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Garrett
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« on: October 30, 2010, 10:03:07 am » |
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Okay here's the deal. This happens quite often and I am not sure why.
I drive my bug around, runs great. Get the motor temperature up - not really *hot* or anything, but normal operating temperatures. I go to the store or something, and park it in the parking lot. I come back 5-10-15-20 minutes later. Get in the car and start it up...
It's running a little rough, and I look at the LM-1 and it tells me the AFR is like 15-16-17:1....it's flipping around all over the place. I blip the throttle a bit to keep it running. Usually does this until I get out of the parking-lot - maybe a little longer. Drive it down the street a bit from stoplight to stoplight and the problem goes away. AFR's are now back in the high 12's to mid 13's at idle.
What gives? Any ideas?
I am running 48 IDA's on a 2276.
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Dougy Dee
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« Reply #1 on: October 30, 2010, 10:15:16 am » |
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It takes a while for the O2 sensor to heat up.
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Garrett
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« Reply #2 on: October 30, 2010, 10:25:23 am » |
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I am trying to figure out why it's running so crappy on start-up when it's already warm though. It never does this on a cold-start-up.
I am guessing it's running poorly because the AFR is all whacked out for some amount of time. Somehow it "fixes" itself after a few minutes and then it starts running well again.
I am not running fuel injection. I am carburated. The O2 sensor isn't influencing the mixture - it's just reading it.
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Donny B.
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« Reply #3 on: October 30, 2010, 11:34:27 am » |
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Are you sure it's not vapor locking? Sometimes that happens to me when I run around and then stop for a few minutes and try to get going again. Remember when you have dual carbs they can heat soak from the heads which are trying to cool down. Do you have an electric fuel pump or stock. I switched to an electric just because of this.
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Donny B.
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martin
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« Reply #4 on: October 30, 2010, 12:48:26 pm » |
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Maybe try tightening the manifold nuts. Sometimes vacuum leaks can come and go depending on engine temp.
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68 White 2.3 efi turbo 194hp/240tq RWHP no boost!
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Ohio Tom (DdK)
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« Reply #5 on: October 30, 2010, 03:43:37 pm » |
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My guess is flooding from gas line boiling (aka: vapor lock) or whatever you want to call it.
Basically, the residual fuel pressure over powers the inlet valve on one/or both carbs and floods that side. The fuel pressure can go very high if the gas lines heat up.
Startup, takes a little while to clean up that flooded cyl and get running nice again.
You can tell if it blows blue-ish smoke on startup.
This is a bad condition and needs to be fixed or you will "wash your rings out" so to speak. Not healthy for a motor at all...
My recommendations are:
1.Make sure your fuel lines are no where they can get cooked by the motor's heat when you shut down. Maybe it's time to re-run them neatly out of the way of heat?
2. I run an electric fuel pump on a separate switch. I always shut off the fuel pump 10-30 sec before shutting the motor off.
This runs the fuel down enough so that it won't flood even if you have inlet valve issues.
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Ohio Tom Simpson. Home of the Killa' Bee.
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Esky
Newbie
 Offline
Posts: 53
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« Reply #6 on: October 30, 2010, 05:48:36 pm » |
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My car does the same thing. I dont get any smoke on startup and my fuel lines are not getting to hot. My car will run like normal in about 10 seconds after driving away. I think it's because of heat soak but i dont know. It will only run like that for a short time like it's lean with a sputter and a pop then back to normal.
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Garrett
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« Reply #7 on: October 31, 2010, 09:22:58 am » |
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I was thinking it was some sort of vapor lock type thing as well. I am running an electric fuel pump (cb performance "carter" from about 1995) and all of my fuel lines are neatly routed and don't touch anything hot. No smoke on start-up. It's definitely running lean on startup when it's doing this - I can blip the throttle and rev it up and it behaves normally - it's just when I let it idle that I'll notice the combination of crappy running and AFR's that may be as high as 17:1. It seems to resolve itself in relatively quick order, but it's annoying!!!
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Ohio Tom (DdK)
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« Reply #8 on: October 31, 2010, 07:11:19 pm » |
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That just sounds like lack of a choke.
You can fatten up the offending clys idle mixture screws to smooth out that some.
Just a small tweak it all it usually takes.
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Ohio Tom Simpson. Home of the Killa' Bee.
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maui
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« Reply #9 on: November 02, 2010, 12:30:32 am » |
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I say Tom is correct because just a couple degrees warmer gas in the float bowl will cause this so like Tom said is to keep your fuel line away from heat if possible. That's probably why it no do that on cool nights or when your carbs are cold. One nother thing is to live with it cuz it ain't no big thing.
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Kehau
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