Fuel, spark, air, but no ignition?

2443 Views 22 Replies 4 Participants Last post by vendeta44, Sep 14, 2012

vendeta44

Discussion Starter · Sep 3, 2012

Just got a cheap mini dirt bike, 50$ and its practically brand new except of course the catch is it dosn't run. Figured it was just carb gunk but nope.

So it fired up once for about half a second then died.

what ive done, when i got it fuel tank was empty as was carb.
-checked for compression (good)
-cleaned the carb (wasn't dirty at all)
-checked for spark (still good)
-Checked petcock (fuel still gets through carb when open and not when closed)
-checked air intake (fine)
-put a bit of gas into the cylinder to promote it to fire

After doing all that the second pull granted a brief glimpse of running but nothing. After that it just refused to turn over properly. I even tryed adding another shot of fuel into the cyl.

got it running on premix 25:1 like i always run my bikes.

any suggestions?

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vendeta44

Discussion Starter · #2 · Sep 4, 2012

after tinkering some more i discovered fuel isnt moving from the carb to the engine. pulled of the spark plug and put my hand over the hole and no fuel came out.

Not sure whats causeing it though

needle is at middle notch and the idle screw is 4 turns out.

EPR

· #3 · Sep 4, 2012

I would look at the intake manifold for cracks or it's warped at the cases. Your metal reeds behind the manifold my be open, or crack and not sealing. Did you take the main jet out and look at it? Has your flywheel broke the key and jumped out of time?? Magnets should be just passed the coil at TDC.

vendeta44

Discussion Starter · #4 · Sep 4, 2012

yeah i checked the main jet it was fine. The spark is fine so im doubting its a issue with the coil.

i was under the understanding the cag engine never ran reeds stock?

so im pretty much stuck pulling the entire engine off the bike arnt i? dammit.....

CAM2

· #5 · Sep 4, 2012

vendeta44 said:
after tinkering some more i discovered fuel isnt moving from the carb to the engine. pulled of the spark plug and put my hand over the hole and no fuel came out.

Not sure whats causeing it though

needle is at middle notch and the idle screw is 4 turns out.

your fuel inlet maybe blocked up with petcock material or the float isnt set right......The float of a carb is like setting the toilet tank height...

cags do run reeds stock,,tin ones...

vendeta44

Discussion Starter · #6 · Sep 4, 2012

CAM2 said:
your fuel inlet maybe blocked up with petcock material or the float isnt set right......The float of a carb is like setting the toilet tank height...

cags do run reeds stock,,tin ones...

Fuel will pass from the petcock to the float. But it stops there. Any tips on how to set the float properly?

Ill tear the carb and engine off the bike either tonight or tomorrow and check for air leaks blockages etc. and tinker with the float.

CAM2

· #7 · Sep 4, 2012

vendeta44 said:
Fuel will pass from the petcock to the float. But it stops there. Any tips on how to set the float properly?

Ill tear the carb and engine off the bike either tonight or tomorrow and check for air leaks blockages etc. and tinker with the float.

set the float a hair richer.........

vendeta44

Discussion Starter · #8 · Sep 4, 2012 (Edited)

okay engine and carbs on the table off the bike now. Working on a mini dirt bike in my apartment kitchen xD

Reeds are sealing and not chipped or cracked.
Carb had no faults besides the long alan bolts that hold the carb to engine were not in very tight
flywheel is fine and coils gapped properly.
I tryed to look at the bore but the dang thing just wont come off :S

im at a loss

the guy said his son only road the bike twice since they bought it last year and it wouldn't start this year. The condition of the bike leads me to believe they were telling the truth.

CAM2

· #9 · Sep 4, 2012

vendeta44 said:
okay engine and carbs on the table off the bike now. Working on a mini dirt bike in my apartment kitchen xD

Reeds are sealing and not chipped or cracked.
Carb had no faults besides the long alan bolts that hold the carb to engine were not in very tight
flywheel is fine and coils gapped properly.
I tryed to look at the bore but the dang thing just wont come off :S

im at a loss

the guy said his son only road the bike twice since they bought it last year and it wouldn't start this year. The condition of the bike leads me to believe they were telling the truth.

coils are cheap.....i have a box of them that spark but werent strong enough to spark the mix under squeeze.......

vendeta44

Discussion Starter · #10 · Sep 4, 2012

CAM2 said:
coils are cheap.....i have a box of them that spark but werent strong enough to spark the mix under squeeze.......

yeah but shouldn't fuel come out the spark plug hole if i remove the spark plug? cause its not.

EPR

· #11 · Sep 4, 2012

If you have the choke on and you pull the rope 10 times, I would think it would be wet, but, If you have a air leak behind the carb, there is not enough flow of air thru the carb to draw gas up the main jet tube.

CAM2

· #12 · Sep 4, 2012

vendeta44 said:
yeah but shouldn't fuel come out the spark plug hole if i remove the spark plug? cause its not.

Only if its flooded it will......only properly atomized mix will vaporize out and hardly none if the carb isnt jetted right....

