Topic: Engine cranks but bike won't fire

[aminemed]

Bike is a 750 k2, fired yesterday with some lag while running and then engine stopped after a few minutes, I couldnt restart it and depleted my battery. Tried again and depleted battery three times in total.

Battery is almost new, above 13 voltA
Changed 2 plugs to new ones as I had spare plugs at home (cylinder 1 and 4)
Fuel is ok (tank derusted)
My plugs are black with gasoline on them
Bike would fire for a few seconds then engine dies

Was running great until this time and firing right away

Can't understand what is going on!

Any tips would be welcome

[dave500]

so I guess this is your first fire up?or was it running when parked last?

[Deltarider]

1. Is killswitch in 'Run'?
2. What did you last have your hands on?
3. Is there still a solid plugcap - wire connection?
4. Connect spare sparkplug to plugcap, lie it against the head to check for spark whilst cranking.
5. Is breakerpoints gap still within spec?

[aminemed]

No bike was firing last time was last Sunday took it for a ride and it fired and for a few minutes before it died yesterday

[aminemed]

And all sparkplug caps are brand new NGK!

[calj737]

Fuel is ok (tank derusted)
My plugs are black with gasoline on them
Bike would fire for a few seconds then engine dies

Black plugs are fouled plugs. Choke still on? Replace ALL 4 plugs, check your fuel level in the bowls with Clear Tube method, and set your carbs to stock screw adjustments. You didn't mention whether its stock intake/induction, or any other modifications, nor what work was performed prior to this effort. 

[aminemed]

Plugs are 2 months old, I changed cylinder 1 and 4 I assume it should fire on 2 cylinders anyways ? No ?

[robvangulik]

With your carbs its so easy to take off the floatbowls to see if there are jets lying loose in there or if anything else is wrong with fuel supply, i'd start there if i were you.

[setdog]

the holy trinity, fuel air spark

you got fuel
you got air
you got spark

"black/gassed plugs", id pull the carbs and do a carb sync

[Keith]

The engine needs 3 things to run....spark, fuel, compression. Those are the basics, start there. Plugs are black, so you are getting at least some fuel. Do you have spark? Pull a plug wire, put a plug in the cap, and hold the electrode against the engine. Spark? Check points...dwell meter is the best method. No Compression? Valves too tight? Catasprophic engine failure? If you have spark and compression, spray combustible fluid in carbs....should fire, showing a fuel problem. Educate yourself...a good mechanic can pinpoint a problem like this in a few minutes.

[aminemed]

K checked plugs resistance so changed also a 3rd plug that was at 3.9 Kohms, so got basically 3 good plugs bike started right away and I run it around the block, engine died again after 3 min so had to push it. Did not start again. I guess this rules out any fuel related issue. But don't understand this plug issue !

[calj737]

K checked plugs resistance so changed also a 3rd plug that was at 3.9 Kohms, so got basically 3 good plugs bike started right away and I run it around the block, engine died again after 3 min so had to push it. Did not start again. I guess this rules out any fuel related issue. But don't understand this plug issue !

Completely wrong. It points to a fuel issue as a major possibility. Pull the plugs you just changed and inspect them. Either do the proper tuning or settle in for protracted and persistent issues.

[setdog]

K checked plugs resistance so changed also a 3rd plug that was at 3.9 Kohms, so got basically 3 good plugs bike started right away and I run it around the block, engine died again after 3 min so had to push it. Did not start again. I guess this rules out any fuel related issue. But don't understand this plug issue !

Completely wrong. It points to a fuel issue as a major possibility. Pull the plugs you just changed and inspect them. Either do the proper tuning or settle in for protracted and persistent issues.

+1 do the proper tuning,

take a step back, you know the bike runs.  i would grab manual and go through the periodical maintenance, and visit valves, timing and carburetors (or is it timing, valves, carbs?).  it may be time consuming but its worth it.  seems to me the bike is begging for a tune up. 

i have do timing on my bike too now that i think about it

[aminemed]

What is then first step I should do ?

