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Discussion in 'Thumpers' started by NEPA 450x, Oct 16, 2018.
real deal tuning fun to see
have a good one!
12-19-2002, 04:54 PM
Join Date: Dec 2002
Last Online: 02-27-2011 06:04 PM
Location: Dallas, TX
Deceleration Popping explained
In reply to:
Subject: Re: DECEL POPPING?
After spending the day on the dyno Saturday, my 450 popped and shot flames out 4 inches after 11,000 rpm runs. The O2 sensor indicated we were a tad rich on the pilot and needle. I attributed it to unburned gases in the exhaust igniting on decelleration and jetting wont help that. Most times a lean condition WILL be indicated by popping, but not always. TW
This is exactly correct! If you think about the mechanics of what is going on upon decel, it makes perfect sense:
You start out with an engine that is turning high RPM with a carb that is open, flowing freely. Next, you close that slide. This has the effect of creating a tremendous vaccuum in the intake manifold (CHOKE!). This vaccuum does curious things:
1. It pulls air and fuel from wherever it can--including the idle and low speed jetting in the carb.
2. To counteract the vaccuum, air will take the path of least resistance--including sucking exhaust gases back into the combustion chamber during valve overlap (the brief period of time that the exhaust and intake valves are open at the same time.
So what does this mean? Well, now you have a disproportionate rich mixture heading for the cylinder AND what little oxygen is drawn in is further diluted by gases that are coming back into the chamber from the exhaust valve. The result is poor, incomplete combustion! Depending on the temperature of the exhaust pipe and gases, reignition is possible once this mixture is introduced into a more oxygen rich environment. This produces the "pop."
Why does a lean running engine have a tendency to excessively pop? The exhaust gas temperature of a lean engine is substantially higher than one that is running on the rich side ( an EGT probe will show this). Therefore, the high EGT serves to heat the pipe more and the gases themselves become a much better source of re-ignition. By richening things up, you are cooling down the exhaust temp and therefore reducing potential re-ignition sources.
Any 4 stroke engine--even those that are flawlessly tuned will pop on decel. It is harmless, but can be annoying--granted. However, I would never alter the jetting of an otherwise performing motorcycle to get rid of it. Go by the seat of your pants and the color of your spark plug rather than the popping as an indication of the jetting of your scoot!
I read alot,lol,
Do 2 wheels 4 wheels,
Intresting read I learned in 68,
Despite the proliferation of electronic fuel injection (EFI), carburetors are still a viable option for hot rodders and even some racers. Why? Because carburetors offer the purest form of fuel induction where fuel and air are mixed and pulled into the intake manifold. It’s easy to control the performance of a carburetor, which is why some racing series still use them – especially in the more budget-friendly classes.
Speaking of budgets – another reason carburetors are still a popular choice today is because they are economical. Hot rodders can get more bang for the buck with a carbureted engine vs. fuel injection. And certain racing divisions only allow carbureted engines to compete. But can the simple carb make as much power as EFI? According to carburetor and EFI experts, they can.
The carb has a performance advantage over many EFI applications. When comparing a carb to EFI, the carb typically makes more power because it shears the fuel into droplets, allowing it to mix and stay suspended in the air inside the manifold. The atomization reduces the chance of the fuel dropping out of suspension, which creates more efficient combustion.
EFI, on the other hand, is sprayed under pressure, and the fuel is not as easily atomized into the air stream. Reversion pulses inside a typical EFI intake plenum can allow the fuel to separate, which will reduce combustion efficiency.
The key to making a carburetor work optimally for an engine combination depends on the airflow capability and how it atomizes the fuel into the combustion chamber. If the carburetor is too big it will be rich at idle and lean at wide-open throttle (WOT). In this case, the fuel is not breaking at idle and there’s not enough vacuum at WOT to pull fuel through the boosters.
To determine how much cfm is really needed, you have to be realistic about the engine combination and use. The combination should already be mapped out for things such as camshafts, converters, heads and intake, vehicle weight, etc. The components used here can have an impact on the type of carburetor you choose.
