1977 GS550 fuel screw.

[Guest]

Hello,
I've been fighting with my GS carbs which have both an air adjustment screw on the airbox side and a fuel adjustment screw on the engine side.
I've found that the PO (boo) had broken the fragile tips off of the fuel adjustment screws and then epoxied the holes for them closed in the carb throats.
I'm interested in finding out if:
A) the air adjustment screws have the range to tune without the fuel adjustment screws;
B) I need a new set of carbs.
Thanks in advance.

[Nessism]

The broken tips can be extracted. Basscliff's website has a tutorial. Basically, use a pointy tool to push them out from the carb throat side pushing backwards.

[Agemax]

The broken tips can be extracted. Basscliff's website has a tutorial. Basically, use a pointy tool to push them out from the carb throat side pushing backwards.

Thats gonna be tricky if the holes have been epoxied.

[Guest]

Thanks guys,
I've since removed the goop over the holes and while the needle tips had been previously removed,
I see that the holes are distorted and not the same size as each other, like the PO forced the the broken tip through the wrong way, eg. from the needle side to the carb throat side.
I have no idea if replacing with new needles will even be tuneable.

[Nessism]

Thats gonna be tricky if the holes have been epoxied.

You're right. My bad for not reading the first post closely enough.

Some heat can help remove the epoxy in the accessible passage where the screw is, but the feed passage from the pilot circuit may be plugged. The brass balls installed during manufacture of the carb bodies can be removed to clean the passages but this is serious rabbit hole stuff. Personally, I'd at least try.

[timebombprod]

Just see what you can do with tuning them before getting another set, that's pretty rough what that owner did.

I

[Guest]

The good thing is that I got it for a song because of this problem.
Apart from the carb problem it's in decent shape.
I read the carb tutorial but I still don't know why these have both an air mix adjustment AND a fuel mix adjustment.
All of the carbs I've done previously have had only one or the other.
I don't know if the distorted/oversize holes will allow the fuel mix needle to function properly and I also don't know if the air mix needle has the range to do it alone.
I'm appreciative of your input so far, folks!

[timebombprod]

Dont have a clue about VM carbs that is pretty odd to have both, might be an advantage with the issue you have

[zed1015]

I read the carb tutorial but I still don't know why these have both an air mix adjustment AND a fuel mix adjustment.
All of the carbs I've done previously have had only one or the other.
I don't know if the distorted/oversize holes will allow the fuel mix needle to function properly and I also don't know if the air mix needle has the range to do it alone.
I'm appreciative of your input so far, folks!

All the Suzuki VM's have both air and fuel mix screws ( The Kawasaki versions have either one or the other).
With the holes blocked and only the air screw functioning they will act like the Kawasaki versions and you will be able to adjust the pilot mix enough on the air screw.
Even with the holes enlarged and new fuel screws fitted you should be able to get them the function unless the holes are severely distorted and the screw taper doesn't seal the hole.
If they do seal it just means the screws will sit deeper in the hole when fully closed and won't need to be set as far out to get the same mix ratio as normal.
This is because with the holes being larger it will need to be opened less turns to allow the same flow rate of fuel.

[Guest]

Thanks for that golden nugget!
I couldn't see why just one or the other shouldn't suffice.
If I may, what was the reason for the dual setup?
Would I be far off if I were thinking emissions?

[timebombprod]

Would I be far off if I were thinking emissions?

That's a real good question I want to know aswell but it definently could be. I noticed the pilot size on the old bikes are more than half as small as the ones on the cv carbs.

[zed1015]

Would I be far off if I were thinking emissions?

Yes! the carbs were set lean for emissions.
The fuel mix screws were set at the factory and capped which is why they are marked as "pre-set" in all non factory manuals.

[Nessism]

I'm curious to learn if the bike will run properly with the pilot fuel system blocked off. There have been guys here in the past who have struggled to get their bikes to run properly only to eventually realize there were one or more fuel screw tips broken off in the carb bodies. Yes, KZ version VM's don't use both screws but could it be the passages in the carbs are sized knowing this?

[xkaes]

The GS550 carbs are set at the factory for emission purposes. The Clymer 1977/1978 GS550 service manual (I recommend it) warns against adjusting them, but then goes on to tell you how to adjust them. You basically screw in the air screws all the way and then turn them back out two turns.

carbs550cc.jpg

I hope the previous owner didn't mess things up too badly. I've read about various ways to remove epoxy -- assuming it is epoxy. I've never tried any removal method -- and it might depend on the type of epoxy.

[Guest]

Thanks for the interest!
I'm done wrenching for the week but I'll keep you posted once the fun and games begin again on the weekend.