Patch

Without reading the replies to this posting I have something to say/////// It is not about the whatever's it is about the members,, Freebird put together a club as much as a forum. I enjoy enjoy tech chit when it comes to combustion pumps, that's not to say I don't enjoy metal work as well... What makes these clubs work is the membership and the willingness to share, read and listen. Remember this and this club will live on. I for one may have and do have other things on the go, in these days my time is limited but even tho at this late our I checked in to catch up... Your input is relevant so spread the word, we are mature, experienced and open to no particular brand, rather just good intellect! Patch

Hmm I thought they were less one or is that the VMax?

Not what I'm saying, the melon has one less tooth than the MKII so MKII is a taller setup. The MKI having one less tooth in the melon is better geared to handle skipping the second gear.

If anyone wants to design a new plenum then it requires an understanding in fluid dynamics, how one gets that is up to the individual. You cannot just assume or take for granted that flows will arrive as wanted. There are restrictions inherent to fluids combined and the effects of distance traveled. Your first challenge is to overcome throttle angles, then to achieve even flow to all ports, then volume then velocity depending on rpm range sought. There is zero reason to bolt to existing intake piping if designing a new intake manifold. Would anyone who knows think that CFI is better than MPI injection for economy or performance? I'd like to remind riders that it is best to read compression before spending time and money on their carbs. This is a standard that is too often overlooked. I knew of a fellow who ran a web forum that charged his members over 1200.00 plus shipping to rebuild there carbs. I asked him why he wasn't suggesting a compression test first? He replied what difference will that make! So tell me how can you reason thru indifference? All these gadgets we see and read about, really - just disregarding of the basics both in theory and good practices. More and more we see questions asked not for factual experience to be shared but rather for confirmation after the fact.

Congrats on your purchase. I would recommend a compression test be done while the carbs are off for cleaning.

I see by your reply that you are schoolable brother Puc. Well as for the rest of your post I could suggest a sensitivity class but in your case likely that would end up being more like a full semester likely causing the instructor to experience a nervous short circuiting and meltdown;) Now it seemed quite obvious in the video that while hesitant Ms. Tippy easily walk up the hill faster than old Tweaks could even get a move-on! I thought watching Ms. Tippy as she paused halfway up likely thinking Tweaks may need a push from that spot on up the hill; defensibly a fine compassionate woman you have Puc With regard to acceleration, yes I hear they can do OK after all, they are missing a tooth in the melon, of course you pay for that extra help at the fueling station. Now thinking about running around the continent with all them missing teeth between 1st and 3rd must mean that 3rd, has much more chewing to get through before being relieved by 4th so, one must wonder how far away is 3rd from retiring? Hmm Puc And yes the seat on the MKII was the first thing to get re stuffed.

Geez guys, has any tried to see the badging more sympathetically? Like an identity crisis? It wants to be a MKII? It wants to be bigger, better, faster? It wishes it could pick up the chicks that the bigger, better, faster brother does? It would like to have more room for chick shoes, slacks, makeup kits, and maybe a mirror with lights? Or travel further with fewer LT’s of fuel, in more comfort? Like maybe have the faded blue fast looking chick magnet appeal of big brother? Hmm Gear heads with little empathy!

Your profile does not say which model MKi 1200cc or MKII 1300cc? There is a universal joint at the end of the drive shaft.I may be in poor condition? If you run it and if it is dry then you will need to replace it. PS check the diff oil for level and best to drain and run a magnet through the oil check for metal bits.

Hi Bongo! I agree with the slow response to rpm. In those vids that I have seen posted the slow response is most striking, also noticing that those I've seen have flow stalls around climbing rpms. Again and as we said in the other post restricting air flow comes at a cost. With such a small plenum throttle plate angles work against flow and will cause flow to shear as it moves across the plate leading and trailing surfaces. This angle will also cause the flow though to deflect of the apposing plenum wall, this creates an eddy current that starves ports! If the exposed welding is as we see here then what attention was paid to the inside? How can one be sure there are no vacuum leaks? I have first hand experience with that carburetor, it was good in its day but was designed around compromise and for a very different intake manifold. We didn't cover back pressure in the other thread and I personally have some very different thoughts around it. This for the most part started with the early 2 strokes which as you all know have a very different design and, back pressures were interfering with filling. On these 4 strokes most have collectors, the piping runs often end up different front and back. There is a difficult to understand sonic plus that takes place which is usually time for best scavenging on naturally aspirated engines. At the same time we try to time our pipes to assist one another through scavenging. The best way I know to explain this is thinking around flow moving past another chamber (equal or not in size) which creates a low pressure (Venturi rules) and this movement will cause scavenging (like adding concentrate to a moving flow)! So usually it is safe too say after the collector you can choose to dump or, the job is done. The back pressure would be best serving if kept as low as possible but high enough to not brake or separate exhaust flows in chamber, think of it as a train loosing momentum and you develop a clearer gotcha;) So keeping exhaust in the pipe moving requires some consideration and minimum back pressure. This is most critical at higher rpms where filling drops off do to fresh fluid flow restrictions above and at intake strokes and is where we face the decision of velocity verses volume.

