engine won't fire
engine won't fire
4th Gear Member
Joined: Dec 2008
Posts: 2,247
From: Yacolt,WA
Well I'd go back to the basics,get the motor at TDC #1 compression stroke and check to see that the dist. rotor is pointing to #1.
Pull the air cleaner and pump the accelerator a couple times with the choke held open to confirm there's gas going into the motor.
If all that is good check for spark at the spark plug.
Is this a long block with the cam and heads already installed?
If so the valve train should be good to go but if all else is right I'd check to see the lifters are opening the valves next and at the right time..
Pull the air cleaner and pump the accelerator a couple times with the choke held open to confirm there's gas going into the motor.
If all that is good check for spark at the spark plug.
Is this a long block with the cam and heads already installed?
If so the valve train should be good to go but if all else is right I'd check to see the lifters are opening the valves next and at the right time..
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October 2009 ROTM
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Common issues, with spark and fuel and no back fire and it sounds good when cranking:
* weak spark
How did you test for spark? Do you know its strong enough to fire a plug? Very common issue with points but can also be a weak coil or anything on the secondary side of the ignition.
A spark tester will proves the flow of current under compression since it is in line.
*Too much fuel
If you are sure you are getting fuel and nothing is happening where is it going? A soaked plug will not spark. The current flows through the liquid on the plug and never makes a spark. Pull a plug. Is it wet?
* No fuel in the intake.
See Y2Ks post
*Plugged exhaust.
Vacuum gage will read near zero while cranking. (plugged Cat or a nest/blockage in the exhaust)
Vacuum gage would be the fastest way to check the valve adjustment also. The starter should sound funny if the valve adjustment is effecting compression. If it is all the valves the motor should spin fast if its some of the valves then the starter will gallop. Plugged exhaust will show as low vacuum. A crate motor should have strong manifold vacuum even when cranking with the starter.
With good vacuum, spark, fuel (without flooding) you will get at least a back fire. Every time I was told this was not the case and a car was brought into me I found that one of the tests was not being done right. I have had people tell me they checked for spark and all they really did was check the coil. I have had people tell me they know they have fuel because they just put on a new fuel pump. I have had people tell me they are sure the plugs are not flooded yet the oil has 2 quart of gas in it (good thing it did not start). I have seen valve covers blown off cars.
Starting fuel is a bit of a cheat but if there is a chance the carb is gummed up and will not flow fuel internally or its just way out of adjustment it can be a good test. Just make sure your are not flooded first. Last thing you want to do is fire either into and engine full of gas. A couple times I have seen cars that once they started on either spray the carb would clean itself out.
.
* weak spark
How did you test for spark? Do you know its strong enough to fire a plug? Very common issue with points but can also be a weak coil or anything on the secondary side of the ignition.
A spark tester will proves the flow of current under compression since it is in line.
*Too much fuel
If you are sure you are getting fuel and nothing is happening where is it going? A soaked plug will not spark. The current flows through the liquid on the plug and never makes a spark. Pull a plug. Is it wet?
* No fuel in the intake.
See Y2Ks post
*Plugged exhaust.
Vacuum gage will read near zero while cranking. (plugged Cat or a nest/blockage in the exhaust)
Vacuum gage would be the fastest way to check the valve adjustment also. The starter should sound funny if the valve adjustment is effecting compression. If it is all the valves the motor should spin fast if its some of the valves then the starter will gallop. Plugged exhaust will show as low vacuum. A crate motor should have strong manifold vacuum even when cranking with the starter.
With good vacuum, spark, fuel (without flooding) you will get at least a back fire. Every time I was told this was not the case and a car was brought into me I found that one of the tests was not being done right. I have had people tell me they checked for spark and all they really did was check the coil. I have had people tell me they know they have fuel because they just put on a new fuel pump. I have had people tell me they are sure the plugs are not flooded yet the oil has 2 quart of gas in it (good thing it did not start). I have seen valve covers blown off cars.
Starting fuel is a bit of a cheat but if there is a chance the carb is gummed up and will not flow fuel internally or its just way out of adjustment it can be a good test. Just make sure your are not flooded first. Last thing you want to do is fire either into and engine full of gas. A couple times I have seen cars that once they started on either spray the carb would clean itself out.
.
