vacuum sync?

[sblankert]

Hey Vmax Pros,

I bought this 86 vmax a few months ago and have been working the kinks out of it ever since.

When I got it, it had horrible gas mileage--like 18 mi/gallon. I did a shotgun carb clean and brought it up to 32 mpg at one point, but it was misfiring a bit, so I did a vaccum sync with a motion pro sync.

Now it has better low end response, but leaning back on the throttle gives a mediocre result, and mpg dropped to 25 mpg at best, top speed around 85 mph.

When it was doing 32 mpg, it had was misfiring, but was able to get up to the 100s easily. It's not like my 2006 max at all, where it can bury the needle and still have throttle left, and I have no idea how fast I've gone on it.

FYI, the vboost is not working, and I have the parts incoming. Could the non-functional vboost be behind this whole thing, or should I work on the carburetor some more?

I have worked on holley carbs before, but never had to sync before owning this max. When I turn each sync screw clockwise/counterclockwise on each side, what exactly is it doing to the carburetor?

Any suggestions on how to work on this short of tearing the carb out and rebuilding it are appreciated. (I don't have a garage atm) :ummm:

 

[dannymax]

Hey Vmax Pros,

I bought this 86 vmax a few months ago and have been working the kinks out of it ever since.

When I got it, it had horrible gas mileage--like 18 mi/gallon. I did a shotgun carb clean and brought it up to 32 mpg at one point, but it was misfiring a bit, so I did a vaccum sync with a motion pro sync.

Now it has better low end response, but leaning back on the throttle gives a mediocre result, and mpg dropped to 25 mpg at best, top speed around 85 mph.

When it was doing 32 mpg, it had was misfiring, but was able to get up to the 100s easily. It's not like my 2006 max at all, where it can bury the needle and still have throttle left, and I have no idea how fast I've gone on it.

FYI, the vboost is not working, and I have the parts incoming. Could the non-functional vboost be behind this whole thing, or should I work on the carburetor some more?

I have worked on holley carbs before, but never had to sync before owning this max. When I turn each sync screw clockwise/counterclockwise on each side, what exactly is it doing to the carburetor?

Any suggestions on how to work on this short of tearing the carb out and rebuilding it are appreciated. (I don't have a garage atm) :ummm:

Your objective during a sync is to adjust the throttle plates so they are all open exactly the same amount.....turning the sync screws opens or closes the plates associated with that screw.

 

[Dragmaxster]

Hey Vmax Pros,

I bought this 86 vmax a few months ago and have been working the kinks out of it ever since.

When I got it, it had horrible gas mileage--like 18 mi/gallon. I did a shotgun carb clean and brought it up to 32 mpg at one point, but it was misfiring a bit, so I did a vaccum sync with a motion pro sync.

Now it has better low end response, but leaning back on the throttle gives a mediocre result, and mpg dropped to 25 mpg at best, top speed around 85 mph.

When it was doing 32 mpg, it had was misfiring, but was able to get up to the 100s easily. It's not like my 2006 max at all, where it can bury the needle and still have throttle left, and I have no idea how fast I've gone on it.

FYI, the vboost is not working, and I have the parts incoming. Could the non-functional vboost be behind this whole thing, or should I work on the carburetor some more?

I have worked on holley carbs before, but never had to sync before owning this max. When I turn each sync screw clockwise/counterclockwise on each side, what exactly is it doing to the carburetor?

Any suggestions on how to work on this short of tearing the carb out and rebuilding it are appreciated. (I don't have a garage atm) :ummm:

Turn your key on and IF your servo opens the vboost pull the round plug when it opens it fullest (harder to sync though). If it doesn't work pull it anyway (leaving it closed) It could be partially open now causing difficulty syncing.
How did it sync up with the motion pro? (not a fan of those).

 

[sblankert]

It synced fine. I'm not a fan of the liquid sync after doing it, however, since the fluid chambers have any leaks around the set screw, it will suck all the fluids into the cylinders. It has to be closed, but not TOO tight... blah. I'd rather have vacuum gauges....

But, with that said, it did sync up.

The vboost is totally non operational. When I put the key in, the servo doesn't do anything.

I don't know what was done to this bike before I got it. Looks like all cosmetic. They kid I got it from essentially threw it at me for my lowball offer to get rid of it, since it had engine problems he didn't know how to approach. The carb shot gun fixed the worst of it.

