250 Engine loses power and dies.

[JimF]

Currently my 250 narrowcase starts, idles, revs and runs fine for a block or two then looses power as the engine dies….

Backing up a week, I rode the motorcycle some 200 miles in one day, and then rode it all over Southwestern Wisconsin the next day without trouble. The bike got a lot thrashing through the corners, hills and such, and performed just as nicely as a 250 should.

On day three I was about 10 miles into the trip home, everything up to this point had been normal, when the engine just lost all power and wanted to die. I kept it in gear, downshifting and using momentum to try and keep the engine running but it just ran without power and brought the bike to a standstill.

A cell phone call to friends with a mega-toy-hauler motor home headed home from the same event with a bay for three motorcycles and only two bays filled were about 10 miles away from me as it turned out. They stopped and waited. The 250 started right up like nothing was wrong and I set upon a course to intercept them.

Everything seemed fine and in my head I almost thought about telling them I didn’t need them after all since the 250 was acting fine.

About 9 miles later the same engine symptom occurred. I coasted down to a stop. Got off the bike, started it again, and rode on to meet the motor home which was now less than two miles from me.

The 250 made it the last two miles and I rode it into the back of the motor home.

These people live some 10 miles or so from my house, so when they got home I started the 250 and it took me home the 10 miles without incident.

Today I went to ride the 250 and it got me two blocks from home when it failed again. I could restart it easily, rev it, jump on and then go a block or a half block before it would fail again.

A couple hours later I tried again, got a block away and the engine did the same thing again.


I am looking for ideas as to what might be happening.

Thanks.

Jim

[Bevel bob]

Mine behaved exactly that way till I cleared out the breather hole in the gas tank cap.

[JimF]

I have the standard quarter turn locking cap. I can't picture a breather in the cap.

I always figured air just krept in around the locking handle's bolt hole.

Have I been missing something?

Thanks

...

Wow. I found the breather hole. I had never noticed it before. Anyway mine appears to be clear. I pushed a dental tool right through it.

Here's the BR6HIX irridium plug exhibiting a white tip over black center electrode. Insulator shows grayish residue. The ground electrode is also a bit gray.

plug1.jpg

Jim

[Bevel bob]

It does sound like fuel starvation, possibly due to some muck in the system maybe blocking the tap filter , ignition problems are usually accompanied by pops and bangs and leave the plug looking matt sooty from unburnt fuel. You do have an insulator on the carb flange ?, I have heard that vapourisation in the carb can be an issue with todays fuel. Check the batterys charge (if it has one). I had similar problems with oil in the chamber fouling the plug only when the motor warmed up enough to burn it,(loose valve guide), but my plug was black and shiney.In all I had problems with just about everything all at the same time!, no wonder the previous owners gave up on it.My tank breather was blocked with polish, a moral there, stop polishing get riding.

[DewCatTea-Bob]

Mine behaved exactly that way till I cleared out the breather hole in the gas tank cap.

____ I would've suspected the same IF Jim's tank didn't have the crack in it (which Jim posted in another recent thread).
__ Jim, have you checked that your points-gap hasn't closed-up ?
If that's okay, then perhaps your ex.valve-clearance has become too tight.


Hopeful-Cheers,
-Bob

[JimF]

Dew-cat-tea Bob gets credit for remembering that the split in the tank would have superseded any blockage of the fuel cap vent.

Fuel flow through the petcocks appears normal, although examination of the petcocks reveals that the internal gauze is torn in some spots. And a week before my trip I lost one of the petcock levers on a ride. The reserve setting on one petcock appears slightly restricted, so that's another reason to buy new.

Does anyone know a good source for quality petcocks that fit the Ducati tank threads?

But I digress....

No battery, so that's not an issue.

The carb is secured to the intake flange by a chunk of large fuel hose.

intake_tract.jpg

Points gap (not spark plug gap) is 0.012" at maximum open.


I will check exhaust valve clearance in the days to come.

On a side note, I put in a new plug and did a 5 minute drive around the block multiple times, enough to drain the float bowl I suspect. I had no trouble with the new plug installed.

Jim

[Bevel bob]

I never go out without a couple of spare plugs of different grades, I'm sure my fueling is still a bit rich on the progression but the difficulty in obtaining SSI needle jets in alternative sizes has stopped the experimentation.

[Bevel bob]

I never go out without a couple of spare plugs of different grades, I'm sure my fueling is still a bit rich on the progression but the difficulty in obtaining SSI needle jets in alternative sizes has stopped the experimentation.

[JimF]

Well, what looked to me to be white is, under a microscope, just pure untarnished silver electrode.

The only thing that looks possibly problematic is the ground electrode. It is black in color, and a gentle swab of the electrode shows that it is not simply covered with a residue.

The inside face of the ground electrode is now visibly concave, exhibiting loss of what I would estimate to be a few thousandths of material in a radial shape from the iridium electrode tip (which is smaller than standard center electrodes.)

I may switch back to non-iridium plugs if the new plug has cured the problem and if I see another similar failure in the new iridium plug. My thinking is that the larger surface area of the non-iridium center electrode might offer more alternative paths to the ground electrode as areas of the electrode become non-viable. Does that make sense?

[maserlin]

Anything electrical can fade and die when it gets hot. I was going to suggest the coil, but if a new plug fixes it so much the better.