Backfiring problem?

itsdesignateddave · 06-19-2009, 1:23 AM

Long time member who hasn't posted in a long (long, long...) time and hoped someone would have another idea. I bought an 03 spirit a few months ago and it doesn't run quite right and can't seem to figure it out. I had an 03 spirit several years ago and it was perfect, so I know it's not "normal" even though several people tried to tell me this. The only thing the original owner said is that it has always run like this (assuming from the factory). Who knows why he didn't take it in under warranty, but thats way too long ago.

When you ride under about 15 it backfires out the airbox side of the carb on only the front carb pretty consistently, and when you downshift at speed (maybe 25+ mpg) and don't hold in the clutch it backfires pretty badly out the exhaust side, again only on the front carb. The back carb/exhaust doesn't at all.

Maybe I'm missing something, but here is what I have done and checked:

I pulled the carbs off and disassembled them and they were immaculately clean for a bike under 6000 miles and 6 years old. At the same time I checked everything to make sure there wasn't anything in the fuel or if one of the lines was pinched. I Checked the jets and all the airways to no avail. The following weekend I pulled everything and adjusted the valves. All of them were within tolerance except an exhaust valve on the back cylinder (not the one backfiring). the last idea was to pull the factory settings off the carb synchonizing screws (can't remember the techincal name) and one side was 2 turns in the and "bad" one was about 1.5 turns. They are now both set about 2 and 1/8 turns out and it seems to have taken away the random backfiring at idle, but it's definitely still there the rest of the time, so maybe I am starting to get on track?

The only other ideas I have are to get the actual tool to synchonize the carbs. It doesn't seem to matter as the front one is always bad and the back one runs great, so I don't think it has to do with that part. The final thing I can think to do is advance or retard the timing to see if it makes a difference, but I was hoping someone had the same problem and has an easy fix without a $500+ factory bill.

One final thought after posting this originally - I am 99% sure it hasn't had a jet kit installed at any point in it's life but I'm not 100% sure. My original shadow had the exhaust drilled out so maybe I missed the backfiring because it was so loud?

daninspokane · 06-19-2009, 1:54 AM

Well I'd have to hear it to make a comparison to mine, BUT I pop ALOT on decel and slow speeds on my '07 1100. Every once and a while it'll give a nice loud rapport/backfire. I've checked around and talked to other spirit owners and they've all concurred it's normal. Some tell me to rejet and get a new exhaust system and that'll fix it.... currently saving up the dough to do just that (want the throaty deep rumble anyways).

I am no mechanic but thought my little nugget of experience might help

ghbzorro · 06-19-2009, 2:14 AM

Sounds lean on the front? What kind of exhaust is fitted? 2 into 1? or 2 into 2? Try fattening up the front and see what happens.

itsdesignateddave · 06-19-2009, 8:14 PM

It's the stock exhaust so it wouldn't have anything to do with aftermarket parts.

The downshifting sound is more of a grumble and pop than a true backfire, so it's probably very similar to yours as well. The popping out of the carb at slow speeds isn't really very safe as it hesitates when it does it as well.

smkeatr · 06-20-2009, 10:50 PM

Both my 06's do that too. One is much worse than the other but it has a few thousand miles more on it. I was maybe thinking it was old gas so I went on some longer rides and ran it almost empty and have been running a couple of tanks of premium through them to no avail. That old gas was in there for several months but that didn't fix things. It has improved on the lower mileage one but nothing for the higher mileage one. I read up on some Shadow forums about exhaust bolts being a little loose but I've tourqued them all to spec. I'm game for a jetting and a set of pipes but not right now. Seems to be a common problem with these bikes.

Tigershark347 · 06-30-2009, 3:00 AM

I have a 2006 Honda Shadow Spirit. I had the same problem with popping on decel like you. You are running lean. Rejet both carbs and put on a K&N Air Filter. You will notice a huge difference in sound and performance. Rejetting, a valve adjustment, and more airflow through the air filter will solve your problem. Also I am running a set of slash cut Cobra pipes on my bike.

smkeatr · 06-30-2009, 10:27 PM

That's the mods I had planned in the near future. Thanks for the advice.

Tigershark347 · 07-01-2009, 1:02 AM

Your welcome. Everything I told you is tied in together. You definitely don't want to damage your valves. It's best to do it all at the same time. It will be few bucks but well worth it. Cycleplex here in San Antonio, Texas did it for $139.00 per carb, 1 jet kit does both $69.00 and valve adjustment $119.00. I got 15.000 miles , looks new, garage kept, and still running strong.

smkeatr · 07-01-2009, 11:28 PM

Did you happen to find out what size jets they used? And the adjustments? It would save me a bunch of trial and error.

Bigtoe · 07-03-2009, 4:00 PM

Quote:

Originally Posted by smkeatr

Did you happen to find out what size jets they used? And the adjustments? It would save me a bunch of trial and error.

Are you gonna jet it yourself? If so call the jet company up and tell them what you plan to do. They will steer you in the right direction. If not the dealer should know which ones they can do.

Although you could put pipes and a K & N air filter in and NOT rejet. You just have to turn mixture screws out after drilling the plugs out to get to them.

smkeatr · 07-03-2009, 10:56 PM

The dealer is the last place I go for help.

When the time comes, I'll get it worked out with the Jet Co.