32mm 250 carbs

[Dinger]

Hi there-new to the site so Hello -right I have seen a thread about this,but have not located a sure answer,or if anyone else has completed this....I have a XS250 with 400 pistons fitted. I have replica but freer flowing universal silencers fitted,and s+b individual filters fited to the carbs. But I have 250 32mm carbs(same type as fitted to the 360's 34mm with the jets fitted in the bowl not the roof like the 400's ),so I guess I would be better off guessing the jets closer to the 360's? I can't see 2mm bigger carbs being alot different in flow rate?250 Standard mains are 117.5,pilot jet 20,starter jet 25....360's are 135,17.5,and 40.Float heights are 26mm +/- 2.5mm according to Mr Haynes.....so my guess will be 140,20(250s standard),and 40....any thoughts apart from a can of worms Any help will be apprechiated

 

[Pork Chop]

G'day Dinger, welcome to the forum. Did you get the bike with the 400 bits already installed or did you do it yourself? What has been done to correct the compression ratio? According to haynes, the xs250 valve duration is shorter than the 400. I am just about to do the same thing to my xs250 & I have ZERO experience but I am learning heaps along the way. My gut feeling is to try richer starter jet - 35?
I am very nterested how you go with this.

 

[Dinger]

G'day Dinger, welcome to the forum. Did you get the bike with the 400 bits already installed or did you do it yourself? What has been done to correct the compression ratio? According to haynes, the xs250 valve duration is shorter than the 400. I am just about to do the same thing to my xs250 & I have ZERO experience but I am learning heaps along the way. My gut feeling is to try richer starter jet - 35?
I am very nterested how you go with this.

Hi Pork Chop,yeah I bought it as it is.....but it had been stored 17yrs.....the comp ration is higher on the 250/360 than the 400(9.6:1 v 9.2:1),and although the valve timing is different with the 400,its the same as the 360(I can't see 40cc making sod all difference),and as the pods/silencers are different I am going to have a muck around anyway I have a spare 250 engine too,but I wanna try and get this working first.....is 35 starter jet richer than a 40 starter jet?

 

[eric123]

35 is leaner than 40

 

[Pork Chop]

Xs400 cylinders & xs250 head bumps the compression ratio up to about 13:1. The squish area in the xs250 is almost half the size of the xs400. Have a look at my thread in my sig & you will see how I am decompressing my engine.

Regarding jet sizes, maybe just start with stock xs400 sizes & go from there. I might do that when I have to rejet in a couple of weeks.

I think one of us is going to be the test monkey for the other.

Cheers...

Posted via Mobile

 

[Dinger]

Xs400 cylinders & xs250 head bumps the compression ratio up to about 13:1. The squish area in the xs250 is almost half the size of the xs400. Have a look at my thread in my sig & you will see how I am decompressing my engine.

Regarding jet sizes, maybe just start with stock xs400 sizes & go from there. I might do that when I have to rejet in a couple of weeks.

I think one of us is going to be the test monkey for the other.

Cheers...

Posted via Mobile

oh s*it,13.1 is too high for sure lol.....as it is the motor starts on choke fine,and when warm,ticks over fine-would it do that with 13.1 comp ratio? I haven't ridden it as no chain on it yet and the wiring is being put back together in headlight. Trouble is I dont know if it's a 400 head on there without taking it apart....I only paid £150 for the bike and spare engine which I heard running,so thought that was a bargain. I don't wanna spend a fortune on a bike only worth £600(?) fully sorted,but have spent alot of time getting it looking fairly good(frame blasted at work,painted etc),so it's a personal thing and I don't give up easily
BTW,my other half has a GS125 which I fitted a chinese 150cc big bore kit from ebay,the piston was a different shape,but I gave it a try....and that's a 20% increase in cc,but all the jetting needed was main jet tweeked from 95 to 102.5 and the pilot mixture altered. But I had to lower the jet needle which I thought was going to be the opposite.Its run great for 4k miles now and is quite torquey for what it is,shame the chinky gaskets leak a little(few drops)...

 

[drewpy]

for 13:1 use methanol fuel

 

[Dinger]

for 13:1 use methanol fuel

probably cheaper than petrol over here too

 

[HoughMade]

13:1 running on E85 with a seriously richened carb would be a hot ticket for an XS400...at about 24mpg.

 

[Dinger]

that a US or British gallon? ;-) but at least if I switch to methanol I can drink it ;-)