Carb Sync problems

[casimage]

I have a 78 GS750EC with Jardin 4 to 1 exhaust, Dyna S ignition, coils and plug wires. The carbs have 110 jets installed.

I bought a Motionpro economy carb sync tool, rebuilt the carbs and put them back on the bike. I attempted to sync the carbs following procedures on this site but it is like I take one step forward and three steps.

The Motionpro has four columns with markings from 2 to 54 in increments of two. When trying to sync, I can get three carbs in the same sector marking but I go for the fourth carb, it knocks out the other three. Then it is back to square one.

Also, the idle gets insanely high. Tried turning the air screws and adjusting throttle valves but I just keep getting deeper in screwing this up. I have pulled the carbs of the bike, did a bench sync and will reinstall them tomorrow and try again.

Is there a particular sector on the Motionpro tool that the carbs should be sync'd at. At what RPM should the sync be performed at? Last question, and probably a dumb one, what is considered a "turn" on the air screw? If the slot is sitting at 9 to 3 o'clock, left to right is full turn moving the end of the slot that is at 9 to 3 o'clock or is a full turn moving that end one full revolution back to 9 o'clock?

Thanks in advance for your help.

[ghwrenchit]

what is considered a "turn" on the air screw?

1 Turn (360 degree's) = 1 turn all the way around.... 4 - 1/4 turn's(90 degrees ea) = 1 (360 degree) turn all the way around.

Picture it like a clock, from 12:00 0'clock:

1/4 turn = 15
1/2 turn = 30
3/4 turn = 45
1 turn = all the way around

Hope this helps....

ghwrenchit

[chef1366]

After each carb adjustment lower the main idle back down to 1-1 1/4 rpm.

[KEITH KRAUSE]

Start over.
Bench synch the carbs carefully.
Turn up the idle adjuster knob enough for it to start. Don't start it yet.
For initial setting, set the side air screws at 1 3/4. Tune the air screws for highest rpm if it starts and idles well enough. Use 1,000 rpm as a base point for setting each air screw and be sure the bike is warmed up before setting for highest rpm.
Bike should be idling at 1,000/1,100 rpm and on the centerstand.
Turn off and hook up vacuum tool.
I always synch at approx' 3,000 rpm. 2,500 works OK too. Use two fans and don't let the motor overheat. If you synch too slowly, let it cool down some.
Note initial levels at start up.
Always adjust the HIGHER level(s) down to match the lower levels. It's easier that way. Try to get them so the difference from the highest level to the lowest is no more than about 3/4". The closer the better but don't get too picky and risk over-heating.
The throttle adjuster screws are VERY sensitive to adjustment. Turn them slowly while observing the level.
Now carefully hold the screw STILL and tighten the holder nut.
Do not over-tighten the holder nuts. 3.5 ft/lb is factory torque.

If you over-tighten the nuts or allow the screws to turn, you WILL see the "last" carb adjustment "pick up" the others. After all, they're all connected to the same throttle shaft.
You just need to be more careful with the adjusting.

[bwringer]

The sync adjustments are INSANELY sensitive -- the problem sounds like you're simply not used to this. One or two degrees makes a difference.

It is difficult to sync carbs correctly the first few times, but after a while you start to learn how much they go out of whack when you tighten the lock nuts, so you back them off just a wee bit before tightening the nuts. That way, you end up in the right place.

Take your time, make sure you are synchronizing the carbs in the correct order (check your manual), make sure your vacuum lines are hooked up correctly (I've gotten this wrong a couple of times, and it is pretty confusing).

Also, there's no need to put much torque on the locknuts at all. Just snug 'em up a little and step away -- more torque just throws everything out of whack. This is very hard for a lot of people to grasp.

Don't run the engine for more than a few minutes at a time, though -- it's easy to overheat if you're having a tough time. The fans help, but air-cooled engines must be moving to cool properly above idle.

[casimage]

Carbs sync'd, other fuel problems

Thanks guys for your help.

Assuming that even a blind squirrel finds nuts, I was able to get the four columns of mercury so that are within 1/2 inch of each other at idle and at 2,500 rpm.

Now I have a problem with dead throttle response above 3,500 rpm. It seems to hesitate then intermittenty runs up to around 6K where it wavers between 5.5 and 6K.

I have a Dyna S ignition, Dyna Coils and spark plug wires, Jardine 4/1 headers and 110 jets in the carbs.

Any suggestions?

Thanks again for getting me this far.

[Nessism]

Did you replace the large O-rings that fit between the head and the rubber carb isolators? This is a VERY common place for vacumme leaks which leads to an irratic idle and sync problems.

Ed

[KEITH KRAUSE]

Did you replace the large O-rings that fit between the head and the rubber carb isolators? This is a VERY common place for vacumme leaks which leads to an irratic idle and sync problems.

Ed

Yup. I agree.
It's not easy to figure out what's wrong by your description, but it could be the above mentioned intake leak.
The classic leak symptom is a colder idle of about 1,100 rpm, but once fully warmed up, the idle is much higher. The warmed up idle on a correctly running bike will only rise about 100/200 rpm.

