Vac advance module? Re: Ignitech and COP

[luvmy40]

OK, I'm going to preface this by saying that I am 3 bottles into a sixer of Commodore Perry so any stupidity on my part is all beer, right...

 

My '83 XVZ12TK is running much better now that when I found her but my fuel economy still sucks.

 

She had 2 dead coils and the carbs were in terrible shape. Parts missing, assembled incorrectly. probably typical of a35 year old bike that had been in Bubba's garage for years. The huckster I bought it from really laid it on thick about how he installed performance cams and tuned the carbs for more HP. We've all heard the talk.

 

Having not been hatched the night before, I didn't fall for the hype but I did fall for the Venture in a bad way.

 

Anyway, I replaced the bad coils, installed new spark plugs and wires(the caps and resisters all checked out),did the valve adjustments, cleaned the carbs up and replaced the missing parts(O-rings, washers and springs in the pilot screws and new bowl gaskets), set the floats and synchronized everything. With the exception of a bad life choice in head cover gaskets, everything came up rosy. She runs great and rides like a dream but I'm only getting 29-30 MPG no matter how I ride her.

 

Would float adjustment have that drastic an impact on fuel economy with this bike?

 

Would a bad vac advance(boost) module have any impact?... Is there a reliable test for the vac advance?

 

Any chance this is a CDI issue?

 

Now just be clear, I'm a tinkerer and will probably tackle the IGNITECH and COP mods at some point regardless. That in mind, is there a definitive DIY, How To and parts list for the COP conversion? And I guess I should ask, if my "boost" module is bad, will anything make any difference?

 

[bongobobny]

OK, all good questions, beer or no beer!

 

As far as fuel economy, yes float level adjustments can affect fuel economy, but driving habits can also affect it as well! If you are used to a big V-Twin, chances are you are not revving the engine high enough! These 4 cylinder engines love their RPM's and need to be kept in the 3500 to 6500 RPM range for better fuel economy due to that is where the power band is! You should never be in 5th at any speed below around 55 to 60 MPH!

 

These carbs are very complex and several things can go wrong and yet the bike will still run! There is a very good DVD out there concerning the proper way to rebuild and set up the carbs. It is geared towards the VMax carbs but is just as appropriate for the Venture carbs as well! Here's a link...

 

http://www.venturerider.org/forum/showthread.php?119186-Bought-Carb-Rebuild-Video-by-Damon-Ferraiuolo&p=1004501#post1004501

 

As far as the vacuum advance or boost sensor as Yamaha calls it, with no vacuum you should see around 2.5 volts with no vacuum, and it should vary from 0 volts to 5 volts depending on whether a positive or negative pressure is applied. See the Service Manual available for free on this site.

 

http://www.venturerider.org/forum/showthread.php?3384-First-Gen-Service-Manuals

 

Also, make sure your Ignition Module is the proper one for the '83 model as that module is specific for only that year. If the P.O. switched modules to a later year, the vacuum advance will be 180 degrees out of phase as with the 83 they used carb vacuum, and the rest uses manifold vacuum. Speaking of vacuum, if you have any leaks that will cause your mileage to go south.

 

The last thing to mention is the diaphragms on the carburetors. Any pinholes at all can and will affect mileage. Watch your plungers for doing the proper "dance" when revving up the engine...

[luvmy40]

I actually never even thought to check if the numbers were right on the CDI. And, now come to think of it the vacuum line was connected to a sync port when I got her.

 

I will definitely look into the videos.

 

I went over the carbs in detail and everything is clean and the diaphragms are GTG. I'm not so sure about the jet block plugs and gasket. I had to replace the bowl gaskets as they leaked significantly after reassembling the carbs, but I didn't have the spare change for a rebuild kit.

[luvmy40]

OK, I do have the 26H CDI so it's plumbed correctly to the carb vac port. I'll have to strip some plastic to get at the boost module to test it.

[CaseyJ955]

If your going to Ignitek then the COP grocery list is basic with no resistors needed. I did both chasing my MPG issue and it runs great, but I still had really dismal MPG, around 25-29. I used Skydocs drop shims and that got me up in the 40mpg area. I suspect the emulsion tubes are worn as they are known to and dropping the needles countered it (speculation). I cant link but search "run for it its the cops" on this site. I documented my simple.COPs there and other great info from many users.

 

Float level is critical on CV carbs, I went 1.125" dry on both my Vmax and Venture with good results. Factory Pro has the info for Vmax and the proceedure and measurement is the same for Venture.

 

If you find the right Ignitek and dont get the Venture directions and/or files I have that stuff and the benifet of guidance from Gary D on getting it optimized. If you need assist PM me and I'll give you my ph #. and share what I know. Im still learning the ignitek and its various adjustments but ill help if I can.