Troubleshooting Your Motor: Why Won't My Motor Start? pt. 2

Troubleshooting Your Motor: I'm Not Getting a Spark!

For your motor to start and run it needs a spark, which comes from both the magneto and the CDI. If one or both of these components aren't working you won't be able to start your engine (let alone use it) not matter how well it's tuned.

I'm getting a weak spark, and my bike is sputtering:

1) Make sure you're getting spark To check if you are receiving power to the spark plug, follow these simple steps.
  • Remove the spark plug from the cylinder head.
  • Re-attach the spark plug to the spark plug cap.
  • Lay the spark plug on the cylinder head so that the metal of the plug is touching any metal portion of the cylinder head. DO NOT HOLD THE SPARK PLUG OR BOOT BY HAND.
  • With the clutch out, push the bike forward or turn the rear wheel. A bright spark should be visible.
2) Wiring Issue If you're getting a weak spark and the bike doesn't seem to be firing the way it should, there's a chance that the cables for the CDI, magneto, and kill switch aren't connected correctly. Check to make sure that all of the electrical connections leading from the magneto are connected: Blue leads to blue, black leads to black as the wires enter the CDI box from the magneto. Follow the white wire as it leads from the magneto up to the kill switch. On certain models, the kill switch may be at fault grounding out against the handlebar. Disconnect the kill switch at the handlebar and attempt to restart the bike. If these components are connected but still don't get a spark, try taking the stock cable connections off of each wire, peeling the housing back, and wiring the cables wire-to-wire (those cheap metal connections may not be making a full connection) 3) Spark plug installation and gap Make sure that a proper connection is being made in the spark plug boot. Inspect and/or replace the spark plug. Correct spark plug gap is 0.038".

I'm not getting a spark at all!

1) Check your wiring connections Double check the connection of the wires, particularly the blue to blue and black to black. Check that no particles are lodged between the side and center electrodes of the spark plug. Try replacing the spark plug or cleaning it by running sandpaper through the side and center electrodes and resetting the gap to 0.038". Re-test for spark with the kill switch pressed in. Try feathering the kill switch. Disconnect the white wire completely allowing the wire to hang free, then re-test the engine. If the connections are free and clean but you're still not getting a spark, it's time to test your components: 1) Magneto testing Take a voltmeter or multi-meter and adjust it to the Ohms setting at 20k. Ohms measures the resistance across a circuit. Check voltmeter across the following wires:
  • Blue wire to the White wire of the magneto. The resistance should be 0.25 to 0.40. New magnetos read 0.31.
  • White wire to Black wire should read 0.0.
  • Blue wire to Black wire should read close to 0.31.
  • If your reading is far off from this, then the magneto is to blame for weak/no spark.
If the readings check out on your magneto, test your CDI 2) CDI testing Run the voltmeter at the same 20k setting. Check voltmeter across the following wires:
  • From the inside of the spark plug boot to the Black wire of the CDI. Your reading should measure 2.0 - 2.7. A new CDI will read 2.3.
  • Spark Plug Boot to the Blue wire there should be no change, or 1.0.
  • Blue wire to Black wire there should be no change, or 1.0.
  • If the resistance is different than specified, this simple test will tell you where your problem lies.
Check out our spark troubleshooting guide video below:
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52 comments

BikeBerry

BikeBerry

“Hello Mark!

Great question, this can be an issue with the carburetor jets, the altitude, and the sprocket. If you are using a 2 Stroke Engine then you would want to change out to higher jets to accommodate the higher pace. Although 4 strokes are more for your higher inclines the 2 Strokes will get the job done with a jet change. Also, you would want to make sure you are using a higher tooth sprocket as well."

Murray

Murray

Just got my bike assembled and rode it for the first time yesterday. All was well.

RYAN

RYAN

Hey, everyone, this is really helpful, it helped me.

BikeBerry

BikeBerry

“Hey Clarence,

We got you covered!!

1. The blue wire from the CDI is connected to the blue wire from the magneto

2. The black wire from the CDI, the black wire from the magneto, and the black wire from the kill switch are all wired together. Once wired to gether they will needed to be ground to the frame or the cylinder head with no paint.

3. After that you have two choices: you can tuck the white wire from the magneto inside of the magneto case and wire the yellow/red wire with the blue wires. Otherwise, you can wire the white wire to the yellow/red wire."

