FZR600R 1994, Keihin carbs, vacuum ports and balancing screw

[Dibnah]

Greetings all,

The idle on my 4HJ engine was smooth enough several thousand miles ago, it has got gradually rougher, engine speed seems OK at about 1100rpm, not hunting but it's not idling smoothly. Runs well above 3k rpm, generally starts OK hot or cold.

New plugs fitted recently, not much better. Now looking at balancing the carbs, which are marked as Keihin, so probably 34mm CV carbs. Tank and airbox off, I can't easily see vacuum ports on the carbs and I can only see one balance adjustment screw on carbs, that's between carb 2 and carb 3.

Do these carbs have vacuum ports? I was expecting to see a male spigot on each carb bore (engine side) like this (Keihins on a Triumph):



Can't easily see spigots and can't feel any spigots, although poor access. I have an airflow meter somewhere which I've previously used on multi-choke Weber carbs, so it will be better than nothing.

I can see one balance adjustment screw on carbs (between carb 2 and carb 3) , is that the only balance adjustment screw? In which case I can probably adjust by ear.



Valve clearances are overdue for checking, so if balancing doesn't fix the problem then that's probably the next step.

[vashtsdaytona]

you gotta help me out, I am not the best at remembering chassis/engine numbers 4HJ

So that is not the motor for the 94 FZR but was transplanted from some era YZF? Please clarify that and I can help you

[vashtsdaytona]

yea yea, thats YZF.... I think whatever its been a while

yes there are vacuum ports 1 per cylinder, in typcially setup they have 4 hoses coming off them, that run to the inside of the frame and clip in, they have caps on them. you remove the caps and hook up to vacuum gauge. the hose nipples are on the carb boots. maybe you are not using yzf boots and what you have dont have them? looking at parts diagram for 94 fzr it doesnt look like they do.

there are 3 adjustment screws, 1 between 1 and 2, 2 and 3, 3 and 4.

id suggest you look at ebay for carb pictures for reference.

https://www.ebay.com/itm/274802286675?h ... ition=3000


https://www.ebay.com/itm/402312432928?_ ... ition=3000

[Dibnah]

Thanks for the replies. I'll get back to the bike at the weekend and then post on here.

[Dibnah]

There are indeed 4x extension hoses from the concealed vacuum ports, thanks vashtsdaytona, 3 of which are blocked off by plugs, the 4th goes to the vacuum tap on the petrol tank. I still can't obviously see balancing screws for each carb, but - with a camera - I can see what might be shrouded pilot screws.



Diagram for a Keihin CVK40 carb (not my FZR) showing pilot screw, I've not adjusted any of these screws on my FZR until I'm certain about the function



Gauges after adjusting the central balancing screw, not perfect but much more rideable now at low rpm:

Edit: postimage or the website settings chopped the 4th gauge out of the image, trying again rotated by 90 degrees

[tuning-forks]

The balancing screws are all in the linkage, like the one in your first post.

[ATTACHMENT NOT FOUND]

[Dibnah]

Thanks tuning-forks.

Looking again at the photos of my bike's carbs, I think that the balance adjustment screws for carbs 1-2 and carbs 3-4 are probably concealed behind flexible hoses. The bike is back together again now, so I won't know for certain until the tank is removed again.



Was the FZR600R sold in the US? It was sold in the UK 1994 - 1996, Foxeye headlights being a visual difference to other Yamaha 600s with fairings, superceded in the UK by the YZF600R Thundercat, preceded by the FZR600

From various websites:
In the UK:
FZ600 air-cooled, 1987 - 1989(ish)
FZR600 liquid-cooled, claimed 89/91 bhp, 1989 - 1994
FZR600R liquid-cooled, claimed 98bhp, 1994 - 1996
Thundercat YZF600R, liquid-cooled, claimed 100bhp, 1996 - 2003
R6 (or YZF-R6) introduced 1998

From various websites, appears that my FZR600R is fitted with Keihin 34mm CVK (or CVKD) carbs, the FZR600 apparently uses 32mm Mikuni CV carbs, the YZF600R apparently uses Keihin 36mm CV carbs

[vashtsdaytona]

yes they are under the vent hoses

[tuning-forks]

Was the FZR600R sold in the US? It was sold in the UK 1994 - 1996, Foxeye headlights being a visual difference to other Yamaha 600s with fairings, superceded in the UK by the YZF600R Thundercat, preceded by the FZR600
...

FZR600R liquid-cooled, claimed 98bhp, 1994 - 1996

The foxeye for those years in North America was designated YZF600R. We try to always specify 'foxeye' on the forum to differentiate them from the 'cyclops' version.
The 'Thundercat' branding was not used in North America.

[Dibnah]

Thanks tuning-forks and vashtsdaytona.

A couple of hours riding on backroads yesterday, the bike still runs well at 53k miles.