Trying to fire on all 4s

[Anonymous]

My GS750 (1978) had been in storage for 10 yrs. Last summer (August) I cleaned out the carbs, changed the oil, replaced the plugs, and got it running, but sometimes only on 3 cylinders, sometimes on 4. A month ago, I tried the bike again, and although it starts, never on 4 cylinders. When i removed a spark plug , and held it close to the engine ( 1/4 inch) the spark was strong. When I grounded the plug to the engine..... no spark.... so .... I then changed the spark plug caps.... and still.... same problem ! By the way... same thing happens on all 4 spark plugs.
Shouldn't I get a good spark when I ground it to the engine ??
So... Im thinking... do I have a grounding problem ?
Oh, well.... whats what im asking.... im out of ideas. Any advice ?

[10yeareer]

Are you saying that when you held the plug 1/4" from the engine the spark arced from the plug to the engine? But, when the spark plug treads are touching the engine, you don't get a spark?


Anyways, It doesn't sound like your problem is spark since the other three cylinders that worked, yielded the same results.

I would check the valve clearances and then pull the carb off the cylinder that is not firing and make sure all the passages are cleaned.

[Anonymous]

following up

Yes, when the spark plug touches the engine, no spark at all. HOWEVER.... i forgot to mention, on one cylinder, that is not sparking, when i remove the spark plug wire from the spark plug, and hold the wire (cap) just above the top of the plug ( but not touching ) the cylinder fires.

[Anonymous]

follow up #2

BTW.... right now... its only firing on one cylinder, sometimes 2

[10yeareer]

hold the wire (cap) just above the top of the plug ( but not touching ) the cylinder fires.

I am sure your using an insulated tool to do this and not your hand but I just want to point out that you don't want to use your hand or you could get zapped pretty good. I learned that one the hardway in my teenage years


Ok, So you are able to get spark at three plugs but one of them you are not getting spark.

Are your plugs in decent shape and gapped correctly?

You definitely don't have a grounding problem. Either your plug is bad or your plug isn't contacting and plug cap.

[earlfor]

Re: Trying to fire on all 4s

From your post, two things are obvious. The problem is in the ignition system or wiring, and something is gnatzelfratzed. :-)

Since we dont know precisely where the problem is, then the most efficient way of fixing it is to check the complete system.

A stock 78 750 would have a points and condensor ignition system.

1. gap the points and set the static timing for the 1-4 cylinders to the |F1 setting and the 2-3 cylinders to the |F2 setting. Point gap should be 14 thousandths. Iif you do not know how to precisesly set this up, say so and I will post a step by step set of intructions for gapping and timing)

2. Remove the gas tank and with a multimeter, check the voltage on the coil + leads (orange/white wire) on both coils. They should read almost the same as the voltage at the battery terminals. Ignition is switched on for this check. (multimeter scale set to 20 V DC) voltage measured should be greather than 12V.

3. Remove the positive (orange/white) wire and the white or black wire from both coils and check the resistance between the + and - terminals on the coils. Resistance should be 3 ohms. It will commonly be between 3 and 4 ohms, and anything between 2 and 5 ohms is within servicable limits. (multimeter scale set to 200 ohms)

4. Remove the plug caps from the 1 and 4 cylinders. Check resistance between the metal connectors inside those two caps. Resistance should be between 30k and 50k ohms. Do the same check between cylinder plug caps 2 and 3. (multimeter scale set to 200K ohms)

5. On the orange/ white lead wire (positive) to your coils, check the voltage of the wire by switching ignition to on, placing + multimeter lead on orange/white wire and black- meter lead on engine cooling fin or frame to ground it. Voltage should be about the same as voltage at battery terminals.

6. Check frame to coil mounting bolts for corrosion and clean if need be.

If the plug cap reading are not within 30k-50k, you can try removing the plug caps (they unscrew from the wires) and trimming 1/4" of insulation from the end of the wire, bending the core wire over the end of the spark plug wire end and then screwing the plug caps back into place. (you may not now have a good connection on the ends)

The voltage of the battery at the terminals with nothing on the bike on (ignition switch off) should read 12.7-12.8 if full charged and about 12.4-12.5 at 50% charge. Anything less that 12.4 is not what I consider within servicable range and I would replace the battery if it will not hold a higher charge than that. 12.0 -12.2 is pretty much a dead battery and useless.

Let me know what you find and depending on test values, we will know where to go.

Earl

My GS750 (1978) had been in storage for 10 yrs. Last summer (August) I cleaned out the carbs, changed the oil, replaced the plugs, and got it running, but sometimes only on 3 cylinders, sometimes on 4. A month ago, I tried the bike again, and although it starts, never on 4 cylinders. When i removed a spark plug , and held it close to the engine ( 1/4 inch) the spark was strong. When I grounded the plug to the engine..... no spark.... so .... I then changed the spark plug caps.... and still.... same problem ! By the way... same thing happens on all 4 spark plugs.
Shouldn't I get a good spark when I ground it to the engine ??
So... Im thinking... do I have a grounding problem ?
Oh, well.... whats what im asking.... im out of ideas. Any advice ?

