Hello,

I think I am having weak spark issues on a giovanni 110CC mini hummer. After a small issue with an external combustion engine (meaning it caught fire) I rebuilt the wiring harness and replaced the plug with an NGK cr7-hsa. I was getting spark with the new plug and on the first try I was able to get the ATV to idle fine and run OK except at top third throttle so I assumed I had a carb adjustment issue. When I pulled the plug, the fouling was very bad so I adjusted the carb accordingly. Now I am get little to no spark at all unless I use a brand new plug so I am thinking that the fouling and top end "bogging" had nothing to do with the carb but with a spark issue. With a new plug I still get spark but with an old plug (even after I clean it) I get nothing or intermitent spark at best.

Does this sound like a weak spark issue and if so, does anyone know what the electrical outputs should be at various electrical connections? I would like to track back the voltages and see where the problem is. Also, what would to correct gap be for a NGK cr7-hsa plug is? My info says 6-7mm but I am getting no spark what so ever at that gap (and it seems rather large for this plug). Is the gap info I have wrong for a cr7-hsa or should I be getting spark with that gap?


Thanks to anyone who can help. My son has given up on the ATV but it has turned into a personal quest of mine to get this thing running again.

Chris.

 

Just saw the excellent wiring diagram done by LynnEdwards. Would I be correct in assuming the outputs would be the same as listed on these diagrams?

Chris.

 

I took apart and traced out the internal schematic of a 5 pin 110cc CDI, and a 4 pin/2 pin 150cc CDI. To my surprise they were exactly the same circuit (other than the connectors). Because the CDI's are the same then I would expect that the inputs and outputs must be similar as well.

 

could you explain what you mean by you " adjusted the carb accordingly"?

was it fuel fouled or oil fouled?

main jets can come lose and fall out, then it falls on it's face on the top third.

allot of the time a weak spark will cause problems when combustion pressure is high [ high load, lugging, or off idle] not to say it's not your problem but weak spark in it's self shouldn't foul a plug.

you can get spark testers or make your own to see how far or strong the spark is... just be care full it's not to far as the coil won't be able to discharge properly [ jump the gap] and it's possible to damage something else...

here is a spark tester, you unscrew it to increase the gap and see how strong the spark is. Ignition Spark Tester with Adjustable Gap - 404, by Thexton

 

Over Rev,

Since I had put the atv back together and could no longer get at the bowl easily, I cheated and leaned out the mixture by lowering the needle. I also tried running with the air filter off. Both resulted in worse performance which would indicate running lean. That is when I pulled the plug and checked it to confirm that I was running too lean. Much too my suprise, the plug was black (way black) and covered in soot as opposed to the ash color I was expecting. This is when I noticed I was having trouble getting spark so getting spark became the focus of my trouble shooting.

A weak spark is just a guess based on what conditions I am seeing.
(intermitent spark when grounded on the cylinder head even with a clean plug, trouble starting, bad performance at full throtle that gets worse with more air, and a black sooty plug if I do manage to get it started). If I can rule out weak spark then that is one less variable and I can stop worrying about the electrical side.

I think I will take the carb off again, clean it, check the main jet as you recommened, lower the needle one slot and try to fire it. If it runs again, I will check the plug before I make any adjustments. I've tried so many settings now that I can't keep straight what order I did things in. How do you tell the difference between gas and oil fouling?

BTW - If these symptoms sound like something else or you think I am way off track by all means don't hesitate to say so. I am no mechanic and am working simply from this web site and a grade 9 small engines class that I took over 25 years ago

Thanks for your help

Chris.

 

haha, well, i'm by no means an expert and others should feel free to chime in and correct me or add anything they might think is helpfull!

for me, it's all about eliminating things as you mentioned aswell.

i wish i could see the spark plug close up... it's not uncommon for a fouled plug not to spark, even out of the combustion chamber. the fact it's not sparking after awhile could be a spark issue but if the plug is appearing to be black and sooty possibly from oil or, wet soaked from gas after a relativly short period, i'd take a close look as to why that's happening. does the plug smell like gas? you can cheat the main with the needle to some extent but the fact that it seemed to make things worse has me scratching my head. but then again you say the plug is covered with black soot..? [ possibly rich]

something i have done quick and cheap to check spark quality is snap off the ground electrode from an old known good plug. if it jumps that gap... i call it good.

i'll try to tag a link to reading plugs here > Spark Plug colour color guide and engine problem chart

what one do you think best represents YOUR plug?

i have read some of your issues with this machine... it can be frustrating but keep your chin up, you'll get'er!