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carby jet sizes

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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Ive only had my 1977 GS750 for just over 4 months now and today I stripped the carbys down to clean them and replace the needles and seats.

I noted that the main jets are 125.5 and that the manual states 105 is the largest.

It does have a large 4-1 transac muffler on it, but its never been on the dyno. Does anyone know a good jet size to start with?

Also it does have the stupid K&N open aftermarket airfilters but I will shortly be changing back to the original airbox and aftermarket washable filter!

any ideas on jet sizes?
 
For a standard bike with airbox on the mains are 100. On later 2v 750's they went up to 102.5 and changed the needles.
 
Stupid YES:

well the single pod replacements that do away with the original airbox are stupid, they are designed for drag / race bikes only nad they kill engines. after 20 years in bikes Ive seen a load killed by such "open" air filters.

Im doing away with these replacements in favour of the original airbox and an aftermarket washable and oilable airfilter which also stops a load of water being ingested when its raining!
 
REPOST:

REPOST:

Ive only had my 1977 GS750 for just over 4 months now and yesterday I stripped the carbys down to clean them and replace the needles and seats.

I noted that the main jets are 125.5 and that the manual states 105 is the largest.

It also has a very large 4-1 transac muffler on it, and the bike has never been on the dyno. Does anyone know a good jet size to start with?

Also it does have the stupid K&N open aftermarket airfilters but I will shortly be changing back to the original airbox and aftermarket washable filter!

any ideas on jet sizes anyone (that hasnt already answered the question)

I hate forums, you always get smartarses that just have to comment on something, like my stupid K&N filters remark!

Get it together, and either answer the actual questions or just shut up!
 
I have a lot of experience with jetting, especially with the VM carbs.
After your remarks, which you yourself said were stupid, you're on your own.
You're kind of weird to react to my first post the way you did. All in fun.
If you hate forums so much, then leave!
 
fiatlancianivaa said:
Stupid YES:

well the single pod replacements that do away with the original airbox are stupid, they are designed for drag / race bikes only nad they kill engines. after 20 years in bikes Ive seen a load killed by such "open" air filters.
Click to expand...

Gee, all of us running pods with hundreds of thousands of combined miles must all be exceptions, huh? It sounds like you already have all the answers (at least in your own mind). Why are you asking us then? :D
 
your attitude really puts me off helping you as well, i'm sure you would be a lot nicer if you were asking a person in person for help.

if you are useing stock filter setup then go with what the manuel sez, if you don't like forums go talk to a bike mechanic, maybe he will tell you how to fix your bike for free :? .

-ryan
 
Re: REPOST:

Re: REPOST:

fiatlancianivaa said:
any ideas on jet sizes anyone (that hasnt already answered the question)
Click to expand...

Why, don't you believe me then????????? :evil:

Go buy a decent manual then you wouldn't need to come into the forums!
 
Thanks for backing me up, intentionally or not. :)
This guy is way out of line. My first post was never meant to sound "smarta$$". I'm surprised he took it that way.
 
Keith,

Very intentional backup. I was going to mention something like you've forgotten more about VM carbs than he'll ever know. But we all know that already and why waste the time on this guy.

Joe
 
Ok, ive got a few replys within one here:

First, KW, im not saying I dont believe what you said, I just want a few more opinions, but I also dont want the smart arses that have replied with shit that is irrelevant. thank you for your post, I actually printed it for future reference!

As to other comments from others saying ive got a "power kit" installed and other comments,

Well Im sorry for being so rude, I seemingly interpreted the difference from the US language to aussie lingo the wrong way! no other excuses. I was wrong in my doing so!

Anyways Ive just been speaking to a guy I know, he is a 57yo retired motorcycle racer and he assured me that even with the larger pipes, the jets will need to be no larger than 115 (mine are 125.5) and that the pod filters ARE CRAP FOR STREET USE, and that I WILL get more power from the standard airbox USING A K&N washable filter element.

He told me he is so sure that he will even cover the costs of the dyno tune @ AU$75 if he is wrong, so thats a pretty substantial bet isnt it, considering it is generally 2 hours on the dyno, so hes looing at $150 if he is wrong! Who on here is prepared to bet that kind of $$?

Anyways, sorry for my rude messages, and thanks for all the help from those who did help, the rest can keep wasting internet forum time and space!

regards
Andrew
 
Andrew you need to get updated information, I also used to race and the thing that I have learned is that technology has changed so much in regards to so many aspects of bikes that what was true 20 and even 10 years ago does not apply now.

Where are you in Australia, maybe I can direct you to a specialist that can give you better information that you get now.
 
It's so obvious...........

Smaller jets=less fuel

More restrictive intake=less air

Less fuel + less air=more power

What were we thinking?
 
Ok maybe I should clarify a bit better:

my brother followed me on his bike and said he was covered in fuel vapour and that my exhaust is BLACK (unburnt fuel) on heavy accelerations.

Im only getting 160km to an 18 litre tank

He had red eyes after an hour ride and following me.

the bike must be OVERJETTED and I therefore need to change them lower.

Any suggestions please?
 
what exactly does the main jet say DJ 125.5 or does it have a little square with a little square in that with 125.5 next to it.

so did you ride the bike after you cleaned it and is that when your brother was soak in rich gas vapor? what do the plugs look like?

-ryan
 
It could be just a matter of lowering the float level?. 125 jet is on the rich side
 
the main jet only says 125.5 the local useless suzuki dealer said its the size.

The ride was after I cleaned it and replaced the fuel needles, and set them correctly.

The plugs are a moist black in colour!

thanks!
 
Ahh, an Ozzie, I'm inclined to be a bit more understanding. :-) For a four into one, and going back to stock airbox and filter, go with mikuni main jet 115. Stock pilots will be fine. Set the fuel pilot screw to 1 1/4 out. Airscrew about 1 3/4 to 2 turns out. Plugs should burn about a light tan. You may have to raise the needle one notch, from stock. Been there, done that.

Earl

fiatlancianivaa said:
the main jet only says 125.5 the local useless suzuki dealer said its the size.

The ride was after I cleaned it and replaced the fuel needles, and set them correctly.

The plugs are a moist black in colour!

thanks!
Click to expand...
 
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