[Anonymous]

Could it be that the sparkplugs are dirty? If they are filthy on the outside the spark will ride down the outside of the plug to the head.

Steve

[Anonymous]

following up...

As per instructions,
I checked the spark plugs... they are not fouled.
I checked the coils, and they have good voltage, as well as the battery.
I checked the ohms, and that is also within specs.
To eliminate the possibilityof gas, i poured some gas in each cylinder, and the engine will not fire up at all.
Still.. when I remove the spark plug, I get a very good spark on each plug, ONLY if I hold the plug 1/4 inch away from the engine. As soon as I ground the plug to the engine, the result is no spark at all.
BTW... I also checked the ignition, and it is a DYNA electronic ignition. Now... since i get a strong spark, is it still possible that I have something wrong with the ignition system ? Last season, I did have the engine running on at least 3 cylinders, sometimes 4. This year...it seems the best I had was 3.... then 2... then one... now no cylinders fire.
And again, thanks for all the advice.

[earlfor]

Re: following up...

I cant help you if you dont answer my questions.

Earl :-)

As per instructions,
I checked the spark plugs... they are not fouled.
I checked the coils, and they have good voltage, as well as the battery.
I checked the ohms, and that is also within specs.
To eliminate the possibilityof gas, i poured some gas in each cylinder, and the engine will not fire up at all.
Still.. when I remove the spark plug, I get a very good spark on each plug, ONLY if I hold the plug 1/4 inch away from the engine. As soon as I ground the plug to the engine, the result is no spark at all.
BTW... I also checked the ignition, and it is a DYNA electronic ignition. Now... since i get a strong spark, is it still possible that I have something wrong with the ignition system ? Last season, I did have the engine running on at least 3 cylinders, sometimes 4. This year...it seems the best I had was 3.... then 2... then one... now no cylinders fire.
And again, thanks for all the advice.

[Anonymous]

answers to questions

Battery is new and fully charged.... engine spins very well... but my meter ready only 11 volts ( maybe a bad meter ?? )

Voltage at coil when i ground the black is 9 volts

resistance on coils is 3 ohms

spark plug caps are at 50 ohms ( thay are all new)

[earlfor]

Re: answers to questions

The first thing to do is have your multimeter checked for accuracy.
12.7-8 is a fully charged battery. 11 volts is a dead battery, and the ignition system will not work at all on 9 volts. Which is it?

Earl

Battery is new and fully charged.... engine spins very well... but my meter ready only 11 volts ( maybe a bad meter ?? )

Voltage at coil when i ground the black is 9 volts

resistance on coils is 3 ohms

spark plug caps are at 50 ohms ( thay are all new)

[Anonymous]

thank you

Thanks... i will check my multimeter.... and then will have results that mean something
thanks again for all your good advice

[Anonymous]

had same problem...

Seadrive1,

I recently had exactly that same problem (spark wouldn't fire in the hole and could arc when out of it etc) with my #2 cylinder.

It turned out that I had a problem in the last couple of inches of my plug wire (or connection to the cap) closest to the plug. When I compared the resistance along bits of the removed wire, I found a dramatic increase near the end of the wire. I suspect that this broke down the insulator (esp. in the strongly curved part), and lead to arcing from the wire to the cam cover. (you probably don't want to test this on a wire that you plan to run on the bike!)

I removed about 6 inches of the plug wire, and replaced w/ 6 inches of a good (copper core) plug wire. Of course, a good solder job, and excessive insulation at the joint is necessary. Now, she's running on all 4 again! \/

Good luck!
mikedr

[Anonymous]

got it going....

So.... I removed my plugs ( which were new.... so i figured it didnt need any cleaning after 1 hour of operation), and saw they were totally fouled !!! Cleaned them, replaced them and wow..... all 4 cylinders fired, smoothly... for about 3 minuites... then the bike appeared to be choking..... no gas ??? ..... I removed ther fuel petcock... and saw a Vacumn line connection to the back of the petcock. NOTHING CONNECTED !!!
Well.... my question !! On my carbs, There are 4 hoses at the bottom, one for each carb.... so I assume they are overflow lines.....
In between my carbs....there are 3 additional hoses..... not connected to anything.... do any or all of these somehow connect to the vacumn port on the fuel petcock ?? If not what connects there.
Thanks again... all the great advice is very helpful, and appreciated.
Irwin

[Anonymous]

got it going....

So.... I removed my plugs ( which were new.... so i figured it didnt need any cleaning after 1 hour of operation), and saw they were totally fouled !!! Cleaned them, replaced them and wow..... all 4 cylinders fired, smoothly... for about 3 minuites... then the bike appeared to be choking..... no gas ??? ..... I removed ther fuel petcock... and saw a Vacumn line connection to the back of the petcock. NOTHING CONNECTED !!!
Well.... my question !! On my carbs, There are 4 hoses at the bottom, one for each carb.... so I assume they are overflow lines.....
In between my carbs....there are 3 additional hoses..... not connected to anything.... do any or all of these somehow connect to the vacumn port on the fuel petcock ?? If not what connects there.
Thanks again... all the great advice is very helpful, and appreciated.
Irwin