Experts caution that getting caught up in the cfm ratings can take you down the wrong path. It is better to instead look at the type of booster, venturi size and butterfly size when determining the right size carburetor for an application.
There is a simple formula many engine builders use to help them select a carburetor – Engine CID x Max RPM/3456. Let’s say you want to calculate a Small Block Chevy 350 with a redline of 6000 rpm. You would take 6,000 divided by 3456 = 607.63. In this case, a 600 cfm carburetor would be plenty sufficient. Our formula figures 100% volumetric efficiency, which most engines are not. You can also use an online “Carb Calculator” available from several web resources via a simple Google search that can put you in the ballpark just by putting in a few key specs.
From there, carburetor tuning is done the old fashioned way – with a few wrenches and a screwdriver. Many top NASCAR engine builders and drag racers of the past tuned their engines by monitoring the spark plugs. The plugs tell the story about what is happening inside the combustion chamber and if it’s lean or rich. While EFI may watch these things for us today, the tools and knowledge you’ll need to make adjustments are more complex. There are still a lot of good reasons to choose a carburetor for your next build.
This article was sponsored by Proform Parts. For more information, please visit our website at www.proformparts.com
I have nothing involved with them,just sharing article, knowledge, it all relevant with fuel,air,waste,
Reason for read is, it says,,can carb make as much as fi,,
So,it's time I learn more about single cyl,fi,
V twins were easy,had a stroke carry u through,intake pulse, ,,
Any one no that 450L shoots 2 loads in for one hit?
Yea lost u
good read there.. it doesnt take into account the modern pump gas blends though. its hard to dial in a carb on this stuff thats basically designed to be pressurized. the carbs just cant vaporize the way they need to. I'll try to find the research papers I read about this a while back and link them here. its not just my imagination..
Im a carb guy at heart, I love FI for round the house stuff but if I were planing a round the world trip or anywhere that goes through the middle of nowhere, a carburetor is mandatory IMO.
Ive cut up a few different Honda pipes in the past, they make use of very interesting designs with all sorts of cones and louvers, etc. but I dont plan on cutting up a 450L one anytime soon. lol
FWIW it was confirmed on the mega thread that the 450L only injects on the intake stroke, are you saying otherwise or that it pulses twice on that one stroke?
This should not loose you,, lol
Intresting that gasses come out to end of can,swerl around baffle,cooling it before it runs back to front,than into cat heating it up,and than exit,
Mars terms,, as it cools outside of baffle,and inside hot cuz of cat,,,
It automatically creates a vacume to draw hot ex out,,,
Anyone undetstand that???
Yes, I won't cut 450L, I'm just looking,learning,since I only did 2 stroke 2 wheels, and roadracer National scca 4 wheel v8s,
But it relative of anything, in strokes,fuel,comp,spark,,
Intresting what sound waves do,I'm a dang venturi guy,, free hp,tq
And bounce like them,lol
Funny that u can't light fire with today's gas,, till u poke flame in bottom of bon fire and shake it,,,than it explodes,throws shit all over yard ,on fire,lol,,,
I now mix used oil with it,oil,,,boy that's another story ,,,it came a long way oil,,,remember 32% paraffin in it in 77-78 I think? It would clot up under 20 deg,I use to have to heat pan up to get oil pressure, ,,and only QS got sued for it, we were a QS dist and warehouse, ,,dealers changed some motors from claims of QS jelling,, we did.
Yep. They've made a dual pipe muffler concealed within a normal looking can to keep the velocities up. If that part itself isn't that restrictive along with the cat it could be that a slightly larger header pipe from the 2019 X (if it matches up) can open it up while the muffler maintains some of the exhaust velocity. If the X has the California nod of approval does that mean it has a catalytic too? if so that mean just that X header which is bigger and along with the different ECU is the source of 3? hp, can't remember what was posted about the EPA numbers. L 42 vs X 45 ish I think.
I wrote lower about gas yeaterday, I was rambling.
