Topic: effects of weak spark

[nuke]

I recently checked my spark and saw what was in my opinion a weak blue spark. (on my 78 750f2)Now I have nothing really to compare to but it doesn't look very strong according to some of the descriptions I have read. I am having problems with curb idle. I won't stay put, takes forever to warm up. Tried all choke positions. I have cleaned carbs 3 times to make sure( alls good, bowls, jets etc), I have synchronized with Morgan Carbtune( great purchase) good air filter, valve clearances in check,no air ingress from carb rubbers. The points have some pitting and when in contact they don't line up as they should (perfect face to face) My question after all this could a weak spark be good enough to run but make it really hard to keep a good idle? I have played with the fuel mixture screw to find its sweet spot....but even then the sweet spot is giving me a lean white plug!!!! Almost like the spark can't burn the right amount of fuel to get the right mixture. (am I way off here) What are the odds that new points could take care of this idle problem.

sorry for the long explanation but I figure the clearer now the easier to answer...maybe


thanks
nuke

[southbound]

Assuming all other tune up items have been done...

Weak spark and lean white plugs generally don't go together...  in other words, if your spark was weak, you'd most likely have black plugs, since you wouldn't be burning all of your mixture.  A blue spark is not only normal, but desirable.  i've seen weak plugs with an orange spark, or intermittant spark.  How's the condition of your exhaust? 

My guess is that not all the passages in your carbs (CV carbs?  if so, i'm not sure the have a "mixture screw".  What year is your bike?) are clear.  take the rack off and make sure you can blow compressed air through the tiny passages pressed into the carb bodies.

good luck!

[nuke]

thanks

its a 78 750 f2. the exhaust condition is ok I guess. just regular 4-1 with cheesy hindle muffler. The reason I say that I have a weak spark is because I read a few threads on Dyna coils and ignition and a few guys were saying that a fat white spark was best. Good thinkin on the white plug/weak spark not goin' together. I'm searching so deep for a solution, toooo deep. I guess a 4th carb cleaning will be in order. . I never took it apart (individual carbs)

nuke

[oldfart]

Blue is a good color.  Good spark.  Voltage wise at least.  Doesn't mean however you couldn't have 50 other things wrong.  Loose caps, corroded wires, bad timing.  Not to mention engine and carburetor issues.

[southbound]

Actually, my mistake...  Honda did switch carbs in the late 70's, but not to CV carbs...  just added an accelerater pump.

[Terry in Australia]

Most common problem on the F2/F3 carbs is blocked pilot jets, I had one so badly blocked in my F2 carbs I couldn't do anything but replace it. They're pressed in, but can be removed by carefully twisting them out with vice-grip pliers, and apparently a fine guitar string is the best for cleaning them if soaking them in carb cleaner and blowing them out with compressed air won't cut it.

Certainly new points should be ordered, but any blue spark is good, a weak yellow spark probably means that your condensors are buggered, and I've never seen a white spark, except in "Lord of the Rings" so I don't know what that's about. My suggestion would be to adjust your valves, (2 thou on the inlet and 3 thou on the exhaust) strip, clean and adjust your carbs, replace your ignition plate (points, condensors and backing plate) gap your plugs and set your ignition timing, and you should see an appreciable difference.

While I'm a big fan of electronic ignition systems, if your battery is weak, or your charging system needs an overhaul you're better off sticking with points, as an EI just won't work if it's not getting 12 volts. Cheers, Terry.

[upperlake04]

Blue is a good color.  Good spark.

any blue spark is good, a weak yellow spark probably means that your condensors are buggered, and I've never seen a white spark

thankyou for that info Masters

Most common problem on the F2/F3 carbs is blocked pilot jets

Terry - a search in the archives shows a thread about the slow jets and how the longitudinal hole has a smaller dia waist in the centre.  Are there other holes in the pressed- in jet, maybe drilled crosswise also?

[hcritz]

Hey Nuke...
Seems the 77-78s run leaner with the addition of the accelerator pumps on the carbs...
My plugs are always pretty close to a white on the center electrode and dark on the metal outer edges...
Be interesing to see what other 77-78 owners have to say.

[eldar]

Yup, the color on the center of the plug should be very light. If you are white, more than likely you are too lean. A small wire is a must when cleaning these slow jets just be careful. Also make sure your accel pump is working. Remove your airbox and with fuel hooked up, twist the throttle and you should see a smalll spray of gas from the little brass posts in at the front of each of the carbs.

[upperlake04]

you should see a small spray of gas from the little brass posts in at the front of each of the carbs.

thats right, you're F should have a big squirt

[hcritz]

Makes for easier starting...just give a few twist and it lights right off!

[eldar]

I doubt the F squirts bigger than the K!