Hard starting question

[jryan]

Got up this morning for a 300 mile ride & for the first time ever the bike wouldn't stay running. It started but just barely would spit & sputter enough to stay running for 20 seconds or so. If I touched the throttle or took it off full choke it died. At least 2 cylinders were firing as I had exhaust out of both pipes but was just barely chugging. Last rode it a week ago & ran fine. So then I dumped some Seafoam & new gas in. After many more tries I was just about to give up the day thinking maybe I had some bad plugs, then on about the 30th start, it chugged for about 5 seconds, then POP (an audible pop or maybe backfire), but immediately it was idling normal. Shut if off & it fired right back up. Rode all day, many stops, no further problems.

 

Any idea what was stuck, fouled, etc? I'm thinking I should check or fix something, but what? I'd like to know so if it ever happens while 1000 miles from home I'll have a clue.

[davecb]

An fouled plug will do that, then when it clears and sparks, it ignites all the gas in the cylinder. That's what causes the backfire....

[Condor]

A heavy Sea foam mix has a tendency to foul plugs.

[V7Goose]

Got up this morning for a 300 mile ride & for the first time ever the bike wouldn't stay running. It started but just barely would spit & sputter enough to stay running for 20 seconds or so. If I touched the throttle or took it off full choke it died. At least 2 cylinders were firing as I had exhaust out of both pipes but was just barely chugging. Last rode it a week ago & ran fine. So then I dumped some Seafoam & new gas in. After many more tries I was just about to give up the day thinking maybe I had some bad plugs, then on about the 30th start, it chugged for about 5 seconds, then POP (an audible pop or maybe backfire), but immediately it was idling normal. Shut if off & it fired right back up. Rode all day, many stops, no further problems.

 

Any idea what was stuck, fouled, etc? I'm thinking I should check or fix something, but what? I'd like to know so if it ever happens while 1000 miles from home I'll have a clue.

There is not much info to go on here. It would have been extremely helpful if you had done the finger test on the header pipes while it was not running right so you could be sure exactly which cylinders were not running right. It is unlikely that only one was bad, since this bike will start and run great on three cylinders. If you want to see just how well, simply pull off one of the rear spark plug caps and try it. Of course, if it was particularly cold and damp that morning, maybe three cylinders would have been as rough as you describe, but I doubt it.

 

I'm more inclined to think you have a problem with the fuel pump. You said the bike had been sitting for a week, so normal fuel evaporation would make the fuel level very low in the bowls, and the bike would behave quite similar to what you describe. Did you happen to notice if the fuel pump was clicking when you first turned the key on? After a week, it should have taken several seconds to stop clicking.

Goose

[jryan]

I didn't have a heavy Seafoam mix, at least until I dumped some in when this happened. I initially thought fouled plug, but the way it was running it seemed like at least 2 were fouled, and I thought that was unlikely.

 

As for the fuel pump, I didn't notice if it was running when I initially turned the key on, cuz it has always fired right up. But I'll be paying more attention now that's for sure. Took it out tonight & started/ran fine again. Is there any way to test for an intermittent fuel pump, or would I just have to wait & see if it happens again? Kinda seems like it's running as normal now...but I'm a little nervous it might happen again at an inopportune time...JR

[Seaking]

Just got back from recent road trip to New Hampshire and my buddy's bike had such a problem.. it would start ok but man it sounded sick, and if you touched the throttle it would cough and die.. restart.. open choke... blech..

 

First thing we did was check the headers as Goose mentioned but they were hot so we knew we had a good fire going and poof.. it started to run great and stayed running great ever since..

 

The ONLY thing I can figure is possible water in the fuel as the bikes sat out in the rain that night (you CAN do that with a Yamaha.. not a Harley, leaving it out in the rain over night..

 

Not sure if water was the issue but that's all I could think off.. we fueled at the same stations and so forth.. but over night parked in the rain.. who knows