| Author | Message | ||
     G4string |
When adjusting the carb air-fuel screw, if one is backing the screw out from light bottom is that leaning the mixture. In other words, moving the needle on the screw inwards is rich and backing the screw out is lean?? Do I have this correct? Thanks. | ||
| Rockbiter1 |
NO...the screw all the way in is lean, screw goin out is getting richer. Don't forget to adjust with engine at operatong temp, so you can see the effect of your adjustments. (Message edited by rockbiter1 on May 19, 2005) | ||
| Rmorin128 |
I've decided to go back to stock exhaust, the police are cracking down on loud exhaust and I don't want to deal with it. I've reinstalled my stock exhaust and carb jets. Does anyone know how many turns out from bottom the stock setting for the air-fuel screw is? | ||
| Ezblast |
2 1/2. GT - JBOTDS! EZ  | ||
| Toniportray |
So I'm just trying to reason out why exactly running lean is bad for the engine. Is it really just extra heat build up? If so, why is there extra heat buildup? Any mechanic knows an engine which is running lean (less fuel than stoiciometric) runs hotter than one which is properly tuned. 2 stroke motorcycles can actually seize from overheating if run too lean. But I'm not running a 2 stroke, so is the same concern warranted? Normal logic would suggest that with less fuel there would be less heat generated, but it is not the case. My understanding is also that a lean mixture actually runs better through the engine, giving a more complete burn and more power (since more heat is produced and the power source of the engine is heat). Obviously, at some point the air ratio is too low to burn correctly, but it seems to me that a lean condition would produce more heat/power and run cleaner in the cylinders. Hence why rpms increase with a leaner condition. Where am I going wrong here, or am I? | ||
| Jerzydevil |
2 strokes are a little different, usually lean and rich on a 2 stroke refers to oil mixture. if you are running lean on a 2 stroke, u use less oil in the mixture and thats why 2 strokes seize when run too lean, too rich and they smoke and foul plugs. | ||
| Ezblast |
Its pretty hard to shut down the racing plug, even the regular Iridiums only partially bogged when the jetting was up at 180 from its current 155 (I run a secondary jetting - Dial a Jet by Thunder products)at partial throttle they ran fine - with the racing plugs I might not have even noticed - lol - my last dyno had me between 12.5 to 13.5 - perfect and even with a cracked boot I'd probably be safe before conditions shut down the bikes motor. That was the reason I switched to use of the secondary jetting - it has a secondary sensor that detects leanness and responds accordingly - I've had it on for over 5 years now and only replaced two o rings so far - not bad longevity for after-market. Highest effective jetting with it was 180 - would be like a 200 in a regular Blast - lol - leaness can melt a motor, richness will just leave you stranded - ;0) - EZ | ||
| Gearheaderiko |
Concur  "leaness can melt a motor, richness will just leave you stranded "Very true. A lot of advancements have been made to engine design. Too rich a mixture and it leaves a lot of unspent gas going out the tailpipe, but a poorly designed engine needs the richer mixture to run (like an engine when its cold). More efficient engines can use a leaner mixture because they dont waste as much gas getting a good burn. This also puts the engine much closer to the 'edge'. If anything goes wrong, it goes too lean real quick. Fuel molecules need to pair up with oxygen molecules. If you just shoved air into one side of the combustion chamber and fuel into the other side, only the air/fuel that met in the middle would burn. One way to compensate is to throw more fuel at it, hoping it would meet up with more air. Or you could mix the air and fuel on the way to the cylinder, so you would have more air/fuel molecules pairing up before they reached the combustion chamber. Same amount of fuel, better combustion (more fuel burned). The better you mix air/fuel the less fuel you'd need than you did when you just shoved them into each side of the combustion chamber. The trick is being able to burn all the fuel you've thrown into the chamber. Todays high tech engines can compensate for deviations in 'mixture' need, or are more consistent in 'mixture' need. Older, less efficient engines use a compromise. I have no idea if I helpfully answered your question or not. This is an awfully long post to get a basic idea across! | ||
| Reuel |
Ok. Here we go. Lean fuel mixtures burn temperatures are not as big a factor as some have interpreted. As you go lean, you have a quicker burn, or energy is released in a shorter amount of time. This causes more of the energy to be absorbed by the top of the cylinder and the piston, where a slower burn has more time to disburse the heat. It also results in less power, which may in turn cause the rider to increase throttle, thereby increasing the first situation. A rich mix causes a slower burn and releases more energy. Heat is disbursed further down the cylinder. The ideal mixture depends on the efficiency of the fuel/air mixing, compression, ring seal, etc. If you go a little lean, you get better mileage. If you go too lean, your engine gets uneven heat stress. Continue, and you get misfires. If you go a little rich, you lose mileage, but gain power. As you go