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Old July 14th, 2019, 10:53 AM   #1
NaturalFlavored
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Bike won't start

Ok guys, the other day I was riding at wide open throttle and it hesitated. Didn't die, I let off the throttle then gave it some gas. It was still a little hesitant to go.
I got it home it was idling fine, turned it off turned it back on no problems, I rode it down the street and back. It stumbled at idle then I gave it gas it died and won't fire up.

I checked it's getting fuel to the carb and to the engine.
It's getting air, I can hear it sucking in. Took off the intake and was making same noise of sucking in.
Took out spark plug and put it on the valve cover and I see spark.
Also have compression.
I tried starting it and it just turns over.
1400 miles.
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Old July 14th, 2019, 12:10 PM   #2
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I'd check spark on both cylinders when you're having the problem. If one cylinder loses spark, it'll die at idle, barely run, etc.. Also check that a plug isn't fouled.
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Old July 14th, 2019, 12:28 PM   #3
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New plugs, it sounds like it isn't even trying to start. It just turns over. I have consistent spark.
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Old July 14th, 2019, 12:32 PM   #4
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You say you have compression... did you use a gauge to check it? I'm wondering if there's a valve timing problem.

You could put a teaspoon of gasoline in each cylinder through the plug holes and see if it runs briefly, as it would if something came through the fuel line and clogged both carbs. That seems unlikely, but so do your symptoms.
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Old July 14th, 2019, 12:40 PM   #5
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I might have to take the valve cover off and see. But the new plug smells of fuel. I put my hand over the intake to cut off air to increase fuel and I get a good amount into the motor.
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Old July 14th, 2019, 01:08 PM   #6
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Need more concrete numbers.

- compression test
- petcock flow in 30-sec
- cc drained per float-bowl
- measure all valve-clearances
- measure spark wavelength with phone-app spectrum-analyser

These numbers will help with a specific direction to take with troubleshooting.

Last futzed with by DannoXYZ; July 14th, 2019 at 04:26 PM.
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Old July 14th, 2019, 04:05 PM   #7
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Quote:
Originally Posted by DannoXYZ View Post
N
- measure spark wavelength with phone-app spectrum-analyser
Is that like asking if the sparks are bright blue or dull orange, except way more complicated?
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Old July 14th, 2019, 04:12 PM   #8
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Originally Posted by Triple Jim View Post
Is that like asking if the sparks are bright blue or dull orange, except way more complicated?
Yup. I've run across A LOT of genetic colour-blindness and one person's "blue" is not same as others'. Having a spark measured at 400nm displayed on screen is 100% distinguishable from one that measures 600nm. No prior experience or training needed. Also "bright" is very subjective and some people report "bright" when it's actually "dim".

I used to sell kit to convert older AFM-based Porsches to modern MAP-sensing. Instructions says things like, "Connect MAP-output to AFM-signal input wire on DME connector (green/red-stripe)". Ended up with A LOT of support-calls and turned out these people, even professional mechanics, had colour-blindness! I modified instructions to say, "Connect MAP-output to DME connector wire #7". Having objective measurable targets greatly improves troubleshooting.
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Old July 14th, 2019, 04:34 PM   #9
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Does the tank look good inside? How old is the gas? Have you checked the inline fuel filter at the carb inlet? Did you drain the floatbowls and look at the condition of the gas?

Seems carb or fuel-related to me.
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Old July 14th, 2019, 04:35 PM   #10
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Well the apps I've been getting have been for sounds not color. If if I'm supposed to get a loud zap from the plug that's not happening. It's there but not a whole lot.
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Old July 14th, 2019, 04:42 PM   #11
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Quote:
Originally Posted by Triple Jim View Post
You say you have compression... did you use a gauge to check it? I'm wondering if there's a valve timing problem.

You could put a teaspoon of gasoline in each cylinder through the plug holes and see if it runs briefly, as it would if something came through the fuel line and clogged both carbs. That seems unlikely, but so do your symptoms.
This is quickest and easiest test to determine if you have petrol flow issue. I missed first two races of last season because my bike ran for 30-seconds on 1st-lap and died! Couldn't figure it out. Petcock had vacuum, it flowed plenty. Had sparks. Wife suggested I really look deep into carbs and here's what I found:

what's that??@#$!%


WOW!!! How'd that get there ?#$%(!&@


I figured it had crawled up carb's vent-hose and died. With it floating around in bowl, there would be random amount of time before it was sucked up. So bike ran fine up and down pit-lane to warm up. Then got sucked up 30-seconds into race, it shut down bike. I pushed bike back to pit and critter dropped out of jet back into float bowl. Bike ran perfectly fine back at pits, full-throttle to redline in 1st & 2nd gears, so I got on grid for my 2nd race. Didn't even get to green-flag when it died AGAIN!

So following my wife's advice (she's always right!), I disassembled carbs and found the spider! Also flossed out all jets, holes and passages for good measure (counted legs and one was missing). Got everything back together and did remaining two races of day. When I got home, I added a little fibreglass gauze to end of vent-tube to prevent future incidents!

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Old July 14th, 2019, 04:51 PM   #12
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Ok so I put fuel into the hole of the plug didn't fire up. I'm thinking I'm not getting a strong enough spark, it's there but I don't hear any cracking noise from the plug. It's been a while since I had to do this so I can't remember what the spark is supposed to sounds like and how much is supposed to be there.
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Old July 14th, 2019, 05:00 PM   #13
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Strange... because spark issues usually doesn't quickly result in non-running engine. It usually starts as slight stumbles under load here and there that gets worse over time.