BikeBerry

BikeBerry

“Hey Matthew,

We got you, look at how to connect the wiring on your <a href=""https://www.BikeBerry/gas-engine-kits/2-stroke-bike-engine.html"" target=""_blank"" rel=""noopener noreferrer nofollow"">Bicycle Engine Kit.

1. The blue wire from the CDI is connected to the blue wire from the magneto

2. The black wire from the CDI, the black wire from the magneto, and the black wire from the kill switch are all wired together. Once wired together they will need to be ground to the frame or the cylinder head with no paint.

3. After that you have two choices: you can tuck the white wire from the magneto inside of the magneto case and wire the yellow/red wire with the blue wires. Otherwise, you can wire the white wire to the yellow/red wire"

BikeBerry

BikeBerry

“Hey Jake!

The OHMS reading that you are measuring is a good enough amount to get the spark going. You want to make sure the CDI is tested around the same as well, if the CDI is not reading then this will need to be replaced."

Mark

Mark

Trying to find out why I can’t go up slight inclines anymore? I try peddling up incline and still end up stalling out. No top speed anymore. Changed clutch pads, spark plugs, carbarator, fuel filter. Any idea what needs to be done? Any help would be appreciated.

BikeBerry

BikeBerry

“Hello Norm.

We got you covered! If you are not getting any spark, you would want to first make sure that your fuel to oil ratio is correct. If it is correct then the next step would be to check the electrical components. If all the electrical components are reading out the way they should then the issue would either be within the wiring or the contact of the magneto. All you would need to do is follow the steps thoroughly and you will be good to go."

BikeBerry

BikeBerry

“Hello Nate,

IF you are experiencing your clutch slipping and with poor acceleration you would need to perform a <a href=""https://youtu.be/zAp8h9WRXwI"" target=""_blank"" rel=""noopener noreferrer nofollow"">Clutch Adjustment. This will place the clutch closer to the clutch pads so it does not cause it to slip up the way that it is."

Clarence

Clarence

My new motor has black, blue and white wires coming off motor but my old connector is black and blue, how do i remedy this

Matthew

Matthew

“Hey, guys.

I was having some huge issues with the engine i called it a lemon a few times and gave up on it. I decided hey let me give it one more try and i am so glad i did because i spoke to this awesome guy mike and he walked me through it all. He took his time on the phone and told me he will help me get it going although it took over an hr on the phone i am relieved because i am good to go now and i love it!!!! great job mike :)"

Matthew

Matthew

Bought motor silver slant 60 to 80 cc and put it on cruiser bike cant get no spark ordered new magneto and coil loop wire no clue what to do right now i got s paper weight please help

Alan

Alan

I just got my motor all set up and i went through all the trouble shooting. i read the electrical current ohms and mine was not reading the right way found out my meter was bad. Just be careful with the meters that are being used becaused i threw out 2 previous electron coils thinking it was bad but it was really my meter.

jonas

jonas

Hey there i recently purchased an 80cc motor. it seemed to work great for the first day or two , but after a couple of rides the motor stopped starting up while i was pedaling. I decided to go in and start it with my power drill and it started up fine.

Josh

Josh

Ngk generator spark plug.not naked.lol spell check messing up CSI and ngk.lol***

Josh

Josh

Just built my Blackhawk house brand angle fire 66cc from bike berry.have taken a few mile rides and I am getting alot of looks. i plan on coming bike to build my grandson his and i am excited.

Daniel

Daniel

I have an 80cc, I believe, and I was not getting spark I found out that my spark plug was dead and I had it replaced still did not work but now I think I am good to go I got to run it for about 15 mins today

John

John

My 49cc keeps doing what it is supposed to be doing I love it

Jake

Jake

HI, my bike will not start, has spark, but ohms on cdi measure about 6-6.5. Higher than the 3 to 3.7 as stated in previous posts here. Spark plug seems wet with fuel? Thanks

ron

ron

hi devin i have spark and fuel going in thanks for this help

Norm

Norm

Hi my name is norm I’m not getting any fuel to my spark plug

Nate

Nate

So I bought a 80cc kit. Installed it with little trouble, had a bit of trouble with the chain but after a trip to my lbs (local bike shop) I fixed that. The current issue I’m having is I am able to get the engine started, and it runs OK most times. How ever it refuses to accelerate even at full throttle. It does sound like it starts to but then it tops put at maybe 10-12 mph. Also at this speed the clutch slips (I think) because it the chain/tire start running rough. What would you suggest I do about the poor acceleration and slipping cluch?

Chad

Chad

That is normal. That is they way you want it. The air compression inside the cylinder is why you can’t push it with the clutch out.

