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Intermittent power loss

6K views 18 replies 9 participants last post by  Larry_J 
#1 ·
I'm having some trouble with my 2005 VTX 1300C that's driving me freakin' crazy. I can't find a pattern, nor can I pinpoint the issue, I only have theories. I'm hoping one of you guys have had or heard of this before and can help me out.

My bike, at times, falls on its face when I crank the throttle more than about 50%. It doesn't matter which gear it is. As long as I'm just cruisin' around I can ride just fine, but if I have to pass someone or accelerate hard out of a turn (interstate on-ramps) the bike just hits a wall and acts like its being physically restrained. Downshifting only makes it worse. HOWEVER, about 25% of the time I'd say the bike is perfectly fine and pulls hard through all the gears and >50% throttle makes it pull even harder (as it should).

For example, if I'm riding on the interstate at 70 mph and I need to pass someone, if I gradually open the throttle the bike accelerates but at some point of the throttle position the acceleration levels off, AND the bike will not go over 80 mph, even with the throttle pinned. Then there are times that the bike pulls hard from 65 mph well on past 80 mph and feels nice and strong. And, as I said before, this "wall" I hit happens no matter which gear I'm in, so it's purely rpm based.

I've cleaned the K&N air filter, done an oil change, checked valve clearances, checked spark plug wire tightness, changed plugs, dismantled and cleaned the carb, and replaced the regulator/rectifier (unrelated--it was dying and needed done, but I figured I'd mention everything I've touched). The battery is new too, but, again, that's unrelated. I also changed the main jet in my Factory Pro kit down one size, but I doubt that would cause this problem, especially since it's a periodic problem. Also, the bike ran just fine for a long while after the swap. I can't figure out what the problem is. I thought for a while that maybe the regulator/rectifier was affecting the spark enough to cause higher rpm lag, but after the swap the bike is the same (only now it sits at 14+V rather than 12V when running).

The bike has just shy of 60,000 miles. Could I have an ignition coil going bad? Wires? Or is there something I'm missing that's obvious to one of you? I will say that when the bike is acting up, there's no sputtering or after-fire or anything like that. It just feels like I have some heavy load I'm trying to pull or something. Also, this happens no matter if the bike is cold or warm. Sometimes I'll leave for work and the bike is running awesome, then half way to work I twist the throttle and it falls on its face, then other times it's the opposite: runs like crap at first, then suddenly on the trip I can pass people with ease and the bike feels really powerful. I don't get it.

Thanks for reading. I really need to get this straight.
 
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#2 ·
Have you checked the slide valve diaphragm???
I had some of those symptons when mine had a few tears in it.
Vacuum hoses, fuel petcock???
Try the petcock mod to make it work w/o vacuum..
 
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#3 ·
The vacuum hoses, last I checked, looked fine. I don't know what the petcock mod is you speak of, but I would rather not bother with that. I don't recall seeing any tears in the slide valve diaphragm when I had the carb off. It's frustrating because it comes and goes. For the last few days the bike has been running great more than it's been running poorly; other weeks it's the opposite.

I guess I could replace the vacuum hoses; not like they're expensive. Thanks for the reply.
 
#8 ·
Thanks, I'll take a look.

Thats what I would check first also...

Chasing down problems can be a total Pain!!!!
1 step at a time..........


.
Yeah, it sucks. I hate problems that happen on occasion with no notable pattern. I prefer things to just break and stay that way. Ha.

I'll be keeping my eye on this thread. Hope you get it sorted.
I'll keep the thread updated for sure.

First thing I'd check is all the ground, connections and terminations.
Then for water in the fuel tank.
Then have coil tested.
All electrical connections should be good. That's one of the first things I did. I did have tear in my right rear spark plug boot from changing plugs. I pulled it at the wrong angle and tore it. I taped it back up, but I don't think I damaged anything other than the outer boot part. I did pull the boot off of the wire, cut the wire back to expose clean copper, then screwed the boot back on. No change (I was really hoping that was the issue--maybe it still is, I don't know). I grabbed a spark plug wire kit from an auto parts store, but I still need to take the time to cut the wires to length and to check that the connectors will fit the spark plugs. There shouldn't be an issue re-doing my plug wires this way if I understand correctly.

There's no water in the tank. That bike doesn't sit long enough to accumulate any moisture in the tank, and my gas cap doesn't leak (I test this every time I ride in the rain. Ha ha.)

I'll look through my manual to see if there is a section on coil testing. I work as an electrical engineer, so I really just need to see what values I'm looking for, so I hope the manual has them. I've been wrapped up with work, school, and my old truck. The truck is just about done, so I'll tackle the Honda this weekend perhaps.
 
