Airbox inlet

The airbox on my Seca has what I would describe as a grommet that extends about 3" into the air box inserted in the inlet, its labeled "duct" in my manual. Thought I'd take it out and see what the difference is, seems to run a bit better, pick up faster? Any one got the "duct" in or out. With it removed the intake area is increased by about a third. I'm guessing its purpose is to direct any water/rain to the bottom of the box, past the filter, maybe quieter as well.

 

i've been using it to tune the mixture on mine to get the 4/1's just right
the main jets jump 2 sizes and a guess would be the "snorkel" changes about 1/2 a size
you will see a change in plug color, not a lot but it's there
i doesn't seem to change pilot mixture at all, i'am noticing it from 5K on up
did you notice the change in intake noise ?

 

Yes I noticed the noise change, just a hint of an older Ducati to it. Havnt checked plugs yet, or pilots, only done a coupla 100k's since I took it out, so with tuning 4/1's are you gonna leave it in or out? Mine has 4/1, but I modified the original collector box myself and put on a single supertrapp muffler, so it may not flow as freely as a complete 4/1 off the shelf.

 

Could it be that the rubber stove pipe you describe as a 3" grommet (and I know exactly what you are describing) is a muffler for intake noise?
Any difference in sound when you pulled it?

 

the last ride was with it out, it still has a flat spot around 5.5K under some conditions and i'd like a little more color in the plugs so i put it in but it got a little chilly for a good ride
it's defiantly a muffler, most noticeable in higher gears before the rpm's catch up with the throttle
heres one for the old timers, ever flip the air cleaner lid upside down on that old 283 so it made some noise?...same sound

 

...i'm guessing an old 283 was a v8...? so is it in or out...

 

I used to run my '79 New Yorker with the air cleaner lid upside down. Didn't make the old 5.9L run any better, but sure sounded cool

As for the snorkel thing in the airbox... I've had mine out for some time. When it was installed, only the bottom part of the air filter got any dirt on it, so it must've provided some restriction.

 

I pulled that rubber stack from my bike today, and wow. I kept looking to see if my muffler had fallen off. I had a noticeable roar, seemed to be more responsive, and did this little pop, pop from the exhaust when i let off the throttle. It wasn't excessive just noticeable. I think i am leaving if off.

 

Well, my consensus is that its better in, ..without doing anything but take it out, my plugs were lean c/w looking good before removal. Yes it sounds different, louder, but overall runs better in. Went on a damn good ride today taking particular notice of how the engine was working, much better than previous with it out, over the same 80K' of road. .....Must be meant to be there....(amateur tuner takes a rest..)

 

my bike seems to run better without it.
have'nt noticed a diff in sound as i wear ear plugs
( the "xj scream"just plain annoyes me")

my muff's are drilled out to give a bit of a rumble,so that may be
why i don't notice a diff.

i'll put it back and post any changes.

 

Rodger that Parts.
NORMFERG, you might be leaning out your mixture a little more with the added air flow (deceleration popping), check your plugs to ensure you are not in this condition and be prepared to rich up the mixture.

 

well i tried it with the snorkel in. i liked the sound but without
extra air there was a tiny bit of diff in the p/u.
i'm at 5100 ft so it tends to run a little lean anyway-a condition
i've been fighting with for some time so i'd rather be on the rich side,
burnt piston crowns will make for a very bad day!

 

Robert, do you think the mixture could be made right with the snorkel out, by pilot screws alone.

 

I don't know Bushy, I've never run my bikes in anything but stock trim. I don't want the hassles of monkeying with the carbs to get things right again. Guess I'm lazy that way but don't let it discourage you if that is something you might want to try. I would just make sure not to break anything so you can put it back together if things don't work out.

 

i seems to me it effects the top end more than idle and low end

 

Thanks Robert, I'll do a plug check. I probably miss spoke when i said it pops during deceleration. It is more like a rumble. I think the reason i saw improvement was because i had already replaced my mufflers with sportster mufflers. But my bike starts easier, and seems to run and idle better. I think the combination of free-er flowing exhaust, free-er flowing air supply has hit the mark. I believe it is better on low and high end rpm wise. But i am relating from where my bike was when i got it. Being new to the XJ i do not know what good/normal for a 40k XJ is. Will it snatch the front wheel off the ground from a 5-10 mph 1'st gear twist of the grip, NO. But it will haul butt. And it will rack up the RPM's. I am impressed with this 4 cycle 4 cylinder.

 

Took the snorkel out of my bike , 1983 xj 750, and it seems to run great.
More pick up, runs smoother, runs 70mph at 5200 rpm, was 70 @ 5500 prm.
have no pops at decelaration, plugs look good. Its amazing the difference.
I am at sea level. dont know if that means anything.

 

i pulled the plugs after a day with the snorkle in, only a tiny bit
richer then norm-still nice and tan/grey. in fact, the middle to bottom of ensulator where we check for WOT responce looks better then before. but over all the plugs look great and the bike screams.