Virago Carb Diaphram radius

[fazil]

Hello everyone.

Today i just changed my 1992 virago 250 cracked carburator intake manifold with a new one. I also had a spare carburator that i've bought from ebay Uk long time ago, i don't remember if it was for a virago 250 or 125 but i thought they were similar and i cleaned it all and decided to install that instead of the original one. But then i realised, the main needle diaphram diameters (metal cylinder radius i mean not the diaphram itself) are not the same.
The spare one was 2-3mm smaller than the original. Main needles looked similar to me.

Then i put on the spare one and it fired up after a couple of tries. And i guess this spare one runs the engine better than the original. I'll try it on the highway tomorrow.

 

[TownsendsFJR1300]

The diameter of the NEW slide is 2 mm's smaller on the replacement vacuum slide?

How's it idleing?.

I'd keep a real close eye on the spark plug.

With that extra play on the sides, you'll have more air being drawn in thru the sides vs with the slide up. Not alot but without the slide opening, the needle sticking down into the main jet is NOT allowing more fuel in(until the slide rises)

You do still have a throttle butterfly after that, I'd pay real close attention to any detonation/leaness, etc.

BTW, the tip of the new one, at least in that picture, appears to me slightly smaller which will give you a richer mixture when at idle and just above idle

 

[fazil]

The diameter of the NEW slide is 2 mm's smaller on the replacement vacuum slide?

Yes exactly very close but 2-3 mm smaller. (the picture is not the exact picture i couldn't take photos unfortunately)
By the way no extra play on the sides, i didn't just switch the slide, i changed completely caburators. The other spare carb bore diameter is also less than the original one.

The idle was very poor with the original carb before, i always had to use choke when cold in warm days also for 10-15 minutes. Now if i still use some choke just after 2-3 minutes warm up, it looses power. That means rich mixture as you mentioned i think.

I'll ride and check it tomorrow then report.

 

[TownsendsFJR1300]

Yes exactly very close but 2-3 mm smaller. (the picture is not the exact picture i couldn't take photos unfortunately)
By the way no extra play on the sides, i didn't just switch the slide, i changed completely caburators. The other spare carb bore diameter is also less than the original one.

The idle was very poor with the original carb before, i always had to use choke when cold in warm days also for 10-15 minutes. Now if i still use some choke just after 2-3 minutes warm up, it looses power. That means rich mixture as you mentioned i think.

I'll ride and check it tomorrow then report.

With the smaller diameter intake runner, sounds like a 125 carb. You'll likely loose a little bit of power overall (like putting a 2 bbl carb in place of a 4 bbl carb but of course not so extreme).


The closest 250 I could find in the US is a 1995 model.;

Yamaha Motorcycle Parts 1995 VIRAGO 250 - XV250G CARBURETOR Diagram

Part #10 is a pilot air screw (idle air screw). To richen up up the mixture at idle (especially cold), remove the cover and turn the screw outwards (CC), maybe an 1/8 of a turn at a time. It doesn't take much..

Part #20, pilot jet also adjusts (its snugged tight, like the main jet, does not adjust like the above) the low speed A/F mixture. Bumping that to a larger, jet will definitly eliminate the cold runnig issue if you can't get enough fuel form the above adjustment screw..

Putting a very thin washer under the "c" clip on the main verticle needle will also richen up the low speed mixture as well. You basically adjusting the needle higher, allowing more fuel to be pulled thru the carb at idle...

Something to consider...

 

[fazil]

I wrote it to Virago tech forum also, looking at the older threads, they say that only difference between xv125 and xv250 carbs are different jets. Nothing about slide bore diameter. Main jet and pilot jets are both bigger for the xv250.

After a ride to work tomorrow, i can think of switching to the old carb.

 

[TownsendsFJR1300]

I wrote it to Virago tech forum also, looking at the older threads, they say that only difference between xv125 and xv250 carbs are different jets. Nothing about slide bore diameter. Main jet and pilot jets are both bigger for the xv250.

After a ride to work tomorrow, i can think of switching to the old carb.

If you can find a parts fisch from Yamaha down under, you ight want to check the carb body part #'s.

One engine is obviously twice as big as the other and yes you can increase the jets. BUT if the carb body is the same, you can't flow anymore air for an engine that needs more air..

I suspect that 2-3 mm difference smaller is a 125 carb (although its not much smaller). If its a Mikuni, it may have a stamping on the outside that states the size/model, ie "34 CV".

Just for S&G's, you may post on there why this carb intake is smaller if they have the same body.

It just seems to me, if its the same excat carb between both engines, then why are your two carbs different sizes.

Also, did you check the jet sizes of each and see if their for a 250 or a 125? That may explain some...

 

[fazil]

First long ride,

The new carb behaves like a restricted carb, after 70km/h.
Small main jet size can cause this i guess.

I couldn't open and see inside of the float bowl side of the original carb because of the seized screws.

 

[TownsendsFJR1300]

First long ride,

The new carb behaves like a restricted carb, after 70km/h.
Small main jet size can cause this i guess.

I couldn't open and see inside of the float bowl side of the original carb because of the seized screws.

If you have a small pair of vise grips, you can usually grab the head of those screws and loosen them. If you want to be anal, you can replace those (now somewhat buggered up) screws with allan head metric bolts

Being their metal srews to an alumium hole, I'd soak with the best penetrant you can find first..

 

[fazil]

I'll replace them if i can loosen.
I tried with pliers but no way. Those philips head screws are very soft.
I'll try with a thin saw to make new screw driver heads.

 

[TownsendsFJR1300]

I'll replace them if i can loosen.
I tried with pliers but no way. Those philips head screws are very soft.
I'll try with a thin saw to make new screw driver heads.

A good pair of SMALL Genuine vise grips should get them loose.

Cutting a notch for a screwdriver likely won't work if it the phillips head screw, already stripped (and you had a good screwdriver and hard grip on the screws).

IME, I would NOT go that route..