A forum for owners of Yamaha TTR250 trail and enduro bikes!

Michael TTR250 · Veteran Member

RE: Air-box snorkel modification

brindabella · Senior Member

today I tried a weird experiment..

I cut and folded a piece of tin so that it would block 50% of the standard snorkel opening (the right hand side of the divider, for what its worth), and taped to keep it secure. yes I did say block 50% of the opening to the air filter!

So what happened? - bike started normally and ran OK at low throttle openings, needed choke for usual amount of time, BUT would not get past 70kph, and opening the throttle to more than 1/3rd was pointless.

Perhaps that test was a bit harsh, so I cut the tin down to a 2cm wide strip and re-folded it, positioning it over the center dividing rib.

Then a went for a ride and it seemed almost normal.
I picked a spot on a slightly uphill stretch of road and accelerated in 5th gear from 60kph to 100kph, noting the point when I got to 100. I did this twice.

Then I removed the snorkel blocking piece of tin and did the test 2 more times.

It believe it was a little better without the 2cm wide blockage (ie in normal trim) but it was hard to tell.

Needless to say I do NOT intend to add any flow restriction in future, and as far as I can see, opening it up could be reasonable option, and I wouldn't particularly be worried about it affecting deep water crossings.

Funny thing that various different ways of cutting/removing/replacing the snorkel are reported to produce different effects.
Perhaps this is because the the airbox does more than just hold the air filter - it shapes the air flow, changes the turbulence, and creates resonance effects. Air boxes are good, no one would think of putting a pod filter on these days. I guess Mr Yamaha would have liked more space for a bigger box but alas, dirt bikes are cramped.

By the way, my old WR250F came new with instructions from Yamaha Australia (dunno how keen Yamaha Japan would have been about it) to cut 2 very large holes in the SIDE of the air box "for closed circuit competition" - they even gave a paper template. I dutifully did this, but without any before and after comparison.

ttboof · Super Guru

I have only gone up one size on the pilot jet left the rest standard .I did try a larger main but found only ended up too rich .

TT-R250M · Super Guru

PlumasDude wrote:
So what are you down under dudes using for jets? (those who have cut out the snorkel or installed bigger snorkel, that is) You probably posted that somewhere but I can't find it. 150/52? (that's yours Jarrah?) I assume I'm stock at 137/52 but I haven't got that far, that's just what my manual says but maybe it comes stock with something different in the US (I'm on a 2003 sold in the US). And you're just using regular gas I assume?

Anyone in the US make this modification?

You have to cut out the snorkel eh? no other way to remove?

Thanks for the tips on needle positions. I don't think I'll get serious about this till I get quite a few more miles on the bike but my first impression of the bike is I'd like some more punch. Maybe its the weight (the bike, not me, of course :).

This is my set-up-

I am from Australia, temp is usually 17-40 degrees.

Ported & polished head (not the one on my shoulders).

Engine: 74mm bore, Wizeco high performance piston & rings.

Exhaust: FMF 4Q muffler/standard unrestricted US header pipe.

Air filter: GYT-R.

Altitude: 930 meters~ (3,050ft)- 4000ft.

6 Sigma #150 main jet set on the second clip position from the top (blunt end).

6 Sigma #52.5 pilot jet, love it. aww aww aww

Air screw position: 2 & a half turns out, 2~1 1/2 at over 3500ft.

..........................................

As to what the AU bikes use-

Some of the older Open Enduro's (steel tank models) use a #48 pilot jet standard. All other TTR250's used a #50 pilot jet and a #147 main with the clip position set in the middle (or one clip position either way if the mechanic feels the need).

To remove the original snorkel is easy(ish). It usually has a little bit of sealant smeared around it so it can be difficult but shouldn't be hard. I simply ''yanked'' it out with my hands. To just remove the snorkel was an upgrade but making the hole larger and fitting a snorkel was better again.

Jarrah

Ps. Sorry for the late reply, I have been busy working on my CT200 and at work.

PlumasDude · Senior Member

FYI I found a few old strings on jets, answered my questions about the US standard sizes, l try to post to one of them to keep it fresh

TT-R250M · Super Guru

PlumasDude wrote:
FYI I found a few old strings on jets, answered my questions about the US standard sizes, l try to post to one of them to keep it fresh

According to www.partzilla.com and the service manual, the US spec is #50 pilot, #137 main. For some reason, Brian seems to think that the standard US spec is #52 pilot with a #137 main but it is not what is specified for them.

