" GRUMPY?
been fighting with this for a week now...... getting a backfire out the tailpipe at cruising speeds around 2500 to 3500 rpm at wot and idle its fine..... any ideas? "
backfires or frequently a shudder style miss from the exhaust are frequently the result of EITHER a missing cylinder (no ignition as the spark plug sparks or fails to spark) pumping it unburnt fuel/air mix into the exhaust where its ignited by the exhaust exiting the next cylinder firing on that bank of cylinders OR an exhaust valve not sealing which effectively results in a similar situation, Id check the plugs as that can frequently point you to the defective cylinder, if its running lean during the transition from idle to W.O.T. the plugs should show that if you know how to read plugs, sometimes a swap to richer jets, a higher power valve number or a different accelerator pump cam can help. as can using a INFRARED temp gun as that cylinder tends to run at a different temp, but Id also re-check the valve adjustment as a too tight a valve pre-load adjustment will result in a burnt exhaust valve and the same condition.
Don,t assume anythings correct,this has caused thousands of mistakes, just take it step by step, verify every potential source for your problem as if it was the first time youve ever seen the engine, start with the basics and check your firing order , and if you can post clear pictures of each labeled spark plug, do a compression check, check your float levels,re-check for vacuum leaks, small ones can be hard to detect but still cause issues,it,sounds like both a vacuum leak, possibly bad timing or timing not advancing as rpms increase, and a accelerator pump thats not working correctly to me, I wish you were local, stuff like this is far easier to isolate with experience, and while I was testing Id set the valves carefully at idle also
leaking exhaust or header gaskets letting outside air (oxygen) into the exhaust could allow UN-burnt fuel to cause that under some conditions,
id also inspect all the plugs and use a VOM / multi meter on each spark plug wire just to verify your not dealing with a defective plug or ignition wire.
keep in mind as oil pressure increases as rpms increase if youve set the valve lash to tight it could allow the valve to seat marginally seal at idle but not at mid rpm ranges, this could also be the result of a sticking valve guide or defective lifter, or worn cam lobe, or defective ignition, so obviously finding the defective cylinder is the first step and doing a compression check and re-adjusting the valves , inspecting the plugs and using a timing light and vacuum gauge to get more info to work with to isolate the cause would be the best idea.LOOK FOR LOOSE OR CORRODED ELECTRICAL WIRING CONNECTORS, in THE WIRING HARNESS, and VERIFY YOUR FIRING ORDER, VERIFY YOUR FLOAT LEVELS AND FUEL PRESSURE,YEAH I KNOW YOUR SURE ITS CORRECT, CHECK IT CAREFULLY AGAIN, YOUR NOID TEST LIGHT IF YOUR RUNNING FUEL INJECTORS , VERIFY YOUR IGNITION ADVANCE CURVE AND MULTI- METER CAN SAVE YOU A GREAT DEAL OF PROBLEMS AND SCRATCHING YOUR HEAD IF YOU TEST BASIC ELECTRICAL CONNECTIONS< RESISTANCE AND VOLTAGE, CHECK YOUR SENSORS AND GROUNDS, A SHOP MANUALS MANDATORY
related links and sub links you can use to locate the source of your problem
viewtopic.php?f=55&t=1639
viewtopic.php?f=55&t=109
viewtopic.php?f=55&t=635
viewtopic.php?f=55&t=1790
viewtopic.php?f=70&t=1015
viewtopic.php?f=70&t=202
viewtopic.php?f=70&t=4683
viewtopic.php?f=70&t=840
viewtopic.php?f=55&t=5229
viewtopic.php?f=55&t=109
viewtopic.php?f=70&t=4683
viewtopic.php?f=44&t=4775&p=15947&hilit=propane+leaks#p15947
viewtopic.php?f=52&t=196
viewtopic.php?f=87&t=3234
viewtopic.php?f=50&t=5726&p=17448#p17448
been fighting with this for a week now...... getting a backfire out the tailpipe at cruising speeds around 2500 to 3500 rpm at wot and idle its fine..... any ideas? "
backfires or frequently a shudder style miss from the exhaust are frequently the result of EITHER a missing cylinder (no ignition as the spark plug sparks or fails to spark) pumping it unburnt fuel/air mix into the exhaust where its ignited by the exhaust exiting the next cylinder firing on that bank of cylinders OR an exhaust valve not sealing which effectively results in a similar situation, Id check the plugs as that can frequently point you to the defective cylinder, if its running lean during the transition from idle to W.O.T. the plugs should show that if you know how to read plugs, sometimes a swap to richer jets, a higher power valve number or a different accelerator pump cam can help. as can using a INFRARED temp gun as that cylinder tends to run at a different temp, but Id also re-check the valve adjustment as a too tight a valve pre-load adjustment will result in a burnt exhaust valve and the same condition.
Don,t assume anythings correct,this has caused thousands of mistakes, just take it step by step, verify every potential source for your problem as if it was the first time youve ever seen the engine, start with the basics and check your firing order , and if you can post clear pictures of each labeled spark plug, do a compression check, check your float levels,re-check for vacuum leaks, small ones can be hard to detect but still cause issues,it,sounds like both a vacuum leak, possibly bad timing or timing not advancing as rpms increase, and a accelerator pump thats not working correctly to me, I wish you were local, stuff like this is far easier to isolate with experience, and while I was testing Id set the valves carefully at idle also
leaking exhaust or header gaskets letting outside air (oxygen) into the exhaust could allow UN-burnt fuel to cause that under some conditions,
id also inspect all the plugs and use a VOM / multi meter on each spark plug wire just to verify your not dealing with a defective plug or ignition wire.
keep in mind as oil pressure increases as rpms increase if youve set the valve lash to tight it could allow the valve to seat marginally seal at idle but not at mid rpm ranges, this could also be the result of a sticking valve guide or defective lifter, or worn cam lobe, or defective ignition, so obviously finding the defective cylinder is the first step and doing a compression check and re-adjusting the valves , inspecting the plugs and using a timing light and vacuum gauge to get more info to work with to isolate the cause would be the best idea.LOOK FOR LOOSE OR CORRODED ELECTRICAL WIRING CONNECTORS, in THE WIRING HARNESS, and VERIFY YOUR FIRING ORDER, VERIFY YOUR FLOAT LEVELS AND FUEL PRESSURE,YEAH I KNOW YOUR SURE ITS CORRECT, CHECK IT CAREFULLY AGAIN, YOUR NOID TEST LIGHT IF YOUR RUNNING FUEL INJECTORS , VERIFY YOUR IGNITION ADVANCE CURVE AND MULTI- METER CAN SAVE YOU A GREAT DEAL OF PROBLEMS AND SCRATCHING YOUR HEAD IF YOU TEST BASIC ELECTRICAL CONNECTIONS< RESISTANCE AND VOLTAGE, CHECK YOUR SENSORS AND GROUNDS, A SHOP MANUALS MANDATORY
related links and sub links you can use to locate the source of your problem
viewtopic.php?f=55&t=1639
viewtopic.php?f=55&t=109
viewtopic.php?f=55&t=635
viewtopic.php?f=55&t=1790
viewtopic.php?f=70&t=1015
viewtopic.php?f=70&t=202
viewtopic.php?f=70&t=4683
viewtopic.php?f=70&t=840
viewtopic.php?f=55&t=5229
viewtopic.php?f=55&t=109
viewtopic.php?f=70&t=4683
viewtopic.php?f=44&t=4775&p=15947&hilit=propane+leaks#p15947
viewtopic.php?f=52&t=196
viewtopic.php?f=87&t=3234
viewtopic.php?f=50&t=5726&p=17448#p17448