This morning my 78 sportster started and idled strange. Last time I rode was two days ago and everything was fine, got gas and parked it under the bike cover. This morning was warmer than it has been (42 degrees, the last time I rode it was 28). Just like normal I depressed the "choke" aka enrichment circuit on my mikuni vm38 and hit the button, instead of instantly starting and idling at high RPM (around 1500) it took a good 5 seconds of holding the button down for it to start on the 3rd try, and after that it wouldn't idle faster than 1200 rpm).

Once the engine was warmed and off the enricher, it ran fine and as if nothing happened. When I went outside after work to go home it gave me the same thing, stubborn to start but ran fine once it was warmed up. Did I get some crappy fuel? Besides today the Ironhead has been running great for the past 400 miles I have put on it so far.

 

I am not familiar with the mikuni, but my first thought is that maybe it was too warm and did not need the enrichener.

 

did you leave the fuel turned on when it was parked? if not i would say fuel drained out of the bowl took time to get it full when you turned on petcock( if its to rich at 42 degrees your tune is way off lol)

 

if you leave the petcock on it will flood, probably bad fuel or a fouled spark plug.. sometimes it just takes more to wake up then others..

 

I think it was that I did not need the enrichment circuit. It started up on the first "turn" without it, but stalled on a low idle, had to adjust the idle screw a tad to keep it up.

 

Sometimes you will need to engage the enrichment lever 'half way' while the engine warms up.

If you leave the gas turned on the carb should not leak fuel into the manifold unless the float needle is not seating.

The floats rise and close off the needle in the seat which prevents fuel from going further than the float bowl.
It is rare that a Mikuni will leak at the needle.
pg

 

I never tried halfway on the enricher lever, it seems to lend itself to either "full on" or "full off" but I will try this next time its in the mid 40's. Thanks!

 

Yeah, try it and see if it helps.
You may have to hold the lever at half way on but it will not take more than a minute or so to warm the engine.
pg

 

More news on the starting. Started it up today after a week of not riding and sitting in the cold. I turned the petcock on and started to undo my locks, and gas started coming out of the overflow at a trickle. I attempted to start the bike (31 degrees) with full "Choke" and it took longer than normal but it did start. It still idled at a lower RPM than it had been before the weird starting.

I also noticed the sound of a knock. Not a ping like detonation, but a clunky knocking sound coming from the cylinder area. Sound is only at idle, much more prominent when the engine is cold. It does not vibrate more than normal, but sometimes when I am engaging the clutch at low speed it feels like the power is not even, but "surging" When the bike is off and riding it feels fine, no issues.

When I got back on the sportster after work I turned on the petcock and still more fuel comes out of the overflow. I gave the carb a swift tap and that seemed to stop the flow. When I parked it at home I left the engine off but the petcock on to see if it would leak but nothing.

 

Well the fuel trickling out is no doubt due to the float needle not seating correctly.
As you did.... a quick sharp tap on the carb body will usually get the needle to seat.

I have no comment regarding the 'knock' you are hearing at this time.
We need more information regarding this knock to try to understand what is causing that.
Also, the funny feeling with the clutch may be related to cold weather. When the temp hits 32° things start to change on a Sportster. Nothing works as smoothly as it does when it is 70° outside.
pg