Cylinder 2 Runs Perfect! But Not The Others Why???

[br1amb]

I bought a 79 GS750L that was in not running. The owner said he used it one day and it ran ok ,but used alot of gas. The next day the bike wouldn't run. It was sitting in storage for 7 months.

Here's what I did.

The bike had no fire...

The spark plugs caps had black tape all over them. Didn't look right removed the tape and found cracked caps or caps that were not in ohm spec. Replaced spark plug caps with new NGK Plug Caps. When I tested the ohm rating from plug cap to plug cap on the same coil it's a about 10ohms lower than spec. Guessing this is because the NGK Plug caps are lowering the ohm. Actually I know this is true because the coils are in spec with the original spark plug caps. Is it ok to run these spark plug caps?

Next I bought a tune up kit for with new points etc...The bike has fire and runs poorly. So i removed the carbs and cleaned them and reinstalled. The bike ran poorly on the bottom end and had tons of midrange almost like it was too lean. I parked the bike and the next morning had trouble starting it like it was flooded. had trouble at idle, but once it got warm it was ok.

My guess is the needle and seats needed to be replaced and gas was running into the cylinders all night. I haven't checked the oil yet but i am 100% positive there will be gas in the oil.

Took out the carbs cleaned them again installed four rebuild kits. I set the carbs to the following specs.

Float level 27mm
Pilot air screw 1.5 turns out
Pilot fuel screws 1 turn out

Cleaned out the gas tank.

Put everything back together. It is running so poorly that i put my hands on the the exhausts pipes to see which one is staying cold.

Cylinder 2 heats up quickly
Cylinder 4 stayed cold the longest but then got hot
Cylinder 1 was warm and took it's time getting hot
Cylinder 3 was barely warm and took it's time getting hot

I am sure there is gas in the oil which would lower compression but I don't think thats the problem. When i checked the fire on Cylinder 4 it appeared to be week. So while it was turning over the engine i grabbed the onto the plug. I got a small jolt but not what I would have expected.

I just installed new plugs today.

What would make one cylinder run so much better than the other three?

Thanks for any and all of your help.

I

 

[Griffin]

If there's gas in the oil, do not run it. You will destroy the bearings if you do, plus if there's enough gas in the oil, you could suddenly find you have far more combustion than you want. Check the oil for gas. If it's there, drain the oil, pull the carbs, and go through every step of the carb cleanup series step by step, omitting nothing. Check float heights on carbs once they're cleaned. Bench test the carbs for leaks before reinstalling. If they leak gas, you probably need new needles and seats.

As for the resistance on the plug caps, it should be in the 25,000 ohm range if I remember correctly. You said your reading was "ten lower than spec". Did you mean 10,000 ohms lower? I have NGK caps on my '81 750E with stock coils, it runs great.

 

[Griffin]

The pipes heating up slowly could just be that hot gas is working its way up backwards into them from your hot pipe, not that you have weak combustion.

 

[Suzuki_Don]

Hi. The 27mm seems a bit excessive to me. I dont know the true float height. Some of the manuals have the incorrect float height information in them. I know the Haynes did for my 550 with VM carbs.

 

[Griffin]

Another thing to do while you have the tank off is to check the petcock for proper operation. In prime position, gas should run freely out of it. In reserve and on, nothing should come out. Install the vacuum tube on the petcock and suck on it. Gas should then freely flow in both the reserve and on positions, assuming you have a couple gallons in the tank.

If the petcock flows gas in on or reserve when no vacuum is applied, replace it.

 

[br1amb]

Trial 2

Trial 2

Let the bike cool down. Restarted this time cylinders 2 and 3 heated up quickly. Cylinders 1 & 4 took way longer to heat up.

I checked the oil and it's not discolored, but you can smell the gas. Going to change the oil.

I have completely cleaned the carbs with carb cleaner and air twice.

I set the carbs to the following specs.
Float level 27mm
Pilot air screw 1.5 turns out
Pilot fuel screws 1 turn out

Rebuilt carbs with all new jets and needles and seats etc. So it's not dirt in the carbs.

Also when i gas it at idle it dies.

Going to change oil any thoughts appreciated.

 

[Suzuki_Don]

Sounds like ignition problem to me with the coil that supplies juice to cyl 1 & 4. Test voltage at coil with ign on. Check out all connections on that coil and wires coming from and to.

 

[br1amb]

Suzuki_Don

" Sounds like ignition problem to me with the coil that supplies juice to cyl 1 & 4. Test voltage at coil with ign on. Check out all connections on that coil and wires coming from and to."

I have tested voltage to the coils when i first got the bike. I think it was around 11+ volts.

I wonder if my point gap is off.

 

[Guest]

valve clearances? cured my cold pipes. boot orings?

 

[br1amb]

I can hear one valve ticking. Was hoping it was because of the gas in the oil.

How hard is it to set the valve clearance on a 79 GS750?

 

[Griffin]

It's easy to check the clearances, all you need is a metric feeler gauge of the right thicknesses.

Adjusting the clearances requires a special tool ($15 or so at CRC II) and you'll have to get some shims in all likelihood.

Do a search on valve adjustment, you'll find dozens of threads.

Also, try turning your pilot screws 2.5 turns out and see what happens.

 

[br1amb]

Griffin,

Do you mean pilot air screws or pilot fuel screws 2.5 turns out?

Thanks man

 

[Steve]

I have completely cleaned the carbs with carb cleaner and air twice.

