Yamaha XT350 1990-1993 Restriction - All Revealed Within!


24 replies to this topic
  • FreddieS

Posted April 13, 2008 - 03:04 AM

#1

Hello All,

I recently purchased a 1993 Yamaha XT350, and I have ridden it around for the past week, but upon finding nice open roads where I think "ill just open the taps a bit" it failed to pull past 60mph.

So, I tried to find a reason why it would be so down on pulling power, to find quite a few threads via google suggesting that it was restricted between 1990 and 1993, alas, none of these threads offered a fully viable solution to the restriction.

So, today, I got a bit bored (its raining :thumbsup:) so I decided to remove the carb, undo the inlets, and Lo' and behold, theyre restricted, almost to the point of the 2nd carb opening being pointless!

So, here are some pictures, to show of the restrictors fitted to a UK 1993 Yamaha XT350.

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Now going through the Yamaha part fiche I can see that post 93 and pre 90 models have different inlet boot part numbers, aswell as different carb numbers, ive already purchased a 2nd hand 94 carb, which is in transit, so I will document any differences between a 93 carb and a 94 carb.

I have emailed my local yamaha dealer to see if they are able to order in the unrestricted inlet boots, failing that i have found a company that has them in stock, but a bit pricey at 80 euro's for both.

So, basically, all the gibber about people saying that they were or werent restricted can be put to rest, as im sure you will be able to deduct from the pictures that they are restricted (the high end carb inlet, is heavily, heavily restricted, upon measurement its around 20% of the full opening available!)

And to finish this essay, heres a picture of my bike :confused:

Posted Image

:thumbsup:

  • fishpost19

Posted April 13, 2008 - 04:12 AM

#2

Can't you cut the stock boot so the whole inside is opened up instead of trying to order them? You'd need to rejet of course, but while you're at it open the airbox for more power.

  • FreddieS

Posted April 13, 2008 - 05:36 AM

#3

Can't you cut the stock boot so the whole inside is opened up instead of trying to order them? You'd need to rejet of course, but while you're at it open the airbox for more power.


The reason im going to order a new set of boots is that if there are any issues with the bike not wanting to start or w/e I still have a good baseline (restricted carb + inlet boots) to go back to.

But yes, I could quite easily grab my dremel and take out the restrictors that way!

Ive heard jets arent easy to get for these though? (could be, a bit like the restrictors, a bit of a myth?) or is it easy enough to get jets/pilots for these?

In the long run im going to be machining a pair of new inlet boots to hold a pair of 26mm mikuni's as this whole dual choke deal is a bit fancy pancy (especially to then just be restricted!)

:thumbsup:

  • shrubitup

Posted April 13, 2008 - 09:29 AM

#4

http://www.jetsrus.com/main_page.htm

This site HAS jets. They don't appear to have your model listed but all you have to do is send them an email asking for them to include your model into their listings. They typically send you an email and tell you that your bike selection will be available in 24 hours. Their prices seem reasonable too.

  • FreddieS

Posted April 13, 2008 - 09:47 AM

#5

http://www.jetsrus.com/main_page.htm

This site HAS jets. They don't appear to have your model listed but all you have to do is send them an email asking for them to include your model into their listings. They typically send you an email and tell you that your bike selection will be available in 24 hours. Their prices seem reasonable too.


Ahh Sweet!

I want to get it running first, as that jet site is in the US, and I am UK based, so the parts delivery time would be quite high compared to me finding the same in the UK.

Im just suprised that its so heavily restricted, especially the high end, as it means the variable venturi would be hardly opening (hence restricting it so much, and struggling to reach top end!)

  • maim

Posted April 13, 2008 - 11:16 AM

#6

i just took mine apart last night and mine are both the same size. maybe they got smarter?

  • FreddieS

Posted April 13, 2008 - 12:54 PM

#7

i just took mine apart last night and mine are both the same size. maybe they got smarter?


It only effects models between 1990 and 1993.

  • shrubitup

Posted April 13, 2008 - 03:24 PM

#8

At Yamaha sports plaza dot com the following prices were obtained for a 1994 XT350 US model. I assume the 1994 will fix your toubles??

1 SKU: 55V-13586-01-00
JOINT, CARBURETOR 1 1 $35.66
2 SKU: 42U-13596-01-00
JOINT, CARBURETOR 2 1 $31.71

  • FreddieS

Posted April 14, 2008 - 12:02 AM

#9

At Yamaha sports plaza dot com the following prices were obtained for a 1994 XT350 US model. I assume the 1994 will fix your toubles??

