Top end tear down?

The photo in your avatar suggests the bike is modified with at least an exhaust system. What other mods have been performed on the bike? Pod air filters maybe? My point is by modifying the bike you have changed the engines needs in terms of the carb jetting. Have you rejetted the carbs and if so, what did you do? Have you properly cleaned the carbs by completely breaking them down, replacing the old and hard O-rings? The '77 VM carbs have a pilot fuel screw on the bottom, and adjusting such a screw open more than 1 turn will result in a very rich condition just off idle. The tips of those screws are very pointy too and often people turn in the screws and jam the tip into the body so tight that they break off. A full review of the carbs is in order unless you can positively speak to these issues mentioned here.

Thanks for the tips, will take note.

BTW, cycleorings.com sells a VM O-ring kit. Don't waste money on "carb kits" which are full of inferior aftermarket carb parts compared to the original Mikuni parts. If you need rejetting anyway that makes "carb kits" doubly a waste of money.

The Bike had a 4 into 1 pipe and pods on it when I bought it. The guy that I bought it from said he had a guy " do the carb work" I guess he meant rejetted. I tried to contact him but no dice. The carbs were cleaned and all the rubber rings seemed good. I adjusted the pilot screw out 1 and a half turns. The pilot screw is on the engine side of the Float bowl, does that mean to screw in for richness, out for leaness. Thanks

No, out for rich, in for lean.
Steve
jetsrus.com/carburetor/a_carburetor_parts_selection.html

swest wrote: No, out for rich, in for lean.
Steve
jetsrus.com/carburetor/a_carburetor_parts_selection.html

I thought it was the other way around when the mixture screw was on the engine side...?

they meter the fuel not the air.
Steve

missionkz wrote:

swest wrote: No, out for rich, in for lean.
Steve
jetsrus.com/carburetor/a_carburetor_parts_selection.html

I thought it was the other way around when the mixture screw was on the engine side...?

If screw is on the side towards the mouth of the carb it's an air screw and in for rich, out for lean.
If directly under the carb close to the engine side of the float bowl then its a fuel mixture screw and out for rich, in for lean.

According to the parts fishe the pilot screw is underneath the carb, not on the side. The underside screw is a FUEL screw, when the screw is on the side of the carb it's an AIR screw.

Realize that this pilot adjustment is just for minor tweaking of the mixture at idle and just off. It is NOT for adjusting mixture through the majority of the bikes running range.

Since the bike has pod filter and a header it's critical to pull the carbs and take an inventory of all the jets (pilot and main, as well as check the needle position), and then adjust as needed. Simply trying to tweak the pilot screw to fix the bike is not advised since you are just guessing. Get the jet numbers and then go from there.

I`m pulling the carbs this weekend, will let you know what the numbers are.

The air screw only works in the lower parts of the adjustments. Past a certain point, it becomes ineffective. The fuel screw is a little better. Both depend on the correct size pilot jets.
Steve

The main jet is 117.5 and the pilot is 17.5. the needle is on notch 3.