Number 4 Carb won't Synch!!!!! I need some advice...

[Anonymous]

OK guys...here goes...

I have a 1978 GS1000 with 53k miles on it, which I just inherited from my father. I've been working on it for a few months (it had been sitting for a while) and have been riding it for the past couple of weeks.

Here's what i've done to it: replaced original coils & wires, new plugs, Uni Pod filters, 4-1 exhaust, Dyna 3 ignition, Dyno Jet stage 3 jet kit, and rebuilt carbs.

A few weeks ago I put the carb kits and the jet kit in...The bike ran OK but had a mild backfire through carbs and through exhaust while cruising. The backfiring would subside when I ran with the choke pulled 1/4 - 1/2. Sounds lean, right? So this past week, I dropped the e-clip and washer on my needles (per Dyno Jet) to richen the mixture. I put the carbs back on today and she fired right up...I hooked up my Morgan Carbtune II and began to synch the carbs at 3500 rpm...

Here's where it gets funny... Carbs 1-3 synch fine, but as I was synching one of these carbs, i notice the "mercury" (stainless rod) on carb 4 pegging the top of the Carbtune. I tried to bring it into synch but I hit the stops on both ends of the adjustment screw (i.e. the needle) without brining it down at all. By adjusting this carb, I WAS however able to make the bikes idle climb an additional 1 grand and rendering the main idle adjustment useless (I couldn't bring the idle down with the main adjustment screw under the carbs until I readjusted the #4 carb's needle adjustment)!! 8O I checked the hose going to carb 4 for a crimp or blockage but found none...I even swapped hoses with another carb. Noticed the #4 cylinder exhaust was cool, so I checked spark...which happened to be BIG & Blue... There was no change in how the bike ran with #4 plug pulled out completely. The carb's bowl was full of fuel and neither the float nor the float needle was stuck.

Here's where I have run out of things to try until one of you fine folks gives me some ideas... :?

What's happening that would cause that much vaccum at that carb...I know the Carbtune is working (the "merc" drops when I pull the hose). Since i'm also getting a cold cylinder, could it be valves? I HAVEN'T checked the valves yet to see if their in or out of adjustment...

Also, is there an approximate vaccum level (in cmHg's) that all the carbs should be synched to?

I'd appreciate any input you folks can give me...What a great site...

Thanks

[SqDancerLynn1]

78 you have the slide type carbs. I would think maybe the slide is open more than the other 3 or maybe not completely closing to idle position

[KEITH KRAUSE]

Hi. You have too much vacuum at #4 which is drawing too much fuel into the main bore. This over rich mixture is temporarily fouling the plug.
I have seen the VM carbs do this and it can sometimes be a sticking slide but is usually because the carbs were not manually synch'd well.
First check the slide for smooth action. If OK, manually re-synch the carbs.
Does your manual show you how to adjust the carbs to the fully closed position? You first back off the idle screw knob so it cannot contact the throttle pulley. Then loosen all the nuts that hold the slide adjusting screws. Then loosen the screws themselves just enough so they are loose and not even finger tight. Make sure you have the proper throttle cable slack and open and close the throttle several times. Now adjust each slide
to it's fully closed position. Just as it seats, STOP, don't seat it any harder.
Do this to all 4. The secret lies in knowing when to stop. Tighten the holding nuts and be SURE the screws don't move. They should all look uniformly closed to the eye. Then adjust the fully open position. (It's getting late so if you need help with this part, I'll post tomorrow.)
After adjusting the fully open position, synch with your vacuum tool.
You should be OK.

[saaz]

I agree with Keith. You have maxed out the possible adjustment on that carb, so time to set them all back to a position where you can synch them.

[Anonymous]

Thanks a ton guys!!!

I don't believe the Clymer gives me the info for manually synching (maybe it does, i'll have to look again) but regardless, I didn't manually synch before reinstalling. I'll give it a shot tonight and let you know how it went...Thanks again!

Do ya'll know the approximate vaccum level (in cmHg's) that all the carbs should be synched to?

I can't believe we've got a site this good to refer to...Ya'll are great folks...Keep it up!!! =D>

[KEITH KRAUSE]

OK, since your manual may not help, here's how to adjust the fully open
position: hold the carbs with the filter side facing you. Push the throttle pulley fully open, hold it, and look up inside at the bottom of the slides.
They should be 0.5 to 1.0 mm above the top of the main bore. If they need adjustment, turn the throttle stopper screw. It's a flathead screw with a spring. You can see it contact the throttle pulley when the pulley is opened fully. You don't need to turn it much. This adjustment is important for good top end power.
Also, I forgot to mention, when you're manually synching carbs for fully closed position, look at the engine side of the slide for uniformity. The cut-away on the filter side is too difficult to eyeball.
The synch' screws holder nuts should not be over-tightened, 3 ft/lb is good.
As for how high the mercury should rise while synching, unless you have a mechanical problem, don't worry about it. If you manually synch well, the levels will be normal. The important thing is to get them as close as possible. Be sure to use a fan or two while synching. I don't worry about the idle reads either. I set them at 3500-4000rpm. After you set them, turn off the motor and open and close the throttle several times. Then re-check.
If you replace or check the manifold o-rings, grease them with some hi-temp bearing grease. Torque should be about 5-6 ft/lbs.
I don't know how well the uni's breath compared to K/N's, but your bike will probably run better if you remove the 2 floatbowl vent tubes. This is a requirement when using a Dynojet kit made for K/N's and a quality 4-1 pipe.
Let us know if you need any help.

