| Author | Message | ||
     Toniportray |
Okay. Here's the latest and not so greatest in regards to this great mystery of my Thumper. I'm going to ignore the other issues with weird noises right now of which I've posted in lots of other forums and topic areas. My new questions welcome for insight involve this little TPS contraption that I suspect is at fault for my issues. The biggest issue I have with my Blast since recovering it from theft is that when I get above 45mph, the forward momentum of the whole bike isn't smooth. The bike bumps forward and backwards, lurching as if the spark's aren't timed right in the cylinder. Sometimes I even hear a pop or ping noise coming from the exhaust manifold area. Initially, I suspected it had something to do with the primary stuff, but a thorough inspection over the last 2 months has found that everything there is in near perfect condition. Here's my new theory. I think the TPS is somehow malfunctioning, and I need your help to diagnose it. Here's my scientific reasons for suspecting that the TPS is the issue. I have static and dynamic timed the ignition system and it's right where it's supposed to be. However, I tested the system by rotating the ignition module clockwise as far as it will go and would you know it? My problem went away.. Well, sort of. The issue of the bike lurching and fussing above 45mph goes away, but my normal low speed operations are impaired. Startups are rather fussy and the bike doesn't like to idle with this modified setting. So then I try turning the ignition module the other way, but as soon as I turn it clockwise past the actual "in-tune" alignment, then the engine pretty much doesn't run. It constantly sputters and just runs terribly. One might think I could then set the ignition module midway between when it works below 45mph and full forward (when it works above 45mph). The problem is, the engine only operates correctly above 45mph when the ignition module is cranked all the way clockwise. If I even move it a cm back towards the correctly tuned position, then the problems above 45mph continue as before. So if you don't see where I'm headed with this already then I'll help direct you to thinking like me. The job of the TPS is to adjust the ignition spark for riding conditions. What I suspect is happening is that I've got the ignition module tuned correctly in the middle area of the module plate, so everything functions normally until the TPS kicks in. Am I correct in thinking that once the vehicle reaches ~45mph, the TPS somehow changes the "ignition advance curve", thereby creating my problems? That makes sense to me considering that I can adjust the timing advance manually by turning the ignition module clockwise so that it is "more suited" for ignition advance settings ideal for the 45mph+ speed range. I suspect that when the throttles get opened up at these higher speeds, the TPS is somehow sending a wrong signal to the ignition system and screwing up the ignition timing in the process. If I'm correct, then then this is normally supposed to improve engine operation but in this case it is fouling it all up. I don't want to just run the bike with the ignition module set full forward (clockwise), because I know that's not tuned correctly and I would want that to somehow damage anything. Besides, doing so doesn't help the lower speed riding; it impairs it (though not by much). So, what suggestions might anyone have for this humble scientist? I think my next test is to disconnect the TPS and see if how the system rides. If this works and the bike runs fine at all speeds with the TPS off, is there any damage that may result from running the bike without the TPS from now on? Will doing so lower performance or decrease gas mileage? I don't want to just assume that the TPS is broken and order a new one. I've spend way to much already from replacing parts that really didn't need to be replaced (although new parts is always good to some extent). I don't want to pay for a new one unless I'm really certain that doing so will solve my problems. I leave this in the hands of the experts. Thanks! | ||
| Reuel |
Get an ohm meter and measure the TPS resistance while you move the throttle from open to close. It should move smoothly. I forget the resistance, but it should be a few thousand ohm difference from closed to open. | ||
| Gearheaderiko |
