Scott S Posted September 10, 2007 Share Posted September 10, 2007 My '23 four cylinder idles good and runs strong through first gear. As I wind out second gear, and sometimes at the top end of third gear I get a sudden loss of power and it backfires. If I let off the gas and then ease it back on I can continue going and it picks up again.I tried adjusting the carb. I have a good old book with detailed description of adjustments for the Marvel on my car. However, I still cannot figure out what makes it backfire in second and third gears.My instinct is to open the needle valve futher on the carb, but this may not be the solution if the backfiring is not contant and is only in higher gears. Thoughts? Link to comment Share on other sites More sharing options...
Mark Shaw Posted September 10, 2007 Share Posted September 10, 2007 Scott, It is probably starving for fuel at high RPMs. Clean or replace your fuel filter if you have one & try again.Open that nedle valve a quarter turn & try again.If it does it primarily when your fuel tank is almost empty, check to see that your vacuum tank is clean properly sealed and your fuel lines are not corroded. Also check for hairline cracks in the pot metal top casting of your vacuum tank. They are hard to see, but they will reduce the vacuum enough to starve the carb. You can fix them from the inside with super glue or JB Weld. Link to comment Share on other sites More sharing options...
Leif Holmberg Posted September 10, 2007 Share Posted September 10, 2007 As well as Mark Show:s advise,take a look at the spark plugs, I hade problem with "flash-over","spark-over" on my 1924 4cyl. The easiest way to check this is to use a 1000 Volt insulation measuring meter.(even could MEGG-meter)Or change to new spark plugs.I also use to oil the valve-stem too. If you have an Electrician friend he can help you to megg your spark plug without removing them,an easy and fast way to reduce if it`s spark-plugs problem. Leif in Sweden. Link to comment Share on other sites More sharing options...
Leif Holmberg Posted September 10, 2007 Share Posted September 10, 2007 To make clear this is not a OHM-meter.This is an old hand cranked Megger.The new ones has batteries. Leif. Link to comment Share on other sites More sharing options...
Scott S Posted September 10, 2007 Author Share Posted September 10, 2007 Thanks for all the ideas. My next thought was a loss of suction in the vacuum tank, but I will check everythin. Link to comment Share on other sites More sharing options...
Brian_Heil Posted September 10, 2007 Share Posted September 10, 2007 You could hook up a temporary gravity fuel supply from a gas can and determine if the issue is fuel starvation assuming the new source you supply has good volume/flow. Link to comment Share on other sites More sharing options...
Mark Shaw Posted September 10, 2007 Share Posted September 10, 2007 Brian's idea is a good one. You can fill the vacuum tank by removing a 1/4 plug on the top & use a small funnel to fill it. Link to comment Share on other sites More sharing options...
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