Front cylinder not firing. Out of ideas! - Honda Shadow Forums : Shadow Motorcycle Forum

DevilEYEaM · 10-20-2012, 05:10 PM

I have thought I had solved this problem twice now but it is still plaguing me.

When my vt700 is idling or low RPMs only the rear cylinder fires but if I rev it up to about 3500rpms the front cylinder kicks in and seems to run fine. And I can drive it down the road and it will kick off and on intermitently the whole time depending on how high the engine is reved and stuff.

I have checked the coils and spark plug wires, checked the pulse generators AND readjusted the air gaps, replaced the spark plugs last night, and even thought I had it pinned as a severed wire in the wiring harness so I jumpered the blue wire coming from the CDI unit (that I've already replaced thinking it was the problem) and still nothing.

Any help will be much appreciated because electrical problems just stop me in my tracks.

Thanks

Scrapdog2grand · 10-20-2012, 05:39 PM

Scratch that, I forgot your not getting spark to the front!!

DevilEYEaM · 10-20-2012, 05:48 PM

Well you've been kinda keeping up with my build so you know I've only had the bike for a couple months and it wasn't running when I got it.

I rebuilt the top end of the engine but couldn't find a set of rings so I got pistons with good used rings and I really don't think that is the problem. The valves I doubt are the problem because they were all very clean and seemed to seat well when I had the motor apart.

I will do a compression test as soon as I find an adapter for my tester but I really thought I had figured it was an electrical problem.

And worth mentioning is that the exhaust pops and backfires when idling down.

rodduc · 10-20-2012, 06:00 PM

Sounds like you might have a cracked spark plug wire, with vibration the core is separating and causing misses. I'd try a different set of wires...or if you can, switch the front/rear wire and see if the rear cylinder starts misfiring.

DevilEYEaM · 10-20-2012, 06:07 PM

Quote:

Originally Posted by rodduc

Sounds like you might have a cracked spark plug wire, with vibration the core is separating and causing misses. I'd try a different set of wires...or if you can, switch the front/rear wire and see if the rear cylinder starts misfiring.

I've already swapped the entire coil including both wires from front to back and its always the front cylinder thats the problem.

RDBMX · 10-20-2012, 11:12 PM

You said you replaced the spark unit (CDI). Does the old one do exactly the same thing as the replacement?

DevilEYEaM · 10-21-2012, 12:18 AM

Quote:

Originally Posted by RDBMX

You said you replaced the spark unit (CDI). Does the old one do exactly the same thing as the replacement?

Well actually I never ran the bike with the old unit. I had most everything together and I was looking for spark and never could get it from the front cylinder.
The spark unit that came with the bike was in really bad condition; no cover, rusty, and the plug had been cut and badly soldered and taped onto the harness.

With so many problems I assumed that it HAD to be bad but maybe it wasn't. Either way, I'm still not getting spark to the front cylinder with the new CDI.

DevilEYEaM · 10-23-2012, 04:03 PM

So being out of other ideas I took the carbs off the bike yesterday and took the front one all apart. I did everything but separate them because they have never been separated from the factory and so I can't imagine that would help my problem. They have also never been adjusted because the caps that you have to drill out are still in place, so everything on the carbs is factory spec.

After taking it apart I looked at all the parts and the only issue I found was a very small nick in the needle diaphram that was right on the edge and I believe inside the seal ring but just to be safe I (temporarily) put a piece of duct tape on it, just to see if was the problem.

Put everything back together and got the carbs back on and...

Same problem. And now I am getting alot of backfire and popping.

DevilEYEaM · 11-05-2012, 10:40 PM

Still looking for solutions for my problem here. I had RDBMX come and he checked all my ignition components and we couldn't find anything wrong to cause my problems and I really don't know where else to turn.

Any other ideas out there?

luisr320 · 11-06-2012, 04:42 AM

Quote:

Originally Posted by DevilEYEaM

Still looking for solutions for my problem here. I had RDBMX come and he checked all my ignition components and we couldn't find anything wrong to cause my problems and I really don't know where else to turn.

Any other ideas out there?

Here are acouple:
- Try using an inline spark tester. That way you'll be able to see what happens.
- For troubleshooting, swap the CDIs.
- Check the carbs synchronization. If they are way off, it may cut the fuel when in idle.
- Check the timing of the front cylinder with a strobe light. Since you have rebuilt the top, maybe the timing chain went in on the wrong place.