DO NOT attempt to remove or adjust the TPS from the carb.This can be a major headache. Disconnect the plug from the TPS. This (if I remember correctly) will also disconnect the 'choke' (enrichner). You will do no harm and probably wont even notice any difference in running. As per your 'theory', we once had a problem on the racetrack where the advance would kick on and off at a very awkward time. Disconnecting the TPS leaves it at full advance curve. Again, the bike will run fine with the TPS disconnected (providing you have no other problems). I've done it many times. Another possible scenario is that the timing cup is loose. That can leave it to shift timing 'at will' but can give you consistent readings when static or dynamic timing the engine. If it is loose and you have a timing light on the marks, they may fluctuate wildly when revving the engine. Pull the module out and check (or recheck) the cup. It would also be a good idea to pull the cup off and check it for wear. If the cup notch is in perfect condition, highly unlikely thats the problem. If that is the problem the notch may even be worn completely away. BE Warned though, its a very small screw that holds the cup on. Over tightening it could break it as well as making removal very difficult if you strip the head. Use a torque wrench on tightening it. Entirely possible you just have a bad ignition module. Also possible you have a short or bare spot in the wiring causing a misfire. | ||
| Ezblast |
See the top of the carb section for resetting your TPS. EZ | ||
| Gearheaderiko |
"See the top of the carb section for resetting your TPS". Better to leave it alone though, if you can. "If it aint broke, dont fix it". Just one more item to pull your hair out on! | ||
| Toniportray |
I double checked the timing with a timing light and I realized that when I increased the throttle input, the two dots would get out of alignment in the timing hole. The manual says to do the test at 1200 rpm (which I did), so maybe the test only works at a constant 1200 rpm. The other possibility is that when I opened up the throttle, the TPS and/or ignition system slowly modified the spark timing, which is read by the timing light. The rest is self explanatory. So I don't know if that's normal for the two dots to begin to disappear when revving, or if those things are supposed to always stay in the view hole. The test was performed with the TPS connected. So I disconnected the TPS unit and started the bike after putting it all back together. First thing I noticed is that the idle RPMs are much higher than normal. 'Course I normally turn the idles way down, so maybe it's idling at some sort of default speed. I don't like it, and maybe someone has input on how I can resolve it. The Idle adjustment screw is all the way out, so I can't pull it back any further. It may just be a consequence of not having the TPS connected. Getting past the initial frustration of trying to figure out another method to get the idle speed down, I suited up and hit the roadway. First thing I noticed while riding was a definite loss in power during acceleration. It just lost it's "kick." The bike also struggles to maintain speed up hills, and there are some pretty steep hills here in Northern California. This bike has always been weak when taking on steep inclines, but I can clearly notice a difference now after disconnecting the TPS. Disappointment aside, I eagerly drove down the streets waiting in anticipation for a long straightaway with minor turns. I finally got to my normal "test spot" of roadway and let the throttles do all the talkin'. As the nervousness began to build as I accelerated through 55 mph, I was ecstatic to watch the needle work it's way up to over 80mph with room to spare and no sputters, jerks, or weird noises. Finally!!! I am truly delighted. This has been a problem I've been trying to solve for almost a year. At least now I have it isolated to the TPS system. The problem isn't fixed entirely, and I'd ultimately like to repair the TPS to get my acceleration back, but I'm still so happy to find my latest theory to have been correct. When hitting the higher speeds, I was amazed how smooth the bike felt. I don't think I've felt that from it ever since I bought it in 2004. So thanks so much for all the ongoing support guys. I'm always to glad to have forums like this around to help me work through motorcycle complications. Maybe tomorrow I'll look at the sensor with a multimeter and measure all the stuff from the manual. If I can get it to work, I'll put it back on because I need as much power as I can get during acceleration; especially with all the hills here. And if anyone has any idea how to lower the idle, I'd greatly appreciate any of that input.  | ||
| Ezblast |
Thats your air screw - adjust idle rpm warm at idle adjust screw, regain some umph by bringing that air screw back into 2 1/2 to 2 3/4out max., reset your tps following either the book method or the old mechanics method I have listed as well. EZ | ||
| Reuel |
Yup! The TPS was probably getting a dirty signal to the ignition, bouncing between the two timing curves. With it disconnected, you're stuck on one timing curve. I was having issues, but I didn't realize it until I made my own ignition. The TPS value moved erratically, and would jump to about 60% when it should only be around 30-40%. | ||
| Gearheaderiko |
