rednecktech

I bought a 89 750 Virago with 28500 miles.The rear cyl. runs about 125 psi The front is 95psi one teaspoon of oil brings it up to about115 psi The fool that had this bike before me adjusted the only valve he could. that was the exhaust valve on the front cyl, he set it so tight that the valve was not closing completely, so it will back fire a lot I reset the valve and it runs better but still backfires after it gets hot. I am wondering if the carbon is so much that it is trying to ignite? The plugs are showing a very rich mixture, but I have rebuilt the carbs and put new plugs . My plan is to place fans in front of the engine,plull everything from carbs,run the engine and shoot marvel mystery oil into the carbs to break up the carbon,trying to clear the cyl. Has anyone done this and made it work. How good will the rings clean up? There is a lot of work on it if this dose not fix the problem. Any ideas ? Thanks for the help.

The 78 is running great for the time. The problem we are having is the rear brake master cylinder is showing signs of old age. We are looking for the whole master cylinder not a rebuild kit. The bike is a 1978 yamaha XS750 special. If anyone knows where we can find a new master cylinder we would appreciate it.

My question is about manifold vacuum on my triple 750. What is the factory vacuum settings when the bike was new. I only have 8200 miles on the bike but the carbs are from another 750.When I bought the bike I found that the needles had been screwed in so deep that the tips were broke off in the bottom of carbs.So I bought a parts bike with good carbs, and they have been reset to balance the vacuum. They are way off in balance,so I set the vacuum balance to 8inches of vacuum with a sync.tool. I'm thinking that it is to lean at this setting. It's a little slugish right at take off,but gets after it with a little more throttle. I don't know whether to go up or down with the vacuum. The bike is a 1978 Yamaha750 Special XS model. If anyone has the answer please pass it on ,thanks,Jim