Electrical, running mainly on one cylinder

Helix · Post by **Helix** » Mon Mar 16, 2009 5:27 pm

Hi

I am currently a new owner of a 74 gt550.

History: Bike has not run since 96. I rebuilt the carbs over winter.

Present: I started up the bike on Sunday with only one cylinder working.
After running it for five minutes the second cylinder began to fire up.

Today I swaped the coil for a known good one with the same results.

The middle cyclinde is not getting spark and the left one get the spark after 5 minites or at higher RPM.

All spark plugs are good.

Any info would be appreciated.

Thanks

Rob

H2RICK · Post by **H2RICK** » Mon Mar 16, 2009 6:16 pm

What compression do you have on the various cylinders ?? Less than 100 PSI minimum on any one cylinder ??? If so, stop spending time and money and correct your problem with the low compression cylinder(s) first.

If you have at least 110 PSI or higher all across then move down to the next step.

How's your battery condition ?? 12.8 volts or better ?? If not, charge or replace battery before going on with troubleshooting.

All spark plugs are good.

Does this mean they're NEW ?? If not, then put some NEW plugs in instantly, preferably NGK B7ES's.....properly gapped, of course....NOT the way they come out of the box.

How's your timing ?? What condition are your points and condensors in ??
New ?? Used ?? Points clean and gaps adjusted properly ??

Fresh gas in the tank ?? Gotta have fresh gas because even if it's sat for a month there's a good chance that it's gone bad if it wasn't stabilized....and even then I'd want to be using some fresh stuff on ANY bike I'm trying to troubleshoot. Modern gas goes bad quite quickly.

Helix · Post by **Helix** » Mon Mar 16, 2009 6:31 pm

Thanks for getting back to me, so fast

I haven't checked compression yet.

Plugs are not new, gas is more than a month old.
Points and condensors look good. There clean, not sure on gap.

I will start tomorrow with a compression trst.

Thanks

Rob

Helix · Post by **Helix** » Tue Mar 17, 2009 6:00 pm

I did the compression test all were consistent at just under 150 psi

tz375 · Post by **tz375** » Tue Mar 17, 2009 8:40 pm

That's a great start. Now you want to see if you have a spark on all three plugs.

You have three choices of ways to test this.

1/ remove all 3 plugs. Insert plugs into plug caps. lay plugs on head and turn it over with the ignition on and watch for the fat spakes.

2/ As above but use spark gap testers available for your local auto repair store for a couple of bucks each - much easier to see the spark.

3/ Similar to above but insert finger into HT lead and determine how hard it smacks you. Just kidding with that one

If there isn't a fat spark start cleaning connections from the battery through the wiring loom and ignition and main switches through to the coils.

Check for a good ground connection from the motor to the frame.

If there is still no good spark on all 3, check and clean the points and look carefully to see if all three are wired correctly.

With the engine running look for excessive sparking at the points - a a sure sign of a dead capacitor.

If the electrics check out OK - clean it all anyway and then start back on the carbs.

Helix · Post by **Helix** » Fri Mar 20, 2009 5:45 pm

I have bought the NGK b7es's as you said.

I was checking the points and noticed that my center point and right point are touching the small tabs (sorry don't know anything about points).

The left point is gapped properly and it is the cylinder that works.

I will re-gap them tomorrow and see if this helps

rngdng · Post by **rngdng** » Fri Mar 20, 2009 6:06 pm

If the points aren't opening, that'll certainly stop it from sparking.

Good luck.

Lane

Barry S. · Post by **Barry S.** » Fri Mar 20, 2009 8:21 pm

After you set the points gap the timing needs to be set, a timing light will work if you have one.

Helix · Post by **Helix** » Fri Mar 20, 2009 9:21 pm

Do I really have to set the timming? If so can I follow the instruction out of the owners manual?

I don't have timming light

H2RICK · Post by **H2RICK** » Fri Mar 20, 2009 10:24 pm

Helix: The problem with the instructions in the owner's manual is...How can you be sure when the points actually open ??
Do you have an analog ohm meter ?? If so, you can get the timing close enough to get you by until you can get hold of a timing light.
The Clymer manual gives the instructions for doing this by using a meter in conjunction with a dial gauge.....but you CAN use the timing marks on the little 3 bladed "propellor" instead of the dial gauge to get piston location.