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Engine Trouble engine sounds like its gonna start but doesnt

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
Last year I built this engine. I replaced the magneto and installed it backwards. When i corrected it it has yet to start.

Here's what its doing. - It has spark, It has compression, it has gas and I mixed 1 standard small bottle of 2 cycle oil with 1 gallon of gas. the carburetor is getting air and fuel the throttle works.

When I try to start it it sounds like its trying, you hear a clink and exhaust smoke comes out the tail pipe.
Im using a pull starter to continuously try to start it.

I've run these tests. This year I took apart the carburetor and cleaned it out with carburetor cleaner. I reassembled the carburetor and used starter fluid still it only runs through one combustion cycle before not starting. and by that I mean, It gets gas and air into the cylinder and when the piston is at the top the spark ignites and explosion that causes smoke but, that's where it ends. It wont keep running.

Yesterday I rented a compression gauge, and tried to test it but the gauge would never go up. It definitely has compression though. I think the gauge was leaking. If I put my thumb over the spark plug hole and turn the wheel it blows my thumb off. the bike is as hard to pull start as my working lawn mower, when the spark plug is in place.

I checked for spark by grounding the plug and pull starting it. Not only could I see it visually but I got shocked when i was holding it a few times.

In summary. It has the simple things needed to start an engine but it only causes one explosion.
 


Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
I thought I'd mention also that when it turns over the smoke that comes out is white with a 25% opacity. I know on cars that could mean a blown head gasket, but I do not know if that same effect is carried over to small engines. Never the less I will check that tomorrow.
 

crassius

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Joined
Jul 23, 2012
Messages
4,572
if motor got full of fuel while you were working on it, that would make it hard to start - read some threads about that

I wouldn't give up on the compression gauge until I got a reading - find where that pressure is going.
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
if motor got full of fuel while you were working on it, that would make it hard to start - read some threads about that

I wouldn't give up on the compression gauge until I got a reading - find where that pressure is going.
I let the engine and gas tank set out all winter without gas. there were no fluids in it when i started but it might have flooded when i was pull starting over and over again.

How do i use the compression gauge?
here's what I was doing, vice grips on the throttle to hold at max throttle, compression gauge in the spark plug hole, bleed the gauge, and I tried pull starting 5 times with both the clutch engaged and disengaged.
 

crassius

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Jul 23, 2012
Messages
4,572
not sure I understand - with clutch engaged, doesn't back wheel turn?

it often takes 30 or 40 turns of motor to pump the reading up to its max

why not pedal it to get a reading?
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
I t
not sure I understand - with clutch engaged, doesn't back wheel turn?

it often takes 30 or 40 turns of motor to pump the reading up to its max

why not pedal it to get a reading?
I tried it both ways with the clutch handle locked and the back wheel spinning freely and on a jack with the clutch lever not locked and the back wheel turning. I will take your advice and retest for compression but I can not pedal. Unfortunately, my jack shaft freewheel is broken (Its wobbly) from trying so much to pedal start it last year. I have been saving up for the heavy duty (HD freewheel).
 

crassius

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Jul 23, 2012
Messages
4,572
hopefully a compression test will tell you something about what is happening

in about 10 years of running a repair shop for these, I worked on maybe 1000 bikes and only seen a pull start once, but didn't have to use it so I didn't - I have no idea how much different starting is with one of those : (
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
hopefully a compression test will tell you something about what is happening

in about 10 years of running a repair shop for these, I worked on maybe 1000 bikes and only seen a pull start once, but didn't have to use it so I didn't - I have no idea how much different starting is with one of those : (
I've started 3 bikes and an engine on the ground with pull starters. They are all very easy when the engine works. Its like 3 pulls on a cold start.
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
I got 30 psi. I didn't have the tool I needed to pull off the head. So ill look at the gasket later. When I do I bought some gasket maker and ill use that if it needs it. I also mae a video I'll be posting soon.
 

crassius

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Joined
Jul 23, 2012
Messages
4,572
25 to 30 is what one gets when a crank seal is leaking, even a horrible gasket leak will get you around 60
 
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