<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">A vacuum leak is more evident at lower RPM, 4-5k is lower on a 1300 Spitfire engine. If changing the main jet to a leaner jet helped that might be because you were getting less air through the chokes because of a vacuum leak somewhere else and thus less air through the chokes meant a better air/fuel mix given the air leak bypassing the carbs and not going through the chokes. Easing the throttle gives the engine a chance to deal with the too fuel rich mixture while stomping on it shoots an over rich mixture into the engine and makes it stutter.<div><br></div><div>At higher RPMs this is not as evident a problem because the air leak is less of a factor when pulling lots of air through the carbs.<div><br></div><div>Did you check for leaks by spraying carb cleaner around the manifold? <br><div>
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<br><div><div>On Oct 16, 2016, at 9:14 PM, D V <<a href="mailto:explore8@outlook.com">explore8@outlook.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Thanks again everyone. I checked the header to head and the exhaust to header connection and everything seemed tight. However I went 2 off hard at turn 4 this morning and my strap that was holding the exhaust is now mostly gone. I never figured out that 180 degree off camber turn all weekend.<br><br>To answer Scott's question, yes. I can brake downshift to 3rd in a turn. Full on the gas out of the turn and it stutters between 4-5k. If I do the same and ease into the gas I can most of the time keep it steady.<br><br>Re working the exhaust system as well as checking the float will be added to my winter maintenance. <br><br>Sent from my iPhone<br><br><blockquote type="cite">On Oct 16, 2016, at 2:21 PM, Barr, Scott <<a href="mailto:sbarr@McCarty-Law.com">sbarr@McCarty-Law.com</a>> wrote:<br><br>Is it temporary? Just as you get on the gas out of a corner and then clears up as the revs rise?<br><br>If so, do you have no oil in your dashpots or have you removed the dashpot pistons?<br><br>Scott (B.)<br><br><br><br><br><br>-------- Original message --------<br>From: D V <<a href="mailto:explore8@outlook.com">explore8@outlook.com</a>><br>Date: 10/16/16 12:53 AM (GMT-06:00)<br>To: Greg Blake <<a href="mailto:gblake58tr3@icloud.com">gblake58tr3@icloud.com</a>>, <a href="mailto:fot@autox.team.net">fot@autox.team.net</a><br>Subject: Re: [Fot] Fwd: Stutter at 4K rpm<br><br>Thanks everyone for the replies. I will inspect the pipe to manifold and manifold to head to see if anything is loose or any leaks apparent in the morning.<br><br>I actually went down a main jet 145 to 140 and that seemed like it helped some but didn't clear up the issue (which is going leaner; opposite of what Greg said).<br><br>It is missing and backfiring when I am full on the gas. I can prevent it by easing into the gas.<br><br>I did notice some gas at my air cleaner to velocity stack connection. I wonder if it is a float issue?<br><br><br>Sent from my iPhone<br><br>On Oct 15, 2016, at 7:35 PM, Greg Blake <<a href="mailto:gblake58tr3@icloud.com">gblake58tr3@icloud.com</a><<a href="mailto:gblake58tr3@icloud.com">mailto:gblake58tr3@icloud.com</a>>> wrote:<br><br>Don't know if my other email made it to you. Backfires on deceleration can be a lean condition. Have you checked your plugs? Maybe something got "adjusted" with the bump.<br><br>Sent from my iPhone<br><br>On Oct 15, 2016, at 12:27 PM, D V <<a href="mailto:explore8@outlook.com">explore8@outlook.com</a><<a href="mailto:explore8@outlook.com">mailto:explore8@outlook.com</a>>> wrote:<br><br><br><br>Sent from my iPhone<br><br>Begin forwarded message:<br><br>From: <<a href="mailto:explore8@outlook.com">explore8@outlook.com</a><<a href="mailto:explore8@outlook.com">mailto:explore8@outlook.com</a>>><br>Date: October 15, 2016 at 10:30:51 AM CDT<br>To: <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a><<a href="mailto:fot@autox.team.net">mailto:fot@autox.team.net</a>>><br>Subject: Stutter at 4K rpm<br><br>Two races ago I went off track and bent my exhaust pipe enough to break the welded joint near the muffler. In the interest of time, I cut the exhaust at the muffler and secured the pipe to the frame.<br><br>At the last race, I noticed the car would backfire at deceleration which I am not surprised but I also noticed a stutter around 4-5k rpm.<br><br>At NOLA this weekend it is more pronounced and comes in when shifting hard from 3rd to 4th. After 5k, it clears up and pulls normally.<br><br>It doesn't seem to be affected by turns and more related to full throttle vs easing into the gas.<br><br>Backpressure from the loss of muffler or unrelated issues?<br><br>1300 spitfire with single Weber 40.<br><br>Sent from my iPhone<br>_______________________________________________<br><a href="mailto:fot@autox.team.net">fot@autox.team.net</a><<a href="mailto:fot@autox.team.net">mailto:fot@autox.team.net</a>><br><br><a href="http://www.fot-racing.com">http://www.fot-racing.com</a><br><br>Donate: http://www.team.net/donate.html<br>Archive: http://www.team.net/archive<br>Forums: http://www.team.net/forums<br>Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/gblake58tr3@icloud.com<br><br><br></blockquote>_______________________________________________<br><a href="mailto:fot@autox.team.net">fot@autox.team.net</a><br><br>http://www.fot-racing.com<br><br>Donate: http://www.team.net/donate.html<br>Archive: http://www.team.net/archive<br>Forums: http://www.team.net/forums<br>Unsubscribe/Manage: http://autox.team.net/mailman/options/fot/levilevi@comcast.net<br><br><br></blockquote></div><br></div></div></body></html>