Tory

Tory

So i just got my 66cc bike kit and for some reason its a little hard to start when cold but im sure thats normal but once i ride it around for a bit and turn it off i can never get it started again once it’s warm

BikeBerry

BikeBerry

“Hey there, Peter!

You’re correct, the motor is going to take a little bit to start. Assuming your electrical components are connected properly, you’re getting spark, your compression is dialed in, your fuel is mixed right, and you’re getting fuel in to the motor you might want to look around your motor to see if there is anything that might be a little off.
For example, check for any air leaks (like pin holes in the case or broken head/exhaust/intake gaskets) around the engine to make sure you’ve got the right temperature in your motor for combustion.
You also might want to see how long you’re choking the motor, or if you’re choking it at all. Not choking the engine will prevent the motor from starting, or if it does start, it will not allow the motor to run for a long time.
You can also check to make sure your motor is level, because a carburetor that’s not level with the ground will not get fuel in to the engine properly. Not only that, but you also want to make sure the gas tank is above the motor and not parallel with or below the engine. If the fuel cannot flow down in to the motor it will not get in to the motor at all, as these motors are gravity fed. If your motor is mounted above or at the same height as the fuel tank your fuel won’t get in to the engine, and your motor won’t start without fuel."

BikeBerry

BikeBerry

“I’m sorry to hear that, because if you’re getting readings from the CDI and magneto then you should be getting spark. At this point if you’re not getting spark here are a few things that you can check:
1. Make sure all of the wires are connected together wire-on-wire. Take the connectors off of the tips of the wires so the copper is exposed. Then peel back the plastic housing on those wires so you can twist the copper together. Once they’re all together, wrap each connection with electrical tape.
2. Assure your wires are all connected properly (you’ll want to refer to the connection guide your engine kit came with)
3. Make sure all ground wires are ground. On the outside of the motor, your black wires need to be ground somewhere on your frame. Internally, most magnetos will have a free wire that’s not soldered to the magneto- this wire is the ground wire. There should be an eyelet connection on it, and that connection goes between the magneto and the crank case, and is held in the one of the bolts your magneto is held in with.”

BikeBerry

BikeBerry

“That’s a good question, Dracy!

If you’re seeing a spark then chances are your electrical components (i.e. your CDI and your Magneto) are in working shape. But if you’re not able to get the motor started, here are a few things to check:
1. Make sure you’re getting fuel in to the engine. That means making sure your fuel is flowing from the gas tank through the fuel valve in to the carburetor, then from the carburetor to the engine.
2. If you’re getting fuel in to the motor check to see if the spark plug is wet. If it’s darker or more clear than usual there’s a possibility your fuel is not being mixed properly. Make sure you’re mixing your fuel at the right ratio for that engine and its break-in.
3. If you’re mixing your fuel properly and you’re getting fuel in to your motor, you might want to check your motor for air leaks. That means looking around your engine for any pin-holes or cracks in the body, any busted gaskets, and making sure the torque on your motor head studs is at the right pressure."

BikeBerry

BikeBerry

“Great question, Peter!

When you’re dealing with the CDI and magneto there are two main issues that are causing a weak or inconsistent spark: the wiring of your electrical components (the kill switch, magneto, and CDI), and their conductivity:

For a magneto, you’ll want to make sure that the ground wire for the magneto sits between the back of the magneto and the crankcase, with a stud through the top of the magneto in to the crankcase. For the CDI you’ll first want to make sure all wiring is done wire-on-wire, which means you’ll probably need to take off the connections of your CDI and magneto, peel the plastic housing back, and wire them together. Then you’ll want to make sure the black wires from the CDI, magneto, and kill switch are all ground somewhere on the frame. After that, follow the wiring instructions provided with your bike engine.
Now if you connections are good, then the issue will lie somewhere with the OHMs reading of your CDI and magneto. With an OHMs meter, test the black and blue wires on the CDI and magneto to make sure they’re giving you a reading. If they’re giving you some sort of output those parts should be working, but if one or both read open then you’ll want to replace the defective parts."

BikeBerry

BikeBerry

“I’m sorry to hear that, Kayla!

The only loose wire in the magneto assembly would be the black ground wire. The ground wire would be between the magneto and the crankcase, and held in with a screw to keep that in place.

The blue and white wires are welded directly to the sides of the magneto, so if it is free floating in the case you’ll either want to try to solder the wire back to its connection point, or replace the magneto all together."