At 3.34 seconds into the video.... Tell me honestly that you would except the stall in flow while cranking it off a light????????????? At Idle do we hear what we would expect to hear off a high lift cam pulling past idle positioned throttle plates? Ask why that is. Progressive 2 barrel carburetor that dates back to the early 70s for the 2000cc early British Fords, it was slow to kick then on those beaters, of little use on a performance machine! Reach out to this fellow, invite him to the forum where he can brag and perhaps he may learn a thing or maybe nothing as he has so much experience having done this once before on a wing??? And maybe Puc can teach him some welding lessons while he here?? Just a thought

On our last ride cross country SK and I stopped for a Tim's, I stretch out on the bike to close my eyes a bit SK stayed in wifi ing. Now SK isn't good around emotional people so he brought this fellow over to my bike and the story went like this; I have a flat, and you know a HD truck and trailer was here in the parking (to or from a rally) I asked if he could help me and he refused, very disappointed sure he could of helped, I can pay! I had noticed him earlier walking in and out of Tims, I nap with one alternating eye open, old habbits;) anyway I walked over and could see what was left of a screw in the turn of the tread just before the wall. Yep no problem we took out our kit and fixed it, we posed for a pic with this rookie then packed up and headed out. Now if we had more class about us we would have done the correct thing after braking the clutch lever earlier in the trip. Smart money would book a room and order a replacement handle, but we had places to go and peoples to see:)

I thought I share these thoughts and add a question. Here is something to think about with the exhaust and intake ports interactions and when for a brief moment they are both exposed to one another during overlap. For this example I ignore throttle angle. @ TDC top/end of exhaust stroke, both the intake and exhaust valves are slightly open. The exhaust fluid has been pushed up and out thru past the ex valve by piston @ velocity; if the port and pipe diameter are correctly sized velocity should continue to be maintained say for the first foot or so of travel. Because both valves are open and according to Venturi, a slight vacuum must exist caused by the moving fluid being pushed out. In other words something below atmosphere exist @ TDC both valves open, 2 flows in progress piston stopped before reversing direction. This overlap is expected to one allow the exhaust fluid to continue out while the slight low pressure caused by the velocity of exhaust will cause the new charge to fill this void, in a sense freeing the exhaust tail, (Kind of best of both cycles/worlds) It is hoped that this rule will help expel the combustion chamber volume of unusable mix replacing it with fresh charge. Keep in mind that for a brief moment the piston has stopped travel and will then reverse moving down. In more than 1 cylinder engines this new intake cycle is an energy blead off the crank as Jeff alluded to. If we change designed exhaust then this has an effect on flow and velocity and therefore has effect on filling. Sometimes you win and sometimes not. Again as Jeff alluded to earlier when atmosphere is removed pressures are unequal, then another rule applies that says pressure wants to equalize. This equalizing generates velocity as the two pressures seek to balance/equalize, this is how we fill the jugs. As the piston now travels down in naturally aspirated engines, these pressure differentials continue and the race to equalize/fill is on. So what’s the problem and why don’t we achieve 100% volume metrics on each stroke?

Well we enjoy spending your money, at your expense of course;)

When reading your answers I was reminded of the old saying that goes like this: If you want 100% fillage then put the head on a hinge! As you know Jeff there is a minimum speed at which the engine must turn or spin to generate enough vacuum, fill and then compress in order to run; that is what the starter does at around 500+ rpm. When the piston is on her intake stroke it produces vacuum because of the difference in size of valve diameter in relation to piston and bore, this also creates velocity of flow. There is a very important angle here that works in relation to the lobe. This angle is that of the throttle plate restricting flow and thus increasing velocity reducing potential volume therefore controlling output. Bernoullie's and Venturi's laws apply meaning that flows restricted increase velocity regardless of fluids and volume in question. Given equal chambers and fixed duration's the filling of jugs is where the trophy is to be won or lost. This also includes every cycle of exhaust and again where both flow volume and velocity are critical sequences. Flow Velocity is key to torque just as flow volume is key to HP. The questions are based on dyno testing and is why I chose the explanations given. The dyno shows and tells where and what is to be found at which rpms and angles of throttle, these are tied together after the build, the results may be used for tweaking or for the driver who is expected to ring out the given performance targets if on a track. If you are running street you would likely want to find your power down low where torque rules (4 stroke) so you will need volume at velocity, one without the other leaves you too low in volume metrics, or wastes displacement! Again this thread was for carb conversions on touring bikes and, is why I think that the runners and plenum plus throttle angles are problematic, given what we have seen.