richer, burning gets sloppy because of lack of oxygen. Carbon starts to build up, and spark plugs get wet, and ultimately lose their ability to ignite the fuel. An engine can be built to withstand excessively lean conditions. Direct injection has been used on some gasoline engines for close to a decade. These engines are built to operate like diesel engines, but with lower compression and a spark plug. Efficiency and horsepower increases of about 20 to 30 percent have been achieved. While modern carburetors and fuel injection has an ideal ratio of 14.7:1, there is a variable venturi carburetor that runs at its best at about 18:1. Similar horsepower and efficiency results occur with this carburetor. Unfortunately, it's down draft, so I can't get one on my Blast without some major modifications. Gas tank's in the way! | ||
| Ezblast |
The words - lean mixture and engine produced by Harley Davidson do not go together well at all my friend. Let me explain: I used to street race and drag race VW's in amateur venues and so the first thing I did was set up the bike the same way. 1st: A short free-flowing exhaust with minimum restriction - The Bub. 2nd: Opened up the air-box to the max and switched to a K&N for max breathing - my airbox mod is now a common first mod. 3rd: I went to Nollogy's 1st gen - capacitors that was supposed to raise the stock coils firing of 45000 to like a 150000 volts, using a hipo non-resist plug wire and a non-resist NGK 6dpr plug - at the time still an ok plug for a Buell to use at the time(the switch over to the much cooler plug in the same time frame as my motor blowing). Running this combo I had at the final dyno before she blew - an AF of 14.5 to 14.0 down the line, with a 30 ft-lb of torque and 32 hp - to the rear - not bad considering the total outlay vs power received ratio. All done up in proper drag race fashion. I did not take into account the fact that a hot plug and a sudden lean condition caused by a torn carb boot together would melt the motor - these are not modern age motors and it would be a grave mistake to treat them as such. My experience - plus that of others also shows that a bit richer with these motors actually nets more power. EZ | ||
| Reuel |
I second that, EZ. Any engine, when run richer than ideal, will push out more power. It's all a balance. Go a little lean for mileage. Go a little rich for power. If you go too far either way, you got problems. I'm almost afraid to look under my head right now, after running too lean for too long. | ||
| Toniportray |
Thanks to everyone for posting, but a special thanks to Reuel. That was right on the money. And it makes sense, which is nice. | ||
| Ezblast |
For a modern engine with hi tensile strength parts and cooling it sure does - not for a Buell Blast! EZ | ||
| Blake |
Too lean is bad when it leads to detonation. Ask EZ. He has the melted parts to prove it. Note: No modern commercial engine will tolerate severe detonation for long, at least not one making similar torque per cc and being pushed hard. The reason a lean running engine is subject to more heat is that the vaporization of fuel sucks a BUNCH of heat from the combustion chamber and incoming air charge. The situation inside the combustion chamber during the intake stroke prior to combustion is much the same as what happens inside an air-conditioner's evaporator (the really cold part). More fuel equals more refrigerant. | ||
| Reuel |
What didn't make sense? What did I miss? The Blast is just more sensitive to out-of-ideal fuel air mixtures than your described engine. I'd like to see under the head of Buellistic's Blast--he's using a narrow band O2 sensor for tuning. Blake--I forgot to mention that. My Fish carburetor would ice over if the temperature was less than 50 degrees outside. I had to rig a hose to pull air from around the exhaust manifold. | ||
| Blake |
Those "super efficient" carburetors all benefit from the same principle, they act as major restrictions (you've heard of "restrictor plates") to flow in the intake tract of the engine. If we restrict the flow of air/fuel charge into the engine's combustion chamber(s), we are restricting the engine's available/achievable power, thus in many cases we'll improve fuel economy, but we'll also kill the peak performance of the engine. No different than running a smaller less powerful engine or setting the throttle stop at around 1/4 throttle. There is no free lunch. (Message edited by blake on April 04, 2008) | ||
| Reuel |
Not the Fish. It's not a restrictor. It puts fuel in the air through holes in the throttle shaft. The fuel enters the air stream at the highest point of turbulence and vacuum. My motorhome got more power and better gas mileage. And, yes, the stock carburetor was tuned as well as it could be. Emissions were comparable to newer vehicles, yet it did not have a catalytic converter let alone any other smog stuff. As I'm sure you know, the catalytic converter was the first step to get unburnt fuel to burn. If you can get a better mix, you can get more of that fuel to burn in the combustion chamber. It works. I have seen proof, and proven it myself. It did the same on a Plymouth Horizon, despite it being too big and the timing not working properly. Got 36 mpg with more power, and that car came with an O2 sensor. So, it's not a free lunch, just less wasted lunch.  (Message edited by Reuel on April 04, 2008) | ||
| Ezblast |
