I have my carbs synced at idle, but when I increase the revs the gauges dont show the same value they are all over the place. One of the gauges doesnt even move at all. When the engine speed drops back to idle the needles are all the same again.
This doesnt seem right to me. All the videos on youtube show the gauges level throughout the rpm range. Any ideas?
A few comments not pertaining to the Magna but bikes in general.
When syncing many say you should set idle around 1700-2000 rpm.
Some instructions ask you to sync to Carb 1, while others say to sync Carb 1 to 2, Carb 3 to 4 than sync them together, not knowing the Magna's procedure I can't elaborate. Make sure you are following the proper guidelines.
The sync meter I made was all over the place around idle also, but you don't drive/cruise around at idle, sync your carbs between the RPM range you use when driving ie: 4-6000 or 3-7000 RPM.
It is good to have a cleaner air filter so the flow to each velocity stack is equal.
I followed the service manual when I synced. Its not just the gauges at higher rpms the engine sounds rough like when the carbs werent synced at idle. I pulled the carbs again and used gasket maker between the lower airfilter box and top of the carbs where the air horns attach. I also didnt like the look of my isolators so I ordered a new set. I cant see an air leak causing my issue but I have to start somewhere.
to test for air leaks, use starting fluid, carb cleaner, something similar and spray around the boots. Spike in rpm = vac leak. Also remember that these slides operate on vac so a vac leak will cause lots of problems.
as far as syncing carbs. Need to sync at normal idle rpm. A sync will match all carbs together which should make the largest difference at idle. Think about it like this... At idle, the slides are only slightly open, where a few thousands of an inch could yield a significant difference (percentage wise) on the total opening of the carb. So when the slides are only slightly open, you could be off 10% or more. Now at WOT, that same fraction that the slides were off might only by .25% off and in theory, the engine would not notice it as much. So a pin hole in a postage stamp is much more significant than the same pin hole in a poster board.
have you considered it is your gauges are off? If you have the cheap ebay ones than my money is on that. Take a few plastic It's and connect all the gauges together and hook them all up to one carb. Start and make sure they all read the same at idle and at higher revs.
I got tired of messing with my cheap gauges and I made my own set using better gauges. I just used them last week to sync some of my old cb carbs and that bike has never ran sooooo good.
(http://s118.photobucket.com/albums/o117/imabass/?action-view&current=f9dc363a.jpg)
I don't know if you can buy them anymore, but I use a "mercury stick" -- four plastic tubes on a common board with graduations in cm on the board, a common mercury pool at the bottom. Plastic tubes go to the four vacuum ports just under the carbs. On the 3rd gen, there is one carb that does not adjust, so you sync all others to it.
The problem with mercury is that there is no damping, and at idle the columns bounce up and down -- by about the tolerance level. When you get used to them, however, you can average with your eyeballs, and this works well. I firmly believe the mercury method is the most reliable and accurate. Quite possibly the least expensive, as well.
I know your are probably shooting for excellence here, but through the years it's been my experience, on the third gen Magna, if you do a precise bench sync and set the mixture screws exactly the same, you will not be able to tell the difference between that and a sync with a set of gauges. What I'm trying to say is unless you are racing and going to the dyno between each tuning, you are just beating your self up for nothing.
Sync'ing is a waste of time if you have not done major carb work or engine top end work, in my opinion. After having taken close to 100 3rd gen carbs apart etc, I have yet to find any that were far enough off (keeping in mind that the acceptable range is fairly broad on sync'ing, and will never get em all the same) to do more than a bench sync.