The 2 dots moving out of the hole is normal with increased rpm. What isnt normal is when the dots bounce in and out of the hole,irratic, without coinciding with rpm changes. The TPS just tells the ignition whether its under full or partial throttle, just like the vacuum operated VOES on other HD products or a vacuum advance on a traditional distributor (it uses throttle position instead of engine vacuum). Whether the TPS is connected or not, the timing will still advance. Recheck the timing and set it per the manual with the TPS disconnected. You really shouldnt notice much difference in running (although since your bike has never really run right, thats a moot point). After resetting the timing, let us know how it runs. | ||
| Toniportray |
Measuring between the #3 P/W and #5 Black wires reveals that the DC voltage is .57-.58. The manual says .5 is perfect, but +/- .05 is okay. I'm slightly out of that range, but there's no chance in hell I'm going to be able to get those tamper resistance star screws even slightly loose to rotate the TPS mount. No chance. I don't know how much a special bit would cost, nor what size to get or where to get it. The Home Depot's here in NorCal are useless as I'm never able to find special rare stuff like this at any of their stores. The maximum voltage reached at WOT was just over 3v DC. The manual says it shouldn't go above 3.7v. No problem there, but the manual doesn't say whether or not 3v is okay. Crazy manual never has enough details. The increase in voltage with throttle seems just fine. The increase is smooth and doesn't bounce around at all. As such, I think I'd rather just leave the whole thing disconnected. However as I mentioned before, the idle is way high and I'd like it lowered. The idle speed adjustment (no, not the idle mixture) is all the way back, so the throttle plate is totally closed. I can't think of how else to slow it down. The TPS and/or auto enrichener must have some role in dropping the rpms because when the harness is connected, I have to screw in the adjustment screw to open the throttle plate more in order to prevent stalling. The idle is so high that most of the time if I shift into first, it grinds. #$(*%. I hate that noise. How can I get my idle down without the harness connected? Where can one acquire that special star bit for tamper resistant screws with the dang hole in the middle of the head? Stinkin' HD. Just put a normal screw there. I refuse to bring it to you just to fix little things like this. | ||
| Slowhand96 |
They have those bits at "Harbor freight" in a kit full of all those anti-tamper bits (about $10.00 or less). If you don't have a harbor freight near you they do have an online catalog. I have also seen those at "tools and more" or "tools+".... in fact I was just at Napa today and saw a kit with those in it complete with a ratchet for about $38.00. G'luck If you still don't have any luck I have a set of those I could let you use, shipping on you... | ||
| Swampy |
If your RPMs are too high your engine may be getting air from somewhere other than the carb. Please check your carb boot first, then your manifold gasket. Then just to be sure make sure you exhaust gasket is not leaking. Then check your carb diaphragm, if it is torn or pinched it could give you a bunch of problems, like not being able to get higher RPMs. Have you tried holding your hand over the carb inlet while it is running to see if it idles down? | ||
| Gearheaderiko |
Concur w/Swampy and I'd leave it disconnected too, at least until you figure out why the rpms are so high. I've never had a problem with idle rpm with the TPS disconnected-it never really changed. You will loose the auto enrichener (choke) function with it disconnected (choke stays on) but it will heat up with engine warm up anyway. What others on the board could do to help you out is unplug their TPS and tell us what happens to their idle. If the concensus is the same then you know you still have other problems. If you havent re checked the timing (With TPS disconnectd), please do so. Advancing the timing (which may happen when the TPS is disconnected) will raise the idle speed. (Message edited by gearheaderiko on March 10, 2008) | ||
| Reuel |
Sounds almost like something's wrong with your ignition module, and not the usual hall effect sensor broken wire syndrome. I'd rule out all fuel/air problems first. | ||
| Toniportray |
Well, I double checked the timing and it's where it's supposed to be with the TPS disconnected and connected. It came out the same. I can turn the module clockwise (I assume making less advance) and the idle will go down, but the timing hole indicates that the more I do that the more out of timing it goes. As such, I'll leave it where it is at perfect timing. I have the stock carb jets and it is mixed to 2.5 turns out. I won't bother changing that around since everyone says 2.5 is perfect. I looked up some Buell Blast vidz on YouTube and listened to folk's idle speeds there. Some of them are higher and some of them are lower, so maybe I'm fine where I'm at. I don't like the higher rpms, but maybe I can learn to deal with it. I've checked the carb, the boot, and all the manifolds, but everything checks out. I think this is just some sort of "default" rpm speed the ignition module uses when the TPS isn't sending a signal. I normally drop the idle down on my bikes below normal, so maybe I'm just not used to the higher rpm's. Like I've said before, the throttle plate is totally closed so it's gotta be the timing module. I'll keep riding around and see if it will work decently. | ||
