AT Decel in a Manual FI Bug?

Carbs & F.I.

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JRR
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Re: AT Decel in a Manual FI Bug?

Post by JRR » Mon Jun 10, 2019 4:32 am

No emissions testing. Can't leave well enough alone. I think I hear an exhaust leak somewhere, but everything sounds like an exhaust leak after installing a new system.

My next crisis is that the engine always needs a second start when cold. Sounds like the cold start valve doing its thing, and the second start is perfect, catches after a single crank. I had issues with the AAR, I may have to bite the bullet and pony up for a new to me one. Would low fuel pressure to the injectors do the same thing? Need to set up a pressure testing rig.

Thanks

JEff

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Amskeptic
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Re: AT Decel in a Manual FI Bug?

Post by Amskeptic » Mon Jun 10, 2019 4:11 pm

JRR wrote:
Mon Jun 10, 2019 4:32 am
Would low fuel pressure to the injectors do the same thing?
NO!
But you might be on to something ... carbon at the intake valve heads (port side) can eat gas vapor.

Set your warm idle speed to 1,050 rpm and adjust fuel mixture for maybe 25 rpm lean from happy place, then test next cold start.
a) it catches and holds - good! it was too rich and too little air flow!

b) it doesn't even start - well, too lean? Adjust mixture for a half to full turn richer from happy place, and see if cold start now catches.

See? No easy armchair answers, ever. Just little forays to differentiate symptoms.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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asiab3
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Re: AT Decel in a Manual FI Bug?

Post by asiab3 » Mon Jun 10, 2019 5:38 pm

You can poor-man-test for low fuel pressure at startup yourself. It's not necessarily a pinpoint diagnosis of anything, but you might tell a difference from your normal starting behavior. Key on, drumstick or wooden dowel into the AFM flap (air filter removed) just enough to hear the fuel pump buzz. You'll hear the song of the pump change when pressure it built up. Start it. And?

Cold start valves can be unplugged for a cold start just so you can see what kind of effect they have. Again, not a lot of science here, just shade-tree communication with your engine to see what it likes and how it behaves on a cold start without the extra enrichment.
Robbie
1969 bus, "Buddy."
119k miles with me.
296k miles on Earth.

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JRR
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Re: AT Decel in a Manual FI Bug?

Post by JRR » Mon Jun 10, 2019 5:48 pm

Thanks both very much,

I'll screw my courage to the sticking place and try Colin's suggestion. Pardon my thickness, Colin, you are talking about the throttle-body idle adjuster?

Jeff

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Re: AT Decel in a Manual FI Bug?

Post by Amskeptic » Tue Jun 11, 2019 5:41 pm

JRR wrote:
Mon Jun 10, 2019 5:48 pm
Thanks both very much,

I'll screw my courage to the sticking place and try Colin's suggestion. Pardon my thickness, Colin, you are talking about the throttle-body idle adjuster?

Jeff
No, that screw in the throttle body right next to the throttle plate where the aceelerator pedal pulls the throttle plate open to give you get up and go? that screw is the idle speed screw.

The mixture screw is on the AFM where air is measured to give you the correct metering of fuel, yeah, there's a mixture screw to vary the proportion of fuel to air. That screw.
Colin :cyclopsani:
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

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JRR
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Re: AT Decel in a Manual FI Bug?

Post by JRR » Wed Jun 12, 2019 4:21 am

Yikes. Ok, have to do some studying. Thanks.

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