has compression, spark, and fuel but won't fire / start - cam chain issue?

homebrew

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Cheers to everyone here for keeping the legend alive and for all the exciting discussions and troubleshootings.
I’m an avid reader for a few years now, but never posted myself. Well now it’s time.

My father passed on to me his 447 XS, it‘s a chopper conversion by the Germans from HM, also called Stiebler. It’s a wild bike.
He was owning it for 30 years and It was sitting in a barn for most of that time. And it never ran fine. And he didn’t ever get it to run properly apparently.
It used to always have a weird mix of ignition and charging issues (both, not ignition issues caused by not charging). Sometimes running better sometimes worse, always backfiring through carbs, one time even blowing the carbs off! We took a closer look and noticed all sorts of issues and worn parts, some of them being a faulty reg/rec conversion resulting in not charging the battery, crappy ignition and, hold tight:
Wrong pistons for the crankshaft that was installed, resulting in a larger combustion chamber and less compression(6 bar)!!

Back to old regulator + rectifier and took the engine apart to change to the right pistons. We tought the pistons might be the main issue. First she was running sweet and charging, dad even kickstarted by hand with 8-9 bar compression, but during the first ride it died and then again running poorly, backfiring through carbs a lot and would die at idle at some point. And then never fired again.
Before it died it was similar to how it ran when I got it in the first place.

Then we did another overhaul:
  • complete new DIY wiring harness
  • New coils, condensers, points
  • New ignition switch ,fuse box, battery (only 15 amps main fuse is "old" taken from a Harley)
  • checked plugs and plug cables
Now compression is still there, carbs work and spark looks very good, blue-ish and about 7mm long, no irregularities.
Cam chain tension set, valve clearance set, timing to slighty after F-mark(slightly retarded).

And it doesn’t do a thing when kicking like a m*****f******.
Multiple occasions each time 20 kicks without pulling throttle, with choke, no sign of life at all!
Only one single firing with kickback after pushing a tiny bit of gasoline directly into the cylinder.
It’s got compression, fuel, spark – so WTF?

Three thoughts I wanted to share that I noticed.

1. Advance unit is sticky – one time I checked timing and was wondering why it’s completely off at full advance, turns out the advance unit got stuck somehow. Am I correct that it does not play a role when starting at idle/low rpm??

2. The pin that is holding the ATU is not pointing perfectly straight up when at TDC, it is off by 2-5 degrees clockwise. Maybe the chain jumped?!?! But if it jumped, wouldn’t this throw off timing and making it impossible to time to F mark?

3. Spark plugs always wet when taking them out after another kicking session without any firing. Maybe the spark is good when testing, but when mounted in the cylinder and under compression?!

What do you guys think? What else am I missing?
I am worried that there’s something fundamentally wrong with engine/cam/cam chain timing. When we assembled it we paid close attention to the mark at the cam.

THANKS for any thoughts on this, I am lost and I want to rip my XS around.

Chris
 
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+1 on the battery.

When you say "carbs work", do you mean they are totally clean inside. Meaning the needle and jets aren't clogged or covered with varnish, and the float bowl move freely?

Sounds like a bike with a lot of CHARACTER.
 
The pin being off could be from a worn cam chain. I had a similar issue with the same outcome, refusing to start. Set the pin at 12 0clock and see where your timing mark is. That will tell you if the chain is stretched out too much to time it properly.
 
Is the battery fully charged?
I’d say so, had it charged overnight and then 12.6V with key off and around 12V at the coils with key on. Didn’t decrease in voltage after having the key on for a while to set timing , kick etc. so seems fine.
 
+1 on the battery.

When you say "carbs work", do you mean they are totally clean inside. Meaning the needle and jets aren't clogged or covered with varnish, and the float bowl move freely?

Sounds like a bike with a lot of CHARACTER.
battery should be fine like I explained.

had the carbs disassembled, all clean from the inside and all moving freely. Fuel is fresh. However it’s been a year since I did this so can’t hurt to open them again to check.
But if the plugs are wet after we tried to dry out the engine from excess fuel with air pressure - doesn’t it mean that she’s getting fuel and should at least start up or show signs of combustion ?

Yes a lot of character. Like my ex girlfriend hehe
 
The pin being off could be from a worn cam chain. I had a similar issue with the same outcome, refusing to start. Set the pin at 12 0clock and see where your timing mark is. That will tell you if the chain is stretched out too much to time it properly.
Well that I didn’t check yet - will do today and let ya know!
 
Welcome homebrew, love to see a pic of the bike.
Definitely free up the spark advance weights.
It's possible to install upside down ( 180° out ) might want to check that.
good luck with her.
 
If I understand what Homebrew explained, the bike ran fine for a while then died during a ride and refused to start.
In my opinion, the cause is unlikely to be in the carbs because they do not get clogged simultaneously.
The battery being presently fully charged, the charging system, even if faulty, can't prevent the engine from starting.
The timing chain can't stretch during a ride and cause the engine to stop.
I would rather investigate completely the ignition system, and, especially the autoadvance unit.
 