I havent seen anywhere in your checklist where it says you tried changing the sparkplug,,,NGK BM6A gapped to .030"

vendeta44

Discussion Starter · #13 · Sep 5, 2012

Got it running. Turns out it was actually the "key ignition lock", it was wired wrong so i just cut it out completely. Running! now its time to sell it for 4x what i paid

EPR

· #14 · Sep 5, 2012

When you turn the key off it probably grounds the coil, and if it was backwards it might ground the coil when you turn it on,lol. I hate the wiring on these bikes. I have to work on my X18 wiring, the rear running light stays on all the time,lol.

vendeta44

Discussion Starter · #15 · Sep 5, 2012

EPR said:
When you turn the key off it probably grounds the coil, and if it was backwards it might ground the coil when you turn it on,lol. I hate the wiring on these bikes. I have to work on my X18 wiring, the rear running light stays on all the time,lol.

yeah man i feel you wiring is the worst part on any bikes. Wiring has stalled my work on my 90cc 2stroke custom scooter for a long time haha.

CAM2

· #16 · Sep 5, 2012

EPR said:
When you turn the key off it probably grounds the coil, and if it was backwards it might ground the coil when you turn it on,lol. I hate the wiring on these bikes. I have to work on my X18 wiring, the rear running light stays on all the time,lol.

Ill tell ya what you need to do,,,Go to Zmons x15 thread and print my schematics

Mark the plugs on both sides with a sharpie and make a small ledger to keep track of the markings are connected to

Pull all the wiring,,switches ,,fuse holder,, charging port and gauges off of the bike...Unwrap the harness then lay the harness out on the ground and hook up the gauges clutch handle and all as it would be on the bike ,,,hook up the battery and make sure the frame grounds are grounded to the battery and turn on the key......you can trace all the input hot leads with a multimeter for the gauges,,turn signal ,horn/high/lowbeam switch so when you cut it out of the harness you know what rewires it back in as a seperate fused circuit...

Cut out the rectifier box connector with as much wiring as you can,,add length where needed...hook up the charging system as per schematic with an inline fuse tree of atleast 5 fuses coming off of the keyswitch to balance the system loads from aswell as add better protection....

After the charging system,,keyswitch,,battery and fuse tree have been installed back onto the bike............

Cut the CDI connector plug out with as much equal length wire as possible,,,,,I use bullet connectors to connect the stator to the CDI and the rectifier boxes to keep the two systems clearly seperated..You need to ground the CDI to the frame and engine good aswell as hookup the kkillswitch side of the keyswitch to the black wire with white stripe just like the schematic shows...

The starter side of the whole thing is quite simple to follow the schematic,,,all my wires are coded to the same wires as the wires in your harness for all......

After you get the charging system harness made wrapped and installed,,,Ignition side made,wrapped and installed,,starter side made,wrapped and installed aswell as remaking the headlight,taillight and blinker circuit custon as per 1988 Honda hurricane600 schematics youll have a very sweet operating bike thats super customized.......

After tackling bthat mod youll be wanting to wire up the whole clan......

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vendeta44

Discussion Starter · #17 · Sep 6, 2012 (Edited)

K well that was a tick off. Had someone come by to buy it today and the cursed thing wouldnt start! ARGGH!

I had it running 15 minutes before, and ran it for 3-4 minutes, waited 15min till she showed up engine was still hot, and tryed to fire it up and no cigar. I even tried putting some engine starter in the jug for a boost and it wouldnt start... Its pretty smoky so maybe its a bit oil rich atm.

I'm going to try and get it running soon here and prop it up on a block and let it run at full tilt for a bit and try and break this engine in.

I've never had to break one of these engines in, is this the best way? I don't have a IR thermo, just a tach. And i don't have the money to buy any other gizmos.

luckily she was cool with it and told me to call her again once i've got it starting properly and she will take it. all is not lost.

Sincerly
-Severely aggravated

RAMIT222

· #18 · Sep 7, 2012

Same thing happened to me on a pocket bike. I figured out the problem when I checked the fuel in the carb. I looked @ it by getting a bit out of the drain plug in the fuel bowl. It looked like fuel floating on water - Which it was. I had washed it using the hose & some water must have got in through the vent in the tank cap. Replaced all the fuel & it ran ine after. Then I got a new hose to attach to the cap vent. So try your checklist of items again. Should start in 1 or 2 pulls.

vendeta44

Discussion Starter · #19 · Sep 7, 2012

RAMIT222 said:
Same thing happened to me on a pocket bike. I figured out the problem when I checked the fuel in the carb. I looked @ it by getting a bit out of the drain plug in the fuel bowl. It looked like fuel floating on water - Which it was. I had washed it using the hose & some water must have got in through the vent in the tank cap. Replaced all the fuel & it ran ine after. Then I got a new hose to attach to the cap vent. So try your checklist of items again. Should start in 1 or 2 pulls.

Good idea but def not the issue.

Looks like cam2 was right from the beginning its a coil or plug issue. I noticed that the starter fluid i put in there well its warm wont ignite at all. Did a bit of searching seen that a sometimes the coils(or plugs) take a fart when they get hot and the spark gets weak.

Electricity man, the failing point of everything good!

EPR

· #20 · Sep 7, 2012

Some weak coils will run for a few minutes till they get hot, and then turn off like a light.

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