    Like I said above, the carb boots are seated correctly. Very easy to get correct with the airbox gone. Two of the vaccum posts are plugged with bolts, the others each have a clamped and plugg vac lines for carb syncing, which was done not too long ago.

    In any case, I would think if it was either of those two, I'd be seeing issues elsewhere, not just at idle and only when when cold? Moreover, it would have been doing it prior to ditching the air box (which it wasn't). I'm fairly sure this is fueling...
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  4. Lc8grrr

    Lc8grrr Vtwin madness

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    You give it maximum throttle when its cold :huh ... and it doesn't run right.. the manual advises 2 bars on the temp guage before doing that.
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  5. ICERIDER

    ICERIDER Adventure Rider

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    +1

    I'd be delighted with your setup if it was doing that when cold. IMHO A properly tuned engine should require choke when cold. 20 deg is a long way off 120 deg.

    I use one of those carb syncrometer things. Just pop it on the bell mouth and I'll bet you'll find they are out. Those things are cheap and light enough to carry around and it'll put a smile on your face when you get it sync'd and purring. A very satisfying small turn of a screwdriver!
    #5
  6. Orangecicle

    Orangecicle On a "Quest"

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    Depending on elevation, you may be a little lean on your IMS screws and a little lean on your mains. It definitely needs the 45s with the ITG and floats at 4mm, so that is correct. Here are my settings right now in cold Iowa:

    Mains: 170/175 (could be slightly larger)
    Floats: 4mm
    Idle jets: 45s
    IMS: FlexJet screws at about 1.5 turns out
    Needles: Factory Pro needles at the middle clip
    Elevation: 850 feet ASL
    Filter: ITG with a CPR pre-filter

    I did have mains at 162/168, and the bike coughed while running down the road. I checked for vacuum leaks and found none. So I pulled the plugs and found they were light tan to white, so the bike was lean. I went up to 170/175, and it no longer coughs. Like I said, I think the mains could go up in size without a problem.

    Also, note that I'm running the red CPR pre-filter. I noticed a difference in the bike after putting on the pre-filter. I know that it adds just enough of additional air restriction to make a difference. Without the pre-filter at this elevation, I definitely would be going up on the mains.

    Best of luck.
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  7. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Poor wording on my part (OP edited) . It's not so much "max" throttle as it is opening the throttle quickly. Point taken though :)



    Orangecicle: The mains I'm using as based on what Sportingwood told me based on his dyno work (actually a little bigger). However, I've seen a few folks like you saying they're using the mahoosive mains with 45's....

    I did some plug testing today across a variety of riding ( several WOT/cut runs, chugging the bike around the block a few times at idle, 40 miles of mixed hard riding)

    [​IMG]

    Looks pretty much perfect to me.

    However, I also pulled the plugs after provoking the above problem (sharp revs at cold idle). Still tan, but seems to have a darker, wet coating, easy to wipe off with a finger. (ignore the wetness round the crush washer, thats just a bit of wd40)

    [​IMG]

    My initial theory was that the idle/pilot circuit is running too lean, but the wet, dark plugs says rich? Or maybe oil?

    I'll verify the carbs are sync'd, and check the boots again...but I'm pretty sure if there's a vaccum leak, it's not coming from there.

    Then I'll try try bigger mains. Failing that, I'll just bloody well use the choke to start it and ride the thing, it goes like mad once it's warmed up. It's just unusual it's now needs warm weather choke now the airbox is gone...:huh
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  8. DirtyADV

    DirtyADV Long timer

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    Double check that your chokes have had one of the cables not fully seated down by the carb resulting in bad backfiring up the carb (flames actually).

    Ran fine with choke when cold but trying to back of it only one worked as it should.

    Should be easy to check without the box.

    Went the CPR route on my new 990R myself.

    [​IMG]

    /Johan
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  9. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Thanks, but the choke cables are brand new, I've checked they're screwed in fully and correctly, and they operate fine. Your symptoms aren't exactly the symptoms I'm getting.

    I use the choke to get it started, but backing off the choke isn't what causes the issue - it's throttle input.
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  10. DirtyADV

    DirtyADV Long timer

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    Hope you get it sorted out, just wanted to point it out so you just didn't miss something simple.

    Cheers!

    /Johan
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  11. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Yeah thanks, any suggestion is good ! :D
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  12. ICERIDER

    ICERIDER Adventure Rider

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    IMHO the carbs absolutely require sync following such drastic alterations. I had that symptom on my standard 950 Adv. Sweet as a nut after sync.
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  13. Sporting Wood

    Sporting Wood I

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    "More alarmingly, it's usually accompanied by smoke wafting out from the intakes, usually mostly the front one. Additionally, the hose at the bottom of the oil reservoir seems to pressurize and spurt oil out! "


    This is the part that's throwing me. I could see where a sync or perhaps a little richer mix could help a little here but...blowing oil out of the bottom of the tank? wtf? Its negative pressure at that fitting, oil being pulled into the motor from the suction pump. In order to pressurize, pressure has to flip to positive, and enough to blow through the seal or a clamp. Either that or its just a weak seal/clamp. Smoke wafting out of the carbs too, shouldn't happen unless there's a bit of off cam timing.

