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[SDCVO]

I have about 5000 miles on my crate 120r and it runs amazing after being tuned by Bob Lobenburg at RC Cycles all the thru the power band but I have occasional problem starting it with backfires and puffs of smoke coming out of the air cleaner while other times (mostly) it lights right off. When i have the problem I will have to try to start it up to 5 times before it will light off and I am worried i might be doing some damage? Went for around 250 miles today and probably start/stopped 10 times with have the problem twice. I would just take it back to Bob but I am in San Diego and I took it up to No Cal so he could tune it but it was very difficult and don't have the ability to get it back up there. I am hoping it is no big deal and not hurting anything in which case I will stop worrying about it. I have attached the Dyno to show how well he tuned it and though I get that it isn't just the dyne numbers that count, it really does run unbelievably smooth and strong with that exception.

[sadunbar]

I have about 5000 miles on my crate 120r and it runs amazing after being tuned by Bob Lobenburg at RC Cycles all the thru the power band but I have occasional problem starting it with backfires and puffs of smoke coming out of the air cleaner while other times (mostly) it lights right off. When i have the problem I will have to try to start it up to 5 times before it will light off and I am worried i might be doing some damage? Went for around 250 miles today and probably start/stopped 10 times with have the problem twice. I would just take it back to Bob but I am in San Diego and I took it up to No Cal so he could tune it but it was very difficult and don't have the ability to get it back up there. I am hoping it is no big deal and not hurting anything in which case I will stop worrying about it. I have attached the Dyno to show how well he tuned it and though I get that it isn't just the dyne numbers that count, it really does run unbelievably smooth and strong with that exception.

How old is your compensator?  Classic sign of a compensator wear - loosing tension...

[SDCVO]

Bike has about 17000 miles, compensator never replaced

[timo482]

Compensator or compression releases

[SDCVO]

Does that make sense that the auto compression release would not work sometimes? When it happens, it almost feels like the pistons have stopped in the wrong place or something. Obviously I am not very mechanically inclined so that might be a very stupid comment i know. The motor is turning over but is either backfiring or coughing smoke. The next time i try it it either does the same thing or immediately fires up

[FlaHeatWave]

Compensator?

What clutch do you have with the 120?

I know that it's a ways, but it's a nice ride back to your tuner...

[SDCVO]

Barnett Scorpion clutch

[grc]

I don't think you actually said if this problem has been occurring since immediately after the tune, or if it's something that has started recently and gotten worse over time.  If the latter, I'd suspect the compensator as sadunbar mentioned previously, since that was a common sign of a worn compensator or weak springs.  As for the auto compression releases, those can stick or have intermittent electrical issues so they may work one time and not the next.  If this is occurring as often as your post makes it seem, I'd think back-to-back compression tests might expose an intermittent compression release.

Jerry

[sadunbar]

I don't think you actually said if this problem has been occurring since immediately after the tune, or if it's something that has started recently and gotten worse over time.  If the latter, I'd suspect the compensator as sadunbar mentioned previously, since that was a common sign of a worn compensator or weak springs.  As for the auto compression releases, those can stick or have intermittent electrical issues so they may work one time and not the next.  If this is occurring as often as your post makes it seem, I'd think back-to-back compression tests might expose an intermittent compression release.

Jerry

With 17K on the compensator, and 135/135+, it's highly likely a worn compensator causing the issue.  Classic symptoms.  Knowing Bob, it's not tune related.  The symptoms don't relate to a tune issue either.  To have it "backfires and puffs of smoke coming out of the air cleaner" a spark plug has to be firing with an intake valve slightly open - which points to a worn compensator.   

[sprinkman]

Make sure your releases are turned on, when they tune sometimes they turn them off.

[GMR-PERFORMANCE]

I would bet that it is fuel related . The pop and cough on start up is due to  lack of fuel. Intake leak or needs a slight bump on cold start fuel and or inj pulse on start up. I have seen some of the most beat to death comps and not one has ever effected how the bike started. Call Bob and he can make a change to the map and reload it . 

[ultrafxr]

Good suggestions all.  I would add another possibility - a weak battery.  Had a similar problem last year on my '07 - it would sometimes 'hang' and then spin again.  Couple times it did cough back like you describe.  Dealer did diagnostic on battery and said it was marginal.  I really did not think that was the problem since it was only about two years old and is always kept on battery tender.  But I went ahead and bought a Deka battery which completely solved my problem.

[Phaq2]

I don't want to hi-jack the thread but my modified 110 kit has similar symptoms on hot starts this past season. Up until it was fine! 

The OP posted "Went for around 250 miles today and probably start/stopped 10 times with have the problem twice" This makes it sound like hot starts to me but ??

Mine's in the shop now and they are looking at the ACR's. My SE comp has 45,000 miles at 119hp/130tq.

[Fullsac Performance]

I would bet that it is fuel related . The pop and cough on start up is due to  lack of fuel. Intake leak or needs a slight bump on cold start fuel and or inj pulse on start up. I have seen some of the most beat to death comps and not one has ever effected how the bike started. Call Bob and he can make a change to the map and reload it . 

I agree. Maybe add just a touch to the "cranking Fuel" table first and see if it helps.

SG

[Hog95023]

My 124 did that too after it was tuned by bob and I had a new compensator.