I got bore camera out last nite,and muffler runs as I wrote,BUT I was wrong were cat is. It is at entrance of can,one cat there that looks like a paint mask filter,good honey comb style with openings you can see easy,about 3 in od ,than there's a really heavy piece that runs into can with 4 ports in it and another cat raised above that .like a after burner.looks like cat part is what's really heavy in muffler.
The 2 lower pipes run the length of can to rear each maybe 7/8 id,
Than around bomb shaped spark/silencer,
Than goes back foward in 1 pipe maybe 1.2 Id about 5 in to chamber were S/A and
Outlet pipe begins .
I'll post pic of some stuff later,,,haha and that's what I did for bday,,lol
Today's gas is like old diesel fuel,than add 10% alk ,methanol, propinal ,that won't light if not under comp,,,
So today's gas is ment to be pressurized and injected, to atomizes it to ignite it,or it puddles and won't burn and runs down port and flashes plug with shit that won't burn,,,
(Sorry for the rambling I'm writing, it's a lean to for me today, and I want to thank you all for putting up with me,,,I'll have a new chain next ride together,promise, ,,
All can see,few understand, ,,)
I always take anything that burns gas has a carb, after sitting,shake the bike, than turn gas on,tip it on side let carb flow out overflow than stand back up wait a couple min,than start it in 3 kicks or cranks,,now hd I do the same but put vac to petcock to flow fuel,,,
I swear if you don't do that ,today's gas ,separates,absorbs water and that sets on bottom of bowl,tank,filter,carb....
And when u try to start it , it just sucks water,alk,shit up first, than it flashes spark plug and shorts it out,,with a carb,,,,
FI,,,it just pores more fuel/water through inj and,pulls or puts timing to engine till it fires up on start, and if anyone has noticed that a cold fi motor also needs alot of cranking rpm to start it,if it was sitting more than a day or 3, intresting to see how a crf 450 w/fi no battery gets Kickstart ed on a cold day after sitting.thats why everything uses iridium spark plugs now, since no other plug will fire any more than 15/1, we're iridium will light a 23/1 afr, and not foul.
Anyone remember all the coil packs early 2000 to 07 failures ,than they mounted single coil packs on each cyl??? But didn't help,,,
Than all of a sudden no more coil pack problems,,,,wasn't the coils,it was the spark plugs doing it,,,,
U got me rambling again,,,Really thanks
How times have changed, ,,,
Me,I'm going back down stairs to cut some baffles up,spend hours ,maybe making something worse or better,,,cuz I can't ride,and keep me sane,happy,
No one needs to be depressed,anytime in life,,, so I go do something constructive, ,
,,no not wash or cleaning,,, that I should be doing,lol
In an hour I'll erase this,and think,yea I'm a nut,,,
1. entrance from head pipe
2. inner and second cat with steel ports lower
3. 2 pipes running to rear
4. rear chamber that than flows around S/A silencer,
5. outer pipe to mid chamber
6. S/A silencer to exit
sorry it only lets me load 4 at a time
Yea I went and slid a 1 3/8 soft plug in exit hole,,, What a dumb shit, cuz it took hours to get back out of there,,,
But kept me busy all nite,,lol
better pic of mid cat were 2 pipes exit to rear
I must of tired my helpers out last nite,but while I was screwing with things they brought me a mouse inside to chase around and fight over,,lol
Intresting now I got you thinking,,lol
hate to slow you down, but i gotta get this spelled out for me.
what am I looking at here?
dark one is your can inlet, cat, and SA?
clean one is a new one? from an X or something else?
Trying to get a pic here...
I thought I read were it pulses 2 times a stroke, but I have no idea, sorry,
That's another days project to figure out,lol
Dark one is oem removable baffle/SA out of 450L,
I bought a NEW 450L one ,,,just to cut up and look at,,,
mid or powerbomb style ,with lots of baffling holes in it, large outer dia.
rear is S/A that sits in chamber that comes from rear to chamber 2/3 back that than flows to exit.
Sorry for bouncing,, and English,, if you don't understand it, just write me and ask,lol OK OK,
I understand a lot I write a lot ,,,,,
ya got to run the rock garden to get it,,lol