| Author | Message | ||
     Cuso4rox |
About three months ago I added the HMF exhaust and EBR race ECM to my 1125 and now it seems to be loading up and backfiring a lot when decelerating, I've changed spark plugs so far, suggestions would be appreciated.... | ||
| Cataract2 |
Sure you don't have any exhaust leaks? | ||
| 99buellx1 |
You did a TPS reset after ECM install? | ||
| Two_seasons |
Sounds like your bike is running lean. | ||
| Dwp138 |
did the backfire start as soon as you made the changes? or has it crept up? | ||
| Dhays1775 |
For what it's worth, mine pops on the decel too. It NORMALLY only does it from 4k to 3k rpms, unless I'm riding pretty hard. Also of note, I'm running the EBR ECM for the K&N and stock exhaust. I have also installed the Twin Motorcycles velocity stacks, K&N filter and a modified stock muffler. (I just cut the end off, ripped out the last chamber, welded in angled outlets, welded it back up, then ceramic coated it.) Has it always backfired or just popped on decel? | ||
| Mhpalin |
I would check for exhaust leaks,I have the ebr ecm for stock ex. and for the keda rt3 for 3 years and no back fires on either bike.You could also check to see if the rubber boots between the throttle bodies and the motor have not come loose this has been known to happen they can pop off when you have a backfire. (Message edited by mhpalin on February 14, 2014) | ||
| Cuso4rox |
Along with the backfire it's doggy at low rpm like its loading up I did the tps reset on install and this just started a week ago ran great for three months maybe oxygen sensor? It's also backfired up through the throttle body's once or twice | ||
| Stirz007 |
What are your O2 sensors reading? (diagnostic mode) | ||
| Cuso4rox |
the front and rear 02 sensors are reading 0.4 but I do have a fuel system pr error code... which I'm assuming the pr stands for pressure... | ||
| Needforspeed |
Interesting, I have the same modifications (HMF exhaust, EBR EMC, K&N Filter) and I get lots of backfire during start up. I worry a bit about it doing damage to my engine. It seems to run fine once running with only a bit of an issue once in a while when coming off the gas. | ||
| Stirz007 |
Backfire is often a result of unburnt fuel in the exhaust side, so unless you've jumped timing a backfire in and of itself will not likely cause any engine damage - might blow out a baffle, though. My XB will do it from time to time when I get on the gas, then chop the throttle. | ||
| 1125rcya |
I ran a hmf pipe and ecm. I would have to say I enjoyed the stock pipe more. I sold the hmf and ecm and went to the barkers exhaust/ ecm.  | ||
| Stevel |
This backfire thing is usually the result of an exhaust leak, but in this case, I don't think so. My reasoning is the design of the cylinder head on the 1125 engine. The head uses an open combustion chamber and is very shallow due to the small included valve angle. Consequently, there is no squish area to speak of. If the motor is an '08, the piston has a small dome in the center which shrouds the spark plug somewhat as well, further impeding flame propagation at ignition. These design features do not tolerate lean conditions well where, under high vacuum conditions, the physical distance from fuel particle to fuel particle is so large that the flame front moves so slow that the charge is not fully ignited before the piston starts downward on the power stroke resulting in a large amount of unburned fuel accumulating in the muffler. In addition, the engine is under square (large bore short stroke), which reduces charge turbulence, further aggravating the problem. In short, unless you are ready to redesign the engine, the only thing you can do is fatten the idle mixture in the fuel map and make certain there are no air leaks in the exhaust system. This will moderate the backfire thing somewhat, but won't eliminate it. The cause of the change is the reduction of back pressure in the new exhaust, resulting in a higher reflected exhaust vacuum during valve overlap drawing some of the new charge out to the exhaust system. | ||
| Needforspeed |
@Stevel, Thanks for the detailed explanation. I had some backfiring with stock exhaust and ECM. Sounds a bit like the more you open up the air flow the less turbulence and at start up it may be running a bit lean on the fuel mapping from EBR causing these backfires at start up. @1125rcya, Thanks for the input. I thought about the Barkers setup before buying the HMF. @Stirz007, Thanks for the comfort. I understood that a backfire can come from a lean condition in the cylinder that causes a pre/post-detention that can blow a hole through the top of the piston. | ||
| Stevel |
I know my explanation may sound strange and counter intuitive, but it's all about thermal efficiency. In an ideal world we think the fuel charge is totally homogenous and stoichiometric at ignition time, but it unfortunately isn't. It is significantly stratified with both lean and rich layers intermixed. At spark time, the flame starts to propagate, but the flame speed will be a product of the space between fuel particles. As you can imagine the flame moves faster along the layers of rich mixture than through the lean areas. The problem is also aggravated and significantly slowed when the throttle is closed. The solution of choice is to confine the charge to the smallest area possible (squish area) and to create as much compression turbulence as well. If the flame fails to ignite fuel particles before the downward motion of the piston occurs, the story is over and the unburned fuel will enter the exhaust unburned. Like most things, engine design is a combination of trade-offs, where open, shallow combustion chambers and small included valve angles offers high volumetric efficiency and more power, the trade-off is low speed, high vacuum efficiency. It should be clear that combustion chamber design is truly a black art. As all you Buell owners know, the poor low speed power,surging and rough running of the 1125 at low speed is a product off those design choices. If you have read all the articles on the RX design, you might have noticed that Eric has changed the design of the cylinder head, but those changes have not been stated. I'm sure he has tried to address these faults. I would love to know what they are. I think he has addressed the large port volume making it smaller, which will increase air charge velocity (adding more chamber turbulence) and I suspect he has added a throttle plate in one intake valve port electronically activated by the ECM, which again would increase charge speed and turbulence at low speed. | ||
