rich mixture/weak ignition?
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rich mixture/weak ignition?
I just put a brand new holly 4160 atop an '86 351w. here's the prob. she starts up perfect, and when she is fully warm she idles perfect. its at that stage in the middle. choke is fully open and she is running super rich, black smoke low rpms and wants to stall. could a weak ignition be the cause?? here's my thinking. when cold Ive got the high idle (throttle plates open) to compensate for weak spark, and when fully warmed Ive got the heat of the engine/plugs correctly vaporizing the mixtue, requiring less spark, but in the middle with engine not quite warm and the ignition weak this would cause me to be rich. Does this make sense?? a few notes: floats-perfect,idle mix/speed-perfect,choke-right on, and it only happens on the first start. please help me figure this one out, this happens to be the wife and childrens rig, and I can hardley sleep at night knowing my 77 runs better than theirs.
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From: Virginia
rich mixture/weak ignition?
I have this happen all the time on some of my vehicles. To get rid of it, you have to put the original air cleaner back on, with the hose hooked up to the exhaust manifold heat stove. If you have headers, you can make up something or they do sell a little heat stove to go around one of the header pipes. Of course you have to make sure the flapper valve is working in the aircleaner along with the temp sensor and hook up the vacuum line to the aircleaner. You may find, while driving on a cold damp day, the throttle will try to stick in position. This is ice building up in the carb bore, and the original air cleaner heat set-up will get rid of this too.
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rich mixture/weak ignition?
cold damp day? haha The part of alaska I live in only had 90 days of no precipitation last year and the high temp for the year was a whoping 68 degrees. Thank you for your suggestion. Ive had to do this to my 300 to prevent icing as well. I tried it on the 351 after reading your post but with no luck. Still the same. My neighbor seems to think its the jets on the new carb they are running #69 and he thinks they should be @ #57-#60.Im going to try to post a new thread. Thanks again! great idea!
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rich mixture/weak ignition?
so I changed the jets down to #60 Ive got the air cleaner all hooked up and STILL icing!! And then I had a thought, and I was hoping you can help me with this one. The engine is a 351 as you know, originally equipted with an egr(no longer). Inline with the egr plate and the exhaust manifold(heat riser) in the crossover there is a vacuum operated flapper that is now non functioning. with this flapper closed wouldn't it prevent warm air generated from the heat riser from reaching the carb?? I tried to run it yesterday without the valve but seeing as I am still using the same egr plate(no egr)of course I got exhaust coming out through the carb so I had to block it off again. But do you think that this may be the cause of my icing problem? Thank you!!!
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Joined: Jan 2001
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From: Virginia
rich mixture/weak ignition?
I'm not sure I got what you are saying, but if you are talking about the flapper valve that fits between the exhaust manifold and the downfall pipe (this is the heat riser valve), then yes, this could be a problem. This valve in the exhaust manifold, closes when the engine is cold. This creates backpressure and makes the exhaust gas from that side of the engine go through the passage through the intake manifold (under the carb) and to the other side of the engine. This makes the intake mainfold and base of the carb warm up faster.
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rich mixture/weak ignition?
there is actually a vacume operated valve on the intake which goes down into the crossover between the heat riser and the carb. I took this out and it seems to have cured the problem. Allowing the heat to reach the carb. Thanks for keeping up with me. I havent had much luck with this site. not sure if my questions have been too off the wall or what but have had little or no response up untill now. thank you.