- Measure spark-plug gap.
- Measure voltage of battery during cranking.
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Old July 14th, 2019, 05:04 PM   #14
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Quote:
Originally Posted by NaturalFlavored View Post
Ok so I put fuel into the hole of the plug didn't fire up. I'm thinking I'm not getting a strong enough spark, it's there but I don't hear any cracking noise from the plug. It's been a while since I had to do this so I can't remember what the spark is supposed to sounds like and how much is supposed to be there.
If you can see the spark jumping across the spark plug electrodes (both plugs) when the plugs are out of the engine and grounded against the motor you will have sufficient spark for it to start. I’ll bet this is fuel related, it nearly alway is with these engines!
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Old July 14th, 2019, 05:24 PM   #15
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Originally Posted by 59096 View Post
If you can see the spark jumping across the spark plug electrodes (both plugs) when the plugs are out of the engine and grounded against the motor you will have sufficient spark for it to start. I’ll bet this is fuel related, it nearly alway is with these engines!
I've run across many cases where that's not true. Especially on high-compression or boosted engines. The compressed mixture is much more difficult to ionize and jump compared to plain air. Even factory ignition-systems that work fine with stock motor, ends up failing to ignite when exact same engine gets higher-compression pistons or boost.
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Old July 14th, 2019, 05:27 PM   #16
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If I remember correctly I had a 50cc scooter that made a cracking noise when I put it on the side of the motor
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Old July 14th, 2019, 10:17 PM   #17
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Yup, strong spark makes a cracking sound. Weak spark may make ticks.
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Old July 14th, 2019, 10:25 PM   #18
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I don't hear any noise from the spark the engine over powers it. I'm going to get new coils and see if that helps with starting the bike.
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Old July 15th, 2019, 05:32 AM   #19
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the odds of 2 coils failing simultaneously? Not so great.

How 'bout battery and charging system condition?

Ignition system dependent on a battery voltage output threshold. In the event of a component failure, the system could fall below delivering needed power output.

May be worth a looksee.
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Old July 15th, 2019, 05:35 AM   #20
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Quote:
Originally Posted by NaturalFlavored View Post
I don't hear any noise from the spark the engine over powers it. I'm going to get new coils and see if that helps with starting the bike.
Do some testing first. Without positively identifying a part as bad through measurements, you’ll be replacing a perfectly-working part with a brand-new perfectly-working part and nothing changes.

- measure resistance of primary winding on each coil
- measure battery voltage
- measure battery voltage while cranking
- key ON, measure voltage at each coil’s red wire

We’re checking for some wiring issues as well. A lot of times, electrical components are perfectly fine, but wiring & connectors in between are defective. Since connectors are not sealed, corrosion is a common source of problems.
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Old October 7th, 2019, 04:44 PM   #21
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Ok guys had a buddy help me out with a compression test and im only get a couple psi. It has good pressure if the hole is open but once we put the tester in it dropped down to nothing.
So what would I look for? Bad valves? Or is it a gasket issue?
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Old October 7th, 2019, 05:23 PM   #22
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Put a teaspoon of oil in each cylinder through the plug hole and test again immediately. If the compression rises a lot it means the rings are faulty as the oil is helping to seal the rings. If not much changes I suspect you probably have a tight valve or two. Can’t really see the cylinder head gasket going bad although it’s possible. Bad cylinder head gaskets usually give a bit of prior warning - water in the oil, bubbles in coolant, external oil or water leaks from under the head ect. Just a thought but perhaps try a second compression tester, the one you are using might have an internal leak?
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Old October 8th, 2019, 12:58 AM   #23
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Quote:
Originally Posted by NaturalFlavored View Post
Ok guys had a buddy help me out with a compression test and im only get a couple psi. It has good pressure if the hole is open but once we put the tester in it dropped down to nothing.
So what would I look for? Bad valves? Or is it a gasket issue?
What do you mean by "hole is open"? You crank with no spark-plug and feel air being pushed out?

Did you:

- remove both spark-plugs?
- use screw-in compression-tester?
- have throttle wide-open?
- use something to prop slides open?
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Old October 10th, 2019, 10:37 AM   #24
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One simple check is to check the torque on the head. Make sure it didn't work loose somehow. That would be an alternative if you don't get any improvement from the oil in the cylinder check. I remember back when I was doing car work that it was having issues with the power delivery on a V8, and one cylinder had low compression. Had spark, fuel, etc. So tried the cheap methods before pulling the head, and a re-torque solved the problem. The gasket was still good, just needed the proper torque.
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Old October 14th, 2019, 06:30 PM   #25
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Ok I started to tear open the engine and took off everything to examine the Piston and couldn't see anything wrong with it or the gasket. I was going to clean the cylinder head and noticed something got sucked in and the intake valve wasn't closing all the way. So I put it all back together after taking that out and it fires up now. I did several hours worth of work for nothing.
Gah what a waste of a day.
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Old October 15th, 2019, 06:02 AM   #26
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That's a new one on me. Could you tell what the thing that was holding the valve open was?
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Old October 15th, 2019, 07:41 AM   #27
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I could not. I looked at everything and it was fine, so I don't know where it came from
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Old October 15th, 2019, 11:11 PM   #28
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At least it was something simple!
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