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Pilot Jet Question

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

Anonymous

Guest
Today I was installing a new pilot jet from one of my carb kits, screwed it in a little too tight, it broke in half. Fortunately I was able to remove the stud in the carb with a precision screwdriver. I am going to use one of the old pilot jets in place of the one that broke, the only thing is that it is 22.5 and the new ones are 15. Will it make a big difference to use 3 that are 15 and one that is 22.5? If so, would I be able to compensate for the difference by adjusting the pilot air screw and pilot fuel screw for that carb differently? I don't want to invest any more money in this bike, and don't want to take too much more time.
 
jets

jets

That is too big a differance even adjusting the air screws. Try and get a new one.
 
What kind of carb kit did you get? If the stock pilots are 22.5, I'm not sure how well your bike will run with 15's unless they're a different make of jet that uses different sizing.
 
I got Keyster carb kits. Anyone know the stock pilot jet size for the '77 GS750?
 
I'm assuming the keyster carb kits are going to use Mikuni jets. The only other company that I know other the Keihin that makes jets (for their carbs) is Dynojet and they're sizing is different but the only kit you're going to find those in is a Dynojet or K&N jet kit. I would find out what the stock pilot jet size is and stick with those and very rarely are you ever going to need to go smaller, especially three sizes.
 
Quite often, the new jets in the carb kits are the wrong size, as you've found. Caveat emptor. The carb needles are usually crap, too.

Clean and re-install the original jets if possible. If not, buy new ones in the correct size -- they're very cheap.
 
The original pilot jets in your carbs were 15s. If you run pods/aftermarketpipes, you could probably bump that to 17.5. The 22.5 pilot jets are WAY too big. What main jets did they include, if any? Did they put jet needles in the kit? What jet needles? Unfortunately, they (Keyster) doesn't use Mikuni's jet needle codes but I know some of them.
 
Your stock pilot jets are 15. Your pilot fuel screw (underneath) assists the pilot jet in regulating the mixture. If you need to richen the pilot circuit, you can adjust this screw out to about 3 1/2 turns before its effective range ends. If you're still lean at that point, you need a larger 17.5 jet.
With pod/pipe mod's, these screws are generally 1 to 1 3/4 turns out.
On a stock bike, these screws are generally 1/2 to 1 turn out.
 
How do you know the stock pilot jets on a '77 GS750 are 15? I did some research on the internet after I posted the question and found a site with technical information on the GS750 that said the stock pilots are 22.5. I am going to go to the library today and look at the service manual there to see
if it says what size the stock pilots are. I don't really trust it though because it is not a factory manual. Anyone have a factory manual that can provide this information?
 
I think all the 750/850/1000 VM carbs have #15 pilot jets.
You could post a new topic here asking for this info.
 
Re: Pilot Jet Question

I bought new mikuni jets from my local dealer about two weeks ago. They cost $2.35. Instead of trying to make something that is wrong work, why not save the hassle and spend the two bucks.

Earl

medicinalmotorcycle said:
If so, would I be able to compensate for the difference by adjusting the pilot air screw and pilot fuel screw for that carb differently? I don't want to invest any more money in this bike, and don't want to take too much more time.
Click to expand...
 
Because I have rebuilt the carbs on an original owner, all original condition 77 GS 750E and a 79 original condition 750E. :-)

Earl

[quote="medicinalmotorcycle"
How do you know the stock pilot jets on a '77 GS750 are 15?
 
Its not that I'm trying to save a couple of bucks, I just wanna have whatever the factory originally put on the bike. If it originally came with 15,
then I'll spend the $6 for a new one. If it came with 22.5, then I'll use the old ones. As far as I know, Suzuki did not make a GS750E in 1977, just a GS750. Anyhow, thanks for all the advice, still looking for a factory manual in the meantime.
 
Somebody out there must have a parts manual and can give you the right jet #. I suggest you go to http://www.zedder.com and order a parts CDROM.

My 850G takes a #40 pilot jet as standard. For now, why don't you use the original jets, and find out what you need?
 
OK, thanks, I called up the dealer, they looked it up on the microfiche and said it said pilot #15, so that website I was looking at must have been wrong unless the jetting is different for a '79 GS750L, that is what the specs were for. I'm wondering if maybe the previous owner changed the jetting on my bike to compensate for the Kerker 4-1. It had #22.5 pilots & 97.5 mains, now it will have #15 pilots & 102.5 mains
 
Very likely the PO went to larger pilots to compensate for the 4 into 1 pipes. I did to eliminate the exhaust popping with my bike, and it did it with the stock mufflers.
 
Be sure you have the correct length pilot jets. There are 2 lengths.
Your carbs use the longer (1 1/8") ones.
 
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