I have an 86 vmax, and my vboost is no longer. I am the original owner, so nothing has been changed on the bike. This just start a few weeks ago. I have checked all of the wire connections and fuzes under the tank cover. Is there anything I can check to diagnose and fix the problem? Do the controllers go bad?

There are several things that could cause it. Servo motor, control cable. You should hear the servo motor cycle when you first turn the key on without starting the bike. Youan pull the air filter box off and watch the servo for proper cycling and check the cable. There is a round plug under the left scoop that you can check. For now just wire the vboost valve wide open until you can find the problem. You may find you like it that way.

Thanks for the advice, I will try taking the airbox off to check the servo. I do hear the servo motor cycle when I turn on the key.

I did check the round plug, and it is connected.

How do I wire the valve wide open.

You can quick and dirty it...
Unplug the round connector when you hear the first whine, but before the second whine.
It takes a bit of timing, but it is doable.
You will immediately notice a lumpier idle after doing this.

It's probably your vboost controller which is under the left scoop.

Mark
#1098

If it turns out to be my boost controller, do I need to replace it, or can I replace it with a t-boost, or some other device? I am not sure these type of devices replace the factory controller.

The T-Boost just tricks the controler into opening the v-boost early so answer is no. In my opinion it is more effective to have the V-boost open from idle or in the stock mode. So I do not see advantage of T-Boost system.

If you hear the servo motor cycle when you turn on the ignition then your next step will to check the cable between the servo motor and valve linkage to make sure it is actually opening. If cable is working properly rev engine to 5000-6000 rpm and watch to see that valves are opening. If they don't open then the controler box is likely bad.

You can disconect the round plug when valve is in the open position however the valve will slowly close up on you over time. So in addition to doing this also tie a piece of light wire to the valve linkage and tie it off to hold it in the full open position.

The best solution is to install a dynojet stage 7 carb kit with the v-boost eliminator tubes.

If you want to retain the stock system I have a complete V-boost system from a 93 max. This includes servo motor,cable and valves, control box intake manifolds and valve boots. It is boxed and ready to ship. $300.

maxout wrote:



This is all good info. That is s good deal on the v-boost system. The controller alone will cost you $100. I'd remove the system and get a stage 7 jet kit installed. A stage 7 jet-kit comes with V-Boost elimination tubes, leaving the V-Boost open all the time. This causes a rough idle and makes it very hard to synchronize the carbs. You will need a GOOD mechanic to synchronize the carburetors. Hang on tight cause this made a huge difference on my '85.
Good luck.

This is good information. I have often considered that mod, but I really don't have the skill or knowledge to pull it off. I did have a kerker 4-1 exhaust installed several years ago.

Does anyone know of a mechanic in the St Louis area that could do this work?

Wow a Kerker 4-2-1 system without a stage 7 kit. Thats like crackers without cheese, bread without butter, anyway you get the idea.