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back fires and losses power

  • Thread starter Thread starter terrylee
  • Start date Start date
T

terrylee

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Got the bike on the road today, first time since last summer.
during all this time I have replaced the stator, r/r, new spade fuse box, new petcock, rebuilt carbs(the right way), rebuilt master cyl. and frt calipers,new wheel bearings, new brake lines, replaced elec. connections to stator,r/r. ignitor. Replace all vacuum lines. Sync. the carbs again today and got them near perfect. Bike ran better than it ever has for the first 10-15 mins, and then all of sudden started backfiring like crazy and losing and gaining power with every backfiring. Got it home checked the plugs (color was grey) and getting nice blue spark on each one. Checked for loose connections(could find none), took back out and ran great for another 10-15 mins. then started backfiring again and feeling like it was running on only 2 cyl. Got back home, getting 12 volts at coils (had already done relay mod.), did test in manual on ignitior and got spark. Took back out again and this time it ran for 30-40 mins. before it started with the backfiring and loss of power again! I feel it must be something breaking down after it gets hot and only working intermittently. Perhaps a coil or the ignitior (even though it tested ok) ? Don't have any spare coils to switch out or ignitior either, any and all thoughts very welcome?:confused:
 
It sounds like a coil problem i had on my '78 GS1000. Approximately 15 minutes into a ride it would start running on 2 cylinders. I thought it was fuel starved and flip to reserve with no change. Pull over to check things and that would be enough time for things to cool down and it would run great for another 5 minutes. Swapped the coil with one from another bike and the problem went away.
Something about the copper windings inside the coil expanding with the heat and the continuity fails.
 
I have had many "ol timers say to me if it sounds like electrical it's probably fuel related.

is there rust in the tank? did all 4 carbs lean idle drop nicely to reassure you did them right? (hope you do not use sea foam or have old watery gas)

ok you have done a lot to the electrical system, you did your carbs, too, so I'm just brain storming.

I had a bike that the stator charged great when cold and broke down with heat.

I've had bad grounding connection that did what you are describing

bad resistor caps, bad spark plug, weird battery with inner plate broken,

Basicly you are going to have to ride around with your tools/ testing devices.

I had these light up plug caps to test spark when riding. a volt meter on board to read while riding etc...
 
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Thanks for the responses guys! I have new spark plug caps, and seems to be charging ok. Strange thing is I got a new air filter yesterday (old one was old), put it on and went riding for an hour and a half and had no problems at all. I can't imagine that had anything to do with the problem since it only occurred intermitetly. Although am getting alot of backfiring when let off throttle, but no power surges. Went ahead and ordered some new coils from Dennis Kirk, since it can't hurt, and can only help, I've been wanting to replace for a while anyway. terrylee
 
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Bad news tried to ride to work this morn. and it immediately started coughing (not quite backfiring) and losing power off and on quickly. So much for my thoughts about something getting hot and then not working properly. Should have new coils waiting for me at home, will put them on tomorrow and see what happens. terrylee
 
I had an intermittent problem with my GS too. When I first had it running It would sometimes backfire and just quit. Let it set for a while and it would re start.
A new set of coils fixed the problem
 
My thoughts too, ordered a set of universal emgo from Dennis Kirk who showed them fitting my 1980, but appears they won't work since they are for bikes with points! Sent an email to them but no answer yet. I don't understand how they could make such a mistake. Can't even figure out how many ohms they are! I'm so disappointed if these wouldn't work. terrylee:mad:
 
What ohms are they ? You need 3 ohm coils, Point systems use 5 ohm coils
 
That one of the things I'm trying to find out from them, not listed anywhere. If they are 5 that means I could use them right? It is ok to have more ohms than you need, just not less? terrylee
 
Checked ohms on primary wires and got 4.3 ohms. So if I use these are they going to cause any problems?
 
My bike has been sitting for a week without the tank while all the parts are at the painter. It never backfires. I did a valve adjust last night and changed three shims on the low side of the specs. Fired it up with what was left in the bowls It didn't make any excessive valve noise , but it did backfire a lot. Have you run it on the prime position to see if It is a fuel delivery problem, because that will surely cause it if it isn't getting proper fuel.
 
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Ran fine when doing carb. sync. with aux. tank hooked up. No loss of power or real problems till after rode it a while. Also has new petcock. Did a valve adjustment right before carb. sync. terrylee
 
Ok, finally ready to do a test ride hopefully tonight or tomorrow. Got coils on (had to zip tie left one under frame to get tank back on), replaced all old connections to coils and relay mod., bike starts quicker than I think it ever has, even with no choke. Got frt. and back brakes all rebuilt (and master cyl.) so can't wait to ride! I only hope this solves by backfiring and loss of power problem I had earlier! This bike has been down since last summer and I have missed it so! terrylee
 
terrylee,

I am having a similar issue with backfiring when adjusting my pilot screw. The bike was great until it heated up. (I am letting it cool down now so I can retry)

I have a carbtuner connected at the same time. When I hear the bike backfire the #1 cylinder vacuum disappear. Sometimes it will blow the carbtuner tube off the plastic connector that screws into the boot.

What did you find about the coils? Did that solve your issue?

Cheers!
 
New coils took care of loss of power after it got warmed up and the backfiring that would occur when this happen. Still have some soft backfiring on deceleration, but not near like it was. Coils also seemed to make bike start quicker and run alot better overall! Happy I replaced them no matter what. terrylee
 
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