Topic: Help a new guy out???

[Beav068]

Okay, here is the background on this bike:

I bought it about 3 weeks ago from a co-worker who bought it new in Japan in 1973.  He then proceeded to put 15k miles on it before deciding to sell it to me and stick to riding his Magna.

So, straight away I took his 4-2 crossover header pipes off and put the original (like new) 4-4 pipes back on, changed plugs and completely cleaned the fuel tank out using heavy duty degreaser, water and a final rinse and dump with gas.  Put new fuel back in and it ran pretty well.  I then pulled the plugs and they were fouled as I expected (he never had bike re-tuned for short 4-2 pipes) and it ran even better.

All was well for a few days until yesterday it started bogging a little when it was warmed up on my second ride.  Acted like it was missing, running rough, etc.  I managed to limp the two miles home where I again pulled the plugs.  Kinda oil fouled again, but not much.  However, the #3 plug cap popped off, so I clipped and re-threaded it back on.  I did the same for all of the plug caps.

Now my problem is that it won't start at all.  I am getting spark on all 4 plugs, but it acts as if it doesn't even want to THINK about starting.  Just cranks over and over with either the electric or kick start.  Any ideas on WTH is going on?  I pulled the cutout switch apart, cleaned all the connections and tried again with no luck.  The switch isn't bad as the plugs get spark in "on" but not in "off".

Could the bad wires have caused the timing to get screwed up or have ruined a part that would keep it from running?

Thanks for your help!!

Tim

[TwoTired]

Might help if we knew what bike you have.

Try different plugs.  If the center electrode insulator has enough crud/carbon on it, the spark takes the carbon path instead of the jump across the gap.

Other than that, the machine is due for a complete and through tuneup, including the air filter.
Cheers,

[BobbyR]

It may sound dumb, but see if you bumped the kill switch by accident. My may also be flooding, u did not mention carb cleaning.

[jotor]

Battery charging?  Sounds like it might have been running the battery down until it started missing.  How fast does it turn over on the starter?  I'd clean and charge the battery and see what happens.  Then check the charging system.

Joe

[Bodi]

Are you getting fuel? Sounds like a lack thereof. If the plugs aren't wet with gas after trying to start it with the choke on, you probably have a gummed up petcock or fuel filter screen.
Pull the fuel line off the petcock and see if fuel spurts out when you select ON or Reserve.

[Lumbee]

...if it ran fine b4 u clipped the plugs, did u put the plug caps back on the right plugs?  Each plug wire must be on the correct cylinder so the timing of the spark is correct...

[Beav068]

Okay, here goes.

1972 CB750K

I got good spark across the plug (they have only been run for 3 days)

Like I said in the post, the kill switch is working and I get spark at the plugs.

The battery WAS low so I tried jumping it from a running vehicle...very good turn on the starter.

There is plenty of fuel in the carbs..I drained them to see if there was water, dirt, etc. in there and all looked good.

I did the plugs one at a time so I know they are on right.

I am guessing that it is just so badly out of time right now that it can't start.  I will try new plugs tomorrow and if that doesn't work then in the shop it goes.

As a side note, I HAD just filled the tank that morning.  Would it be possible that the fuel was so bad that it won't even fire now?

Tim

[Lumbee]

..if u'r sure ur' timing/spark are on, I would look at the carbs.  Pull both the slow/main jets and make sure they are clear.  If you havn't cleaned the carbs yourself, heres u'r chance.

[dusterdude]

hell,i would drain the tank and try different gas.what the heck,its only 2.87 a gallon.

[KB02]

hell,i would drain the tank and try different gas.what the heck,its only 2.87 a gallon.

Where the heck are buyin' gas? I'm coming out there!!! 

I would agree with pulling the carbs and giving them a good cleaning.

Now I know this sounds dumb, but is your petcok turned on? And how is the choke working? Opnening and closing properly?

Like I said, start with a good cleaning of the carbs and also pull off the points cover and check them out. It's possible (unlikely, but possible) that the screws came loose and it's sliding around on it's own. It's usually the simple things that make us scratch our heads the most.

[Beav068]

Thanks for all the replies.  I have indeed verified that the petcock is on, the carbs have plenty of gas, the kill switch is in the "on" position (and the off position shuts off spark to the plugs so I assume it is working properly), and I had already pulled the points cover and everything appears to be okay.

I am thinking that since it ran fine in the morning (before fillup) but then crapped out in the afternoon (after fillup) then I must have gotten some seriously bad petrol.  I will follow the KISS rule and start with new plugs/fresh gas and then see where that leads me.

Thank you all again, and I will let you know what happens next!

Why did I buy a 33 yr old bike again?  (This is what my wife asked me last night)

Tim

[Bodi]

A spray can of starting fluid (petroleum ether and some lubricants) is good to diagnose fuel problems. Remove the air cleaner and shoot a second's spray towards the intake plumbing, try and start immediately. If it fires then dies immdiately, there's a fuel problem somewhere; plugged up carbs, petcock, tube, whatever.
The starting fluid can makes a sweet flamethrower if you spray it near a match, very entertaining.
Don't use this stuff inside ever, ether is mucho explosivo.

[Gordon]

Why did I buy a 33 yr old bike again?  (This is what my wife asked me last night)

Tim

Just tell her the finer things only get better with age... and then give her a kiss. 

[Beav068]

Too right Gordon!!

Maybe I'll show her something else that has gotten better with 37 years of aging. 

Tim

[jotor]

The starting fluid can makes a sweet flamethrower if you spray it near a match, very entertaining.
Don't use this stuff inside ever, ether is mucho explosivo.

I used starter spray to dispatch the bugs my kids collected for school projects.  Put them to sleep permenantly with no visual damage.

 

[Beav068]

Well gentlemen, I want to thank you for your help.  I didn't follow my own KISS rule and made it harder than it had to be.  The solution proved to be to simply trim the plug wires, re-attach the plug caps, replace the plugs (just a TOUCH wet) and the bike fired right up and runs great.

The devil really IS in the details.

Thanks again,

Tim