No holes in new pilot jets??

[BillyRok]

In cleaning and going through the carbs on my XJ I noticed the pilot jets had zero holes in the side, not the 6 or 8 hole version I'd read so much about. So I ordered new 47.5s from my local Yammy dealer. Picked them up today and the packaging says "Yamaha Genuine Parts & Accessories" on it. Guess what...no holes in the sides of these jets either It wouldn't seem that Yamaha would sell jets for a bike that would cause tuning issues so I'm wondering if these "no holers" will work as well as the "6 holers" or do I need to return these and look else where? And if they will work, why the 2 different designs? Thanks

[TopCatGr58]

And if they will work, why the 2 different designs? Thanks

That's Yamaha for ya! Yep, the XJ's pilots are no holed design, they changed the carbs a bit so the pilot circuit gets it's aeration separately, not directly thru the pilot jet, therefore no holes. Enjoy!

T.C.

[DGXSER]

After George sid his evaluation of the pilot jet holes, I opened up the tunnel on a scrap carb body. The air comes in AFTER the jet. So I happened to be talking to some folks who specialize in Mikuni carbs to figure out what is correct for my GSX. They told me those holes create a turbulance in the air flow.

For whatever reason, I know they make a difference in how a bike runs. So I continue to believe it is important to get the right type installed.

[Dan Hodges]

Pilot Jets

That's Yamaha for ya! Yep, the XJ's pilots are no holed design, they changed the carbs a bit so the pilot circuit gets it's aeration separately, not directly thru the pilot jet, therefore no holes. Enjoy!

T.C.

Hi TC it's been a while since I was here but I thought I would share something on this pilot jet issue....I just purchased a set of 42.5 pilot jets part #4Go-14142-42-AO for my 81 Special from my local Yammie dealer and said jets have no so called holes on the side portion of the jet. The jets I took out had no such holes either and I can't remember if the ones before that did or not. I bought my bike new and no ones hands but mine has ever touched the carburetors. I have changed the pilot jets several times over the years and I do recall a set of # 45's having side holes but I can't say for sure if any of the 42.5's I took out had side holes or not. I've got the original PJ's somewhere in my stash and I'll dig them out when I get some time. The pilot jets are a pain and I don't even try to clean them anymore, I just replace them every two years when I clean the carbs. I have Dyno-Jets stage 3 jet kit, K&N pods along with 3.75 inch neoprene extensions (velocity tubes) between the carburetors and pods. This year I had to buy a new gas tank as the original developed a leak and gave up the goast. Luckily I found a NOS tank at Donelson Cycles here in town and I snagged it for a small fortune.

Dan

[TopCatGr58]

Hey there Dan,

Yeah, I noticed, but it's nice to see you're still around even if it's mostly in lurking mode! George(GloweVa) had done some experimenting with the pilot jets, the circuit and the pilot AIR jets, and where the air got into the mixture in the carb bodies, and found that the air came into the carb bodies on the later model carbs AFTER/downstream of the pilot jet towers/holes, he has a G and SG model. I loaned him a bank of the 79 carbs to test this out, but we theorize that the air mixes IN the pilot jet tower and that's why the pilot jets have side holes. But the later model carbs don't necessarily need the pilot jets with the side holes because they mix the air after the pilot jet, and your comments about your carbs WITHOUT the side holes confirms this theory.

Also, MikesXS.net web site mentions that the pilot jets you receive from them may also not have side holes and are not needed, but I think that would depend on the year of your carbs.

Note: BS 30/96 type Pilot Jets WITH Side bleed holes
holes and those without side bleed holes are
completely interchangeable.

Yet....all of their photos of the BS30/96 pilot jets are shown with sidebleed holes!?

What's also a bit curious is that I just looked at the microfiche for the 79F carbs pilot jets....they are NOW listed as Unavailable from Yamaha, but the same sized pilot jet albeit with a different prefix # are listed as still available, and I think that is the ones that folks have stated they've gotten from Yamaha and do NOT have the side bleed holes!

79 F: 256-14142-42-A0 JET, PILOT #42.5 Not Available

81 H: 4G0-14142-42-A0 JET, PILOT ( 42.5)

Still think some more research is needed with regards to the pilot jets, whether the side bleed holes are needed or not in the early model carbs. But we do know that the K&L brand of jets are the wrong ones moreso because their gauging of the metering orifice isn't the same as Genuine Mikuni jets, and the overly rich problems folks have had with them is probably due to that metering orifice and not so much for the # of side bleed holes.

T.C.

[GLoweVA]

I've been running 2 of my 4 pilot jets on my SG with 2 of the 'normal' 6 holers and 2 of the 'weird' no holers. She seems to be running just fine and the plugs show tanish in color too.
If I had 2 more of the no holers, I would have put them in too to see if all 4 would run okay, but alas I needed only one and I had 2 so, I put both in to see if it made a difference and I haven't seen any.

I haven't had a chance to look into the loaned '79 bank that TC let me tinker with, maybe this weekend.

Right now I've got another flat front tire, so no riding until bike bandit delivers.