Thread: starting - what am I missing?

New here... I recently inherited a '74 CT70 with 5800 miles on the odo. It is in semi-rough shape overall but I was told it was running "just last week". I would like to make this a project for my son and I - picked up a new NGK C7HSA plug, figuring that would come in handy for starters. When I got there, I noticed there was a champion plug in there, and was very surprised to see the diameter of the thread into the cylinder was much larger than the NGK - the little NGK did not fit(?)

So I tried starting with the champion well-seated in there and followed the starting procedures outlined on this board elsewhere (3 kicks with choke on, ignition off - then switch on, give 1/8 throttle and kickstart again).

Nothing, not even a hint of ignition. Very little resistance on the kickstarter. Then I removed and grounded plug. There is spark, but very faint/small and yellow. Noticed a hissing sound with each kick coming from the block - suspect blown head gasket?

I have a feeling I am doing something wrong, but can't imagine what. Any guidance on what to do next appreciated. I am currently planning to taking a compression tester out tomorrow and see what that yields. Thanks for any advice!

Is the battery installed? A good, or bad battery, does not matter, you need to complete that circuit. Don't ask me how I know this.

Scooby

Sounds like the spark plug hole in the cylinder head was stripped. Someone may have put in a helicoil for the larger plug. Weak spark could be a sign that your points need to be cleaned or replaced. Could also be your condensor. I do not like engines which have been tampered with, refering to your spark plug size. The wrong plug size would effect operation of engine as well.

I had same problem this week.
This is what I found.

1. Weak spark --> adjusted points and fixed that.
Note: I ran a direct circuit from stator to coil to sparkplug to eliminate all the other electrical issues. ( do this by attaching the small black wire from Coil ( within frame under seat ) to the black wire coming from stator
2. Low compression --> found that valve was sticking --> replaced head with one off another motor and fixed that.
3. Hissing sound from cylinder --> gaskets bad --> bought a roll of gasket material from autozone ( $5), made sketch of gasket, cut out with sissors --> fixed the leaking head.
Given all the above, she ran at max RPM! ( unfortunately, tho, she blew up the other old head... so I am back to square one! But I did get her running!!
Good luck

Thanks for the responses... I think the helicoil has indeed been fired in here. i can push start it and it runs OK, but will definitely need a rebuild at some point. Rings must be toast, as there is significant blue smoke. It is a miracle the thing runs at all!

Has anybody else ever run a bike with a larger thread size plug for a long period of time? I am wondering whether there are any long-term problems and whether I should get a brand new head, vs. rebuilding this one.

Personally I would get a different head with plug threads the correct size. If she is smoking bad it needs a rebuild anyway which probably means new rings , cylinder bored or honed, new gaskets, o rings, valves etc. I believe DrATV OPERATES HERE has complete heads for sale.

Originally Posted by Squeebles

Thanks for the responses... I think the helicoil has indeed been fired in here. i can push start it and it runs OK, but will definitely need a rebuild at some point. Rings must be toast, as there is significant blue smoke. It is a miracle the thing runs at all!

Has anybody else ever run a bike with a larger thread size plug for a long period of time? I am wondering whether there are any long-term problems and whether I should get a brand new head, vs. rebuilding this one.

Lots of people helicoil or keen sert their sparkplug holes once they are stripped out. I have been wrenching on these things for more than 10 years and I have personally never stripped a plug hole...doesn't mean I haven't encountered them stripped though.

What I do is actually drill and tap the hole out from 10mm to 12mm and install the same reach plug from another application. I don't know it off the top of my head, but you can find the right one on the NGK website. Works just fine and will run until you strip that one out! No reason to belive anything would be different. Its a much cheaper and cleaner solution than a keen sert or helicoil or whatever. I don't deal with them. If the hole is stripped...it is stripped and I go to the next size.

Thanks for all the great advice, this site is excellent! I did an oil change to Rotella 15w40 and that slightly heavier oil really cut down on the smoking. but it does need a rebuild at some point soon.

On the plug issue - I went to my local Autozone (i know, i know...) to ask them to check what 12mm NGK plug would cross with the c7hsa, in terms of depth, heat etc.. They had no clue where to begin to look for that info. I poked around the ngk site with no luck, nothing else comes up but the c7 for the C70. So I am a bit stumped... there is a champion in there now and it runs OK, so I could cross that to its NGK equivalent - but that is assuming the person who put the Champ knew what they were doing.

Anybody else out there have a similar problem and have to use a 12mm plug and if so which one? Thanks in advance,