Its finished

[CJM]

Finally got the 416 down to my shop to tune it. I did take it for a test drive there and it seemed ok, took it for a ride at home and slight slight pop on decel (lean).

Im gonna yank the plug, but I think its fine. Before I had it done it was popping like CRAZY, now its just very slight and not all the time. Mostly its popping slightly when you come from a high rpm (say 3rd or better) and use the engine to brake (downshift) to say 2nd or 1st. Only complaint is WOW this suckers hot now, but the headers arent turning blue.. I mean I am running 11:1, 416, HC II and I have the spal fan pulling heated air basically into my legs...

But I found something interesting out in my recent google searches on this stuff..check this out..makes perfect sense actually. A car for example wont do this b/c of fuel injection-but a carbed one will and I seen./done it.



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!

[JOHNDOE83]

well yes and no....lol.

The carb has vents that keep it from creating that tremendous vaccum.

Also the plug chop isnt very accurate unless you really know what you are doing, most people go by the tan color, when actually there are four areas of a plug that get color, to properly tune it by the plug you need to look at all these four parts on the plug. "not just a tan color"

The phrase "flawlessly tuned 4 stroke" is nearly impossible to do with a carburated engine, unless you have a serious dyno with a serious computer program, and many many hours, it aint gonna happen.

Mine will not pop on decel, and its tuned well but far from "flawless".

Brand new utility quads and rhinos dont backfire on decel, neither should a new 400ex.

This isnt intended to start a argument, but most of that last part is mostly opinion.

The phrase poor incomplete combustion and reignition is possible would be "detonation". which comes from poor timing and extreme lean conditions.

[dalejiw25]

Without listing your jet sizes it's hard to help you. To me it sounds like you're lean on the pilot jet or a/f screw. The better informed we are the better we can help.

[CJM]

I played with the AF screw, it actually made it worse now despite me putting it back where it was.

The plug is pretty which on the porcelain too. And I said the headers werent blue, poor light (it was dusk) and they didnt seem it-oh yea its getting to hot due to it being lean.

Im taking it back tomorrow and I want it done. They didnt comment what jets they put in, just they set it up for 416 and 11:1 on 93 octane.

Hey, I paid for it they better make it right. And FWIW honda carbs suck, my old suzuki pos 230 I could play with all day and it was sooo simple...then again it is over 20 years old lol.

Ill let ya know how it all turns out.

[JOHNDOE83]

90% of all mechanics wont or donot know how to jet.....

once i went to the "honda dealer" and asked for jets and they asked why would i need it rejeted!!!!!!!!

if the air fuel screw made it worse you need a bigger pilot jet...if the plug is still white, you need pilot, main and needle adjustments.,

they didnt specify jet size cause they didnt even look i bet?


Well, if it was a machine shop, they set it up for 416, 11:1, 93 octane, but the jetting would be up to you....they just set up the motor, not tunning motors.?

[CJM]

Nah I put the motor together myself.

This dealer is actually pretty good, they work on race bikes for some local racers at E-Town by me.

Hey, as we all know jetting is like a game that takes awhile to be played and eventually you get some points-but sometimes it takes awhile.

Im confident they will fix it, or I want my cash back.. I know they did take the carb off, b/c the throttle cable was pinched and when I made a right turn it throttled up. The clamps were also not where I left them.

Course, if anyone can recommend a good atv tuning shop complete with dyno or perhaps a good, good tech in the central NJ area (close to freehold) I would be happy too.

[CJM]

Got it back, dealer did the tune free of charge. Told me they had originally changed the jetting and now messed with the A/F screw. They also said if it still isnt right I can bring it back free of charge to be done again till it is.

Took it for a 5 min ride and yea its better cause its running much cooler-before it was hot as hell even after 2 mins.

Downside is its popping on decel still slightly-but I think I know why. I like my lexx exhaust except it is designed HORRIBLY where it connects to the header and seems to be causing an exhaust leak.

It uses this aluminum spacer to make the header pipe fatter and its only an inch long. The problem is the pipe doesnt reach the end of the header flange and I have a 1/2in gap where the end of the header collar is till the pipe begins. I siliconed the junk out of it and its loose again. Im not sure what to do except fabricate a bracket that moves the actual mid pipe and exhaust closer to header pipe or make the exhaust header fatter at an exhaust shop and use a clamp or make a longer spacer..IDK wtf to do. Maybe I should buy another pipe?