[Anonymous]

Well, a bunch of junk came up last night, so I wasn't able to get back on it...I'll get to it on Sat. and let ya'll know how it went...

Thanks again for all of the info...

[KEITH KRAUSE]

Hi again. Just to add to my first reply, after the manual synch' turn the idle screw up a few turns or it won't start. (just wanted to be complete with my info.)

[Anonymous]

Just to give ya'll the update...

I got the carbs in order (I think) but noticed the slide adjustments on #1 and #4 were needed to be adjusted considerably higher to bring them in synch than did carbs 2 and 3. Thought, "Oh, well", and went for a nice 50 mile ride (& watched my buddy ditch his 93, garage-kept, 6k mile, Honda Shadow 1100, that he'd owned for a week). By the time I got home, I was running on 3 cylinders. Number 1 cylinder plug was carboned over, but still firing. Number 4 cyl. was wet and the plug was completely dead. Cylinders 2 & 3...the plugs looked good...A little grey on the tips...(at least I think that's good). I decided to go ahead and check the valve clearance...Cylinders 2 & 3 were perfect, but cylinders 1 & 4 were way tight...

So...

After gashing my hand trying to fabricate a valve shim tool and eventually giving up, I'm now waiting for the tool to arrive on Wednesday. By Wednesday night, I'll have an idea as to what shim sizes to get and get my cylinders back in order. Everyone kept saying, "check your valves before you synch..." But since I know better than they...

Anyway, does this sound like the correct senario for the probs. i'm describing? I hope so...As always, any input you may have is certainly helpful...

[KEITH KRAUSE]

Yes, correct valve clearance is important to carb synch'. So is ignition timing. After you set the clearances and check timing, re-synch' and let us know what's going on.

[Anonymous]

Well, it's been awhile, but here it goes...and thanks for all of the carb-synch advice guys

It ended up that I had 1 tight valve on #1, 2 tight valves on #2, #3 was within tolerence, & 1 tight valve on #4. So now all of my valves are within tolerence. I went back and re-synched the carbs and went for a ride. Fifty miles after the valve adjustments, #4 plug died...soon after, plug #2 died. Those plugs were wet...My garage smells like fuel...Seems like it's running rich.

Am I right in assuming that getting rid of the tight valves is causing the bike to run rich?

I have put a DynoJet Stage 3 in the bike, but have put less than 400 miles on it since the install. I haven't yet gone through their test that they tell you to run to get the carbs right , but I will try to do that this weekend. I'll probably need to go back to the leaner setting.

A few more questions if you wouldn't mind answering...

1. On a 78 GS1000, where are the "Pilot Screws"? Are these the screws on the underside of the carbs (Mikuni VM26) that Clymer tells you not to mess with (that they're factory preset)? DynoJet never says anything about "pilot screws", so I have no idea how to go about adjusting them, or what will happen if I do... Are pilot screws the same as a fuel mixture screw? (I know where the air mixture screw is \/ )

2. When I first pulled my carbs apart, I had a small nylon washer above the e-clip on my needle and a much thicker nylon washer below the e-clip.
The guy at DynoJet said it sounded like the carbs had been rejetted before, and to put BOTH the thin and thick nylon washers on the needle below the clip. Is this right? It looks to me like it shouldn't make any difference below the clip, but i'd like to know for sure.

I'd love an answer to some of these questions, and always look forward to any other advice you can give me.

Thanks again guys...

[KEITH KRAUSE]

