Need help with backfiring

[PEPXS400]

Hey guys!
Need help with why my 1980 xs400 is back firing through the carbs. Check out the video and let me know what you think. Thanks!!
FYI election ignition. No points. Rebuilt carbs and valves are set. It was doing this before I rebuilt the carbs, that is the reason why I rebuilt them.

 

[danalpatt]

you sure cam timing is correct?? next thing on that left side by top of the motor isnt that timing adjuster for spark plugs did u change it to electric???

 

[PEPXS400]

Are u talking about this? I'm not sure on the timing. My thought was that the timing was off. But it is electronic, so no adjustment?

 

[PEPXS400]

Timing

 

[danalpatt]

that is cool looking the timing to me looked likeit was a hair off i thought u could undo the 2 screws and turn the hole assembly. but it looks really close so ima doubt that is the problem and you are sure ur valves are not to tight that they are not fully closing allso u said you cleaned carbs did u tare it right down and clean all holes with a poky thing to make sure every passage was clear i had a similer problem with carb back fire when my cam timing was to far advanced it was causing a bit of exhoust to blow into the carb have u checked your valve timing with the bottem end (t) timing mark and made sure the piston is at TDP (top dead center)

 

[PEPXS400]

It was the timing!!
I messed with advancing and retarding. Got her dialed in now
Thanks for your help!!

I will try and get another video here after a bit so everyone can see the difference. HUGE!!

 

[danalpatt]

nice buddy good to hear man
so my next question was it spark timing or cam timing

 

[PEPXS400]

It was the spark timing. I think the PO messed with it.

 

[xschris]

In your first video it looks like your petcock vacuum line/hose to the intake manifold was loose and not plugged off. This would cause missing and back fires as it would lean out one carb. Also throw off the sync of the carbs.

 

[danalpatt]

well im glad you got er fixed thanks for letting us know what the fix was

 

[16VGTIDave]

I'll second what Chris said. It's an easy mistake to make, that I've also made. I now keep a couple golf tee's in the box with my spare carb jets.

The ignition video was cool, but I question the relevance. I'm fairly certain that isn't where or how to check the ignition timing on a SOHC engine. For the sake of your engine, please follow the correct procedure as outlined in the manual.

 

[PEPXS400]

Thanks Guys! The manual does not say how to adjust the timining without points. The left coil has a intermittent pause not sure that could be a cause of any problems.
I also ran into the problem of it running rich and carbon fouling plugs. I think I need to pull the tank back off and adjust it all again with the fuel vacuum plugged.
Again, thanks for all the advice!!

 

[xschris]

Page 133 of the haynes manual has the TCI timing.

 

[PEPXS400]

What does the LF stand for? Pardon my ignorance on that

 

[BBS360]

That's when the Left cylinder spark plug Fires.
How about a strobe video of the LF mark?

 

[PEPXS400]

BS360, the video with the strobe is the left cyclinder. That just got me thinking, the video shows the left cylinder, but it is hitting the top mark. So, should it be hitting the bottom mark?
I will shoot a couple of vids tonight. One left and one right.

 

[BBS360]

As Dave was saying, viewing the pickup coil with a strobe light is totally irrelevant.

You need to take off the inspection cover over the alternator to expose the alternator rotor viewing port. That's where the LF mark is.

 

[PEPXS400]

I will do that tonight and post it. Forgive me, I'm new to the working on motorcycles

 

[PEPXS400]

As promised. Every thing seems to be adjusted right.