mende21 Posted July 23, 2009 Share Posted July 23, 2009 Hi, I'm about to overhaul my carbs and I'm not sure what main jet sizes to use. The stock jetting for my Maxim is 115 right and 125 left but I can't figure out why the sizes would be different because the engine is symmetric. Even the intake cams appear the same. From what I have read, upping the main jet a size should help a stock bike and I'm not sure if I should try 117.5 right and 127.5 left or just 127.5 for both. A stock Seca also uses a 117.5 and 127.5. All of the 650 carb diagrams I have seen show the same size main jet for both cylinders. Has anyone experimented with using the same main jet on a Maxim or Seca 400? Thanks Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 24, 2009 Moderator Share Posted July 24, 2009 Hi, I'm about to overhaul my carbs and I'm not sure what main jet sizes to use. The stock jetting for my Maxim is 115 right and 125 left but I can't figure out why the sizes would be different because the engine is symmetric. Even the intake cams appear the same. From what I have read, upping the main jet a size should help a stock bike and I'm not sure if I should try 117.5 right and 127.5 left or just 127.5 for both. A stock Seca also uses a 117.5 and 127.5. All of the 650 carb diagrams I have seen show the same size main jet for both cylinders. Has anyone experimented with using the same main jet on a Maxim or Seca 400? Thanks there was two different types of dohc xs400, 36hp and 45 hp you may have the 36hp one. Link to comment Share on other sites More sharing options...
mende21 Posted July 24, 2009 Author Share Posted July 24, 2009 Yes, but the Maxim and Seca 400 use mismatched main jets on the same engine. The left carb main jet is four sizes larger than the right and I don't see how that makes sense. I think I will try one size larger from stock in each carb and see how it runs. The 117.5 main must not be very common because my local dealer didn't have any or even a slot for that size in their inventory. I'll have to try a dealer in the next town today. Link to comment Share on other sites More sharing options...
mende21 Posted July 28, 2009 Author Share Posted July 28, 2009 I found all carb parts I needed and finished rebuilding the carbs last night. It seems to run well now. At least on my illegal midnight rides around the neighborhood (registration and inspection come later in the week). I'll have to get it up to speed to see how the larger main jets work out. FYI Most the carb parts for the xs650 with 34mm carbs will work in the Maxim 400. I bought nearly everything from mikesxs for a lot less money than what the dealer wanted. The only thing different is you don't need the pilot jet plug and you need to cut an extra hole in the float bowl gasket for the big alignment lug on the float bowl. Link to comment Share on other sites More sharing options...
1984maxim400 Posted March 8, 2010 Share Posted March 8, 2010 so really the xs 650 bs34 carb is just like the kogyo xs 400 carb and my main jets are a 125 and a 115 so how much bigger can i go can i put too 135s or a 125 and a 135 or what? ps are they the Large Round Type or small Round Type Link to comment Share on other sites More sharing options...
mende21 Posted March 8, 2010 Author Share Posted March 8, 2010 so really the xs 650 bs34 carb is just like the kogyo xs 400 carb and my main jets are a 125 and a 115 so how much bigger can i go can i put too 135s or a 125 and a 135 or what? ps are they the Large Round Type or small Round Type Yes many of the parts are interchangeable. I had to replace both of the slides and the dealer wanted $200 each. Mikes had them for the xs650 for around $60 and they pop right in. I tried one step larger on the mains. 117.5 and 127.5 It seems to run well without any bogging. If you modify the exhaust or intake you might have to go bigger. I believe the mains are large round (if I am remembering the right bike). Link to comment Share on other sites More sharing options...
dtmf Posted March 9, 2010 Share Posted March 9, 2010 i have my main's set @ 130 both side's . i also have custom pipes and pod's . when i ran with the off set carb set up like stock the side with the lower jet size was way lean . i also have used mikesxs for alot of part's for my 82 seca xs400 Link to comment Share on other sites More sharing options...
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