Hi. I have experience with these carbs and the Dynojet kit. I have a '79 GS1000E with similar mod's.
First of all, it DOES MATTER how the plastic/nylon spacers are installed. The thin spacer goes under the e-clip. The thicker spacer goes above the e-clip. If they are reversed, the result will be a richer than anticipated mixture. For your second question, the pilot screws are underneath and to the front of the bowls. They may still be sealed by the factory. If they are, you must be careful in turning them. They can be tight and the heads can strip easily, just like the side air screws. The factory puts a sealant on the threads to help stop people from adjusting them. They are commonly set at different points to allow for differences in each cylinder. They are generally 3/4 to 1 1/2 turns out from the factory.
With your pod filters, you will need to adjust them. Turning them out richens the mixture, in leans them. When you seat them, DO IT LIGHTLY so you do not break off the sharp tip inside the carb. Use a very good fitting screwdriver. Keep notes on how far out each screw was adjusted. I have had better luck by turning the screws IN first and then cleaning out any sealant, then adjust them out to where I want. Some people say using a heat blower will help loosen the screws.
With your mod's,(I don't know what brand of 4-1 pipe you have) I would start by adjusting each pilot screw 1/2 turn more out than it was. Remember, they are'nt necessarily adjusted the same. Next, adjust your side air screws to achieve the highest idle once warmed up. Turn them out 2 at a time, in 1/2 turn increments to more easily hear the rpm's, then re-adjust your idle screw knob to about 1100 rpm.
As for your needles, put the e-clip in groove #4 from the top, with the Dynojet metal washer on top of it. Be sure to put the factory nylon spacers on correctly. If you have a quality pipe such as Vance & Hines megaphone, I would suggest putting the e-clip in groove #4 with NO METAL WASHER on top of it.
Next, use the Dynojet 138 main jet. I have found the 142 is a bit too rich and causes some bogging at higher speed roll-ons. Once the needle is raised to the above settings, the 142 mains "overlap effect" is just too much and creates bogging. Also, I have K&N pod's and a 1085 piston kit, so if my motor does'nt like the 142's, your's will not either. Go with the 138's.
The floats need to be close to .95" with the bowl gasket removed. Remove the 2 floatbowl vent tubes. They restrict the venting.
In my experience, synching the carbs with a vacuum tool is required. Get the levels to within 1 cm of each other at about 3500 rpm. Don't be too concerned about idle levels. If the 3500 rpm levels are off as little as 2 cm, you may experience mixture problems. For example, if 3 are level with each other and 1 is 2 or 3 cm above them, that higher one will draw more fuel and run richer than the others. Be patient and get them adjusted right. These carbs are very finicky. Put a couple of fans on the motor to avoid over-heating. If you do a good manual synch' first, you will have an easier time of it. DO NOT over tighten the carb slide adjuster screws. 3 ft/lb is correct.
If your COLD valve clearances are within .03-.08mm you're OK.
Make sure your ignition timing is correct. Gap your plugs to .026".
Test ride and get some plug reads. Let me know if this helps. I'm a very slow one finger typer, so it's nice to hear something back if I helped. Keith.

[KEITH KRAUSE]

One more thing. Dynojet warns us about possible "driveability" problems with re-jetting. The only minor complaint I have is I get a couple of spits at cold start ups. Usually it has to be about 55 degrees or colder. I have tried adjusting the pilots out more and larger pilot jets. This only causes other problems. It's not a big deal, I can live with it.
Just for your information.

[Anonymous]

Keith and the boys (and girls )

All of my pilot screws have been adjusted at one time or another (i'm the 3rd owner), so I really have no idea where the factory settings should be, but i'll start with the settings you gave me Keith. The 4-1 pipe looks like a Vance & Hines, but it doesn't say. Regardless, I plan on putting a new V & H Megaphone on it within a month or so, so I'll jet as if I already had.

I wasn't really confident with the guy I talked to at DynoJet when he told me to put both of the nylon washers under the e-clip, but I did it anyway...If what ya'll are saying is correct, it's no wonder my bike is running rich! Also, Dynojet advised me to install the 142 mains, so those will come out too.

I'ma try and tackle this stuff on Saturday, and I'll keep you all posted...
Thanks for all of the info...I'm not too proud to say "keep it coming"; I need it!

Honestly, I want to thank all of you again (esp. Keith Krause) for all of the input. If I didn't have folks like you and a site like this, I'd be in bad shape.

Sincerely,
Thomas Ashley Summers, aka Spit IX 8)

[earlfor]

I dont know what the book calls for for your bike, but my 79 750E with VM carbs has been balanced to 23 inches of mercury at 2500 rpm for the past two years and that setting seems to work well. That would be 63.5 cmHg @ 2500 rpm.

In synchronizing your carbs, if #4 is off the top of the scale, the slide cannot be raising as throttle and rpm are increased, As rpm increases, throughflow volume increases. Normally, the slide would raise and vacuum levels would remain relatively constant. For an increase in rpm/air volume processed, the slides are supposed to raise which increases the crossection of the carb throat which maintains a constant intake velocity. For the vacuum level to increase off the scale, the increased volume has to be passing through a restricted opening (the carb throat) If the slide was raising as it should, the velocity would not be increased as it is. An increase in velocity will siphon more fuel and I would expect the cylinder to be very rich, Possibly to the point of not firing.

When first time synching my carbs, I loosened all the adjustment on the top of the slides (inside the carbs) and set each slide to fully closed as a starting point. Can you stick your finger into the throat of carb #4 and check that the slide will actually raise and is not sticking or rough?

Also, check to be sure the throttle cable is slack and not still holding the throttle open when in the closed position.

Make sure the throttle idle adjustment knob is turned so as to not be changing the idle settings.

Check to be sure the choke cable has enough slack to actually be off when it is pushed to off.



Earl

Thanks a ton guys!!!

I don't believe the Clymer gives me the info for manually synching (maybe it does, i'll have to look again) but regardless, I didn't manually synch before reinstalling. I'll give it a shot tonight and let you know how it went...Thanks again!

Do ya'll know the approximate vaccum level (in cmHg's) that all the carbs should be synched to?

I can't believe we've got a site this good to refer to...Ya'll are great folks...Keep it up!!! =D>