Carb sync'ing issues - Advice/suggestions??!!

[banff_springs]

Good morning. After going through the forums I've found a lot of useful information however didn't feel any of the threads answered my question. First off, this is what I have and repairs I've performed.

Own a stock 1998 1200cc VMAX. No mod's have been done to this bike.

Maintenance I've performed on the bike to-date:

1. Rebuilt carb's;
2. Constantly using Seafoam in fuel;
3. Purchased Morgan Carbtune Pro for sync'ing;
4. Checked and re-checked all rubber boots (VBOOST, Carb's and Airbox) for vacuum leaks (none found);
5. Performed Shotgun cleaning method several times (little to no improvement).
6. Fuel filter replaced;
7. Several oil changes;
8. Spark Plugs changed for Iridium plugs;
9. Put dielectric grease on coils and boots;
10. Replaced Air Filter.

Issue I am having is, according to Yamaha Shop Manual, the vacuum pressure for the carb's should be 22cmHg....closest I can get carb's #1 & 2 is between 18-20 ccmHg. Carb #3 can be sync'd close to 20-22cmHg however, carb #4 sitting right around 36-37cmHg. Carb #4 doesn't want to budge during any adjustment of "Screw B" (rear-most screw on Right side of carb's). All A/F screws set at 2-1/2 turns out from bottoming. For the life of me, can't get the carb's to sync. Bike idle is set at roughly 1050-1100rpm (closely monitored throughout adjustments).

Anyone have any idea's as to what I am looking at here? While the carb's were completely off the bike, I did a rough "bench-sync" using two small drill bits in the throttle plate. Also used a micrometer to check my throttle adjustment and it was WAY out..(has not since been adjusted to the 0.59" it's supposed to be.

VBOOST was noticed to be "bottoming out" and should be a 0.3" gap from the stop screw. Has now been adjusted as per Shop Manual. VBOOST seems to be working as advertised.

HELP!!

 

[dannymax]

Don't worry about the numbers, you're just looking to get the carbs to open at the same time.

The screw on the left (sitting on the bike) will sync #1 to #2....#2 won't move....the rear screw on the right side will sync #3 to #4....#4 won't move. The forward screw on the right side brings #3 & #4 (this adjustment will move #4) in sync with #1 & #2.

Curious why you had to do the shotgun after rebuilding the carbs....:ummm:

How many miles on it?

 

[marsmax85]

ALSO wondering when you drain float bowls is there any particles in the jar after collecting ? gas tank rust ? rust in fuel pump ?

 

[fmcandrew]

I'm with Dan on this one...If your bike is not running well after complete rebuild & synch then there is another issue (fuel/air/spark). Is your bike running? Can you read the plugs? How is it acting when running?

 

[tugla]

plus on ahoce comments for the sync.

side note...these bikes run great with reg ngk plugs....no need on iridiums....imo

 

[jfeagins]

Banff states his issue to be he can't get all four carbs into sync.

If the one carb is that far out, and you can't get any satisfaction before running out of threads on it's adjustment screw, then you either have a bent tab on that carb, or more likely, IMO, you have an error on your re-assembly of the carb rack.

 

[banff_springs]

Don't worry about the numbers, you're just looking to get the carbs to open at the same time.

The screw on the left (sitting on the bike) will sync #1 to #2....#2 won't move....the rear screw on the right side will sync #3 to #4....#4 won't move. The forward screw on the right side brings #3 & #4 (this adjustment will move #4) in sync with #1 & #2.

Curious why you had to do the shotgun after rebuilding the carbs....:ummm:

How many miles on it?

Shotgun was done as a precautionary measure.
I have 21,000 Km's on the bike.

Carb's #1 thru #3 are now sitting @ 22cmHg however, #4 is sitting @ 38cmHg.

 

[banff_springs]

ALSO wondering when you drain float bowls is there any particles in the jar after collecting ? gas tank rust ? rust in fuel pump ?

I have been getting small particulates out of carb #3 however, #1, #2 and #4 seem unaffected.

WAS rust/dirt in original tank however, did a swap with Sean Morley and have installed a refurbished tank.

Bike was ran on original tank before I knew what was in it. Suspect some debris did get past filter however, have changed out the filter once a month to be on the safe side. Maybe it is costly but, I seem to sleep a bit better knowing there's a clean filter on it.

Just disconnected fuel line from rack and turned key on several times to see what was coming out of pump and aside from some very minute pieces (and I do mean tiny).....by the 6th/7th time I turned pump on, fuel was sparkling clean......also to note...I was tapping gently on pump as fuel was ran.

