Timing woes
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Junior User
Joined: Jun 2012
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Timing woes
Ok sports fans I have 33 degrees total timing on my 78 351M, it has a moderate cam from previous owner, and the symptoms I am experiencing are hard starting (the engine revolves once before the spark gets there?) and dieseling. It starts but seems to run fast and but strong. The carb has recently been cleaned, no clog in fuel filter, good fuel pump and tight dizzy. Any insight would be appreciated?
Thank You
Thank You
Elder User
Joined: Apr 2018
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33 degrees total is pretty close to ideal (34-36). The fact it's hard to start AND dieseling leads me to believe you're running too much initial advance.
Where's the initial timing set? where's the mechanical timing set? You may need to back off the initial timing and make up the difference with more mechanical timing by using a larger advance slot.
After the above changes you will need to adjust the idle speed on the carb.
Where's the initial timing set? where's the mechanical timing set? You may need to back off the initial timing and make up the difference with more mechanical timing by using a larger advance slot.
After the above changes you will need to adjust the idle speed on the carb.
Lead Driver
Joined: Jul 2017
Posts: 9,606
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From: San Jose, CA
Does it crank slowly too? Or just not fire up right away?
And frankly, one revolution before it tries to start is not exactly bad. In fact some older trucks would love to start that quickly!
Ditto on checking initial timing.
Other things that can make it slow to crank or fire are weak ignition, starter getting old and tired, deteriorating battery and/or battery cables. Headers putting too much heat into the starter motor.
If yours is not cranking slowly though, let us know just exactly what it is doing and how it's different from before. 'Cause like I said, one revolution isn't exactly a slow starting engine.
Other details, such as when it started doing this might be helpful. If it's done it since you've had it, etc.
Choke adjustments, timing adjustments, making sure you push the throttle however many times your engine likes it, all that stuff adds up.
You DO push the throttle initially when it's cold to set the choke, correct? And you do pump the gas maybe once or twice after that just to see if that helps?
Sorry if you know all that and have driven old trucks your whole life. But it comes up fairly often nowadays when someone's been driving EFI vehicles too long.
Good luck.
Paul
And frankly, one revolution before it tries to start is not exactly bad. In fact some older trucks would love to start that quickly!
Ditto on checking initial timing.
Other things that can make it slow to crank or fire are weak ignition, starter getting old and tired, deteriorating battery and/or battery cables. Headers putting too much heat into the starter motor.
If yours is not cranking slowly though, let us know just exactly what it is doing and how it's different from before. 'Cause like I said, one revolution isn't exactly a slow starting engine.
Other details, such as when it started doing this might be helpful. If it's done it since you've had it, etc.
Choke adjustments, timing adjustments, making sure you push the throttle however many times your engine likes it, all that stuff adds up.
You DO push the throttle initially when it's cold to set the choke, correct? And you do pump the gas maybe once or twice after that just to see if that helps?
Sorry if you know all that and have driven old trucks your whole life. But it comes up fairly often nowadays when someone's been driving EFI vehicles too long.
Good luck.
Paul
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X2, they do slip over time.
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Laughing Gas
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Ok sports fans I have 33 degrees total timing on my 78 351M, it has a moderate cam from previous owner, and the symptoms I am experiencing are hard starting (the engine revolves once before the spark gets there?) and dieseling. It starts but seems to run fast and but strong. The carb has recently been cleaned, no clog in fuel filter, good fuel pump and tight dizzy. Any insight would be appreciated?
Thank You
Thank You
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FTE
Thank you for all your quick and helpful responses!
Ok guys I went out and gave the gas 3 good quick pumps to set the autochoke, and she fired up without delay or kickback.
I will check the timing marks and follow the suggestion on checking initial timing. I wish I could post a video showing what is happening as my ability to describe the problem is inadequate.
Thank you for your help
BMS
Thank you for all your quick and helpful responses!
Ok guys I went out and gave the gas 3 good quick pumps to set the autochoke, and she fired up without delay or kickback.
I will check the timing marks and follow the suggestion on checking initial timing. I wish I could post a video showing what is happening as my ability to describe the problem is inadequate.
Thank you for your help
BMS
Lead Driver
Joined: Jul 2017
Posts: 9,606
Likes: 1,175
From: San Jose, CA
How old is the distributor? Maybe you've got too much initial advance and checking the total advance only gave you a misrepresentation because it's not advancing fully anymore. Old distributors do like to mess with our minds on occasion.
Well ok, they mess with us on LOTS of occasions! Which is at least part of why they no longer exist.
Sounds like you have a timing light, so why not just retard it a bit. Don't worry as much about what the numbers are, but instead on how much you retard it.
So retard the timing say, approx. 5° from where it is right now. Maybe more, but you can start with five. Don't worry about what the marks say, and don't worry about the total at this point. Just retard it, re-set the idle back to 650-750 rpm with the carburetor, and see if any of your symptoms go away.
Quick and easy experiment. May not tell you just what's going on yet, but it'll give you more information to use in your search.
Paul
Well ok, they mess with us on LOTS of occasions! Which is at least part of why they no longer exist.
Sounds like you have a timing light, so why not just retard it a bit. Don't worry as much about what the numbers are, but instead on how much you retard it.
So retard the timing say, approx. 5° from where it is right now. Maybe more, but you can start with five. Don't worry about what the marks say, and don't worry about the total at this point. Just retard it, re-set the idle back to 650-750 rpm with the carburetor, and see if any of your symptoms go away.
Quick and easy experiment. May not tell you just what's going on yet, but it'll give you more information to use in your search.
Paul
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