Topic: Fresh rebuild problems/ timing

[Joemetal861]

I put an 836 kit in my 78k, rebuilt it all nice like. I tried to start it and realized it was out of time and had aligned the notch on the cam down on accident.
With a little work we popped the valve cover and realigned the cam shaft on the sprocket with the notch up at tdc 1/4.
I cleaned the carbs, triple checked the plug wires also...
Now, when I try and fire it up it backfires very loudly and when you shut the key off you hear like a "gasp" like it releasing pressure.
Does this sound like I tweaked the valves from trying to start it out of time or is there something else possiaby wrong? 


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[Don R]

You might do a compression test.
  I think it was determined that at 1/4 T and the notch down you turn the crank 1 full turn and the mark is now up and the crank is back to 1/4 T. IE, there is no 180* out on a cam.
 We would have to guess based on the information given, a valve could be bent but not for sure.

[Joemetal861]

When I rebuilt I accidentally put the notch down and aligned the T1/4
This would be wrong. Correct?


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[Vinhead1957]

Don't think you bent a valve with that setting. It will end up in that position with proper timing.   The crank turns twice the rpm of the cam. If you turn the crank once the cam will end up notch down. One more time it will end up notch up. Is it possible you have the advancer in the wrong position? Did you change anything in the spark timing?

[Joemetal861]

No I never messed with the spark timing, it is in it's original setting.


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[PeWe]

My engine can give a gasp or fart when switching on the key when there is fuel in the cylinder and ignition ignite the plug.
Maybe similar behavior when switching off.

I do not think that you will hit the valve if the cam is 180 degrees wrong. I did that mistake when timing the cam. My struggle with cam sprocket and chain moved everything that was correct when starting the fight. I saw that during the timing session. No valve-piston hits despite rather hot cam. CX-7 with 10mm lift 265' duration.
As 125-75 with 3 degree more.

I did a mistake 1984.....
Worse with 1-2 cogs wrong cam chain-sprocket. I did not check, too hurry, cam chain slack on wrong side. Cam + sprocket had marks that I could align them with without timing degree wheel... I heard the sound of valves hitting pistons. r-r-r-r-. Engine out, fixed cam timing and started OK. I saw the marks in pistons later on. Valves not bent.
I learned to always turn around the engine with cam chain tensioned, without plugs and see how the marks repeat after each revolution..

[Joemetal861]

So what your saying is no matter if I put the notch on the too or the bottom it would align the same?
Is there something I can do with the time advance to see if it will fire? 


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[Vinhead1957]

It is easy to check! Line up the timing mark 14 T and check the cam position. Turn the crank one turn and check where the position of the cam

[Joemetal861]

Well not all that easy, still have to pull that valve cover!
Ok well what am I looking for after I've turned it once?


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[Vinhead1957]

I'll try to get pix

[Joemetal861]

That would be awesome


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[madmtnmotors]

Sounds like the leads from the points to the coils got switched (or the plug wires got reversed). Just made that mistake recently (Dyna coils) and I thought I was being extra careful. terrible backfire (flame out the exhaust), wouldn't start, but once corrected she purrs like a kitten... 

Okay... an ANGRY kitten!   

[Joemetal861]

Well given one and four are two long wires which go to the outside and the two and three are short and go on the inside, it would be hard to mix them up. Specially if the the two outside ones are interchangeable and the two inside ones are too, correct? I never took the coils off the bike either so they lay in the exact position they were when it ran!
I sure Wish this was the problem!


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[Joemetal861]

Maybe I crossed the wires that are in that white wire that come from the advance? I believe there is three wires in that.


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[Vinhead1957]

https://www.dropbox.com/s/gkzw32rd667wvv7/DSC07342.JPG

https://www.dropbox.com/s/cql6rorfxjzllli/DSC07341.JPG

https://www.dropbox.com/s/8ablreaemrvaos0/DSC07336.JPG



So the timing marks T 1-4 line up with notch up or notch down.   

I will say you didn't do any valve damage.  I would go through setting the valve lash with the timing marks. Remember that there should be no tension on the valve spring at their proper timing mark. The rocker arm should should have no stress on it.

[Vinhead1957]

 1 and 4 fire at the same time 2 and 3 fire at the same time also.  The difference one cylinder is on the fire stroke (1) and the other(4) is on the compression stroke.

[Vinhead1957]

Here are pix another way

[madmtnmotors]

Well given one and four are two long wires which go to the outside and the two and three are short and go on the inside, it would be hard to mix them up. Specially if the the two outside ones are interchangeable and the two inside ones are too, correct? I never took the coils off the bike either so they lay in the exact position they were when it ran!
I sure Wish this was the problem!


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If you are using the stock coils, then blue to blue and yellow to yellow you should be fine with the points to coil wiring.

[Joemetal861]

No they aren't stock and I believe it doesn't have points anymore.
The problem may be the wires are crossed coming from the crank case to the wiring harness for the coils. I'll check when I get home.


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[madmtnmotors]

No they aren't stock and I believe it doesn't have points anymore.
The problem may be the wires are crossed coming from the crank case to the wiring harness for the coils. I'll check when I get home.


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That was my problem. Had a color blind (blond?) moment and switched the blue and yellow, since the wires connect direct to the coil (without the colored lead for reference as with the stock coils) I had inadvertently wired the 2/3 pickup to the 1/4 coil and vise/versa. 

[Joemetal861]

Here are pix another way

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[Joemetal861]

@vinhead
I'm not sure how to replay to a certain comment ha
So your saying with notch up at T1/4 if I spin the crank one time the notch should line up at the bottom at T1/4?


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[madmtnmotors]

1 and 4 fire at the same time 2 and 3 fire at the same time also.  The difference one cylinder is on the fire stroke exhaust (1) and the other(4) is on the compression stroke.

And vise/versa (FTFY)

[Joemetal861]

Madmtnmotors thank you. You have solved my nightmare, SHE RUNS!! That is what I shall name her "Nightmare"! Wires were crossed!


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[Joemetal861]

Madmtnmotors thank you. You have solved my nightmare, SHE RUNS!! That is what I shall name her "Nightmare"! Wires were crossed!


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[Joemetal861]

How many quarts you guys put in, my Manuel tells and another book tell me 2 different amounts.


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[madmtnmotors]

Madmtnmotors thank you. You have solved my nightmare, SHE RUNS!! That is what I shall name her "Nightmare"! Wires were crossed!


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Good to hear. Definitely one of those forehead slap moments... 

was for me anyway!