That puppy has been the topic of conversation before on the BADWEB - check it out. The trick is finding a carb that will work well - Mikuni, Weber, Del Orto, Kehein - are about it - the key words being working well. So fare the only other carb thrown on a Blast has been a HSR 42 Mikuni, and that was for hi performance reasons. EZ | ||
| Reuel |
I once mulled over the idea, but I had 2 limiting factors. 1: it's a downdraft, 2: it's probably too big to get a smooth air/fuel mix adjusted from idle to WOT. Question: What effect does one get by changing the length of the intake between the carburetor and head? With the mileage my Blast gets, it just isn't worth it to modify the bike to the point that I could mount it. It'll most likely end up on my Jeep this spring or summer. Fuel injection is still looking like a good next step once I'm satisfied with the ignition project. | ||
| Ezblast |
Hows that going anyway - I read a bit about it on your sight - any further developments? EZ | ||
| Reuel |
The tough part is self-tuning. Seems the best power for spark advance can be slightly past the point of knocking. I haven't managed to destroy the engine yet. I'm working on my next prototype design, which will live under the seat and have a control panel somewhere near the speedo. I'm having other issues, too, but I'm working past them. I'm rewiring it so that all 3 TPS wires go to the controller, which gives me a more linear value for the throttle. I should be typing all this on my web page, huh? I'll update this weekend and get it up. I got my own web server, too, so I'll post that once I get my page moved. | ||
| Ezblast |
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| Gearheaderiko |
"Question: What effect does one get by changing the length of the intake between the carburetor and head? " Basically its supposed to increase velocity in the intake manifold creating a ram air effect, 'supercharging' the a/f mix into the engine. Great for high rpms. Low rpms suffer. | ||
| Reuel |
Another vote against bothering with the carburetor, unless I decide to race. | ||
| Buuueller |
Some car manufacturers used both short (for low end torque) and long intake runners. When RPMs go up a butterfly opens allowing air flow through the longer runners bring power up the RPM range. | ||
| Slowhand96 |
That sounds backwards to me, at least for automotive applications, I don't know about bikes??? But for a car, a long runner for low/mid torque and short fat straight runners for high RPM '''Long Rams were standard equipment on 300Fs and 300Gs. They were designed for peak torque at 2800 RPM. Short Rams were standard on the 300J and were used on the optional engines for the 300F, 300G, 300H, and 300K. Short Rams were designed for peak torque at 3600RPM"""" This info was stolen from here... http://www.chrysler300club.com/uniq/allaboutrams/a llaboutrams.html Since Mopar was one of the first to use ram theory in a street car, check out: http://www.chrysler300club.com/uniq/allaboutrams/r amtheory.htm http://www.wallaceracing.com/runnertorquecalc.php http://auto.howstuffworks.com/question517.htm http://www.team-integra.net/sections/articles/show Article.asp?ArticleID=466 | ||
| Slowhand96 |
When in doubt, go with what Erik says. Every time I disagree with him I get an education. | ||
| Buuueller |
Damn, Im dyslexic | ||
| Gearheaderiko |
I stand corrected, but something still doesnt make sense. I will continue to search for the answer! (but if David Vizard said it...I believe it!) (Message edited by gearheaderiko on April 14, 2008) | ||
| Reuel |
In short, it looks like you can tune the intake for best power at certain RPMs just like you can the exhaust. If I was to just add a 90 degree elbow to the intake manifold, I might be OK. Maybe I'll try it after all, as a winter project, if I can get my wife to let me get a space heater for the garage. | ||
| Fast1075 |
Don't forget that most production engines are designed for "must fit" and in the case of motorcycle engines, especially the Harley based engines "appearance", throw in a healthy dose of "beancounter blues" and you end up with a "production engine". Looks and power usually don't co-exist...the most powerful bike engines today are hideous lumps hidden by bodywork. All because they have the intake/exhaust and camboxes where they NEED to be to be most efficient. The effect of intake tract lenght can be calculated..basically, the intake tract starts at the back side of the valve and ends at the intake opening, whether it is the mouth of the carb or the end of a velocity stack. The shorter the lenght the more pronounced the effect at high rpm...it's all about the timing of the reversion wave...the P-3 is a whole new ballgame for me...I never messed with a pushrod motorcycle engine till I bought mine a short time ago...all the 4 stroke motors I have ever tuned would just be getting on the cam when the P-3 is in dangerland. Nallin mentions quench problems with the production head/piston that surely contribute to detonation...I have seen dyno pulls on engines (not P-3's, but DOHC) where minor differences in quench made major differences in power output and detonation control...the "inverted" quench in a stock P-3 could concievably cause overrich spots in the quench area...a sure recipe for detonation...especially at low rpm/high load WOT. (Message edited by fast1075 on April 14, 2008) (Message edited by fast1075 on April 14, 2008) (Message edited by fast1075 on April 14, 2008) |