The bike feels like it isn't getting enough air, even though it has a new filter. I'm not sure why syncing it would reduce the gas mileage, but when I synced it, the misfiring stopped. Now it just has a soggy response and worse gas mileage than before, when it was misfiring.

Also, it doesn't sound like my "quiet" 2006 at all, it sounds like a Harley. tHE 86 is all stock, however, but I have no idea how the old 80's bikes should sound. All my vmaxes have been 1995+.

 

[jfeagins]

Fuel pressure OK? Filter checked/replaced? Fuel pump operating properly? Check/replace spark plugs recently? Redo the shotgun to see if it has any affect? Have you set your A/F mixture screws for best off-idle response? Inspect all carb & vboost rubber boots for leaks/cracks? Airbox properly seated onto the tops of all four carbs? These Vmax carbs can be very, very finicky about some of the most trivial things........

 

[Dragmaxster]

It synced fine. I'm not a fan of the liquid sync after doing it, however, since the fluid chambers have any leaks around the set screw, it will suck all the fluids into the cylinders. It has to be closed, but not TOO tight... blah. I'd rather have vacuum gauges....

But, with that said, it did sync up.

The vboost is totally non operational. When I put the key in, the servo doesn't do anything.

I don't know what was done to this bike before I got it. Looks like all cosmetic. They kid I got it from essentially threw it at me for my lowball offer to get rid of it, since it had engine problems he didn't know how to approach. The carb shot gun fixed the worst of it.

The bike feels like it isn't getting enough air, even though it has a new filter. I'm not sure why syncing it would reduce the gas mileage, but when I synced it, the misfiring stopped. Now it just has a soggy response and worse gas mileage than before, when it was misfiring.

Also, it doesn't sound like my "quiet" 2006 at all, it sounds like a Harley. tHE 86 is all stock, however, but I have no idea how the old 80's bikes should sound. All my vmaxes have been 1995+.

I owned the motion pro carb sync for one day. Bought it on Ebay and sent it back the next day. This one is well worth it and ships fast too.
http://www.carbtune.com/
My advice would be to get it synced as close as possible, pull the carbs off the rubber boots then wire the vboost open.You will feel a difference in the ideling and more pull throughout.
If you've done carb work these are not that hard to work on. The main problem with these carbs are gumming up the jets in the jetblock.
What pipe do you have on it and if stock is it drilled out?

 

[sblankert]

Replaced fuel filter, and since it seems to be running rich, I'd say fuel pressure is ok. Fuel pump clicks when ignition is turned, but haven't checked pressure. Replaced spark plugs with correct irridium plugs and new wires, but did not change anything. Checked all fuses (for vboost) and they are good.

The vboost controller seems to be dead. I put in a working servo I've had laying around and it did nothing when the ignition was plugged in.

Anyone have working vboost controller they can part with? There are none on ebay I can find...

 

[Dragmaxster]

Replaced fuel filter, and since it seems to be running rich, I'd say fuel pressure is ok. Fuel pump clicks when ignition is turned, but haven't checked pressure. Replaced spark plugs with correct irridium plugs and new wires, but did not change anything. Checked all fuses (for vboost) and they are good.

The vboost controller seems to be dead. I put in a working servo I've had laying around and it did nothing when the ignition was plugged in.

Anyone have working vboost controller they can part with? There are none on ebay I can find...

Sean may have but is in europe now.
Have you tried taking the back off the controller and looking for solder that has melted and come in contact with another point?
Making a manual controller? Mine cost $7.

 

[tugla]

just checking you are turning the three sync screws and not the four a/f screws?just reading your first post thats what i got from it.

 

[wildweasel_pt]

Theres only three as the front left iirc (#2) is the reference one and has no tuning capability.

 

[Dragmaxster]

Theres only three as the front left iirc (#2) is the reference one and has no tuning capability.

The front left syncs the #1 carb to #2 carb.

 

[Traumahawk]

The front left syncs the #1 carb to #2 carb.

The left front carb is #2.....but is still considered the master carb. left rear is carb #1.

Here is a pic of the cylinder orientation.

 

[Dragmaxster]

The left front carb is #2.....but is still considered the master carb. left rear is carb #1.

Here is a pic of the cylinder orientation.

That's what i said. I was refering to the screw.