| S21125r |
"I suspect he has added a throttle plate..." From what I've read they are altering the intake cam timing between pairs and using a cross flow port just above the valve head to promote swirl. Me thinks the IAC circuit is probably used to feed the cross flow port - seems like a natural fit. OT a little... What is the over/under on how long it will be before someone gets a pair of RX heads/cams for a 25 retrofit? | ||
| Blownharley |
Stevel, really?? At spark time, the flame starts to propagate, but the flame speed will be a product of the space between fuel particles. As you can imagine the flame moves faster along the layers of rich mixture than through the lean areas. So you're basically saying that the more fuel, the faster the combustion?? This would be interesting to have explained more in detail.. | ||
| Stevel |
Blownharley, I am saying that the spread of the flame front is greater across rich areas than lean ones. Speed of combustion is different. That is controlled by the availability of oxygen as well. This phenomena was utilized by Honda on their CVCC 3 valve engine as a way of propagating the ignition across a very lean mixture of about 19:1. Gasoline requires a fuel air ratio range of 12.5:1 on the rich end to about 16.5:1 on the lean end for STABLE combustion. Outside of that, bad shit happens. Correct combustion occurs when all the induced fuel is burned leaving no unburned hydrocarbons or excess oxygen. This is called a stoichiometric mixture. This ratio for gasoline is about 14.9:1. We control this ratio by restricting both fuel and air to control power. To prevent the erratic flame propagation under low throttle, ideally we should also vary the physical size of the combustion chamber, but no one has figured out how to do that. We compensate for this problem by changing the fuel air ratio at low throttle by using a richer mixture, but that too is a band aid, not a fix. To address Stirz007's statement and the bad shit I mentioned, the erratic flame propagation can also cause a phenomena called detonation. The best way to explain this is that detonation is a collision of different flame fronts. When this occurs, the burn rate increases violently, causing a very rapid rise of both temperature and pressure easily exceeding the melting temperature of aluminum. This phenomena can be caused by a multitude of things from bad fuel (low flash point)(dieseling), pre-ignition (glow plugging) from excess carbon build up or hanging gasket particulate. Severe damage occurs when the engine is under heavy load and it sounds like someone is hitting a piston with a large hammer. Most of us have heard the phenomena and call it pinging or engine knock like when using heavy throttle at low engine speed in high gear. The pinging we hear is caused by compression ignition at the hottest part of the combustion chamber and that flame front colliding with the flame generated by the spark plug. The higher than normal compression temperature is caused by the low speed of the motor allowing the intake valve to be open long enough to fill the cylinder completely to atmospheric pressure and then on the compression stroke the temperature rise exceeds the flash point of the fuel. | ||
| Mhpalin |
Okay the bike ran great till it backfired through the air cleaner K.I.S.S Known issue when the bike backfires like that the intake neck will pop off AIR LEAK check this first Not this check for ex. leaks Not this check 02 sensor Not this check ECM take new stuff off put stock stuff back on K.I.S.S.  | ||
| Cuso4rox |
I appreciate all the input fellas, all that's left for me to do is get some dyno time and hopefully get a diagnosis and a solution before I do some damage... | ||
| Needforspeed |
@Stevel, Since most of my backfire issue is at start-up what gives? I get loud backfires without a start and then it will start after a second or third try on the starter. Nothing is hot. There might be unburnt fuel in the exhaust because it takes a couple of turn overs before it starts. It runs great once I get it running except the occasional small backfire when I cut the throttle at mid to high RMPs. But I would expect that from most bikes that have racing ECM with more free flowing exhaust and intakes. Thanks for any help you can provide. | ||
| Stevel |
Needforspeed, All backfires require fuel in the exhaust. This requires injected fuel without fire in the engine.......more I can't say. Perhaps at start-up, the spark is being inhibited or it is fuel from the last engine run. Only you know the surrounding circumstances. For instance, if the condition occurs after more than a day of disuse, you can eliminate the latter. | ||
| Thefleshrocket |
Stevel, one discrepancy--you state that an undersquare engine has a large bore and a short stroke. The opposite is actually true--a bore that is wider than the stroke is long is actually called oversquare. Other than that detail, your explanations were well-written and informative. http://www.thenakedscientists.com/forum/index.php? topic=34958.0 |
