Hi Guys

My buggy won't start anymore. So I took the carb of, it's being cleaned ultrasonically by a pro at the moment.

I noticed my spark is pretty weak. I'm not getting any blue/white sparks. Just a little blue/purple lightning about the tickness of a sheet of paper. I have this problem on all 4 sparkplugs.

But I can't figure out what's causing the bad spark. I gues it can't be the coils because the problem is on al 4
I have a lot of spare part lying around so I changed the CDI and the R/R, that made no difference.
I increased the ground on the CDI and R/R, that also made no difference.
I checked the fuses and cleaned all the connectors I could find with contact cleaner.

The battery voltage is about 12,5V normally and 11,5V when cranking.

I did not build this buggy myself, I bought it this way and have driven it plenty of times so the wiring is done the correct way. I just lack the skill the find out where the problem is right now.

I checked the wiring diagram and noticed the black wire (with green dots) coming from the CDI is not grounded like on the diagram. It is connected to the positive side on my buggy, very strange. If I cut it there is no spark at all.

Any help would be greatly appreciated guys. I don't just wonna start cutting and replacing wires randomly.

grounded wires from CDI
DSC_0318 by Bierlempie, on Flickr

fuses and relais
DSC_0320 by Bierlempie, on Flickr

coils
DSC_0321 by Bierlempie, on Flickr

the weak spark
DSC_0328 by Bierlempie, on Flickr

 

First off how old are your plugs?

Second, when testing for spark the plug should be TOUCHING the ground and you should be looking at the spark between the plug electrodes, NOT spark between plug and ground as you seem to be doing.

Third, where exactly is the black wire w green dots coming from and going to? Looking at a wiring diagram of an F3 right now and can`t really find anything of that color. Just because a wire is black doesn`t necessarily make it a ground wire. Is your diagram for an F3? The fact that it`s a custom built buggy puts an extra curveball to the problem as there`s no knowing are all the wires the original color or not. The fact that it has been working would suggest to a carb/vacuum/spark issue. Swap the plugs after you get the carbs back (remember that if they have been disassembled from each other you have to sync them or it will not run right.)

Do you have a fuel pump on it? Is it priming?

 

The plugs are all new. They were wet when I took them out.
Also I think the engine compression is OK, but my meter is not working properly I think. It shows about 100-110 PSI on all cylinders (this should be 180). Since they are all about the same I don't think the head gasket is blown. The engine power was good before, although it would not rev above about 11500 RPM.

The black wire is coming from the center of the CDI, on the diagram it's marked as pure black, but mine has green dots on it. I haven't been able to figure out where it leads to exactly, but if I connect it to the positive lead of the battery I have the weak spark. But the PDF of the diagram is a very bad scan so maybe I'm reading the colours wrong. It has the letter E of B by it I think.Can you maybe send me a picture of your diagram?

When I hold the sparkplug thread against metal I have a very small blue/purple spark 'in' the plug.

The fuel pump is working fine.

Any other reasons you guys can think of that would give bad spark?
Starter relay/starter button maybe?

 

Was looking at this. What exactly do you refer as a CDI? (capacitor discharge ignition), these bikes do not have a CDI box. The ECM? as in the large-ish netal box with many wires? According to that diagram it doesn't have a black wire other than the one that has white dots and goes to the coils and to the strater motor after changing color at the starter button.

Start relay/ start button plays no part in the forming of a spark. Not directly anyway.

 

Just a dumb thought: are you sure you got the plug cap order right? The spark during cranking isn't much to talk about. If you got a spark on every revolution it should start. Have you tried giving it some start spray? Not being able to rev properly would suggest you are leaning out on high revs. Is the exhaust how extensively modified? I'd try lifting the carb slide needles a notch.