Engine Trouble PLEASE help....AGAIN!! Engine stuttering

[tbrookes2000]

Hi All!
Ok listen...I finally got my bike going good with the help of you all, and a new speed carb...but NOW...the engine (after about 200 miles) has started to "stutter"...[nahhhhnannnnnnaaanaaaannnnn...instead of Nnnnnnnnnnnn) it runs fine sometimes...then stutters...hits a bump.....stutters.......like it's not getting enough spark or the spark is intermittent. I have changed to a new CDI, new 8mm plug wire, and NGK and Autolite plug. But it STILL does it. I'm thinking it's the coil, or the magneto. I am ALSO thinking that a coil from a 65-66 Volkwagen might work. I'd liek to get a 12 volt magneto (I HAVE heard of them) to see if this would correct the problem. What do I do? I have gone to the lengths of even researching how to make a new higher powered CDI. ANY suggestions or pointed in the right directions would be MUCH appreciated! I have almost 350 miles on this bike (see pic) and I love riding it...Have about $450 invested so far (bike, kit, Accessories)) and willing to put more if it makes it better. HELP!

 

[darwin]

Usually a stutter is a fuel problem, sucking air, carb/float or fuel supply. Thats where I'd be looking. Generally an electric problem involves no spark or timing if keyway is sheared.

 

[motorpsycho]

are you sure it's not 4 stroking? your description sounds like 4 stroking to me...and since you added the new carb, it adds up.
if it is 4 stroking, the air-fuel ratio is too rich.

these engines don't have a coil....they have a cdi(which is different than a coil).
the magneto is only about 6 volts, not sure how you'd get a 12 volt magneto to work.
then with a 12 volt magneto, you'd need a compatable cdi (a v.w. coil will not work).
I'm no expert on electronics or ignition systems, so please, someone correct me if i'm wrong.

 

[Skyliner70cc]

Did you clean out the new fuel tank before you ran your engine? Rust is common in a new tank and often clogs the carb. Did you remove the fuel filter that is built into the fuel valve and install a inline filter? I've have had similar engine issue with clogged filter in the valve filter and have gotten stranded.

Good luck and please share what fixed your problem.

 

[tbrookes2000]

PLEASE help....AGAIN!! reply

Thanks for the info guys...with this info I'm going to get to work on it straight away...I'll let you know what worked. Thanks a bunch for the help!

 

[Al.Fisherman]

Also if not mentioned already, check your wires for GOOD connections, and don't use the frame as a ground. Also disconnect the kill switch, and see if it might be that.

 

[tbrookes2000]

Again thanks

Yeah...I cut the kill switch wires on the WAY to work on morning thinking that might be it. I have heard so many others say that these kill switches are junk so I thought no big loss...however...it did not good. So I'm working on the filter, leaning it, and checking for clogs as suggested. I will let all know how this comes out (fingers crossed)
Thanks!

 

[KCvale]

What is your current gas type and oil mix?

The thing is in my experience especially with non-customer repairs is it just don't matter.
When a good motor starts running poorly the very first cheap and easy step I take is replace the fuel.
Did you know gasoline has a half life of only 6 weeks or less?

Drain all the current fuel from everything including carb and get yourself a clean fresh gallon of Premium Gas in a clean 1 gal gas can and add 4 oz of new 2-stroke synthetic oil to it (32:1) for your broke in motor is my advice to start with.

Premium gas won't give you any more power, it is just a much cleaner fuel with less Ethanol junk which are additives that are not friendly to our bikes, and it has a bit longer shelf life.
Heck, you could probably run these motors on diesel or kerosene in a pinch, but they would run like you describe so a very good place to start even if that isn't the main problem.

If fresh fuel don't fix it, before you get to trying new ignition system parts what is the exact plug in it and how does it look?
White, Tan, Gray, Black?
You mentioned replacing the plug wire? What is that about?
Better wiring is always better with these things, good for you ;-}

When it comes to motors, after fuel it is all about spark as you know, but what makes that spark is no mystery, gap it right and you can get some kind of spark from most any plug, but even with great fuel a crappy plug or maybe just the wrong heat range number could cause a little loss of performance.

Well now I have gone and and done it....
The middle number in an NGK plug number is it's 'heat dissipating' ability.

As for a good spark plug the NGK Iridium BPR7HIX - 5944 Stock Number. SBP has them.
Note the 7, that is NGK's heat reference, that number can be anything from about 5 to 8.

It works like this:

Engine Speed and Load

* If the engine is to be operated at high RPM, under a heavy load, or at high temperatures for long periods a colder heat range may be needed.
* Conversely, if the engine is to be operated at low speeds or at low temperatures for long periods, a hotter heat range might be needed to prevent fouling.

The higher that middle number is, the cooler you motor will run.

If you live in Alaska go with the lowest number you can get.
Live in the desert like me? Go high baby, I run the 7's here ;-}

ONE CAUTION ON THESE PLUGS!!!!
They are a tad bit longer than stock and add a bit more compression but I have heard some kits pistons hit it, Skyhawks don't so I don't know first hand but thought I better share that to.

 

[HeadSmess]

ngk B (thread diameter) P(may hit piston) R(resistor) 5/6/7/8(heat range) H(threaded length) S(...who knows?)

the B is important.

the P may be important depending on piston height.

the R may be important if you have a radio and may possibly prevent premature cdi failure

the heat range, yes, is dependant on area and use. so a slow engine, cold engine, winter engine, uses a low plug, which gets hot. a fast engine, desert engine, uses a high number, a plug that stays cold....

has no bearing on the temperature the engine then runs at. combustion temperature is unaffected.

iridium is a few extra dollars for a plug that will last for roughly the life of five to ten engines....

multi points are silly, and once again, extra dollars on uneccessary items

 

[tbrookes2000]

Ok all. Heres the scoop.
I have cleaned the tank, fuel line, carb, and gone to PREMIUM fuel instead of the regular unleaded. It DOES run MUCH better (although I havent changed to a hotter plug yet)...AND I have oiled the throttle cable.
I rode it to work last Friday..it did it somewhat (the "odd running). I oiled the throttle cable before I left work..and I gota say....in 4 months of having this kit..I have never had such an enjoyable ride. SMOOTH, CONSISTANT running, steady "buzz" of the engine! I was able to actually watch the scenery, and what was on the road letting my mind wander instead of spending the whole trip LISTENING to the engine and going thru the "flow-chart" in my mind as to what might be causing this anomally. She DOES seem to run perfect in the afternoon when its hot (Im in Arizona), and still do it som in the morning...So I assume I might need a wee bit hotter plug.
Thanks for ALL the help! Now that she runs like she's supposed to..I'll be going to work everyday and enjoying my rides more )