svinkle
Member
- Joined
- Feb 7, 2007
- Location
- Portland, OR
I've been chasing idle issues with my B20 with HIF6 carbs. I rebuilt the carbs, surfaced the manifold, replaced all intake/carb gaskets, and checked that the brake booster is not leaking. Float level is 3/32 gap with carb body. Choke is only on the front carb. It's got a 123ignition distributor, timing is 10 degrees BTDC and advances correctly. Carb B20 with an early F head.
I've read this thread at least ten times.
Here's a very long checklist of what's going on:
- I can never ever even come close to passing the lift pin test. Even after 3+ extra turns rich, engine bogs and stalls. When turned way richer, it takes longer before the idle drops, but stalls nonetheless.
- At the "base" 2 1/2 turns, acceleration is a little bit hesitant and jerky. Turned 2 turns richer, it accelerates much more smoothly.
- I have to back the idle screws pretty much all the way out to get the idle below 1000rpm.
- Manifold vacuum reads ~14in (the late ign timing part of the gauge). Advancing the distributor raises vacuum, but not enough before idle becomes too high. Raising the idle via idle screws raises vacuum just a little.
- I have a metered port off the manifold connected to a vented oil cap. If I plug that port, the idle lowers a bit. Seems like this is just acting like a vacuum leak?
- When I rebuilt the carbs, the pistons only marginally passed the drop test. Not sure if this affects idle or just acceleration.
- Choke and Hot start valves are adjusted correctly and don't interfere with the throttle/idle adjustment.
- I've sprayed carb cleaner in every spot I can reach and appear to be no vacuum leaks.
- There seem to be two different specs between different heads... I've tried both. Currently at the tighter option.
- Compression test was ~135-140 across all four cylinders. I bought the car 5 years ago with a bad head gasket and replaced it immediately. Rob at Vol-tech took one look at the head and handed me "the thicker gasket". I took his word for it, and I'm assuming/hoping that the consistent low pressures are due to the thick gasket.
Spark plugs. I had them out a few months ago when I took this photo... I think they're in order 1-4, but might have gotten them mixed up. The 1-2 manifold runners are much darker than 3-4, which I always chalked up to the front-only choke.
<a data-flickr-embed="true" href="https://www.flickr.com/photos/vtslickster/50245315088/" title="Untitled"><img src="https://live.staticflickr.com/65535/50245315088_721ce16917_z.jpg" width="640" height="480" alt="Untitled"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>
Video of Vacuum at idle
This has driven me nuts for years, and as you can see I've checked a lot of potential causes, but haven't come up with anything. I fantasize about the lift pins just making the idle raise then settle nicely. Anything stand out?
I've read this thread at least ten times.
Here's a very long checklist of what's going on:
- I can never ever even come close to passing the lift pin test. Even after 3+ extra turns rich, engine bogs and stalls. When turned way richer, it takes longer before the idle drops, but stalls nonetheless.
- At the "base" 2 1/2 turns, acceleration is a little bit hesitant and jerky. Turned 2 turns richer, it accelerates much more smoothly.
- I have to back the idle screws pretty much all the way out to get the idle below 1000rpm.
- Manifold vacuum reads ~14in (the late ign timing part of the gauge). Advancing the distributor raises vacuum, but not enough before idle becomes too high. Raising the idle via idle screws raises vacuum just a little.
- I have a metered port off the manifold connected to a vented oil cap. If I plug that port, the idle lowers a bit. Seems like this is just acting like a vacuum leak?
- When I rebuilt the carbs, the pistons only marginally passed the drop test. Not sure if this affects idle or just acceleration.
- Choke and Hot start valves are adjusted correctly and don't interfere with the throttle/idle adjustment.
- I've sprayed carb cleaner in every spot I can reach and appear to be no vacuum leaks.
- There seem to be two different specs between different heads... I've tried both. Currently at the tighter option.
- Compression test was ~135-140 across all four cylinders. I bought the car 5 years ago with a bad head gasket and replaced it immediately. Rob at Vol-tech took one look at the head and handed me "the thicker gasket". I took his word for it, and I'm assuming/hoping that the consistent low pressures are due to the thick gasket.
Spark plugs. I had them out a few months ago when I took this photo... I think they're in order 1-4, but might have gotten them mixed up. The 1-2 manifold runners are much darker than 3-4, which I always chalked up to the front-only choke.
<a data-flickr-embed="true" href="https://www.flickr.com/photos/vtslickster/50245315088/" title="Untitled"><img src="https://live.staticflickr.com/65535/50245315088_721ce16917_z.jpg" width="640" height="480" alt="Untitled"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>
Video of Vacuum at idle
This has driven me nuts for years, and as you can see I've checked a lot of potential causes, but haven't come up with anything. I fantasize about the lift pins just making the idle raise then settle nicely. Anything stand out?