1 SKU: 55V-13586-01-00
JOINT, CARBURETOR 1 1 $35.66
2 SKU: 42U-13596-01-00
JOINT, CARBURETOR 2 1 $31.71


Those are the parts!

Alas, i can get them from a site within the UK for a bit more (but a shorter shipping time)

  • FreddieS

Posted April 14, 2008 - 01:55 AM

#10

Well ive just ordered aforementioned boots within the UK for £60, which is a price i can live with seeing as it near enough doubles the power of the bike!

Hopefully my 94 carb will arrive during the week aswell so I can get it running nicely before im back at college.

  • jsnmid

Posted April 14, 2008 - 05:27 AM

#11

i just took mine apart last night and mine are both the same size. maybe they got smarter?


They never restricted any of the North American models.

  • FreddieS

Posted April 19, 2008 - 01:11 PM

#12

Well i got the new parts earlier in the week, and glad i spent the money, as the new boots were, as suspected, unrestricted, and the difference is huge!

Has so much more low down, and ive seen 80 out of it on the flat against the wind, that was inc lifting off to avoid going into the back of a car.

Posted Image

Ive checked the spark plug and it isnt running lean, so all i can presume is the 2nd carbs variable venturi was just not opening enough due to the restriction...

  • capn_banks

Posted June 02, 2009 - 12:58 PM

#13

I just posted this message (below) on a number of forums so I too can confirm the restriction myths. Also a UK bike, 1991 model. Glad to hear that it doesn't run lean, but will it work ok with just one side derestricted or do I need to do both? Also Freddie where did you get the replacement boots from and what year are they for?
----
Hi guys,
Im having some workshop trouble and was hoping someone could help:

My '91 XT350 was letting in air at the right hand (secondary carb) joint between the cylinder head and the carb. This was because the rubber joint had come away from the metal base, apparently a common problem in XT350's.

Anyway, I ordered a genuine yamaha part replacement from http://www.cmsnl.com
Using the microfiche I identified the correct part. However when it arrived it looked different to the original.

Posted Image

The part on the left is the new replacement. The part in the middle is the old one and the part on the right is just the rubber from the old one.
As you can see there is a smaller hole on the original (and it is all one piece, not an insert).
Looking in manuals and microfiche I couldnt find anything that looked like the original joint.
Will fitting the replacement cause any problems or do I need to have the same as what came off the bike?

Also the joint on the left side (primary/idle side) also has a smaller hole, although its larger, just large enough to poke a finger in.

Thanks

  • maim

Posted June 03, 2009 - 03:25 PM

#14

the new one is the unrestricted one. your origonal is a restricted type one. it will bolt in no problem and give you more power to boot. a site member from europe posted these up last summer so we could see the difference. you would prefer the un-restricted boot hands down.

  • capn_banks

Posted June 04, 2009 - 12:06 AM

#15

Will I HAVE to rejet?

  • maim

Posted June 04, 2009 - 01:42 PM

#16

should not have to. you will want to check the plug after a few good wot pulls to check if it is too lean. if you are running stock airbox with no mods to the bike it should only be standard xt350 lean as they all are from the factory.

post a pic of the plug up after you run it and we will be able to tell you weather or not you will have to jet it.

  • capn_banks

Posted June 05, 2009 - 02:31 AM

#17

cool thanks
gotta sort another problem first:
at idling speed there is a small pop/clicking noise every 10 seconds or so and maybe after a minute the bike will cut out if not revved.
My bike was doing this worse before because air was getting in through the boot but I have now replaced this.

Check out this video of someone elses bike doing it:

http://s263.photobuc...25052009057.flv

Its from another forum.
Anyone got any ideas?

  • jsnmid

Posted June 05, 2009 - 08:19 AM

#18

Adjust Pilot screw.
Out = richer
Somewhere around 3 1/2 turns out is the norm.
If adjusting it doesn't do anything, check to see if the tip is broken off or the passage that supplies fuel to it may be clogged.

  • capn_banks

Posted June 06, 2009 - 01:48 AM

#19

is the pilot screw the one that's hiding behind the bracket?

  • jsnmid

Posted June 08, 2009 - 07:05 AM

#20

is the pilot screw the one that's hiding behind the bracket?


Yes, I think we're talking about the same place.
It's on the front side of the float bowl. The bracket covers it a little. I ground a little notch in my bracket to make adjusting easier.
Over here they put a little brass plug in the hole so you can't adjust it but it's easy to drill out the plug. Not sure if they do that on your version.




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