Jarrah

PlumasDude · Senior Member

My manual says 137/52, haven't ad time to check

TTRfan · Super Guru

US carb spec.jpg

My US manual shows the same which is why I put 137/52 in the FAQ but, Jarrah is THE carb expert and I have therefore amended the FAQ to 137/50 and am assuming a printing error was made in the manual wink

Brian

PlumasDude · Senior Member

Makes sense, thanks

TT-R250M · Super Guru

TTRfan wrote:
My US manual shows the same which is why I put 137/52 in the FAQ but, Jarrah is THE carb expert and I have therefore amended the FAQ to 137/50 and am assuming a printing error was made in the manual
Brian

I cross-referenced my full repair manual and it has a #52 pilot specified. However, I do not think that #52 is correct as every owner I have helped on here has had a #50 pilot jet installed. The carb mystery continues... wink

Jarrah

TTRfan · Super Guru

To support the 137/50 theory, Boats only list the #50 pilot jet for the TTR250..........

chrisstdt · Senior Member

My bike has standard uk jets with needle clip down one notch and fmf rear can ,would you recommend rejetting when i cut my airbox ?

Kevingrahambutler · Veteran Member

I'm not yet a expert on the ttr's but I can tell you that on the delivery of the ttr last month it came without the snorkel fitted, went out around the borders trail riding to find it was a bit lumpy as if it was taking to much fuel, the clutch was slipping in sixth also the clutch cable was stiff, to be honest I was a bit disappointed, ordered a new clutch, clutch cable, bar risers, from brian, fitted the items this morning been for a ride with the snorkel fitted I think the bike likes this much better, it was a much better note from the exhaust, acceleration was better, if I had to do a mod to increase power this is not the way I would want to go.

Andy_C · Veteran Member

Theres a fair few TTR owners that have "uncorked" thier bikes by opening the airbox and rejetting,including myself,it doesn't always go to plan and some "tinkering" may be necessary with jets,mine was simply not opening the airbox hole big enough for the new jetting but when completed my bike ran much better and was just as reliable. So don't dismiss this option completely.

-- Edited by Andy_C on Friday 18th of April 2014 12:55:39 PM

PlumasDude · Senior Member

Just be prepared to spend some quality time with your carb and lots of testing, this is definitely not a one and done mod. Especially tough if you live in town and aren't street legal.

Kevingrahambutler · Veteran Member

If that's the way u folk what to take the ttr to squeeze that little bit extra who am I to say different, for me Today I climbed every hill in second today, some big buggers, traveled 75 mph on the stretches on the Tarmac, the fuel was good too, plenty for me, I also ride a 1200gsa and for the life of me there are guys on the BMW forum taking the bike to a garage to have the ecu remapped so they can get the bike to do more, I know one or two of them personally and I've thought to my self you can't ride what you've got never mind doing that to the bike,

I've rod with some very good bike lads that can do things with a bike I can only dream about, they all told me the same thing learn to ride the bike, make changes to the bike so it fits like a glove then you will enjoy the bike,

Also said If you want to go fast don't buy a 50cc

Cubber · Super Guru

I'm with you there, Graham, 100%. It must be "wor Geordie" logic.

I have a GSF 1200 that I ride when I want speed, comfort and fun.

When I want dirty fun I opt for the TTR.

I am still learning to ride each and every on of my bikes since passing my bike test first go in 1963! biggrin

Martyn

Kevingrahambutler · Veteran Member

God Martyn you old bugger lol,,,,,,, I was born in that year,,,,,,is that when passing your test was to ride to the end of the street and then turn round,,if you don't put your foot down you passed,,, I only bought the ttr as my klx is in the work shop on a rebuild,,now I'm in a spot of bother as I really like the ttr,,,,
Yes Martyn from makem land m8

Jumpn · Veteran Member

Some the pictures are no longer showing in this informative thread. I've removed my snorkel, but am wary of cutting up the airbox. I was wondering if when enlarging the airbox, that you need a snorkel type intrusion down to the filter to perhaps get increased flow, rather than just an open box without anything direction for the air to flow through. A previous post had the top of a downspout extension in the top. I'm wondering if a length of the same diameter spout into the box would do well.

Upon re-reading, it sounds like that is what Jarrah has done. Maybe the others didn't do that, and explains why they didn't experience to same gains he did.

-- Edited by Jumpn on Monday 27th of March 2017 03:49:39 AM

martin555 · Veteran Member

is a bigger air hole really needed or a stock 2004 TTR 250 will not profit anything of this?

www.perthstreetbikes.com/forum/showthread.php

I mean, without exhaust tuning, is any real use or plus result of this?

thx

PlumasDude · Senior Member

I think it improves stock performance, the snorkel is really restrictive -- take the seat off and rev it hard the snorkel sounds like a vac.

I have only used the stock US pipe, but I just bought a 2002 with a pro circuit T-4 and promptly cut a hole in the box, so I'll get a chance to play with the main jet.

Moo · Senior Member

If you take a look at the Australian dirt bike magazines that have been posted on this forum, they were very interested in tuning the TTR for max performance and found that the stock airbox was pretty restricted..