MachZ carbs on an srx

C

crazykid

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Nov 21, 2004
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WINNIPEG MB
Hello guys, i tried asking a few questions on an old 38TMX post and didnt get anywhere,i should have started my own post in the first place, my mistake. Anyhow i just picked up a set of carbs off a mach z,i checked them out and found 430 mains and 50 pilots, One of my questions is does anyone know the needle clip position it needs to be at? Also i noticed that one of the brass tubes that sticks out of the bottom of carb in the floatbowl was shorter than the other two, Is this normal? Please let me know, Thanks alot.
 
First of all, what modifications are done to your sled? It's pretty hard for us to help you with jetting if we have no idea what you are running. You're going to have to be more specific in what you mean by "tubes". Do you mean the nozzles (your main jets screw into the bottom of them)? If that is the case, they should all be sticking out the same. Actually, everything should be sticking out the same.
 
Ok its a 780 with some aggressive porting, with 155 comp,i was really only asking about the needle clip position, but if you any input on jetting ill be glad to listen to what you have to say, any info that you i get on here is always a help, Thanks. The tubes i am talking about are the little skinny tubes that stick out the bottom of carb, not main jet tube, not pilot jet tube,its a small diameter tube its about maybe 1 1/2 inches long on two of the carbs and about 1/2 inch on the other one. I cant get pics right now but ill try tommorrow. Thanks
 
aren't you the guy that bought that 780 big bore off of ebay, that originally was posted in the classifieds here? also, didn't you get your jetting help and jetting straightend out on this big bore? i remembering you asking for jetting help on this thing before.
 
Yeah thats me but i wouldnt say i got it straightened out, Besides i am now looking for help with a Machz carb on a bigbore, as the title states. THANKS ANYWAY!!
I just want to hear from anyone that has used these carbs on a 780 bigbore, I just want to know the position of the needle clip that is used on a bigbore. Thanks to anyone who replies, and if you feel i am asking a stupid question or repeating myself then there is no need for you to reply, there are many other people that i am sure would be glad to. Thanks again
 
I'm no carb jetting guru but if your looking for a place to start I'd suggest raising the needle up,lower the E clip,so your rich and then use plug and piston wash readings for fine tuning from there.Usually most carbs have the stock setting at the center notch on the jet needle but if your not sure what you need drop at least one notch and look at the readings.Unless you can get a reply from someone with this exact setup I think your in for more trial and error tuning.
Where these are Mach Z carbs your jetting probably wont be that far off as your about the same cc and hp but still I'd say your in for a bit of testing and tuning to get it right.
 
You will either be in the 3rd or 2nd clip position on the needle, and those pilots are probably too big as well. You'll probably end up with 40's or 45's. Of course, this all depends on many variables...........the porting specs on those cylinders, ported cases or not, which pipes you are running, airbox or filters, etc...

Now, that is assuming the brass inside the carbs have not been changed. What brass is even in those carbs? What needles? What nozzles? That will make a huge impact on needle position and main jets.
 
crazykid said:
Yeah thats me but i wouldnt say i got it straightened out, Besides i am now looking for help with a Machz carb on a bigbore, as the title states. THANKS ANYWAY!!
I just want to hear from anyone that has used these carbs on a 780 bigbore, I just want to know the position of the needle clip that is used on a bigbore. Thanks to anyone who replies, and if you feel i am asking a stupid question or repeating myself then there is no need for you to reply, there are many other people that i am sure would be glad to. Thanks again
Click to expand...

wasn't trying to get you upset or anything. just thought you had everything straightened out before and was confused @ you asking the same question again, but now i understand.
 
Well guys, Here's what i have been able to gather up, The mach z carb has for a nozzle, 327 stamped on as well as either a Q4 or O4, and needle 8AGY1-41 the clip is on the third groove with the plastic washer underneath.Mainjet 430,pilot 50. Now the srx is a 780 bigbore with aggressive porting, compression of about 155,no case porting YET, Vforce3 reeds,i will be gutting the airbox as per valin's recommendation to someone else in another post, And ill be running the stock pipes. Hope that helps a little bit. Thanks
 
If they are o-4's, you're in good shape. With those needles and nozzles, clip in the 3rd to start off (and I mean start off......so do alot of plug checks.......we are not responsible for anybody burning their motor down due to jetting recommendations). Also, you'll probably want to install 45 pilots if you have some laying around. If not, try it with the 50's first, and take it from there, but I'm sure you'll end up lower for a trail setup.

You need to do one more thing.....and that is check your compression ratio. If you have aggressive porting specs, and you have 155 lbs of compression, you are going to have to cut your domes larger because your compresion ratio will be too high for pump fuel. If you don't know how to measure and calculate your compression ratio, PM me.

Also, do me a favor and measure down inside the cylinder from the top of the cylinder to the top of the exhaust port, and let me know what that measurement is in millimeters.

Who build those 780 cylinders?
 
OK, Well the exhaust port is 31.40 mm, i measured some other stock bore cylinders i have lying around. They all vary a bit from 31.61,31.72,and 30.40 which is one of a set of ported cylinders i bought off of a justin? guy dont remember. Now these numbers are making me wonder just how non aggressive my BB's are. I dont know?There is pics on this forum if they will help, Under USED 780 KIT. Thanks
 
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Well, I wouldn't call your cylinders aggressive. On stock 2000-2002 SRX cylinders, the ports are 32mm, so yours aren't raised all that much. My exhaust ports are quite a bit higher. Your motor will make good power, providing the rest of the porting was done properly, and from looking at the pictures (although it's hard to tell from looking at a picture), they look fine.

But, having lower port timing would give you a higher cranking compression, so your compression ratio might not be too high at 155 psi. Hopefully your gauge reads high. You still have to measure those heads.

Stock pipes, 11.5 or 12:1 compression ratio, 38's, I'd say you should be in the 165-170hp range, safely, on pump fuel.
 
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