BikeBerry

BikeBerry

“Good afternoon, Christian! There are a couple of things that could be going on with your motor. Now, if you’re getting spark your electrical components should be in working order, which means your problem lies within either the carburetor or the compression:

1. If the engine isn’t being choked long enough before you open the choke the motor will not start, and if it does start it will not stay running. When the choke is wide open you’ll introduce too much air in to your fuel, which will cool the fuel and it can’t combust if it’s too cool.
2. The compression on your head could be off. This could be due to a busted gasket, so remove the head of your motor and check to see if the top or bottom head gasket are split or broken, as well as the other gaskets around your cylinder."

BikeBerry

BikeBerry

“Hey there, Josh! Sorry to see you can’t find something helpful for you. If your motor suddenly stops while you’re riding there could be one of three things going on with the engine:
1. The engine isn’t being choked long enough before you open the choke. When it’s wide open you’ll introduce too much air in to your fuel, which will cool the fuel and it can’t combust if it’s too cool.
2. The electrical components (CDI and Magneto) might have shorted out. This could be the case if you’re not getting spark, so try testing the CDI and magneto with an OHMs meter to see if you’re getting a current out of them.
3. The compression on your head could be off. This could be due to a busted gasket, so remove the head of your motor and check to see if the top or bottom head gasket are split or broken, as well as the other gaskets around your cylinder.”

BikeBerry

BikeBerry

“Hey there, Josh! Sorry to see you can’t find something helpful for you. If your motor suddenly stops while you’re riding there could be one of three things going on with the engine:
1. The engine isn’t being choked long enough before you open the choke. When it’s wide open you’ll introduce too much air in to your fuel, which will cool the fuel and it can’t combust if it’s too cool.
2. The electrical components (CDI and Magneto) might have shorted out. This could be the case if you’re not getting spark, so try testing the CDI and magneto with an OHMs meter to see if you’re getting a current out of them.
3. The compression on your head could be off. This could be due to a busted gasket, so remove the head of your motor and check to see if the top or bottom head gasket are split or broken, as well as the other gaskets around your cylinder.”

BikeBerry

BikeBerry

“That’s a great question, Kevin!

When it comes to CDI’s and magneto’s giving you a spark there are two things you want to check on them: their installation and the electrical current.
The way the magneto and CDI are installed in your engine will determine if the connections are wired together properly. For a magneto, you’ll want to make sure that the ground wire for the magneto sits between the back of the magneto and the crankcase, with a stud through the top of the magneto in to the crankcase. For the CDI you’ll first want to make sure all wiring is done wire-on-wire, which means you’ll probably need to take off the connections of your CDI and magneto, peel the plastic housing back, and wire them together. Then you’ll want to make sure the black wires from the CDI, magneto, and kill switch are all ground somewhere on the frame.
Now if you connections are good, then the issue will lie somewhere with the OHMs reading of your CDI and magneto. With an OHMs meter, test the black and blue wires on the CDI and magneto to make sure they’re giving you a reading. If they’re giving you some sort of output those parts should be working, but if one or both read open then you’ll want to replace the defective parts."

BikeBerry

BikeBerry

“That’s an interesting issue, Shane!

It’s good to hear that your motor will run, but it’s a shame that it doesn’t run the way it used to. Now, if you’re able to start the motor and it runs, you spark and air intake are good. If your head studs stripped and you had to replace them I’m thinking you have one of two issues, both related to a possible air leak:
1. Bicycle engine kits will have different stud sizes from model to model. Though most 2-stroke engine kits look the same, studs (particularly the head studs) will come in two difference sizes: 6mm or 8mm. If the studs you’re working with have a little wiggle room within the cylinder, chances are you have the wrong size for the cylinder. You’ll want to get a bigger size of studs.
2. If your studs stripped out of the crank case, you might have an air leak. If the studs can’t seal properly it can throw the compression off, and if your compression is off you won’t be able to ride like before. Inspect the motor head stud ports in the crankcase to make sure they’re not stripped. If they are stripped, you may need to either seal the studs inside of the crankcase with Loc-Tite (this is a last resort) or replace the crankcase."

Electric motor

Electric motor

Bearing and winding failure is the most common motor failure. The fundamental reason is usually excessive heat. preventive maintenance practices often restrict on-line electrical measurements to interpret the current levels.

peter callier

peter callier

hi i just bought a new motor does it take some time to get started i can’t remember ?

