Hello, thumpers. Been reading this great site for a while, and now I have a problem. A couple pro mechanics have said “maybe-this-maybe-that.” My repair ability is strong, but knowledge is spotty. Anyone want to play the diagnosis game?

2001 Savage, 8,000 miles, 4,000 of those since bought a year ago.
Warm weather, above 70 degrees: Bike always starts and runs with no problems.
Cool weather: Bike starts fine, but dies or stutters awfully once warmed up.

Starting  behavior is same whether use choke to start (colder air temp) or do not (at 60-70 degrees). After a couple minutes of warming, and when choke turned off if used, revolutions slowly decrease until stall. Can restart with much throttle, so much that gas may come out carb vents. On restart revolutions are normal, but slow to stall again. There is a small amount of black smoke from tailpipe when giving gas to keep alive.

Riding behavior (if take off before warm, or ride into cool weather): Couple minutes after starting, engine stutters horribly for a few seconds (chugga-chugga, power loss), then runs well for 10 seconds, then continuously repeats this cycle. Dies at idle. Can usually keep running with continuous, generous throttle.

Running at high RPM does seem to help when behavior less severe (moderate air temps).

Problem appeared suddenly. This was after a couple months garaged in winter, with no storage prep, but had been riding again for several hundred miles.

Have very mild leak from head gasket since purchase, one year. (At least I think it’s head gasket.)

Fixes Tried:

Replaced spark plug (blackly caked). No change.

Bike shop didn’t experience behavior. Thought it rich and leaned mix half turn; put ring clean in gas. No change.

Higher (medium) octane gas. No change.

Tried carb cleaning, with limited knowledge/ability. Both ends of air horn and the bowl looked pristine clean. Float traveled freely and no apparent damage. Throttle plate moved freely. Cleaned nothing; didn’t know how to check anything else.

Pro mechanic friend suggests I replace the ignition coil next.

Mr. Hyde wrote on 06/23/09 at 11:53:28:


Afraid that's too simple. Won't deal with stutter at speed, and really, it's worse than that. When I say awful and horrible stutter I'm serious. (Cool is at or below 70 degrees.)

The standard jetting on the Savage is pretty poor. Contact LANCER, he has jet kits for sale. He can also give you a few other ideas about what could be wrong. Could also be dirty air filter. Cheers.

Try cleaning air filter or for a test, just take it out.  Don't run long without a proper filter though.

Does it run any different when petcock is set to PRIME?  

Battery in good shape at least 12.3vdc (50%)  or 12.6vdc(100%)?

The mild oil leak is probably the very common and minor cap plug over a head bolt - my drips don't reach the ground yet either.

I've been able to reproduce the symptoms you mention three different ways- air, fuel and vacuum.  

Air filter.  From my experimenting with various filters and filter media:

a little too restrictive- idle fine, rev fine, slow accelerate fine with very casual riding up to about middle rpm range, start to stutter under medium spirited riding, cough and sputter under full throttle and high engine load.

moderately restrictive- idle fine, start to stutter when revving, stutter when slow accelerate with very casual riding up to about middle rpm range, cough and die with full throttle or high engine load.

very restrictive- stutter when idling, and revving kills engine.

Fuel. Tired of putting the tank after doing some work to see if she runs, I made a test gas tank out of a plastic water bottle, lawnmower gas filter and clear fuel line.  The filter is mounted to the bottle cap. Just fill, hook other end of the line to the carb, turn bottle upside down and viola.  The other day I used some gas out of a gas can that had been sitting in the garage for maybe 6 months.  Started, idled a little rough, stuttered with any revving.  Emptied fuel bowl, filled bottle with gas from the tank, primed, started, ran fine.  

Vacuum.  When I first used the bottle I didn't plug the vacuum line.  Started, idled a little rough, stuttered with some good revving then got progressively worse.

Air, fuel, vacuum.  Always check them.

And here's a new observation from the last cool day.

Re. head gasket: While using much throttle to prevent stall at idle, I saw a tiny but vigorous pfft-pfft-pfft of something gaseous coming from the front center of the head gasket.  Is this definitely the problem or just highly suspicious? How serious is that behavior?

I spoke too soon. Problem came back with a vengeance tonight at 80 degrees. Never happened at that temp. Very humid.

And... setting petcock to Prime cleared it right up. Switching back and forth several times confirmed.

What does this test tell me?!  That the problem is in vacuum or petcock as Yonuh suggests?

OK, that's how I read it too. Will think about the RES thing. The plug I changed could have been original as far as I know, so it may mean little.

Thanks for help! I didn't even understand I had a vacuum operated petcock a week ago. Talking helped me figure out new things to look up. Fingers crossed now.