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Chasing an air leak - need suggestions
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flightofphx
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Joined: September 11, 2017
Posts: 114
Location: AZ
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PostPosted: Sat Apr 01, 2023 7:25 pm    Post subject: Chasing an air leak - need suggestions Reply with quote

I have a 2276 with stage II heads, FK8 cam, and dual 48 IDA carbs (clones). I have been chasing an air leak on 1 -2 and I am almost out of ideas.

Short history, when I bought it the total timing was set at 40 and it was jetted with 70 idles and running rich. I put 60 idle jets in it and brought the timing back down to 30 total and started to tune the carbs. I noticed the pump jets were dripping and I replaced the O rings and they still dripped. I could only get them to not drip by reaching under and holding the trottle shaft. I pulled the 48 IDA (Spanish) off and I am on a waiting list to have them refurbed. In the meantime, I bought some recommended Chinese 48 clones off ebay. (I know, I know, hit or miss). My current issue is an air leak on 1 and 2. I can cover the stacks with my hands and notice a slight decrease in RPM, but the engine keeps running choked. I pulled the carb and manifold and replaced gaskets and made sure the flanges were flat (slight filing). I replaced the carb gasket and the top and bottom plates are flat. I restarted and immediately after starting the car cold, I could choke and kill the engine with my hand over 1 or 2 velocity stacks. I thought it was fixed. But, as soon as the engine heated up to operating temp, I can no longer choke with my hand over either stack. I sprayed starter fluid around the carb halves, and both end of the manifold and do not hear a change in RPM. Also, with the snail gauge on I can adjust the idle speed and it will move the meter up or down. If I turn in the idle mixture screws all the way in AFTER it is at operating temp, the engine will keep running. If I leave them in and let it cool all the way down it will not start unless I turn them back out a turn or more.

If I cover 3 or 4, it dies right away. Tomorrow, I am going to swap the carbs and test. In the meantime, I am wondering if anyone has ideas?
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Mikedrevguy
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Joined: October 15, 2008
Posts: 2237
Location: Medford, OR
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PostPosted: Sun Apr 02, 2023 7:52 am    Post subject: Re: Chasing an air leak - need suggestions Reply with quote

Where’s fuel pressure set?
Could swap carbs left to right and see that the problem follows the carb.
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74 Thing
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Joined: September 02, 2004
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PostPosted: Sun Apr 02, 2023 2:15 pm    Post subject: Re: Chasing an air leak - need suggestions Reply with quote

Could be a valve guide is moving on the intake.

Next time you take off the manifolds look at the valve guides and compare them port by port. If one is moving it will be in a different position.
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