[madmtnmotors]

K checked plugs resistance so changed also a 3rd plug that was at 3.9 Kohms, so got basically 3 good plugs bike started right away and I run it around the block, engine died again after 3 min so had to push it. Did not start again. I guess this rules out any fuel related issue. But don't understand this plug issue !

Completely wrong. It points to a fuel issue as a major possibility. Pull the plugs you just changed and inspect them. Either do the proper tuning or settle in for protracted and persistent issues.

+1 do the proper tuning,

take a step back, you know the bike runs.  i would grab manual and go through the periodical maintenance, and visit valves, timing and carburetors (or is it timing, valves, carbs?).  it may be time consuming but its worth it.  seems to me the bike is begging for a tune up. 

i have do timing on my bike too now that i think about it

+2

Your recent thread about leaky carbs that mysteriously fixed themselves means that every possibility is on the table.

http://forums.sohc4.net/index.php/topic,169826.msg1971094.html#msg1971094

Properly functioning carbs don't leak, ever, so rule out everything else by verifying point gap, timing, proper spark, nice new clean air filter and spark plugs, properly vented fuel cap, cam chain tension, and anything else I might be missing from the 3000 to 10,000 mile tune-up. Get at least four extra sets of spark plugs since you're already fouling plugs you'll likely be fouling several more before you get it sorted.

I hate working on carbs so I try to rule out everything else first. Hell, at one point I went so far as to do an engine swap to avoid rebuilding the carbs, but the replacement engine (with the same carbs) had the same poor running issues as the original motor! So I ultimately rebuilt the carbs. I would not go to such an extreme today, and I have gotten pretty good at cleaning and adjusting these multiple carb assemblies, but I still don't like it... 

[setdog]

download the manual

i think you can google cb750 k0 k7 shop manual

last time i looked dotheton had a good link

find the periodical maintenance section

[strynboen]

have you first drowned the plugs..they often shorts aut..just of the fuel and some sooth blends up...take a gas burner and heat them up..so they dryes good up...and then rotate the engine to blov all fuel aut...and then put the still hot plugs inn..and try to start..use no choker and open trottel..to get as mutch air in the engine.to help the mix to lean a bit up...

[minimo]

Black spark plugs, especially wet ones point to a very rich fuel setting.

You’ll need to freshen up your sooty spark plugs before you try anything new. Wear your proper protection (goggles, gloves etc).  Pull all your foul plugs. Grip each plug with some pliers and torch the electrode tip until it becomes about red hot. Let that rest until they cool down to touch.

After you have some clean plugs, make friends with this link:
http://forums.sohc4.net/index.php?topic=5410.0


Sent from my iPhone using Tapatalk

[aminemed]

Hank you for your help I will try that after solving a much bigger iasue: my spark plugs is stuck in cylinder 2..it fell inside..can't pull it from there

[minimo]

Can it be pulled out with a telescoping magnet? Needle nose pliers? Chopsticks?


Sent from my iPhone using Tapatalk

[evinrude7]

how did the spark plug fall inside?

[aminemed]

That is a very good question, now it is lying horizontally..

[minimo]

Be careful not to force the spark plug too hard on its way out; you might bend the electrode. Be sure to check the gap before reinstall.

It’s helpful to provide photos here too whilst describing issues. Gives us a better sense of what we’re trying to mentally picture.


Sent from my iPhone using Tapatalk

[madmtnmotors]

Now it is lying horizontally..

Holy cow, I didn't even think that was possible. Take your time, try to shift it around a little bit, both side to side and front to back until it is lying loosely. Maybe use a thin probe between the fins to get it standing up, just don't force anything. A small inspection mirror and a small telescoping magnet might help.

[setdog]

how did the spark plug fall inside?

i want to know too.  this seems impossible unless is broke apart