Greetings all -
I'm having trouble fighting high idle (~900). Everything was running well - I had tuned via lean drop to an idle of 650 with a vacuum of 19-20. Ran this way for about a year. Seemingly overnight the idle went to 1200 and vacuum of ~15. Tore into everything and found a leaking EGR J pipe / cooler, all of which I have fixed; this helped the vacuum (16) but did not correct everything. I do have a significant leak at the exhaust pipe just before the muffler - but I don't think this explains things.
I have:
Verified proper timing
Checked / adjusted valves
Fixed / replaced EGR components
Multiple smoke / carb cleaner tests have confirmed no intake leaks
All throttle linkages move freely.
Pulling up on the gas peddle will slightly reduce the idle, but it will increase when let go.
Started messing with the carb - I had rebuilt this about a year ago using the great videos @Pin_Head put out.
The idle mixture screw does not reduce idle when screwed in. Again I think all intake vacuum leaks are addressed.
Looking into the carb with the engine off - I noted that the secondary butterfly is not completely closed. With the engine running I can see fuel being drawn in under the butterfly - is this normal? Should the secondary butterfly be completely closed at idle? I'm thinking this is my problem, but can't understand why it was running well and now the change.
I can move the secondary butterfly manually by directly manipulating it - it doesn't seem to be stuck.
Sorry for the book! Any insight really appreciated.
First pic - engine off
Second pic - engine running - you can see fuel just under the butterfly (kind of cool)
I'm having trouble fighting high idle (~900). Everything was running well - I had tuned via lean drop to an idle of 650 with a vacuum of 19-20. Ran this way for about a year. Seemingly overnight the idle went to 1200 and vacuum of ~15. Tore into everything and found a leaking EGR J pipe / cooler, all of which I have fixed; this helped the vacuum (16) but did not correct everything. I do have a significant leak at the exhaust pipe just before the muffler - but I don't think this explains things.
I have:
Verified proper timing
Checked / adjusted valves
Fixed / replaced EGR components
Multiple smoke / carb cleaner tests have confirmed no intake leaks
All throttle linkages move freely.
Pulling up on the gas peddle will slightly reduce the idle, but it will increase when let go.
Started messing with the carb - I had rebuilt this about a year ago using the great videos @Pin_Head put out.
The idle mixture screw does not reduce idle when screwed in. Again I think all intake vacuum leaks are addressed.
Looking into the carb with the engine off - I noted that the secondary butterfly is not completely closed. With the engine running I can see fuel being drawn in under the butterfly - is this normal? Should the secondary butterfly be completely closed at idle? I'm thinking this is my problem, but can't understand why it was running well and now the change.
I can move the secondary butterfly manually by directly manipulating it - it doesn't seem to be stuck.
Sorry for the book! Any insight really appreciated.
First pic - engine off
Second pic - engine running - you can see fuel just under the butterfly (kind of cool)