#11 · (Edited)
Ign coil resistance measurements are 32k - 36k from sparkplug connector to sparkplug connector.
1 or 2 ohms on the primary.
Honda specifies "Peak Voltage" using a peak voltage adapter.
I used a 600v 1 amp diode and a .1 ufd capacitor (250volts or higher) to make a peak voltage adapter.
170+ peak volts @ idle, 275 peak volts @ 2 - 3k rpms. 100v minimum at cranking
IGN Pulse generator minimum peak voltage is 0.7v.
Ever notice a cylinder colder than the other, comparing exhaust pipe/port temps.
IGN switch puts +12v on the IGN coil, ECM puts on the Ground.
With IGN sw ON, put your ammeter from Ground to the ICM side of the coil.
You should measure current, if a 2 ohm coil then about 6 amps.
You can do this through the ICM connector.
1300 have a problem with the Black or the Green ICM wires breaking off at the most forward
two wires of the ICM connector.
Usually the engines backfires at the intermittent connection and dies when the broken wires separate.
 

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#13 ·
I'm pretty sure I found the problem. I finally got time to mess with the bike and I pulled the carb vacuum slide first and found at least four cracks in the diaphragm. I found a year-old thread of a guy who replaced the diaphragm for $20 plus $8 shipping from JBM Industries. I just sent an email to them requesting an invoice for a replacement. I found a few OEM replacements (part number 16111-MEA-671), but for this bike you have to get the entire slide with diaphragm which is anywhere between $70 and $80 (for a freakin' piece of plastic and rubber--seriously?). I'll try the $20 route and see how that goes. JBM has how-to instructions that are pretty clear, plus the old thread I found has some helpful tips as well. I'm very mechanically inclined, so I expect this lesser expensive route to be my best choice. Yeah, I can afford the $80 OEM one, but why spend the extra money if you don't have to? Right? The bike is still able to take me from A to B, so having to wait longer (potentially) on a cheaper part isn't a big deal. JBM is located in Ohio, and I'm in VA, so I hope the shipping will be relatively quick. Maybe I can have the new diaphragm in next weekend.

 

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#15 ·
I have a shipping confirmation from JBM for the replacement diaphragm. In the meantime I thought I'd try to repair the old one since I really have nothing to lose. I did a lot of research into diaphragm repair which mostly lead to replacing the diaphragm or using some stuff called "Honda Bond" you get from the dealership. Being that it's Sunday and all dealerships are closed, I got the bright idea while walking through Wal-Mart to get a bicycle inner tube repair kit. What I found were these little patches that you simply peel and stick. They were just under $4 for 6 patches, so I grabbed two packs. I first cleaned up the diaphragm with degreaser, then covered each hole/crack with the patches. The patches are Slime brand and are called Scabs (kinda gross name actually) and pictured below. The directions tells you to rough up the area before applying the patch, but I didn't bother. Here they are:



Well using the entire patch for each crack turned out to be a mistake. Duh, I know, most of you probably would have thought more about how stiff these things would make the diaphragm. I had this in the back of my mind, but I was at least smart enough to put the carb back together and use my air gun to blow air into the carb to see how easily the slide could move. Well, the slide didn't move at all and the amount of air I was blowing should have been more than enough to make the slide move. Anyway, the Scabs stuck on there REALLY well, so taking them back off was a huge PITA. Live and learn.



Luckily while removing the patches I didn't damage the diaphragm even further. I ended up cutting the Scabs with scissors and covering only the cracks just slightly. Seeing as how crazy these things stuck the first time, I realized I wouldn't need a bunch of coverage to seal the cracks. Here's what I ended up with. This method made the boot move much more freely:



And with it back in the carb you see the diaphragm sits nicely in place. I put the carb back together and blew some air in again and found the slide moves as it should.



I'm sure most of you are wondering how well these things will hold up to gasoline, and I'm wondering also. I put the patches on top because in my way of thinking if they do come loose from the fuel, then they won't be able to go anywhere and cause problems. At the very least I know the bike will get me from A to B even with the leaking diaphragm, so this experiment seemed worth the effort. I have the replacement diaphragm coming, hopefully, by the end of the week, so at least for a week I'll try this setup and let you all know how it worked out. I will travel roughly 300 miles this week going to and from work and school, so if it holds up fine, then I think my $4 fix was worth it.

Also, I took the bike for a test ride of about 4 miles. I wanted to get up to speed and test the throttle response, and I'm pleased to say that the bike pulls as hard as it used to. At the end of the week, or whenever the replacement diaphragm shows up, I'll post more pictures of the patch job so we can see how well it holds up.
 

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#16 ·
Take a piece of one of the scabs and let it soak in a jar with some gas and see what happens. If it dissolves the material or adhesive it could possibly plug up your jets.
Just my .02
 
#18 ·
The scabs are adhered to the top of the diaphragm and the jets are in the bowl. I fail to see how the jets can be affected even if they were to totally dissolve in gasoline vapor since little if any liquid fuel gets in that little chamber. They would have to dissolve and somehow get into the float bowl to clog the jets. Even if a scab comes loose, it'll sit up there in that chamber until I remove it when the new diaphragm comes in.


You can get replacement rubber for the diaphragm.
If you read the posts you'll see that I already ordered one and I did this repair as an experiment/temp fix for a few days. I figured it was worth doing in case someone is in a pinch sometime and absolutely needs their bike. They might like to know you can repair the diaphragm as a temp fix.
 
#19 ·
60 miles down so far and the bike is still running strong. The replacement diaphragm should be here any day now. JBM is only a few hours away from me, so I imagine shipping will be on the quicker side.
 
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