My engine has been running great for the past 3 yrs. Always drive it a couple of miles on good days. Lately it has been giving me fits....

It starts cold immediately. Runs and idles fine at first. As soon as it has warmed up a bit, maybe 3-5 minutes, it's trouble. Seems to start missing. Not the steady firing sound. If I open up the throttle it gets better. This pattern continues with more throttle required to run smooth. Eventually it gets worse and eventually dies. Once it dies, it won't start.  If I let it sit over night to cool down, it starts immediately. After 3-5 mins we're back to the same trouble.  

I have:  overhauled the carb (bath),and checked the valve clearances.

I'm pretty much stumped presently. Never had an engine act like this. Could a coil act up like this or some other electrical element? Any suggestions are appreciated.

Mods include: Supertrapp muffler, rejetting, chain drive, bigger seat.
 

Well actually down and back to the mailbox about 2 miles. Since the act up I don't do much more. Don't want to get stranded. Battery seems fine. When cold it starts right up.

Forgot to mention it's an '03 Savage. Don't remember the jet upgrade. I bought them from one of the members here maybe from the Carolinas. That was 3-5 yrs ago at least. It has run great since.

Battery seems fine. When cold it starts right up.


I understand that that's how you feel about it. I see why. I also know these guys and these bikes. Based on your description of how much you ride and the difficult to diagnose problems a marginally charged battery can cause, suggest you go with the advice.
The petcock can do bizarre things, too.

After you've done that and if it makes no difference, see if someone can loan you their ignition box. Those can break down as they heat up and quit working intermittently. No idea whether any Savage owners have had ths one, just throwing it out there.

Check the fuel cap is venting air. A blocked vent and vacuum in the fuel tank might be to blame too. Pull off the fuel line to the carb, put the tap on prime and let the fuel run out. Should hear the cap whistling as the fuel pours out.

Hope it's an easy fix.

Thanks for all the suggestions. Am waiting for a new battery to arrive. Should be this week.  I did charge up my battery and ran some tests again. One thing I forgot to try was removing the gas cap to eliminate a plugged tank vent. When I remembered about it, I realized I couldn't remove the cap with the key in the ignition.

Did pull the petcock vacuum hose off when it started acting up. I plugged it with my thumb and didn't see any change.

Had a voltmeter across battery terminals to see if any change.  13.4 volts showed while running when I first started it.  Once it started acting up it had dropped some, but still at 12.2 V.

Other things I noticed were: existing battery is 3 yrs old (Big Crank, not a name brand).  Spark plug shows running rich. Probably why it starts right up when cold. May remove another ring from my Supertrapp. .

Rectifier is around $200. Hope it's not that. Only have 3500 miles on it.
I'll keep my fingers crossed.

Thx again Verslagen1, Justin_O_guy2, Gizzo, & Dave.

Finally got back to my bike.

Installed a new Yuasa battery. Ran without the gas cap to eliminate a plugged tank vent. Same results.

I have been reading other posts. Deltaplanet used the term "loping" when describing his engine idle problems. That describes mine pretty well.

I was wondering about the chain tensioner I've seen that mentioned plenty. Thought of that because when the "loping" starts it reminds me of a friend's car that had a racing cam. Its idle sounded similar. I still have the stock tensioner. Any chance that could be involved?

Are you saying the engine lopes as in runs fine one second, stumbles the next, rinse, repeat? Sounds like a carb issue to me.

Thx for all the suggestions. Just to update.....

Have taken the petcock out of play, I believe. Haven't run out 2 tank fulls of gas though. I feel much like a fool riding around on a bike with engine issues.  I run the petcock on Prime and plug the vacuum line to the carb. Then added another line to the carb and plugged it.

Was able to find a pick up coil for cheap and eliminated that.
The float valve arrived and replaced it. That actually gave me some encouragement. It took a lot longer to act up, but did.

I know I'm running rich. No matter how cold it is. It fires right up without choking. That tells me rich at idle. Plus the plug (which I also replaced) shows rich .

My main jet is 150. The pilot jet is a 55. Stock spacers. I'd like to try something less for the pilot. I found out the stock one (which has vanished after two housing moves) was 52.5. I'd like to try going smaller than 55.

Would also like a source for jets besides my dealer. Any help there would be appreciated.

The weather is incredible here for February. I'm looking forward to tasting bugs. Thx