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Is this a vacuum leak or not?
https://slantsix.org/forum/viewtopic.php?t=12993
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Author:  '74 Sport [ Sun May 15, 2005 12:39 am ]
Post subject:  Is this a vacuum leak or not?

Finally got Aaron's slant running on its own today. Had a huge timing problem at first. Two foot flames shooting from the carb look pretty cool, but it's not very practical. Got the timing set somewhere just under 10 deg. advanced and was staying fairly steady, but idle is hard to keep.

When the engine warmed up, the choke thermostat opened the plate to almost a vertical position, leaving about a 1/2" opening at the front. It was running rough and surging. Someone helping us suspected a vacuum leak. When he manually closed the choke plate, the rpm raised considerably and the engine ran smoother. Is that a sign of a vacuum leak? Running better when choked down doesn't make sense to me, not that I know much about this.

Jerry

Author:  slantzilla [ Sun May 15, 2005 5:48 am ]
Post subject: 

Yep, that is a sign of a major vacuum leak. Spray carb cleaner around the intake ports/carb area until you see a change in engine speed.

Did you bolt the intake/exhaust together before you bolted them to the head? :shock:

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