Jet weirdness

I was cleaning the FJ600 carbs and one of the main jets went missing.

I went looking at the parts diagram and it states the jets are either 105 or 102.5. Doesn't say what determines which is installed. However, the jets I have are marked 160. The 550 carbs are supposed to have 112.5 jets, but the ones I have are marked 165.

I am fairly certain these are all original, due to the amount of crust and the fact that both sets of 550 carbs I had were the same.

I am thoroughly confused.

 

Re: Jet markings

I think I just figured it out.

The main AIR jet is supposed to be 160. I guess the guy who stripped the carb screws before me mixed up main jets and air jets.

 

Re: Jet markings

About the two sizes of mains for the 600: According to my book, and Len's listing for the Eurospec '84 550L that also used the BS32 carbs, the 105's go in #1 and #2; and the 102.5's go in #3 and #4.

I'm not sure that's right, it may be a "transferred error" like the 650 Seca intake valve clearance thing.

I would think that they'd go in pairs of 1/4 and 2/3, since the inner two cylinders run hotter than the outer two.

More research is in order. But both sizes are used on the bike.

 

Re: Jet markings

+ 1 on Fitz's recommendation. The inner two cylinders #2 & #3 will use the 105 main jets. #'s 1 & 4 will use the 102.5's. The 160 pilot air jets go in the air intake horn on the back side of the carbs, where the air box boots attach. The main air jets are fixed and are not removable.

There are actually two reasons for the staggered main fuel jets:

1) The inner two cylinders on an inline 4 engine will not get as much cooling air flow, so running a slightly richer mixture with the larger jets will aid in cooling those.

2) There's more air volume from the airbox that feeds the center two cylinders when a stock airbox is used. That creates the need to richen the mixture for those as well.

I have them staggered on my water-cooled X for both reasons stated above. There may be the slightest variation in power output from each cylinder (barely detectable, if at all). Definitely good insurance to set up your main jets with a stagger as to not to lean out the center two and burn up your engine.

Tony

 

Re: Jet markings

Given the messed up screw heads and the crappy cleaning job (emulsion tubes ranged from half-clogged to full clogged) I'm not particularly surprised.

I am surprised he pulled the main jets, but didn't clean the tubes...

 

Re: Jet markings

The TURBO bike also has "inner-outer" jetting.

 

Re: Jet markings

Guess the PO didn't go to the "Church of Clean".

Good point TIMEtoRIDE on the 650 Turbos, as they had staggered mains from the factory.

Tony

 

Re: Jet markings

According to our info, the FJ600 models used:

#102.5 is used on:
FJ600 California models

#105 is used on:
FJ600 non-California models


The parts diagrams can be confusing on models that have 49-state/California versions of the same bike; even though you click on the (for example) FJ600L model bike, when you get to the carbs folder it will actually list the parts for both the 49-state (FJ600L) and the California (FJ600LC) models. That is why the both the 102.5 and the 105 sizes are listed.

 

I went back and checked all the jets. I am now more thoroughly confused.

All the air jets are 160.

AND all the main jets are 160.

That should be way oversized. Maybe someone was messing with two sets of carbs?

Looks like I should be getting some 105 jets to make this right.

 

This means progress is being made.

The don't call them "previous owners" for no reason........

 

That is true. This was a lucky break. If I didn't lose a jet, I wouldn't have gone checking them all, and I would have probably spent weeks trying to get it to run right.

For sure...

 

That's why it's imperative to check and verify everything on your machine.

Never trust what a previous owner did, or says has been done.

While you're at it, you may still want to stagger the main fuel jets for the reasons we stated above. I would go a size up on the outer two, and drop in 107.5's if your close to sea level.

Tony

 

Personally, I WOULDN'T stagger them unless I found documentation that it was factory set that way......


Dave fox