another pilot fuel screw question

[Guest]

i was at a bike night near where i live and got to talking to a fellow GS owner. we got to talking about little problems we've run into and carbs came up. i had told him how much of a nightmare my fuel screws have been and he told me that earlier model (76-77) vm26s did not have a pilot fuel screw just an air screw. he told me that he had simliar problems with several of his GS bikes and just switched to the "old" style carbs and didn't have any problems. is that true that 76-77 did not have fuel screws? sounds a little odd to me.

[BassCliff]

Hi,

The VM carbs have a pilot fuel screw and a pilot air screw. See:

VM Carburetor Rebuild Guide
(Courtesy of GSR and Paul Musser)


Thank you for your indulgence,

BassCliff

[shinzon1]

thats what i thought, but seeing as i've only had experience with my set i just wanted to be sure.

[hampshirehog]

If I remember correctly the very first batch didn't have fuel screws. In fact most VMs (used across a very wide range of bikes) don't have fuel screws.

Here's a link to a diagram of a VM26SC (note the C):

http://www.kentkawparts.com/pages/Oe...9%2f070032B-13

[shinzon1]

but i don't understand how it would get sufficient fuel at idle. i'm no expert on motorcycle carbs by any mean. i'm used to my camaro. it doesn't care how much fuel it gets as long as it gets a lot. I.E. 6 MPG.

[hampshirehog]

The fuel circuit remains the same - just not adjustable via a fuel screw, only the air screw.

[shinzon1]

could the same thing be acheived by simply running the fuel screws all the way in? is the old style still pretty accurate or is that the reason the adjustible screws were added?

[Nessism]

could the same thing be acheived by simply running the fuel screws all the way in? is the old style still pretty accurate or is that the reason the adjustible screws were added?

No, you can not do that.

Those are tried and true carbs, that are easy to tune. If they are properly clean, properly jetted, and the rest of intake system is properly maintained, they should be trouble free. Set the fuel screw to 3/4 of a turn open from lightly seated. Make sure the fuel screw tips are sharp and not broken off in the carb bodies. Set the air screws to 1.5 turns open and the bike will run decently. Tune the screws from there, but you shouldn't need to move them far other wise something else is wrong.

If you have pods or a header all bets are off. In particular, with pods the jetting will be drastically different and require some serious work.

[shinzon1]

ok. thank u. u can probably find some of my other posts on carb issues. mainly fuel screw problems. that is y id love to do away with them. everything has been done correctly, cleaned repeatedly, double and triple checked. yet i still have issues. compression is good and valves r perfect.

[Nessism]

Fuel screws only effect mixture just off idle. Unless that's where your bikes running problem lies, it's not related to the pilot screw settings.

[Steve]

ok. thank u. u can probably find some of my other posts on carb issues. mainly fuel screw problems. that is y id love to do away with them. everything has been done correctly, cleaned repeatedly, double and triple checked. yet i still have issues. compression is good and valves r perfect.

Your keyboard is missing a bunch of letters, too.

Yeah, I'm a grumpy old man, but I am used to reading AMERICAN, not "text".

.

[shinzon1]

yeah. sorry. i was on my phone last night typing it up. my problems are just off idle. i have a surging problem. and cant get rid of it. reguardless of settings. plugs 1 and 4 look great. 2 and 3 are definately lean. but the bike runs great every where else. coil resistance and cap resistance are perfect. i double checked it a while back just to make sure. on a different note. where should the needle clip be? i've seen a lot of different things on that. i currently have mine in the middle position. i've also seen for stock in the 5th(richest) position. i currently have a mac 4 to 2 exhaust and a K&N filter in the stock air box with the snorkel removed.