If I understand what Homebrew explained, the bike ran fine for a while then died during a ride and refused to start.
In my opinion, the cause is unlikely to be in the carbs because they do not get clogged simultaneously.
The battery being presently fully charged, the charging system, even if faulty, can't prevent the engine from starting.
The timing chain can't stretch during a ride and cause the engine to stop.
I would rather investigate completely the ignition system, and, especially the autoadvance unit.

Yes Sir Mr Bruno ..that is what I am saying also ,,I would look at the plugs so they are not bone dry on both sides
I have never encountered in 40 years that both carburetors die at the same time not giving any splutter och backfiring at least at one side
However it is reported there are a solid blue spark which I have never seen in 40 years

spark looks very good, blue-ish and about 7mm long, no irregularities.

I would consider squirt a little starter fluid into the plug holes put the plugs back and try But it can be a bit risky

i agree with Mr Bruno i would look at ignition timing and so

There is however the chance that if the rotor is shorted to ground it can pull down the system voltage making it to low and not starting
So the idea of taking the charging out of the system and try with battery only is a good idea : Not sure but perhaps removing a fuse does it
 
Wow thanks for so many good thoughts on this, didn’t expect that my first post will receive this much attention.

So..we were back at it, no success.


  • Unplugged the rec and reg and all other loads so that only ignition was powered and no risk of anything causing voltage drop
  • Disconnected the killswitch just in case it creates resistance
  • Changed to a spare pair of condensers, coils, breaker plate, plug connector and wire, and brand new spark plugs
  • Tested compression, it’s 116 psi and 145 at full throttle
  • ddouble-checked the pin for the ATU, actually it is at 90 degrees when at TDC, we must have looked at it when TDC was slightly off the last time. photo.

Again plugs were wet after kicking and no sign of combustion at all, not even the slightest feeling in the kicker that the engine is firing.
Still has good spark when taking out the plugs and testing them.

To me it absolutely seems like ignition / timing just like you guys were saying too but I don’t know what else to try.
Thinking we might have made a mistake when assembling the cylinder top end but since she was running fine at least for a very shot ride it seems more like ignition.
again, I‘m lost. We’ve brought so many dead bikes back to life in the recent years , never had anything mysterious like her.

She’s cursed!
 

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Yes Sir Mr Bruno ..that is what I am saying also ,,I would look at the plugs so they are not bone dry on both sides
I have never encountered in 40 years that both carburetors die at the same time not giving any splutter och backfiring at least at one side
However it is reported there are a solid blue spark which I have never seen in 40 years

spark looks very good, blue-ish and about 7mm long, no irregularities.

I would consider squirt a little starter fluid into the plug holes put the plugs back and try But it can be a bit risky

i agree with Mr Bruno i would look at ignition timing and so

There is however the chance that if the rotor is shorted to ground it can pull down the system voltage making it to low and not starting
So the idea of taking the charging out of the system and try with battery only is a good idea : Not sure but perhaps removing a fuse does it
starter fluid I didn’t use - correct me if I’m wrong but with 120-145 psi compression, fuel and good spark there should be something happening. At least something noticeable as an attempt of combustion :-D But it’s not doing anything at all.
Plus, she kicked back already only by adding some fuel directly into the cylinders
 
Air. Fuel. Spark, that was what I was taught. Missing link is at the right time. ???
The more you put in, the more she,s yours. Best of luck!
 
If I understand what Homebrew explained, the bike ran fine for a while then died during a ride and refused to start.
In my opinion, the cause is unlikely to be in the carbs because they do not get clogged simultaneously.
The battery being presently fully charged, the charging system, even if faulty, can't prevent the engine from starting.
The timing chain can't stretch during a ride and cause the engine to stop.
I would rather investigate completely the ignition system, and, especially the autoadvance unit.
Thx for the little summary there. Would you say that the autoadvance unit can stop the bike from firing? In my understanding it’s only advancing the timing after a certain rpm but not at starting/idle. I observed it today while starting and it kept being closed, so no advancing in timing.
I’m still at slightly retarded from the F mark at both cylinders.
 
Aeehh The Plugs have spark when You are grounding them against the Cylinder head out of the engine
Strong fine spark Both sides ?
And the plugs are wet ?

Is that right so far Please report.

If wet and spark -- I would shift the ignition timing in small steps gradually .se if anything changes
 
Can’t wait for the final verdict - in my humble opinion it must be related to the timing of the spark, but then why would it have worked for a short burst when you started it first ? I’m puzzled !
 
Welcome homebrew, love to see a pic of the bike.
Definitely free up the spark advance weights.
It's possible to install upside down ( 180° out ) might want to check that.
good luck with her.
How do you know if it’s 180 degrees out ? If the pins on both sides of the rod are not pointing same direction ?

That’s the only pic I’ve got right now. Quite a unique build and I‘d love to get er back on on the road this summer.
 

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Air. Fuel. Spark, that was what I was taught. Missing link is at the right time. ???
The more you put in, the more she,s yours. Best of luck!
I know right ? I’m starting to question what I was taught, questioning reality, the universe.

Thanks mate. We‘ll get there.
 
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