 

[banff_springs]

I'm with Dan on this one...If your bike is not running well after complete rebuild & synch then there is another issue (fuel/air/spark). Is your bike running? Can you read the plugs? How is it acting when running?

The bike runs like a scared cat. As the A/F mixture screws were messed with before I owned it, am doing my best to tune it. Plugs are running clean. No gum/gunk on plugs, very light brown and clean. Sits and idles at 1,000 rpm nicely.

Was having a top-end issue hence why I took carb's apart.

 

[banff_springs]

Banff states his issue to be he can't get all four carbs into sync.

If the one carb is that far out, and you can't get any satisfaction before running out of threads on it's adjustment screw, then you either have a bent tab on that carb, or more likely, IMO, you have an error on your re-assembly of the carb rack.

Bent tab? How does that affect the vacuum?

With my number being so high, suspect vacuum leak however can't see where. All the rubbers are in good shape, clamps are snug/tight and everything "appears" in good order.

Re-assembly appears pretty straight forward.....I'm not overly rough with carb parts as I know they are delicate.

Is it possible the A/F adjustment screw is out of whack as it leans/richens the fuel?

It would appear now that the #4 carb is the only one I am having issues with as I have #1 thru #3 as per the spec's in the Yamaha Shop Manual.

 

[banff_springs]

plus on ahoce comments for the sync.

side note...these bikes run great with reg ngk plugs....no need on iridiums....imo

Tnanks. Think I'll switch at beginning of next riding season as for me, this season is almost over..

 

[jfeagins]

A bent tab might make the linkage off far enough so that you can not get the proper adjustment to bring that carbs' butterfly to close enough to match the other 3 carbs. The little springs in between those carb linkages can prove to be a real PITA while re-assembling also. I've found myself putting them back together incorrectly on more than one occasion, until I figured out what was going on.

 

[banff_springs]

A bent tab might make the linkage off far enough so that you can not get the proper adjustment to bring that carbs' butterfly to close enough to match the other 3 carbs. The little springs in between those carb linkages can prove to be a real PITA while re-assembling also. I've found myself putting them back together incorrectly on more than one occasion, until I figured out what was going on.

Good thing to note. I have carb's in complete teardown mode right now. With work commitments, etc,..now looking like it'll be a winter project...sadly it means my riding season is over right now....

 

[jagco1]

You still have enough time to ride, For me when I syc my carbs had to adjust them along with tuning the idle screw on the lift side under the carbs for all to 4 working together. If I remember right I turn the idle screw out a little because 1" was a little off than the other 3 cylinders. Then touch up the syc on all.

 

[maleko89]

Could have a crack in manifold. I've had that before. When's last time you adjusted valves? Are you sure sync gauge is working correctly?

 

[banff_springs]

Could have a crack in manifold. I've had that before. When's last time you adjusted valves? Are you sure sync gauge is working correctly?

I suppose it's possible. I've never adjusted the valves. Bike is "new" to me last year. Finding all sorts of things. I've spent a lot of late nights and early mornings getting my bike ready to ride. It spent a good portion of it in the garage last year being worked on. I've put a little over 6,000 Km's this year alone...never a glitch, bog, rough idle or hint of it being sluggish.

My sync tool of choice is the Morgan Carb Tune Pro which requires no adjusting. It's brand new and have sync'd this bike (and others) with no problem. When I move the hoses around......whichever hose is connected to #4, it's the one out of sync.

With work requirments and such, I'm going to be gone for roughly a month and a bit....and from where I live.....that means snow on the ground when I get home.....time to hang up the key and helmets until next year. Will spend winter in basement "pouring" over carbs in hopes of an early Spring so I can re-assemble. I don't have a heated garage thusly all work is done outdoors.......guess I have a project for the winter.......

 

[dannymax]

Need some clarification here....the forward screw on the right side moves #3 & #4 simultaneously....when you turn that screw only #3 will move and #4 doesn't?? :ummm:

 

[jfeagins]

With work requirments and such, I'm going to be gone for roughly a month and a bit....and from where I live.....that means snow on the ground when I get home.....time to hang up the key and helmets until next year. Will spend winter in basement "pouring" over carbs in hopes of an early Spring so I can re-assemble. I don't have a heated garage thusly all work is done outdoors.......guess I have a project for the winter.......

Put it on a center stand and ride that bad boy in the garage. lol :biglaugh:

 

[tugla]

if you look down all four carbs with bike not running. pull the slides out of the way do they all look closly open the same amount. the one carb with high vacume should he visable open more.

 

[SFCMcGan]

if you look down all four carbs with bike not running. pull the slides out of the way do they all look closly open the same amount. the one carb with high vacume should he visable open more.

Wouldn't the one open have low vacuum?