    I've never put a cam in one tooth off before so I couldn't tell you what it does but...I may would add it to the list.
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  14. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    This was my first suspicion. I didn't think I was that big a numpty, but you never know...

    I pulled both covers and checked TDC front and rear - all the respective croses and dots are where they should be. At least its an easy exercise with no airbox now! :D

    What it's doing is forcing a little dribble/spurt out past the hose clamp in this pic.

    [​IMG]

    It was a little lose, but still not leaking during normal running.

    When I say spurt, I'm not talking "Nurse!! We got a bleeder!!". More "I don't remember my floor having drops there....".

    But yes. WTF indeed. My uneducated theory was lean detonation making the thing kick back and force the oil pump in the wrong direction, but I don't know if that's possible/makes mechanical sense.
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  15. Sumi

    Sumi Long timer

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    IMO the leak is because of a faulty seal inside the reservoir (the green one which is at the base of the screen). I had this with a brand new seal, and had to change the seal for a new new to solve it (+ a little silicone or whatever just to be sure it seals properly) :) If you lay the bike on it's right, you can get away with little oil loss and only a little mess - you have to be fast though:D

    I think that the oil leak is completely unrelated to the backfiring issue. Have you pulled that screen recently (like during an oil change?)?
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  16. ICERIDER

    ICERIDER Adventure Rider

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    Could be right about the oil pump running backwards against the check valve I suppose. Anyway that is secondary to the main issue and should go away if you can stop the backfire. The other risk you are running now is you are giving all you carb/vac connections a hard time plus your starter clutch/can chains etc with this backfire.

    I'd go over those connections yet again just to make sure you are not sucking air. Do you have a very lumpy idle? Don't want to get you further into trouble but if you haven't got sync eqpt to hand note where the sync screw is and have a play with it. Very small adjustment one way or the other should get cylinder chiming in if its out.

    I'd still say all you have is a cold backfire made worse by out of sync. Good luck.
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  17. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    No, it's definitelyrelated to the backfire - it only happens when that occurs.

    I know the green seal you're talking about. Bu that's not the site of the oil leak. That seal is up and behind the metal flange than bolts to the reservior. That's not there the oil leaks out. The oil is coming out of the black rubber hose at the clamp. The pressure is actually enough to push the black hose physically down several mm. Do it enough times and I imagine it would pop clean off, now that the surfaces are all oily.




    Idle is totally fine once warm, or if I use the choke - consistent 1400rpm, no wavering. If I try to start it cold without the choke, the first minute or so it idles low (about 1000rpm) and needs some slight throttle input to stop it dying out. Just like trying to get it going on a really cold morning....except its summer. Once its at one or two bars, it's all daisies.

    Your concerns about stressing other areas echo my own, which is why I'm not going to try and get any repeat performances. I'm going to have the carbs synced when I get a leakdown test done next week, see if that helps. Failing that, I'll try bigger mains, then lowering the needles. If none of that works, I'll just leave it the hell alone, and use the choke to start it from now on. It's a problem i have to TRY to provoke, so I just won't try. It's running fantastically everywhere else, and that's what matters, I guess.
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  18. Head2Wind

    Head2Wind MotorcycleMayhem

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    It _SHOULD_ require the choke to start when cold, if it does not the jetting is _TOO RICH_. The puff of smoke from the intake is related to a intake 'back fire', and will happen if the engine is too cold and too much throttle input is applied. I think that your expectation of the engine to run like its EFI is faulty. With carbs, it _SHOULD_ not run 100% correctly until its 100% warm.

    The 45 pilot should be plenty of fuel for a quick warm up after full choke to start, dropping choke back to ~80% almost right away, then off in about 30 sec, the engine should idle ~1000-1200 until full warm idle should be ~1400. I have been tuning/running 42 pilots but with the bigger mains (178/180) and #3 clip with 4mm floats with WINGS mufflers and large inserts. I requires full choke to start cold, but when full temp its crisp and runs really well. I have found that the muffler/exhaust system flow rates make a significant difference on the fine tune setup of the jetting to get it just right. Of the two 950 SE that I tuned for the MX1000, both were the same EXCEPT the exhaust systems and as a result the bike with the longer/larger secondary pipe and open muffler required more fuel to get it to run right.

    One thing that you might check is make sure that the Factory Pro pilots are 100% clean. I have seen machining debris in more than one pilot jet fresh from a FP kit...
    #18
  19. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    When I'm not intentionally trying to fuck with it, this is literally exactly how the bike starts at the moment....

    I'm going to go out there and suggest my problem might be a 'PEBCAK' scenario. :lol3
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  20. Jdeks

    Jdeks Accepting and supportive of everyones feelings.

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    Can I get some thoughts on plug color from folks?

    This is after 300km of varied riding, from low revs to highway to WOT. This is with an ITG foam filter, 168/170 mains, 45 pilots, FP needles on 3rd clip, 4mm floats, air jets stock.


    [​IMG]


    To me, that looked like the tips were too white ie lean. So I cleaned the plugs, upped the mains to 170/172, and did the same ride again:


    [​IMG]

    This looks a better color, but now there's a lot more of these little golden lumps on it...what are they?


    170/172 with the 45 idles is much richer than recommendations for this filter but the plugs in the first pic seemed to have white tips to me.

    I'm still getting slight bogging down low though so I suspect 45's might be too right for my bike.
    #20