Rebuilt carbs with all new jets and needles and seats etc. So it's not dirt in the carbs.

When you "cleaned the carbs", did you take them completely apart, dip each carb body in Berryman's or Gunk carb dip overnight, then re-assemble? If you did not do that, then you need to do them a third time, but do the whole job this time. After sitting in the dip overnight, all the gunk in the little passages behind all your new jets will be softened. Now you can squirt some spray carb cleaner and/or compressed air through all of them to make sure they are clean. Be sure to wear safety glasses, as some of them come right back at you. :shock:
Also, when you installed your carb kits, did you keep the stock parts? Sometimes the kits have parts of questionable quality, so it might be better to clean the old parts and re-use them. It is also rather distressing to see how few o-rings they actually give you in the kit and how many more you really need. You can get a complete o-ring kit from cycleorings.com for not a whole lot of money, probably half of what you paid for just ONE of your rebuild kits. When you order your o-rings, be sure to also get the o-rings for the intake tubes. These are the tubes between the carbs and the cylinder head. While you are changing those o-rings, you will notice the (lack of) quality on the screws that hold the intakes in place. You can get stainless steel replacement screws from cycleorings, as well. Your total investment there should be less than the price of one of your carb kits, which you probably did not need. :-s

.

I can hear one valve ticking.
How hard is it to set the valve clearance on a 79 GS750?

Are you sure it's a valve ticking? Clearance would have to be rather large to hear a valve ticking. If you have a rubber hose avalable, use it as a stethoscope and move around the engine to find the source of the noise. My money would be on a leaking exhaust gasket. They can "tick" and sound just like a loose valve.

How hard is it to set the valves? Not very hard at all. Do you have a manual? It does not really matter whether it is a factory manual, Haynes or Clymer, they all have a decently-written procedure. There is also a nice tutorial on BassCliff's 'little' website that shows you with better pictures than any of the manuals. You can also send me an e-mail with a request for my spreadsheet that helps you with the math to determine shim sizes and also helps you keep track of your shims and clearances from one service interval to the next.

.

 

[br1amb]

Steve I understand what your saying about cleaning the carbs by dipping them overnight. What i did was spray carb cleaner in every hole with the jets out and watched the carb cleaner come out of the corresponding hole. In the past this has always worked for me. Got i hope it's not the carbs.

 

[Griffin]

Griffin,

Do you mean pilot air screws or pilot fuel screws 2.5 turns out?

Thanks man

Fuel screws. ut now that I think abou it, are the plugs in 1 and 4 wet and black after you've run the bike and got no fire? If so, belay my last. IF they're wet and black, try turning the fuel screws in .5 turns o those two carbs.

I've a feeling you've got a couple things going on here, but you need to explore the simple things one at a time first.

 

[br1amb]

Griffin

I will check them tomorrow morning.

Thanks again

 

[br1amb]

Coil voltage

Coil voltage

Hi guys,

I know very little about electrical and that seems to be my problem.

Set ignition points to .018.
Zero fire at plugs
These are new points and before I used the feeler gauge I cleaned each feeler with lacquer thinner and wiped off feelers with towel so no oil from the feeler gauge would get on the points.

No fire at plugs.
Thought that maybe oil from the feeler gauge got onto the points and cleaned the points with lacquer thinner very carefully.

No fire at plugs
Grounded open points with a screw driver and there is spark at the points.

Coil 1 = cylinder 1 & 4
Coil 2 = cylinder 2 & 3

Key On
Coil 1 = 9.2 volts
Coil 2 = 9.2 volts

However I am currently charging the battery and there is 12.78 volts across battery posts

What voltage do i need at the coils? I am guessing 12volts.

Any ideas? Your help is appreciated.

 

[doctorgonzo]

I don't know if 9.2 is low enough to make you not fire, but search for "coil relay mod" and it will explain how to get that back to closer to 12 volts.

 

[br1amb]

I don't know if 9.2 is low enough to make you not fire, but search for "coil relay mod" and it will explain how to get that back to closer to 12 volts.

I have read the coil relay mod a while ago but thought it was more of a performance tip. I will look at it again.

Bike 79 GS750L

Voltage across fuses while grounding to battery terminal.
Fuse box is on the side of the battery

Voltage across battery = 12.10 volts
15A Main = 11.38 volts
10A HD Lights = 9.97 volts
10A Signal = 9.98 volts
10 A Ignition = 9.91 volts
Coil = 9.2 volts

I can't see any fire or feel any fire even when grounding spark plug. However the bike starts on 2 & 3 cylinders. As it runs on these too cylinders all the sudden cylinder 1 starts to sputter and then cylinder 4 starts to become alive. But 1 & 4 only come alive after 2 & 3 are hot.

New NGK spark plug ends tested out 4.9k - 5.0k
Coils ohm out

Any ideas?



I am grounding the plugs to the frame to the head bolts etc. once in a while you see spark but it's weak.

 

[Suzuki_Don]

First of all remove the spark plugs. Place a phillips screwdriver of the correct size in the end of the spark plug lead where it normally attaches to the spark plug. Hold the metal shank of the screwdriver 1/8th to a 1/4" from cylinder head fins and crank engine. You should get a good healthy spark. If you don't then that has eliminated the spark plugs from the problem. I would then swap the wiring on the coils from the points which in effect puts the other coil to 1 & 4. If 1 & 4 then run OK the problem is with the original coil on 1 & 4.
Hope this helps. Cheers. Don.