| Ezblast |
Ola! - idle should be at 1200 rpms - replace das boot - I suspect that for sudden hi idle. For V&H, Stock, and Pro-Series 2.5 is good, for the rest 2.75 is good. EZ | ||
| Krid80 |
I hate to ask, but have you tried the idle adjustment screw? | ||
| Ezblast |
lol | ||
| Slowhand96 |
I've heard that setting the idle below normal is bad for a Harley. The Neil at American Thunder jumps on my ass every time I pull in with my idle low, he says that anything below Harley recommended idle the oil pump isn't turning fast enough to build enough pressure or volume. ???? I dunno, makes sense to me. | ||
| Buellistic |
read your HAND BOOK and Factory Service Manual, "YES" sometimes it is correct ... | ||
| Toniportray |
I reset the TPS by rotating it all the way back as far as it will go, and it now shows .5volts as it's supposed to. Right on the money. It's better than before, but it delayed the timing problems from 55mph to 65mph. It doesn't fuss as much as before, so it was an improvement. I lowered the advance a bit so that the two dots show up closer to the front of the timing hole (not dead center) since I believe the issue is that the TPS is advancing too much prematurely and the cylinder is igniting just before TDC, putting some kick into the opposite piston rotation (BAD!). Delaying the idle/1200rpm timing helped a ton. I rode for 40 miles ranging from 70-85mph and had no problems until the last 5 miles of my trip. I started to get the lurching and chugging again, but it was very mild. Putting the TPS back on completely fixed the idle speed issues. It's not an air leak problem or an issue with the carb boot. I think when the TPS and auto enrichener are disconnected (from disconnected the whole harness), the ignition system starts off at the "cold idle" speed (which the auto enrichener controls during cold starting), but then never gets a signal to turn off the cold idle speed, so it keeps running at that higher idle speed during all operations. Believe me, it's way above 1200 and it makes it a pain to ride. With it disconnected, the engine also starts to die each time I add throttle from a full stop. It takes a lot of effort to prevent it from stalling when just beginning acceleration. I really have to open it up, but too much and it stalls. Since it's so fussy with the two units disconnected, I'm determined to resolve the issue without disconnecting the harness. Like I said, it ran almost completely fine at high speeds since I retarded the ignition advance, but it still farted around a bit near the end of my trip. I'm going to try lowering the advance just a bit more and see if it completely stops the issue. Is there any harm in running the bike with a slightly less than full advance? Maybe less power, but I don't think there are any lasting consequences of doing so. The other thing I may try is keeping the harness connected, but disconnecting the TPS from the carb (not too hard to do since it just requires taking out two screws). That way, the TPS will just keep telling the ingition to stay at normal advance timing since there won't be a signal of 2.5volts to change the timing curve. That way, I can keep the two units running so my idle remains where it should be all the while eliminating the issue of the TPS advancing the timing too much even though it is currently set right at .5v where it should be. I'll keep you posted.. | ||
| Swampy |
Toniportray, I would now look at a malfunctioning ignition module. I don't know why your idle will not come down. You must have an air leak somewhere. Look things over very carefully before you doo too much more(Look, me the guy who said you have a malfunctioning ignition module) | ||
| Reuel |
Fast idle, or auto enricher, works by going fast when it's cold. Once it warms up, it goes to normal idle. Without being connected, it can never warm up. | ||
| Gearheaderiko |
Not entirely true. It will warm up with the engine, just not as fast. Its also richens the mixture (which I'm sure you know, just omitted for brevity). | ||
| Reuel |
You're right. I was about to leave, so it was a much shorter post than it could have been. When cold, it lets in more fuel and air, with emphasis on the fuel. As it warms up, it moves to close the overly rich intake port. Without electricity, it depends on heat from the engine to warm it up. Thats what I would have posted.  | ||
| Muckerpuck |