[casimage]

Where do I find the rings?

Thanks again, guys. When I took the carbs off of the bike, I did not see any O rings on the manifold boots. The carbs appear to fit into the boots and are held in place by a screw clamp. Of course, I did not remove the manifold boots but I have gotten rather adept at pulling off the carbs so I will so again.

I have been a few parts sites but I am unable to find even a diagram or part number for the O rings in either the carboretor section of cylinder head section. Any suggestions?

[KEITH KRAUSE]

Thanks again, guys. When I took the carbs off of the bike, I did not see any O rings on the manifold boots. The carbs appear to fit into the boots and are held in place by a screw clamp. Of course, I did not remove the manifold boots but I have gotten rather adept at pulling off the carbs so I will so again.

I have been a few parts sites but I am unable to find even a diagram or part number for the O rings in either the carboretor section of cylinder head section. Any suggestions?

The manifold o-ring sits in a groove. It seals the manifold to head space.
Yours should be the same as my '79 GS1000E. Suzuki part# 09280-32006.
Yours are most likely hard, flattened and cracking.
Apply a coat of some hi-temp bearing grease to help them last. I also suggest getting rid of the stock Phillips manifold bolts and replacing with Allens. Then you can correctly torque the mainifolds to 6 ft/lb. Don't over-tighten. It just flattens the o-rings and lessens their service life.

[bwringer]

The o-ring shuffle in pictures:

http://bwringer.com/gs/intakeorings.html

The part number given are for 80-83 GS850; yours will look almost identical but are probably different.

[casimage]

found the rings

Keith:

Thanks again. I ordered the O rings and will probably do that next weekend along with getting allen screws to replace the current ones.

Can you suggest a spark plug gap for use with the Dyno ignition, coils and wires? I run a MSD on my car and they suggest a wider gap to handle the increased spark. Thought it might be similar in motorcycle ignitions.

[KEITH KRAUSE]

Keith:

Thanks again. I ordered the O rings and will probably do that next weekend along with getting allen screws to replace the current ones.

Can you suggest a spark plug gap for use with the Dyno ignition, coils and wires? I run a MSD on my car and they suggest a wider gap to handle the increased spark. Thought it might be similar in motorcycle ignitions.

You're welcome. Be careful of stiff manifold bolts. The Phillips are easy to strip the heads off. I use a very good fitting bit in my impact driver. There's very little room to whack the driver, but in my case, I never need to hit it. My driver bit fits so well that I just pull in/lean in on the driver, turn, and the bolts always start coming out. My driver also allows a very good grip.
Dyna does recommend a larger gap, but I'm not sure how much it is at the moment.
I still adjust my gap to the middle of the factory gap range (.6mm to .8mm), which is .7mm. I recently replaced my plugs "for the heck of it" after nearly 25,000 miles. A "birthday gift" to the bike actually. I've run a Dyna S for that whole time. Some pipe/pod/piston mod's. I was anal about the re-jet. My plugs were still literally perfect and no noticable change in gap. Maybe a tad "tighter" if anything, most likely because of a light carbon coat on the ground electrode, nothing more. The ground electrode tip was still very good and square. So my stock gap didn't mean I was getting less service life due to higher voltage reaching the plug.
So Dyna may be right, but I stay with the stock gap and have no problems.
I could have gone who knows how many more miles before the gap/electrode tip started showing wear. I think people change their plugs too often. Waste of money. But many people have problems with the bike that requires they clean and change plugs often.

[bwringer]

Yup, use the stock plugs, no matter which ignition/coils you're using -- on my bike and many other GS models, they are NGK B8-ES, but yours might be different. I think they're the same, though.

Fancy plugs are utterly useless, and many have proven to be worse than useless.

Advance and Pep Boys auto parts carry NGK plugs for cheap -- they're usually $1.79 or $1.89 each, while the motorcycle shoppes want almost $3 each. You may need to ask for stock number 4011, since B8-ES doesn't compute in some stores. (Both numbers will be on the box, but the stock number is the only one in the computer.) Don't let them sell you some Platinum/split electrode/flavor of the week plug.

I change mine once a season whether they need it or not, and they've never really needed to be changed or regapped, even after 20,000 miles or more.

If it makes you feel more macho or something, feel free to open up the gap a bit. It won't make the slightest iota of difference in the way the bike runs.

Spark plugs and wires are realtively cheap and easy to replace, so there's a whole industry built around trying to convince people that magic spark plugs and spark plug wires are going to give you more power, whiter teeth, and relief from ho-hum breath.

The reality is that ignitions simply need to operate reliably and up to spec. There's no performance benefit at all to a "hotter" spark, more voltage, huge wires, etc. Dyna coils are simply reliable, cost-effective replacements for deteriorated OEM components, plus they have the added benefit of allowing you to change the wires separately, instead of the molded in wires on OEM coils. (You get your pick of cool spark plug wire colors, too!)

Even for engines in a highly modified state, the stock plugs are still the best choice.