YellowLark Posted February 19, 2001 Share Posted February 19, 2001 Finally diagnosed a sharp tapping sound heard when my '66 Skylark 340-4 is at idle. It's the exhaust manifold heater valve between the left manifold and the exhaust pipe. Seems it rattles when warm when there is not a high enough rpm to push a lot of exhaust pressure to hold it open.<P>OK - do I really need to replace this thing, or can I just cut out the valve mechanism and replace it as a hollow spacer?<P>The reason I am asking is because I thought the purpose of this valve is to direct hot exhaust to the carb bottom when the engine is cold. However, when I recently replaced my carb, I found that the passage trench on the intake manifold at the front of the carb base was solidly blocked with crystallized carbon. Probably had been for 25 years. Dissolved the carbon, but it makes me think that the whole concept hadn't worked for a long time, and that it probably wasn't needed.<P>Any suggestions? Should I order a new valve, or can I do without it?<P><P>------------------<BR> Link to comment Share on other sites More sharing options...
Guest John Chapman Posted February 19, 2001 Share Posted February 19, 2001 Yellow...<P>I rebuilt the one on my '65 300... it's on the right side. Mine rattled because the thermal spring was stuck open and put no tension on the valve wend cold. I've not noticed it rattling when hot. I used anti-sieze compound to lube the pivot pins after decarbonizing the insides.<P>I've seen recommendations to block the passages in the manifold for better fuel economy from running a cooler intake. Intake heating is of dubious use in SoCal or other warm areas. I plan to remove mine when I switch to the four barrel manifold and a new carb. JimmieB probably has some more knowledgable input on this.<P>Cheers,<BR>John<P>------------------<BR>John Chapman<BR>BCA 35894<BR>1965 Skylark Convertible (Some Assembly Required)<BR> jmchapman@aol.com Link to comment Share on other sites More sharing options...
Guest Posted February 19, 2001 Share Posted February 19, 2001 Replace the spring...not too hard, will make the noise go bye bye too!!!<P> don55 Link to comment Share on other sites More sharing options...
Guest Posted February 20, 2001 Share Posted February 20, 2001 As important as cold starts/warmup are so is iceing. just as on airplanes when all the elements are right, temp, humidity,and air speed ice will form in and out of the carb. it is a ploblem where I live, the foggy cool Sacramento Valley of Calif. I have had several cars of my own and many at the shop with this proplem. in mild form its stalling even a warm engine at the first stop after miles of freeway or expressway. the idle jets or ports are covered with ice. it melts quickly because the air speed (down the carb) has droped and engine heat can win out. in worse form it can plug part of the carb and make a rich condition or worse yet freeze the linkage part open and make driving unpredictable or uncontrolable. I have found a good exhaust system with low back pressure and a working heat riser gives the best of all worlds on the street. driveability, fuel mileage,and safety increase. I have lived in colder and warmer places where these problems are rare. I am not a stock nut but Buick didn't do all the casting work and make heat risers just for fun. JIM Link to comment Share on other sites More sharing options...
Guest John Chapman Posted February 20, 2001 Share Posted February 20, 2001 JimmieB...<P>Thanks for the input...<BR>As a flier (on occasion) of small recip engine aircraft, I should have known better. I'll be keeping my riser heat! A 'flameout' on the freeway can be even more exciting than at 3,000 feet in the clouds and just as health-inhibiting.<P>JMC Link to comment Share on other sites More sharing options...
Jyrki Posted February 20, 2001 Share Posted February 20, 2001 You're correct - you get more power and less octane requirement without it. Most performance intakes don't even have the passage. You can live without it. I removed the system from my 83 Caprice exhaust manifold, and have had no cold start problems even at -13F !!! Link to comment Share on other sites More sharing options...
Don Caithness Posted February 20, 2001 Share Posted February 20, 2001 I've had mine forced open for years now. Just hold it in the open position and tack weld the shaft to the spacer body. Unless you are operating in sub zero weather you shouldn't have any problems. If you want to replace it there is one on ebay. <P>------------------<BR>Don Caithness<BR>Technical Advisor<BR>1967&1974 "A" Body<P> <A HREF="http://appraisals.webjump.com" TARGET=_blank>http://appraisals.webjump.com</A> <BR> collectorcarappraisalservices@attcanada.net Link to comment Share on other sites More sharing options...
The Old Guy Posted February 20, 2001 Share Posted February 20, 2001 I remove the heat riser in all my cars and have never had a problem. It does occasionally stall at the first stop ,but in my GS which I race ,it seems to make more power,as the cooler the intake ,the denser the charge. Link to comment Share on other sites More sharing options...
YellowLark Posted February 20, 2001 Author Share Posted February 20, 2001 Thanks for your reponses.<P>Since I live in the Washington, DC area, and only use the car on sunny weekend afternoons, I think that maybe I can avoid the icing situation. I'll either open it up with a Dremel grinder or remove it.<P>And, see what happens. If stalling is a problem, I'll know why and buy a new valve.<P>Can I just remove the valve, or do I still need it in place to have the exhaust pipe fit? <P><BR> Link to comment Share on other sites More sharing options...
Don Caithness Posted February 20, 2001 Share Posted February 20, 2001 Harry,<BR>You will need to leave the body of the heat riser in place unless you want to have your inlet pipe lengthend to compensate. Link to comment Share on other sites More sharing options...
Jyrki Posted February 21, 2001 Share Posted February 21, 2001 If iceing is a problem, pour Red Line Fuel System Cleaner into your tank, one bottle per 100 gallons of fuel. The lubricant in it will "coat" the butterflies & ports so ice cannot stick to them Link to comment Share on other sites More sharing options...
Guest Posted February 25, 2001 Share Posted February 25, 2001 The ice forms both in and out of the carb. Its the ice in and around the linkage a gas line antifreeze/lube can't help. JIM Link to comment Share on other sites More sharing options...
Guest Posted February 27, 2001 Share Posted February 27, 2001 Carburetors just Suck. As soon as I have $1500 dollars to Blow I'm going to get Injected. Link to comment Share on other sites More sharing options...
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