Rare Throttle-from-Idle Issue...

[Honch777]

Hay folks,

Every blue moon, when I rev from idle, the engine (as best as I can describe) "gasps" instead of revving. This is a rare occurrence that only happens when I crack the throttle, never when rolled on... but I'd like to know what is causing this.

Any input would be appreciated, thanks.
- Honch

 

[rchuff]

Year and model mite help?

 

[Negative]

Mine does that ..... I've been trying to study around and see if there's something as far as "acceleration enrichment" values that might be better suited to work with my bike than what's already in my bike's ECM ... I tend to blip the throttle a tiny bit before I crack it to prevent this cough noise ... lol

 

[fishxb12]

mine does the same. I have a buddy with a sportster and his throttle is a lot more responsive. I was kinda wondering if it was normal also.

 

[lotusexcelle]

These are heavy flywheeled twins (well.. lighter than most twins.... but still). They are NOT full-throttle-from-idle bikes. Period. What you are doing is going from IAC controlled running to WOT and the engine just cannot correct for those two states so quickly. In other words the engine is programmed for a slower rev delta than what you are demanding, and which it has no idea how to correct for.

Mine does this with both the original ECM and the Race ECM, so I don't think there is a way to fix it. Just don't do snap-throttle revs. Not made for that. I would suspect the sportsters simply don't breathe well enough for this to be a problem.

 

[Honch777]

Year and model mite help?

'04 XB12R

They are NOT full-throttle-from-idle bikes. Period. What you are doing is going from IAC controlled running to WOT and the engine just cannot correct for those two states so quickly.

Not sure if it makes a difference, but it wasn't WoT. Only about 1/4 throttle, just a quick crack like you would for a downshift.

 

[Negative]

Now mine doesn't do it with just that small of a throttle blip ... it will from idle though ... but if I just slightly bump up the revs, say to 1,500 and then crack the throttle open it'll rev no problem ... it's just from a dead idle it won't .... it's not really much of an issue to me, I've just always been curious as to why ... every other bike I have (including my S1 ... yes yes I know it's carbed and all that jazz) has no problem with this ... JUST my XB

 

[Honch777]

Bump for justice, still wondering about this...

 

[user_deleted]

still wondering about this...

why? lotus explained it perfectly and clearly. wonder no more. it is the nature of the beast.

 

[Honch777]

Well what he was explaining was WOT from idle, which I do understand.
My problem is just a small bump from idle to like 500 RPMs above idle, like what you'd do once a stop light turns green.

 

[Negative]

Could possibly be the TPS having a few dead sectors on the lower end of it's travel ... I understand the nature of V-twins with heavy flywheels and stuff but there's no reason for the bike to cough and sputter when I do it from 1,000 rpms and do it just fine from 1,300 rpms ... I've been wondering about this since I first got this XB running again ... I just priced a couple of TPS sensors from parts warehouses around here and I'll probably be swapping mine out pretty soon ...

 

[WIGGLE2]

I've posted this several times, so I will do the 'short' version. Try different fuels. I'd always gotten fuel at the same place. I had this issue. Dealer told me to try Sunoco. I did. Problem went away. put other fuel in....problem returns. Sunoco back in, problem gone. I couldn't argue after that.

 

[Honch777]

Hmm, would have never thought about it being the fuel...

I typically just get 93 from whatever station is close once I get the Low Fuel light, heh.

I'll give that a shot tho, thanks for the input.

 

[Negative]

Same here !!

 

[WIGGLE2]

I argued with the service manager, as the bike was almost new at the time, and I figured they were just blowing me off because they didn't know how to fix it. I've been in the performance/racing engine industry all of my working life. (nearly 30 years). I thought I had a pretty good grasp on 'hydrocarbons'.....I was proven wrong. As I stated...I couldn't believe it, so I did my own experimenting. There ARE a lot of differences in 'pump' fuels I found after doing some research....especially here in the northeast (north in general though), where they have 'winter' and 'summer' blends. There are a lot of theories out there....from the firing order intervals which induce strange scavenging effects to blah, blah, blah.....SOME of it IS the nature of the beast as some have posted. BUT...I DO know what you are experiencing and it IS annoying. You go to pull away at an intersection...it coughs out the intake and nearly shuts down. You get the clutch in and 'save' it, clean it out and start over again. In the meantime there is some 17 year old chick barrelling up over the hill while texting her bff and never sees you!! Yeah...it sucks!! IF i had not tried this I would say it is a shot in the dark. But...it is worth a try. Also make sure, (and it sounds like you would be on top of it), that your TPS values are correct.

 

[Theycallmecrash]

Its just how it is and will be.

 

[XBBrad]

I have poor crack throttle performance. Like going slow through parking lot or traffic. As you turn throttle right off Idle is sputtering then takes off. any help be useful. I have had mine cough like those sbove but olny at home or work after starting. Never at stop light that would be nerve racking and scary if your cutting traffic ( legal in CA).

 

[gbalias]

a lot has to do with the ignition timing at and off idle.

but unless youre EXTREMELY familiar with what that entails, i say live with it.


its dumb that they use 0deg of advance down there.

 

[WIGGLE2]

its dumb that they use 0deg of advance down there.

I'm sure it has SOMETHING to do with EPA/emissions.

 

[gbalias]

i wouldnt doubt it.

but while the emissions may be to a certain point, the fuel consumption is drastically increased.

even worse these arent vvt engines so the only way to keep tq levels up at such low rpm is to tune the ignition.

iirc when i tuned my bike, i worked in a slight increase in ign timing BELOW the rpm i want to keep at idle. youd be surprised how little tps opening you need when the engine is making efficient power. I set mine at 13 (8bit) and she purrs at 950-1000rpm idle nice and steady.