whats the process for removing the float from the bst 40 carb, doesnt have a float pin like the bst 34. once removed, the main jet is the one in center, is the pilot jet the one that is recessed in the hole attached to the main jet tower? i know, stupid questions, but its my first time in a carb. also, when i remove the jets are they under a lot of tension? and when putting them back in, how much do you tighten them? i've got the service manual and so far it hasnt been much help, of course the carb they use for the pics is the bst 34! also, if and when i get this out. if all i do is take the bowl off and not the diaphragm cover, is it ok to spray carb cleanering all in there, or will it damage the diaphragm or anything else. i also have some electric connection cleaner like the manual says use.

 

well bud i can help ya with the jet question and the pilot jet. I was tightenin my main jet in mine the other month and i overtightend it and it broke loose from where it was seated. Hadnt been right since so i bought a new carb the other week and solved al the problems hahaha. As far as the pilot jet yes its the one thats recessed in the hole. Make sure you tune it for where you live. Like mine i had to tighten it an turn it back out 1 1/2 turns. Good luck man hope i helped ya out

 

BST40 float assy just pulls up, o-ring on tube hold in place.Be careful,after pulling up float assy that you dont let needle on float tab fall off and needle valve seat in carb can easily fall out also! Main jet is easy to see its the round slot head,pilot jet is recessed. NOT necessary to remove diaphragm in top of carb. Tighten only until SNUG,dont overtighten! Make sure you can see through pilot jet after cleaning. Compressor and blow gun handy. Dont spray carb cleaner up into diaphram area. Use air blower through pilot jet hole to make sure clean,BE CAREFULL not to blow air through main jet opening with diaphram still in! can dislodge spring and slide needle! You can raise slide with your thumb,while holding pressure on needle itself,THEN can blow air OR carb cleaner through! BST40 a little more tricky than the BST34. Good luck PS electronic parts cleaner actually better,less likely to damage any rubber parts!

 

I did mine on the SP450 with a friend that knew his way around carbs. He was removing things
so dang gone fast I can't tell ya if I would remember. Nothing was hard about it to clean/service
but remembering everything that came off to put back exactly in place is another thing. But that
said, I would do the carb cleaning myself next time and become more of an expert.

OPT, would you recommend the idle adjustment as part of the clean service? We did and it
worked out great, really fine tuned. I was amazed at how easy it was to turn TUNE the thread
screw that the bottom. I would think even with normal riding it turns so slightly, I hadn't touched
it since but after my hardpack trail ride next, I think it will need a few more adjustments.

Is there a chart as to what RMPs at IDLE (Park or Neutral) should be for this 4 stroke carb
quads? Mine specifically the SP450.

R'

 

On the cable mounted idle screws on the BST40 carbs they DO have a problem sometimes of backing off and idle lower, as they get older they can get hard to turn and try to seize up.You can put a small amount of antiseize on threads! Also on many of my service machines the cable support wire breaks and I find them laying down under carb! I Like the old straight idle screws myself,no problems. Idle should be somewhere around 1050-1080 rpms usually. On your spts 450 should have the BST34 with the straight idle screw! Rpms should be about the same.

 

Thanks OPT, good info.!

Regards,

R'

 

thanks for the info guys, it'll be a couple of days before i can try it due to work. hopefully i wont mess things up too bad [img]i/expressions/face-icon-small-smile.gif[/img]