360 Low RPM hesitation
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Senior User
Joined: Sep 2008
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From: Santa Maria, CA
360 Low RPM hesitation
I have a 75 360, which is completely stock. When the motor comes to operating temp,under load and when under 1/2 to full throttle it will almost completely stall. If you hold the throttle down down it will continue to stumble. When throttle is released it will come back to idle and run fine. It has this stumble between idle and 2k, after 2k the engine runs great. The accelerator pump has been replaced and works, the plugs are good, it is set at 10 btdc. I have experimented with different timing settings and the problem is greatly reduced when the timing is extremely advanced, but obviously it does not run well at higher rpms. I have an electric fuel pump, so i am pretty sure it is getting enough fuel.
Any help would be appreciated, thanks.
Any help would be appreciated, thanks.
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Senior User
Joined: Sep 2008
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From: Santa Maria, CA
So apparently i was in a little to much of a hurry switching dizzys with a spare i had, and as i was pulling the dizzy out the oil pump shaft disappeared. I cannot see it anywhere, where might the shaft have gone, and how can i get it back. Can i drop the pan and hope its somewhere in there? I would really not like to pull the motor apart at the moment.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
So apparently i was in a little to much of a hurry switching dizzys with a spare i had, and as i was pulling the dizzy out the oil pump shaft disappeared. I cannot see it anywhere, where might the shaft have gone, and how can i get it back. Can i drop the pan and hope its somewhere in there? I would really not like to pull the motor apart at the moment.
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Senior User
Joined: Sep 2008
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From: Santa Maria, CA
And to top it off, i did not notice the shaft was not in place until after i drove around the block, and looked at the oil pressure gauge. It was ticking quietly when i shut it off, lets hope she runs for a while after i get it all back together. Today is not my day, don't do things when your in a hurry.
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Senior User
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From: Santa Maria, CA
So i am back to a new problem now. I switched carb's with the one i had on my 390 and it ran great, rebuilt it and put it on and am still having a issue. Now regardless if the truck is moving or in the driveway when u give it 1/4 throttle it stumbles and if left at 1/4 throttle stalls. If u give it more gas revs up great, or less it runs fine. While driving down the road at a consistent speed while at 1/4 throttle the same thing happens, it begins to miss and backfire through the carb. At all other throttle positions it runs great, and smoth.
What gives?
What gives?
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Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Check to make sure the accelerator pump is working. I had on once that the drilled passage from the pump to the squirter was plugged.
Also make sure the adjustment is correct on the accel pump linkage also, so much slack in the system will also cause this.
Also make sure the adjustment is correct on the accel pump linkage also, so much slack in the system will also cause this.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Check your timing and also to make sure the timing chain hasn't jumped.
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Senior User
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From: Santa Maria, CA
Timing is still at 8, i will have to pull the cover and take a look, I was hoping that was not the case, but i have done most else.
Junior User
Joined: Jun 2004
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From: Richardson, TX
I was having a similar issue and it ended up being the timing advance (vacuum) causing it to go haywire. With the advance disconnected, the stumbling went away. Of course it was down on power/economy due to retarded timing, but at least it ran "ok" and identified the problem until it could be resolved.
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Joined: Oct 2011
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TXstroker is right, I run mine with the vacuum advance completely off!
When I connect it, it idles horrible and runs like crap. My 390 is bored out more than stock so I have no problems with lagging. I can floor it and no problems.
Try disconnecting the vacuum line and stopping it up so there's no leak, run it and see how it runs.
When I connect it, it idles horrible and runs like crap. My 390 is bored out more than stock so I have no problems with lagging. I can floor it and no problems.
Try disconnecting the vacuum line and stopping it up so there's no leak, run it and see how it runs.
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From: Southern California
I would check 2 things, yes the distributor timing (advance to ensure its working) and the adjustment on the accel pump (also if you used any adhesives, some might have "escaped" and partially block a passage