It's not about my build Puc. It is showing torque above 5252. The comment about 6500 rpm was me stating that I don't usually need to push my touring rides above that! I've tried to leave that build out of this thread. But because here we are I can say that, as one of my targets is range (fuel tank) needing to run high revs to make use of torque would cause me to miss all my targets for the touring bike, the Kat is a different story. Now if as in the barb conversions we were to only take a small piece of why intake runner lengths can improve bottom end torque, then it is not enough to justify converting to one single carb when and where it will shut of torque too early over canceling the potential range of any given touring bike I know of! In the 4 stroke dyno results they clearly demonstrate the filling challenge via scavenging diminishes at higher the rpms and is what we would expect to see in these posted carb conversions with restricted flows? Remember these conversions make no suggestions relating to cams. Cams are the timing limits so in these conversions one would need to change duration of the lobes or starve the engine!

I found this, half is two stroke then the four stroke. These tests done for mods of cams and exhausts. Note the comment about loading the dyno up @ these higher rpms. You could think of it as cruising on the flat then climbing a hill.

Impressive! Now that you have her pretty well equipped whatcha want for her? Hmm

This video is worth the viewing for the first 2 minutes and the last minute! What makes this so funny is the comment section, really worth opening them and reading suggested work around's and, one lady's "enough internet for today remark"

This was my self imposed caution Puc throughout this thread. I know that torque is found by manipulating volume metric efficiency, ratios and duration so I shoot thru these, then you can prove via dyno. Now if I am moding a touring bike then I will state what I am dynoing for at what angle are of interest to me, then go for broke and print off the results; then I can finalize my tune based on the important stuff not just the higher HP output! I see no entry you posted that is wrong rather you wanted to based on 5252 take a stand. SO, I live in the prairies, I can stand on the rails with another and ask "do you agree that the tracks join right under that 2nd electric pole?" as you know if we walk to and stand at that point.... You mention measuring in ohms what if we get a solid swing and we then assume the wire, contact or coil is good would that be definitive or, would that suggest we load test knowing there is a problem and can now assume that it will be proved only under load and temp conditions????????????? really a good thread Puc & Jeff and you made it so cause ya made me dig deep

Really? NO! 5252 is just an overlap of graph. It is just the scale math.

​ I will tell you all the dark side but not the ratio targets. The true evaluation of torque is based on displacement. The challenge will remain volume metrics, duration and angles. These are just my opinions, not judgments, they are as mentioned based on wins and losses as well as, the good fortune of having shared experience with much smarter guys willing to share than myself, that does not mean they figured it out for me, but rather they set me straight, more than once.

