Restricted XS400 DOHC 1983

Martis

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Thank you all for the answers on this topic over the years
To summarize:
De-restricting Yamaha xs400 DOHC
1. Intake Boots marked 20KW on the edge replaced with Boots marked with 12R.
2. Jets changed to: #127.5 on the left, and #117.5 on the right for your mains, #35 for your starter.
3. CDI/TDI unit: from TID12-08 12F-10 to TID12-07 12R-10 (red plate)
4. Camshaft - Restricted cams are marked "F"

Everything marked with F (cams, ignition 12F-10, carburetor joints) is from restricted model.

Restricted intake:
k3979f.jpg

intake-jpg.17468



Restricted cams are marked "F"
cams.jpg


And 45HP cams has 2mm higher lift (left 45HP, right 33HP)
cams2.jpg



CDI/TDI:
tid12-07-jpg.18098


Restricted CDI/TDI:
tid12-08-jpg.18099


Possibly only difference is this resistor:
ignition.jpg
 
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yeah, in europe you can't ride with a bike over 33hp (i think) for first two years you have your license, so yamaha restricted some xs400's just for that. I'm trying to find out where the restriction is so i can take it off to get more power :)
 
It's a similar principle to that of graduated driver's licence.
One way to do it is to buy a small bike, like a 250 which has less than 33 hp to start with and then move to a larger bike in 2 years or whatever. That's the advice I got and followed, however, it wasn't compulsory that I do it - I could have started off on a 6 cyl GoldWing.
The 2nd way is to buy a larger bike but have it de-powered for 2 years until you graduate. Nowadays they seem to be able to do it with a 33 hp electronic Engine Control Unit. "Back in the day", they likely did it with a restrictor plate to limit the intake.
Here are some links which maybe some of you can make sense of:
 
Where is it restricted? Thought i'd ask, I know some of you guys should know it. Can't seem to find it myself, is it electrical or what.

Thanks

Update: With some help, i found it.
k3979f.jpg

I don't know if you can see it, but it goes from 3cm on the outside to 2cm in the inside of the little tube thing.

Now i need help with two more things. I need two more of those tubes between the carb and cylinder, if anyone knows where i could get them for cheap, please write bellow.

If i take out that restriction, am i going to have problems with the ECU and the engine not running how it's suposed to? If anyone has any idea about these things, share with me.

Can't thank you guys enough for all this help i'm getting in this forum.

So the tube thing is your carb boot. You can get new ones without a restriction.

I'm willing to bet that your only issue will be that you'll need to rejet with bigger jets. Also available online. If you're keeping the stock airbox, then stock jets are #127.5 on the left, and #117.5 on the right for your mains, #35 for your starter.
 
So the tube thing is your carb boot. You can get new ones without a restriction.

I'm willing to bet that your only issue will be that you'll need to rejet with bigger jets. Also available online. If you're keeping the stock airbox, then stock jets are #127.5 on the left, and #117.5 on the right for your mains, #35 for your starter.

Helped me loads, wish there was rep system on this forum sometimes.
 
Bump: Updated the thread.
If i take out that restriction, am i going to have problems with the ECU and the engine not running how it's suposed to? If anyone has any idea about these things, share with me.
I don't think bikes of this age had anything like an electronic control unit restricting hp. Just the physical restrictor plate you found. Follow B-W's line on this. From all my reading on here, all I know is that every time anything happens around the carbs - even if the boots spring a small leak - the things need re-jetting. That includes changing the air-box, substituting free-er flowing air filters, looking at it sideways ...:wink2:
I noticed, Martis, that you posted elsewhere that you were only 17. I know Norway isn't in the EU (dodged a bullet on that one) so am I right to assume that Norway does not have the same kind of restrictions on what a new rider can ride as do the bankrupt countries?
We wouldn't want to be counselling you on how to circumvent your country's licensing laws. :doh:
 
I don't think bikes of this age had anything like an electronic control unit restricting hp. Just the physical restrictor plate you found. Follow B-W's line on this. From all my reading on here, all I know is that every time anything happens around the carbs - even if the boots spring a small leak - the things need re-jetting. That includes changing the air-box, substituting free-er flowing air filters, looking at it sideways ...:wink2:
I noticed, Martis, that you posted elsewhere that you were only 17. I know Norway isn't in the EU (dodged a bullet on that one) so am I right to assume that Norway does not have the same kind of restrictions on what a new rider can ride as do the bankrupt countries?
We wouldn't want to be counselling you on how to circumvent your country's licensing laws. :doh:

Norway has the same restrictions. Have to ride a big bike with maximum 33 hp for first 2 years and then no restrictions.

I, however don't give a crap about this law because my seca de restricted makes 42 hp ( i think) and cops wont even notice it.
 
Hi Martis,

This is an old thread but i will try..

how did you finish ? i am dealing with the same issue. I own the restricted version.
I suppose 3 thing are different

1. manifolds
2. carb jets
3. camshaft

I am not sure about the camshaft ? can you confirm?
 
I'm also dealing with derestriction of my bike (12E)
I'm half way there :D

On restricted version the exhaust camshaft has marking (E) engraved.
Also Check your ignition module. There are two versions available.
 
Found old pictures from my archive.
As you can see 12E intake boots are very restrictive.
Also the best performance upgrade was the ignition module swap (plug and play). With restricted module engine was really struggling to rev high enough.
After swap, engine easily hit 10k mark at load and was pulling strongly through all rev range (you'll have to check you jetting though).
Also there are two versions of timing keys (with one hole and two). I have not found any information regarding these and if they are different.

Hope this helps :)
 

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