I doubt it's the exhaust. First thing would be to insulate the fuel lines, especially if they run alongside the exhaust under the running board. Under the bonnet you may need to fit a heat shield if the fuel lines run close to the exhaust manifold. Agriemach sell a range of products for this.
http://www.agriemach.com/index.php?osCsid=g2skl4o6cmgq7a8c2b004s85h5But this could also be an ignition problem. If you have electronic ignition, try changing the module. Despite a common held belief that they fail and that's it, failure can be heat related.
