:: Yamaha Virago XV Forums That Rock!!! Tech Help Very slight bottom end bog, skipping (SOLVED)

#1:  Very slight bottom end bog, skipping (SOLVED) Author: shmalphy Post Posted: Tue Jun 15, 2010 10:58 am

I have my bike running pretty good now. I am trying to get the carbs as perfect as possible.I adjusted the vacuum pressure using an oil manometer and the pilot circuit with a colortune plug. Both seem perfect but there is a very slight bogging and skipping that occurs when the throttle is slightly open. It goes away completely after 1/4 throttle. I have the pilot screw adjusted pretty far out on the front cylinder, so I am thinking I might benefit from shimming the needle.

Also, I am trying to learn her language. It seems at idle to 1/4 throttle she makes a humming noise, and when i get to 1/4 throttle, it changes a loud rapping noise. This is from the larger stream of air/gas that is introduced from the main, and is normal right? I also get a slight decel pop, is that normal as well? I know the first gen carbs have their flaws, so I have been thinking all of these things are normal for them, but I just want a second opinion.

Last edited by shmalphy on Sun Jun 20, 2010 1:25 am; edited 1 time in total

#2:   Author: coalstoves Post Posted: Tue Jun 15, 2010 11:59 am

You may benefit more from cleaning the pilot circuit of the carb (The decel pop's the give away) . 1st Gen has a removable pilot check the size and see if you can go a size bigger early V-gos were stingy with the pilot circuit .

Read somewhere that 1st gen Hitachis do not work in single carb setup .

Also check the condition of the screens in the tank and confirm the float levels using the clear tube method . Adjust the pilot screws to proper settings and synch again check the petcock function and adj the valves before resync, sounds like your close all but for a dirty pilot circuit.

#3:   Author: shmalphy Post Posted: Tue Jun 15, 2010 12:39 pm

ok sounds good. I don't have a single set up i got the stock duals. I will run some seafoam and see if that helps.

another hypotheseis is that the slop in the linkage is causing it. It idles with even pressure because I used the adjustment screws on the sides of the carb to adj at idle, and the screw in the middle to adjust at 3000 rpms.

#4:   Author: shmalphy Post Posted: Tue Jun 15, 2010 8:53 pm

I added some seafoam and topped it off with Shell 93 Ultra then took it out for a 40 mile ride. I had been using 87 octane. I was doing a lot of engine braking to really work the seafoam through. It seemed to help the decel pop, but there is still another problem.

When I try to go along at a steady pace, at about 3000 RPMs just below 1/4 throttle (which is where I spend most of my time cruising) I get uneven power, and cutting out and popping. I can roll on the thottle and get pretty even response if I do it quick enough but it just seems to fart along as I cruise, or if I roll on the throttle really slow.

If I open the throttle wide, it runs really well with smooth power through the RPM range, but that is just gonna get me in trouble.

I have checked for vacuum leaks many times, and can't seem to find any. I also checked the battery tonight it was 12.8 before I started and at idle and 14 when I revved it up.

One thing that I just remembered is that there was a bunch of black junk in my carb last time I took it off that was coming from the air intakes. I took out all the rubber and cleaned it, but I think there might be something in the frame making the air filthy. I think it is because I used so much starting fluid trying to start it when I first got it.

I am gonna check the carbs tomorow and see if they are mucked up. If so, I am thinking of going with the forced air intakes, should be a cheap mod with a couple UNI filters.

#5:   Author: coalstoves Post Posted: Tue Jun 15, 2010 10:42 pm

A Lot of Viragos wont even run with the air cleaner off, the mod you are describing will amplify your problems and possibly prevent the bike from idling without rejetting the carbs, keep in mind jets sizes are limited for hitachis and can be expensive .
Your new description still has me looking at the pilot circuit maybe even more so now.

#6:   Author: shmalphy Post Posted: Wed Jun 16, 2010 7:49 am

Keep in mind, I still have seafoam in the tank. I will let that run out and see if it persists.

I saw Bykrmom do that mod, and it seemed simple. I will try to find it the link later.

#7:   Author: shmalphy Post Posted: Sun Jun 20, 2010 12:33 am

well I figured it out I think. I had the colortune plug in and saw that the back cylinder fires intermittently. While looking at it I realized there were flames shooting out the exhast gasket. Well there is the problem, classic decel pop caused by bad exhaust gasket. I will mark this as solved for now, even though I haven't even ordered the part.

I just got back from a 200 mile ride to Laconia, even though I knew I prolly shouldn't ride it like that, I had to get to my first rally on a bike. It was great, made it home safe, can't ask for more. Tech Help Very slight bottom end bog, skipping (SOLVED)

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