FZR 400 '90 1WG Carb Question

[nwdothage]

I have recently bought a '90 1WG. It was a really good deal and I got a ton of extra parts. However, it didn't run well and I figured (wrongly) that I was keen enough to sort the carbs out. The carbs that were on the machine were stamped 3BF, which made sense to me and matched the engine serial prefix. But they had two torn diaphragms and two of the idle mix screws were stripped out.

So, after scouring ebay, I found an identical looking set for sale in nova scotia for $60 and I pounced on them. When I got them, I noticed they were stamped 1WG. Odd, I thought. Also of note was the fact that my original 3BF carbs only have one pilot AIR jet. The 1WG carbs have two at the opening of the venturi. My maintenance manual also lists 2 pilot air jets in the schematic. Other than that, the two sets are identical.

I have been able to assemble one good set of carbs now, but the bike will still not idle correctly. All my jets are the stock sizes and the air mix screws are 3.5 turns out per the maintenance manual. (however, it started immediately and idled better at 2 turns out)

The valves are confirmed to be in spec. It does have a Yoshimura slip on and a K&N filter in the stock air-box. I would think that with the stock 87.5 main jets that it would still start and idle ok, though.

I am really stumped on this. Is it the fact that my two outside carbs (1WG's) have an additional pilot air jet? Is it my pipe and filter? A combination of the two or some other random fact I am missing?

Any help would be appreciated.

Thanks,

Nick

[Evilchicken0]

The main jets don't control the idle or low running.
I have a later type of bike but I use 2.5 turns out, make sure the carbs are balanced and then reset the idle using the adjuster screw, on some bike the adjuster can be a bit knackerred so make sure it's really turning.

K+N filters don't really change a lot, it's more the airbox that restricts, you might lift the needles 1 notch to compesate for the can + filter but that's just a guess you'd be better off with a dyno run to get it spot on.

[nwdothage]

I know that the main jet doesn't affect the idle circuit very much. That was somewhat my point is that even with slightly wrong main jetting, it should still start and idle fairly well, I would think.

My main question is if anyone knows why there would be differences in the two sets of carbs? Is one a Canadian/California model or something?

The body castings are identical between the two sets. The original 3BF set even has a spot for this mystery pilot air jet that hasn't been drilled.

I have synced them and reset the idle to no avail. Would it make sense to block the second pilot air jet on the 1WG carbs and see if it helps?

I may just end up taking it to a shop and walk home feeling like a failure...

[Evilchicken0]

Oh well ....

There are quite a few models of FZR400. Originally they were a Japan market bike and they evolved with Genesis '86/87: FZR400R SP 2TK '87, FZR400R 3en1 '88 and 3en2 '89 - these are the 1WG models. Jap road regulations meant the road worthyness tests were so stringent it was easier to buy a new bike than take it, so the cost of secondhand bikes dropped rapidly which in turn meant they bought up as Grey import bikes.

Meanwhile yamaha decided to officially import some of these bike into the states - which is probably what you bought. These bikes are based on the Genesis but have other bits from later bikes - I think Yamaha were maybe using up some old stock. They did this later than their home market 3EN series about 1990 .... confusing huh ?

Parts of the carbs were also used on other bikes and they could be backward engineered for the earlier engines

3EN2 1WG carbs





The Californian model would probably have had some kind of emission control which could be the reason.

[nwdothage]

I see. Thank you very much for the information. I definitely have one of the american 'genesis' 1WG imports from 1990. It was blue/grey and has the deltabox swingarm and two pot front calipers.

So, basically a carb stamped 1WG could have come off of a genesis, a 2Tk, a 3EN1, or a 3EN2? That is crazy!

I think I will try and block the extra air jet on the two donor carbs and see what happens. Seems like it would be hard to nail a uniform mixture if two carbs are getting more air than the other two...

[FZRRDRZ]

I’ve had a few banks of these in my hand recently, experimenting and swapping parts around...

What I know about ‘em is that the 400 manual lists carb “Type” as “Mikuni BDS32” for all models. However, pages later it distinguish between carb “I.D. marks": 3BF-00 (non Cali.), 3FH-00 (Cali. model).

The manual lists stock component sizing (jets/ needle position/ throttle valve size etc.) for both as the same.

The carbs I just buried under my air box came from a California EXUP model and as far as I can recall, the only thing that distinguishes them from the 49 state model is that on the fourth cylinders carb, mm away from the butterfly valve (closed), there’s a small hole leading to a spigot that exits the carb body, that then turns upward. It’s intended to connect (through tubing that has some kind of inline check vale) to the top of the gas tank.

So, with (almost) 100% confidence, I think all 50 state carbs came stock with identical jetting and a difference between the two (hence, the different I.D. numbers) is the spigot.

(It does seem improbable that emission weary Cali carbs had identical jetting to the others but I haven't seen otherwise… )

[nwdothage]

So, it sounds like my 3BF stamped carbs with the single pilot air jet are the stock carbs for my '90 1WG Genesis. My identical 1WG stamped carbs with two pilot air jets must be off one of the other "1WG" models that found its way to Canada? Wonder why my maint. manual shows both air jets?

I'll try blocking that second air jet and see what happens. Thank you guys so much for the information! Great site!

[willandrip]

Your 3BF models are very close to our 3EN2 models but with a Genesis seat unit/rear plastics from what I can make out.

[Evilchicken0]

They look closer to the Genesis to me, the frame is Genesis not 3EN.

Why don't you just the 1WG carbs complete bet your engine runs on them

[nwdothage]

Running all 4 of the 1WG carbs was my initial scheme. But, as it turns out, two of the idle mixture screws were stripped in them as well...

So, I only have four good bodies out of 8 carburetors. 2 3BFs and 2 1WGs :-/

[FZRRDRZ]

Crud. Ebay can be a gamble sometimes.

Maybe a skillfully set Heli-Coil type insert? (I don't think I've used one that small but I'm guessing their out there.)

Or maybe some kind of epoxy/ JB weld/ aluminum repair goo, hardened around the inserted (fully seated) screws-- something gas-proof that is, that allows you to back the screw out when done.

It shouldn't take much to hold that thing in there as the I.D. threads aren't really holding any weight or serious tension.

[nwdothage]

Here is a picture showing my quandary...

[Evilchicken0]

To be honest, look for another set of carbs.
There might be somebody on here who has a reasonable set