Happy biking

10-20-2012, 05:10 PM	#1 (permalink)
DevilEYEaM Member Join Date: Jul 2012 Location: North West Georgia Posts: 120	Front cylinder not firing. Out of ideas! I have thought I had solved this problem twice now but it is still plaguing me. When my vt700 is idling or low RPMs only the rear cylinder fires but if I rev it up to about 3500rpms the front cylinder kicks in and seems to run fine. And I can drive it down the road and it will kick off and on intermitently the whole time depending on how high the engine is reved and stuff. I have checked the coils and spark plug wires, checked the pulse generators AND readjusted the air gaps, replaced the spark plugs last night, and even thought I had it pinned as a severed wire in the wiring harness so I jumpered the blue wire coming from the CDI unit (that I've already replaced thinking it was the problem) and still nothing. Any help will be much appreciated because electrical problems just stop me in my tracks. Thanks __________________ 1987 Shadow VT700 project/road ready??? 1985 Yamaha Virago 700 Daily Rider

10-20-2012, 05:39 PM	#2 (permalink)
Scrapdog2grand Senior Member Join Date: Sep 2011 Location: New Jersey Posts: 1,500	Scratch that, I forgot your not getting spark to the front!! __________________ 1999 VLX 1998 SA750 2003 SA750 http://www.cycleterminal.com Motorcycle Terminals, Connectors,Relay Kits, Accessories, Wiring diagrams. Site still under construction. Last edited by Scrapdog2grand; 10-20-2012 at 05:43 PM.

10-20-2012, 05:48 PM	#3 (permalink)
DevilEYEaM Member Join Date: Jul 2012 Location: North West Georgia Posts: 120	Well you've been kinda keeping up with my build so you know I've only had the bike for a couple months and it wasn't running when I got it. I rebuilt the top end of the engine but couldn't find a set of rings so I got pistons with good used rings and I really don't think that is the problem. The valves I doubt are the problem because they were all very clean and seemed to seat well when I had the motor apart. I will do a compression test as soon as I find an adapter for my tester but I really thought I had figured it was an electrical problem. And worth mentioning is that the exhaust pops and backfires when idling down. __________________ 1987 Shadow VT700 project/road ready??? 1985 Yamaha Virago 700 Daily Rider

10-20-2012, 11:12 PM	#6 (permalink)
RDBMX Member Join Date: Jun 2012 Location: North Georgia Posts: 38	You said you replaced the spark unit (CDI). Does the old one do exactly the same thing as the replacement? __________________ Bike #1: 1986 Honda Shadow VT700 Bike #2: 1993 Honda XR250L Cage: 2003 Honda Pilot

10-23-2012, 04:03 PM	#8 (permalink)
DevilEYEaM Member Join Date: Jul 2012 Location: North West Georgia Posts: 120	So being out of other ideas I took the carbs off the bike yesterday and took the front one all apart. I did everything but separate them because they have never been separated from the factory and so I can't imagine that would help my problem. They have also never been adjusted because the caps that you have to drill out are still in place, so everything on the carbs is factory spec. After taking it apart I looked at all the parts and the only issue I found was a very small nick in the needle diaphram that was right on the edge and I believe inside the seal ring but just to be safe I (temporarily) put a piece of duct tape on it, just to see if was the problem. Put everything back together and got the carbs back on and... Same problem. And now I am getting alot of backfire and popping. __________________ 1987 Shadow VT700 project/road ready??? 1985 Yamaha Virago 700 Daily Rider

10-20-2012, 06:00 PM	#4 (permalink)
rodduc Junior Member Join Date: Oct 2012 Location: Round Rock, Texas Posts: 10	Sounds like you might have a cracked spark plug wire, with vibration the core is separating and causing misses. I'd try a different set of wires...or if you can, switch the front/rear wire and see if the rear cylinder starts misfiring.

11-05-2012, 10:40 PM	#9 (permalink)
DevilEYEaM Member Join Date: Jul 2012 Location: North West Georgia Posts: 120	Still looking for solutions for my problem here. I had RDBMX come and he checked all my ignition components and we couldn't find anything wrong to cause my problems and I really don't know where else to turn. Any other ideas out there? __________________ 1987 Shadow VT700 project/road ready??? 1985 Yamaha Virago 700 Daily Rider

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