Serve Gunter

Serve Gunter

I give! I have five(5) cdi coils all new never gotten a spark from any one of them. I run the above ohms test and 4 test 6.1 to 7.0 from boot to blk wire no other readings. The mag tests are spot on for both mags I have . I still don’t have any spark. I have had this kit on my bike for over 2 months haven’t been able to ride it yet. One new cdi has no readings what so ever. Help!

Dracy Bilbay

Dracy Bilbay

I installed the 80cc and having a problem. I had the motor running for like two min and shut off now can get it started! It’s got a little spark like a light blue. I ordered a new cdi just waiting on that but what could be the issue

Peter

Peter

“Hi all.
Just put together my bike kit.
When I wired it up and tested it I was getting a spark.
When I tried to start it properly it wouldn’t start for me.
I am now not getting any spark.
I stripped the spark plug cable, and can feel power is going to the spark plug, but it is still not sparking.
I tried other spark plugs, which are not sparking either.
They work fine on my chainsaw, so it’s not the plug.
I’ve disconnected the kill switch, but still no spark.
Any ideas on what it could be would be appreciated, I have ordered anew CDI, but I am not sure if that is the problem.
It will take about 20 days to arrive from China.
I will order a new magneto too, but am wondering what else it could be.

Thanks.

Peter"

Kayla parker

Kayla parker

My bike was just working I I go to ride it today not working so I unscrew the cap that leads to the white blue and black wire and I find my blue wire not hooked to anything ware does it need to be?

christian

christian

My 80cc 2 stroke engine for bike won’t start…it ran great for a month…my spark plug fell apart…got a new one..I have spark but won’t start…any suggestions?

Josh

Josh

Hey .. Everything was going fine but it stopped running while going and i have no idea why. None of these troubleshooting pages help. What could be up?

kevin

kevin

I have 80 cc motor ran three days can’t get spark I have bought 3 cdi and 3magnito please help

shane murray

shane murray

I have an 80cc kit, I have been riding for a few years, and have figured out every issue I have ever had using youtube, etc. A few wks ago, my exhaust bolts stripped out so I bought a new top end. I swear every since I put the new top-end on, it’s been hard starting, lags serious power and torque if these things had it…I just put a racing carb on it yesterday, I have had no change in power, it used to hall ass until I replaced that part…any ideas?

BikeBerry

BikeBerry

Hey there, Stephen! Like another rider asked in this section, if your electrical components keep shorting, here are a few ideas of what could be happening:
1. The way your magneto, kill switch, and CDI are wired is somehow creating a short, which is taking out one of those components
2. If there’s moisture build-up around the bike (for example, if you ride in cold weather and bring the motor into a warm area, causing condensation around the engine), some of that water could have gotten on to the magneto or CDI, causing a short
3. Some newer magnetos have a thin layer of resin on them, which- if not scraped off before installation- can melt, affecting the wiring on that magneto, causing a short
Let us know if either of those ideas is what’s going on. If not, we’ll keep on trying to get you back up and running.

BikeBerry

BikeBerry

Hey there, Dewayne! If your electrical components keep shorting, here are a few ideas of what could be happening:
1. The way your magneto, kill switch, and CDI are wired is somehow creating a short, which is taking out one of those components
2. If there’s moisture build up around the bike (for example, if you ride in cold weather and bring the motor in to a warm area, causing condensation around the engine), some of that water could have gotten on to the magneto or CDI, causing a short
3. Some newer magnetos have a thin layer of resin on them, which- if not scraped off before installation- can melt, effecting the wiring on that magneto, causing a short
Let us know if either of those ideas are what’s going on. If not, we’ll keep on trying to get you back up and running.

Dewayne smitj

Dewayne smitj

I’ve had trouble with my 80cc electrical ever since I put it on my bike in August. I put new magneto and cdi on two weeks after I got it .six weeks later its out again.I just got new cdi and put on and still no go I’m lost

Stephen

Stephen

80cc had spark 4 2 weeks with off switch in lost spark, on second cdi,tired of buying them,any suggestions tried all trouble shooting, ? Please help

BikeBerry

BikeBerry

When you first install the engine it will be a little rough to move, as it still needs to break in and loosen up the gears. However, if your rear tire is locking up it could be that the clutch is tightened a little too much. Click here to check out how to loosen that clutch up so you can roll without any problems.

Ciaran

Ciaran

Hey I just bought a 80cc engine kit off eBay when I pull the clutch in the bike rolls forward easy but when I let it out and try and push the bike forward the back wheel locks up is it ment to be hard to push the bike forward when the clutch is out

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