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Old 10-28-2013, 07:50 PM   #1
Jdeks OP
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Eh? Backfiring/smoke through carbs with ITG filter

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!

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?

Jdeks screwed with this post 10-29-2013 at 04:13 AM
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Old 10-28-2013, 10:56 PM   #2
Sumi
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Carb sync, vac. leak are the most likely causes.
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Old 10-28-2013, 11:23 PM   #3
Jdeks OP
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Quote:
Originally Posted by Sumi View Post
Carb sync, vac. leak are the most likely causes.
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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Old 10-29-2013, 02:53 AM   #4
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You give it maximum throttle when its cold ... and it doesn't run right.. the manual advises 2 bars on the temp guage before doing that.
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Old 10-29-2013, 03:07 AM   #5
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Quote:
Originally Posted by Sumi View Post
Carb sync, vac. leak are the most likely causes.
+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!
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Old 10-29-2013, 03:09 AM   #6
Orangecicle
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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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Old 10-29-2013, 04:11 AM   #7
Jdeks OP
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Quote:
Originally Posted by Lc8grrr View Post
You give it maximum throttle when its cold ... and it doesn't run right.. the manual advises 2 bars on the temp guage before doing that.
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)



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)



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...

Jdeks screwed with this post 10-29-2013 at 04:17 AM
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Old 10-29-2013, 06:20 AM   #8
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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.



/Johan
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Old 10-29-2013, 03:55 PM   #9
Jdeks OP
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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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Old 10-29-2013, 04:14 PM   #10
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Quote:
Originally Posted by Jdeks View Post
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.
Hope you get it sorted out, just wanted to point it out so you just didn't miss something simple.

Cheers!

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Old 10-29-2013, 05:09 PM   #11
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Yeah thanks, any suggestion is good !
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Old 10-29-2013, 05:37 PM   #12
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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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Old 10-29-2013, 10:44 PM   #13
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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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Old 10-29-2013, 11:17 PM   #14
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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.
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!

Quote:
Originally Posted by Sporting Wood View Post
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.
What it's doing is forcing a little dribble/spurt out past the hose clamp in this pic.



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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Old 10-30-2013, 03:46 AM   #15
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Quote:
Originally Posted by Jdeks View Post
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!



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



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.
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

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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