Gen 1(1999) Busa TPS issue, I'm sure for the millionth time.

[Paul Dettore]

Hi all, new to the forum but familiar with usual thread rules and I've lurked as a guess for quite awhile as I frequently work on Busa's and would like to say thanks for all the info you guys have already unknowingly given me. With that out of the way, 99 Busa comes to me with all the typical symptoms of the Gen 1 and unfortunately all the usual goofing around had been done to it prior to me, and now that it didn't work they decided to bring into my shop. Only mods I see are power commander and brocks shorty exhaust. Bike would start and idle, soon as gas was applied stumble very hard thru about 3500 rpm then scream to the redline but was also backfiring very hard they the pipe...Changed plugs which were a little to the lean side.Disconnected the PC to try and get a baseline, checked injectors, had them sonic cleaned and reinstalled them...same issue. Disconnected the pair valve and nearly all backfiring went away. Checked TPS position and the mark on the dash was high, I adjusted it to the middle and the problem actually seemed worse. So out of curiosity I started adjusting it to the extremes just to see and all the way low, problem got way worse yet the complete other way(high on the dash) and suddenly the hesitation went away...not just a little I mean completely gone zero hesitation but its smells as if its running pig rich right now. Am I best just trying a new TPS or is something else the possible culprit? The customer heard the bike today and was so excited it ran like this he wanted to take it lol, I don't feel comfortable letting it leave with the TPS so out of wack like that. Any help would be appreciated and hopefully as a member now I can return the favor someday.

 

[1bondoman]

I'd lean towards the fuel pump being weak. Usually when I mess with a 99-00 busa that's not acting right I'll unplug the vacuum line from these sensor and see how it runs. If it gets better then it's a weak pump issue. When you take vacuum away from the map it richens it up a lot.

 

[Paul Dettore]

Will try that when I walk in tomorrow morning. Bikes like this cause me to lose sleep, hence my late night forum joining lol. I was ready to start messing about with the pump but the sucker lost the stumble and started revving straight from idle I was a little thrown. If nothing else it should be good preventive maintaince since they seem to be troublesome anyway. Thanks.

 

[1bondoman]

I'd almost bet adjusting the tps a certain way makes it think it's getting more throttle and dumps. More fuel.

 

[twotonevert]

Welcome to the oRg, glad to have you.

 

[Paul Dettore]

Tried removing vacuum lines, no change. Only with TPS at extreme high bike runs and idles. Also when i do set it at middle, not only does the bike chug but the TPS line on the dash goes haywire, sometime climbing up, others down, even I know its securely in place. I know they can finnicky but its dead middle when I tighten up, start the bike, go to rev it falls all over itself and the line goes wacky. Could it be as simple as replacing this TPS?

 

[1bondoman]

That's a possibility. You got one to try?

 

[Paul Dettore]

No lol. I'm still leaning towards replacing the fuel pump anyway to at least eliminate this as a problem. I've seen mention of aftermarket ones that seem legit and since its external and easy to change think I'm gonna go that route first. Thanks again man, appreciate your time.

 

[1bondoman]

Make sure u replace both screens

 

[Paul Dettore]

Hey guys...replaced fuel pump, replaced both screens and cleaned the little thumb screen....cleaned the screens coming from the tank at the petcock....problem persists. It seems a little better for sure, but still when TPS is set at center, and from a dead idle I crack it it stumbles for just a split second then is fine. I've also bypassed the pairs system, disconnected the PC3. Only when I turn the TPS to the upper(rich) direction does it seem less of a stumble, but then clearly the bike is running rich. I'm losing sleep over this lol, I hate to just move on to cleaning injectors but judging by how bad the screens were I guess i have to consider that a possibility

 

[Paul Dettore]

Geez this bike is killing me....so I've been tinkering all day, coincidentally I was revving it and my hand was on the airbox and I though I felt a boom....took the filter lid off so I could see top of the TBs and after a few revs boom huge backfire thru on of the TBs...wtf. What's next? Could this be a timing issue or worse now? I hate to have to tell this guy that this problem may be more internal now..especially if its something like bent valve maybe?

 

[1bondoman]

Bent valve wld be easy to find. Do a compression check. Take the tbs off when doin the test or hold the throttle wide open.

 

[SeaMonkey]

There's actually three filter in the fuel assembly Did you clean that little screen?