Perhaps we have reached the point where a fresh worksheet is in order? Jeff brings to the table his study and principle's that as an engineer guide his thinking so no disputing that fact but the applications of, are what drive enthusiast. The first part that I think may confuse some is vacuum diaphragms, Jeff expresses the other side of the coin. Here you go Puc, there are two pressures at play here; if on one side we lower than atmosphere yet do not increase pressure on the other, the the vacuum pump will move recording to design strength. In a CV it will pull back the piston and metering needle. If we increase pressure on the other side thru flow pressure then it will do the same except it will be quicker to overcome resistance such as from the return spring. Think of it as power assist. But in application and thru a carb there's more to it and is why the pistons bonce. Now if we take two odd numbers and add them we will end up with an even number, that is the rule, we don't question it. If you were helping a young mind and asked, find the eq. common denominated to say 8 and twelve and they answer 4 that would be correct. If you wanted to see if they really understood the question you may ask next, what is the lowest eq, com denominator, after you could add in with fraction so to pop them out of thinking only in even numbers. It really is about understanding math as a tool. If a young fellow asks me to sort thru his busted something, and I ask that he disassemble it first then offered up my wrench/tool did I set him on the right track? Well not if I didn't explain the reason for the ears being a different length or why he may need a long one.... So my point is that we over time take things for granted, forgetting the basics. Bernoulli's and Venturi laws and explained theories are in play even in torque/HP. We know air is a compressible fluid, we know that is has density and viscosity, we also know these are variable so, we use the above two principles to plan around. My opinion here Jeff Venturi disagrees with some of the connections made to pressures. When we choose plenum we must choose wisely, then we must prove our choice, and we can't do so effectively by bolting it into use before we have completed the math. All angles in a build are critical. All restrictions and interruptions have consequences. Air is the medium we choose to carry our fuel except in direct injection applications. (past blows or injectors) Lets agree that engines are basically air pumps with a combustion cycle. Combustion is the trophy we strive for, so to is it the challenge. Why? This would be a good time to strike a match and, either use a stop watch or count it off in your head. Striking of the match is ignition as the match begins to burn over time is and that is duration and the remaining problem! Combustion is in fact a chemical reaction, the heat generated expands the gasses in the confined area from the combustion chamber to end of stroke. (same problem) Time is expressed as duration first in the extraction of the energy from the fuel which requires oxygen, then ignition and time to expand, duration again, hmmm going to need to change angle of ignition then. Playing with these tables is what performance is all about; regardless of displacement. Stoichi facts out for us a target based on known efficiencies, lambda measurements are a relatively new tool to us, as a method of measuring where we are or what reality is... We can choose to alter ratios for different reasons, one guy may say I built to run lean, the other says I running rich because I increased the X do to say a flow limitation? They each face the same problems and will go at their builds based on whats worked for them in the past and what or where their targets are. Jump in anytime guys.. Calling an Arnold;)

HaHa you guys are rolling! Unfortunately I have a project proposal I need to keep my head around for the next day or so... Haven 't dared read all the posts cause I know it'll distract me. I did read what came in by mail tho. Forgive me if you covered it.. Naturally aspirated limits - volume metric efficiencies what happens after the testing starts (think it thru) and if we are spinning the crank then there has to be torque, but what is working against us that ties these together? We covered it earlier in the thread.. chat soon

I get what you are saying Jeff and, I know we share here for similar reasons, this is what the club thrives on. My experience is around trial and error wins and expensive losses;) The line below I would have been wiser to leave out as it is insuffient on its own. "Of course a 4 injector with 4 throttle bodies would producer better performance at all throttle angles with less losses. The challenge with the control box inputs remains the same so for the price 4 has the biggest gains when at the ports even with stock unmodified heads and cams" I touched briefly on it and will again in the other thread where Puc is being stubborn line 1) I am curious about how you tested it? If you were'nt able to simulate operating conditions then yes it would be a wash. 2) the problem with accepting turbulence as I know it is, for one it is actively disturbing flow. Now Jeff it is then you may have a stall above the injector?! Thru modeling you know a smooth flow provides more of what we usually want and, when we cut thru it, pressure changes are expected. Now if we are trying to mix fuel/air then that will happen further down. 3) is the new way of the old take on the dark art of porting. But in short it should induce less drag by adding lift which should help keep velocity up so percentage (usually measured as loss or the less you lose the more you gained) in flow should mean better filling of the jug. Many don't agree so it can be a bit of a touchy topic(: 4) that is what I too would aim for. If you get the pulse timed in, the injector will behave differently. Now I know through some experimenting that flow and velocity above is very important and in our fooling with fueling we had some rpm limitations while running open, just like the CVs! 5) I am curious about this and what the effects would be? all existing ports of course would be closed off existing in atmospheric condition but, with a 90* injector position I wonder if that casting geometry wouldn't play out some positives??? 6) Lag is often right when and where you least want it but was not what I was referring to. The lag has to do with pressure drops and time it is just is what it is. A quick example, the slide has lag designed into it on the ventures if using stock numbers, this is a plus. I would expect that the slide number for Vmax would be different although I have never studied them! Lag if found only when and where you expect it,,, is a OK, consider it a winding up. (track thinking is different)

OK Puc same dilemma new approach. I wanted to take some time between to think of how I might express this differently, yup I sometimes think slow. Would you agree that in the mentioned graph, torque is still present past 5000 rpm? Yes or No Would you also agree that in a naturally aspirated engine, low pressure is the fuel delivery system used to transfer the charge or fill the jug? Yes or No Would you agree that low pressures alter in direct relation to the throttle angle? Yes or No Would you agree then, that torque peaks seems to correlate to peak velocity? Yes or No Anyone who would like to, should pile in and consider this an open conversation.