i had similar problems when i first got mine,weirs power loses above 45mph all the dinkin around with jets boots, carb cleaning , timing ajustment , nothing worked, till i tried a known good ignition modual. then she was good as new. so just because the ignition still seems to work ok dosnt mean its not the culprit. | ||
| Toniportray |
Hurray! Someone with a strikingly similar experience. I'm glad to hear I'm not the only one with an abnormal ignition timing system. My new question of which the repair manual does not answer is this: If the bike is tuned already to full advance timing, then why would HD put on a TPS that advances the timing further?! When the timing is at full advance, the spark timing is optimal since the mixture ignition is occurring right at TDC to provide maximum power delivery. If you advance this any further, then the spark will occur before TDC, thereby producing this "back-kick" that I get from the piston being pushed backwards into the opposite-of-desired rotation. Why then is there a TPS to advance the timing further if one has correctly set the timing to be at full advance anyway? Won't this inevitably lead to complications and rapid piston wear? I know the TPS is supposed to increase the rpm's to improve fuel economy and power, but if one already has the timing tuned for maximum advance, what good can come out of advancing it more as the TPS does? | ||
| Gearheaderiko |
I'm going to try to make this brief. Spark only (if ever-engines vary) occurs at TDC when the engine is at idle. As engine speed increases, spark is advanced. The gases in the combustion chamber can only 'burn' so quickly. The engine needs extra time (in relative terms)to burn the air/fuel mixture the faster the rpm, so the spark is advanced. The TPS is supposed to account for throttle position as an engine under load needs different spark advance as say an engine under deceleration. Thats as brief as I can make it. It may be wise to pick up a book on engine theory. Usually any good high performance book will explain this relation between timing and engine rpm (it can be any automotive or motorcycle book). Or I'm sure it can be found online. | ||
| Reuel |
I'll try to put a little more detail. The Blast at stock settings sparks at about 10 degrees before TDC at an idle. As engine RPM increases, spark happens further before TDC as Gearhederiko explained. At high rpm and high throttle, some modules can spark at 45 degrees before TDC. The stock module looks for a signal from the TPS so it can determine something above 1/2 throttle. When you go past 1/2 throttle, the spark advance is less. That makes 2 timing curves. Under low throttle, there's not much in the cylinder to slow the piston down as it reaches TDC. At high load/high throttle, there's more fill in the cylinder, so it is more tightly packed, thereby increasing volatility. (Oversimplified, I know...) To keep the same advance curve at high throttle would cause detonation otherwise. Air temperature can also affect timing. On a hot day, you want spark to be less advanced, and at high altitudes, you want spark to be more advanced. There are lots of factors to consider when determining exactly when the best time is to fire a spark. Not enough advancement, and you don't get as much power from the fuel. Too much, and you smack the piston into the cylinder wall. Maximum power for the spark can be a little after the detonation point. (Message edited by reuel on March 21, 2008) | ||
| Gearheaderiko |
Reuel: Since you're the resident ignition module and TPS expert (and I'm too lazy to go through the wiring diagram-and the info would be helpful here), if I wanted to just disconnect the TPS without disconnecting the 'choke' too, what wires would I cut (at the carb)? Or would I need to splice some other wires together to bypass it? I'm going to look into other replacement ignitions and since most(all except perhaps fuel injected?) use VOES and I dont think a variable reading of the TPS would do much good to a module used to reading the on/off of the VOES (might even burn out the module?). The choke on a twin carb doesnt seem to give the same high idle on a Blast, so I'd like to keep the enrichner (for now). | ||
| Reuel |
You don't need to cut anything. Just pull the 3 wires from the TPS out of the Deutsch connector and wrap them in electrical tape to keep them safe in case you want to use or sell your TPS later. There are two things on the carburetor that have wires. Find the one that has 3, and you have the TPS. If you only find 2 wires, that's the autoenricher. If you've never handled a Deutsch connector, let me know and I'll find illustrated instructions somewhere. | ||
| Gearheaderiko |
Thanks. I didnt know how intertwined the 2 might be. As far as the douche connector, its an hours worth of work to pull it apart until you figure it out, then its 2 minutes. Very simple when you know how. Very frustrating when you dont! | ||
| Reuel |
You're telling me! | ||
| Gearheaderiko |
LOL! |
