I should have bought a carb sync tool a while ago

I finally got some time, and picked up a MotionPro SyncPro (glycol filled). My '86 has been idling very inconsistently, and roughly, often trying to stall out if I set the idle at 1200rpm.

What I don't like about the SyncPro is that it doesn't give any units for the reference marks (or maybe it's just non-linear, so it can't give any). But I following the directions, calibrated it to about 1/3 of the way up, and then hooked it to all four cylinders.

#2 was way down from the rest (1" or so on the SyncPro), with #4 about 1/2" up from that, and #1 and #3 together.

I spent some time swearing and burning myself (through mechanix gloves) but got them all to read within 1/8" or so of each other on the SyncPro (vs. 1" off). Those adjustment screws are hard to get to. Engine was idling much better.

I ignored the bit of directions that said not to blip the throttle or rev too high, but kept an eye on the levels as I did so. I was VERY happy to see that as the throttle opened up, the levels stayed very close together. On a closed throttle from high rpm, #3 and #4 both had a bit higher vacuum, but that settled down as the engine came back to idle.

It just sounds so much smoother and more even all across the rpm range. Unfortunately, I can't ride it today to find out. We've had about 3" of rain today. But that makes it a great time to work on the bike.

This turned out to be a pretty easy job, aside from accessing the sync screws themselves. The SyncPro makes it pretty easy, and all the ports are present and tapped, and the SyncPro comes with adapters that replace the screws in the ports.

 

Good to know, I have that same tool hanging up in the garage still in the package.

 

The glycol Motion Pro is crap, it is meant for smaller bikes, I had it suck the fluid out on my CB. I ordered a Morgan carbtune so carb synchro is next on my list after adjusting the valves today.

How are you supposed to get at the mixture screws when they are on the inside of the carbs??

Is there another special tool I need to buy to accomplish this?

 

Didn't cause any problems on my VFR. I following the instructions on fully backing out the calibration screws first, and with the bike running, no glycol was visible in the tubes until I started screwing them in to calibrate at a given reference mark. It notes it's not to be used with over 40cmHG (15inches mercury), but that's a fair bit of vacuum. I was going to also hook up my vacuum/boost gauge, but couldn't find it, so I don't have any idea how much vacuum I was pulling.

Mixture or sync screws? The mixture screws are behind plugs that come off with a drill and a screw. The sync screws are on the throttle linkage between the 4 carbs. remove the left lower fairing panel, and then look up between the carbs and you'll see 3 screws pointing down into the V. Mine had purple marking fluid painted on them. The rear two are easiest to see (and get to). If you don't have small hands, it's going to be a pain. I found a 7mm deep well socket (1/4" drive) on a 1/4" ratchet worked fairly well, but I tended to just turn the socket by hand (while wearing mechanix gloves so I wouldn't be burned by the oil pipe in the bottom of the V).

No special tools needed. I used:

- 1/4" drive ratchet
- 1/4" drive, 7mm deepwell socket
- phillips screw driver (#2 and #1 tips)
- 8mm combo wrench (to remove the 5mm adapters when done, when the one in #2 cylinder was a bit stuck)

One thing I found is that you must be certain to only twist the screws, if you push on the adjust screw while you twist it (or are fumbling to get the socket on the screw), it will open the throttle blade in one or more cylinders (depending on which screw it is). Lots of patience needed until you get the hang of the feel. Then it's pretty easy.

 

You can just use your tachometer too.

Turn one screw all the way in and count the turns.
Set all four the same. start it up and lean one out and watch the tach. As soon as the RPM goes up as much as possible then back it out 1/8 turn.
Do this to each carb.

 

OK, the service manual is pretty nebulous on what to adjust for synchronization.

"Synchronize to specification by turning the adjusting screws with a carburetor pilot screw wrench." Meh.

Since there are only three screws to adjust, I take it one or two is the reference carb?

 

I have yet to adjust the carbs on a VFR, but this tool is a life saver on the older inline 4 bikes;

Motion Pro - CARB ADJ TOOL

 

That works for the idle mixture (pilot), but not the vacuum sync (throttle linkage).

 

Yep, #2 is the reference, with the idle set screw and the throttle cables on it. The adjuster for #4 (Front Right) is between the front carb fuel bowls. The adjusters for #1 and $3 are between their fuel bowls at the other end of the throttle linkage.

 

They point down into the V, so you'd need the right angle version:

Motion Pro - PILOT SCREW ADJ TOOL

This one with a 1.5-2" long bit would make it pretty easy, but $$:

Motion Pro - CARB TOOL 90 DEGREE W/BITS

Although, if I was going to be doing this a fair bit, I'd buy it in a heartbeat.

 

The biggest difference about the original tool I pointed out is that it is a hex nut driver with a screwdriver down the middle of it. You can hold the adjuster screw stationary while you loosen the lock nut, make the adjustment, and tighten the locknut without changing tools. Either way, it sounds like it wouldn't work on the VFR carbs anyway, due to the angle of attack.

And I've had my eye on that expensive right-angle tool, Woody77. I have the first one you linked too, and it fits most carb pilot screws I've had to get to. It doesn't have very good "feel", due to the flexible shaft, but it works. I just don't need the right angle capability enough to justify the cost of the expensive version. It would be fun to have, just because, but I'm a recovering tool-junkie as it is... :biggrin:

 

There's about 4-5" of room in there, tops. It was a really tight fit for my hand and a deep-well socket being used as a nut-driver. It probably should have taken <5 minutes to do the adjustment, I was fiddling for over 30 minutes, most of it just trying to get socket on the adjusters.

No recovering here, I'm a tool junkie, and I know it. I'll keep it in mind that the cheaper one does work, albiet with a springy feel. Should be enough to make the job easier.

 

Yes I understand.
But if it is a bike that has not been messed with or had the carbs taken off it should be very close.
I realize that those springs between linkages could loose tension over time .

 

I'm not sure if mine lost tension (they were all adjusted in the same direction, though), they are 24 years old at this point. Or it could just be other stuff changing in the engine and a slow shift of the vacuum pulled in each cylinder (crud built up in the carbs, too).

 

Man, I SOOOO need to get one of those! If I could afford one I'd have bought one over a month ago. Mine is suffering at idle to the point that I have to have the choke on 1/4 in order for her not to stall out on idle after she's reached operating temps. I'm still a bit unsure with the whole manual sync instructions - I mean, I get the jist but... I guess it comes down to that whole "Never done it before and afraid I'm gonna screw it up" type of thinking. If I botch it and can't ride it, I'm screwed cause my car's been de-insured for the time being till I find some work and can afford it again.

 

You can go home-built if you have the time and space to store it (the small size of the tool was the decisive factor for me, the garage has enough clutter already).

 

Can the homemade manometer tool be made for a V4? is there anything special that needs to be done for this engine type?

thanks,

P

 

No, nothing special, just make sure you put some restrictors on the ends towards the engine (i.e. aquarium tubing).