Idle problem, reverse engine rotation

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Horsehead

Horsehead

Joined
Nov 4, 2005
Threads
29
Messages
310
Location
High Point, NC Greenville, SC
I searched the forums and can't find anything specifically related to this. Here's my problem.

The engine will run at a higher RPM, but when it goes to idle it cuts off. Not only does it cut off but it's pretty violent, the crank does some crazy reverse spin action and exhaust gas/ fuel is shot out of the top of the carb. The distributor is on tight, so I don't think the timing is an issue. I pulled the carb yesterday and checked everything I could think to check. The Idle Solenoid is working, there didn't appear to be any clogged passages or anything like that. Any thoughts?
 
This condition can occur for a multitude of reasons:

Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for sparking unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, non-smooth metal regions within the piston chamber can cause this same problem, for they can glow red. It has also been suggested that an improperly rated sparkplug can retain heat and cause the same problem.

A carb. that does not close entirely can contribute to running once the engine is off, for the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporise oil gases from the engine crankcase and provide ample fuel for dieseling.

Incorrect timing.

An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to combust.

Idlespeed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turnover and combust more fuel and lock itself into a cycle of continuous running. As the last piston comes to it's compression stroke upon slow down, a explosion accurse causing a reverse motion
 
Which begs the questions: do you know what your timing is, do you know the LOWEST speed at which your engine will run without dieing, and do you know the temp of the engine when you shut it off?

Also curious about oil pressure. Call it a hunch.;)

Best

Mark A.
 
When I was with him. It would start right up and run for about 3 or 4 seconds and then die. BUt when it died it would couter rotate and surge while spewing gas out the carb. I have never seen this happen. If you started it up and ran it over 1000 rpm it would run fine. I did notice on the short 2 mile trip over to his place the engine temp was running slightly hot. I thought this was because the idle circuit was clogged and it was running lean. I coasted where I could so as to not burn a valve.

But seeing a 2f spin backwards while spewing gas out the carb was a whole new experience.
 
That's a weird one. How many reverse turns is the sucker making? I think you are describing "dieseling" and it is caused by too much idle speed, or the throttle hanging open & fuel sucking into the warm engine where it gets lit off. For mixture to get spewed out the carb - backfiing, it must be igniting while the intake valve is open, probably, as described above, by a hot area in the combustion chamber. Other cylinders must be lighting off just as the compression stroke begins, with enough force to counter-rotate the crank. It is the only time it could happen & cause that effect. Think about it. Remove all linkage and check the movement of the thottle plate. Backfires can bend them. If it is OK, unwind the idle speed screw & try it again. De-carbonizing the combustion chamber will help, too.
 
You ask how many reverse turns? Most common is 3... some engines with heavy flywheels (more torque) may go a few more..
 
Well I put the newly cleaned and tuned carb back on today... pushed in the gas, pulled out the choke, and she fired right up and purred for about 5 minutes. Then I started to push the choke in some, about 1/4 at first, then about 2/3 and then all the way, and as soon as it reached an idle it died. But, no reverse rotations this time. It just cut off... I tried everything I could think of and nothing seemed to help, then it started doing the reverse nonsense again. So, I'm thinking I'm just going to have it towed to the Toyota dealership and let them fix it...
 
grant5127 said:
You ask how many reverse turns? Most common is 3... some engines with heavy flywheels (more torque) may go a few more..
Click to expand...

This one about 20 or 30. I'm serious I have never seen and engine do this.
 
Horsehead said:
Well I put the newly cleaned and tuned carb back on today... pushed in the gas, pulled out the choke, and she fired right up and purred for about 5 minutes. Then I started to push the choke in some, about 1/4 at first, then about 2/3 and then all the way, and as soon as it reached an idle it died. But, no reverse rotations this time. It just cut off... I tried everything I could think of and nothing seemed to help, then it started doing the reverse nonsense again. So, I'm thinking I'm just going to have it towed to the Toyota dealership and let them fix it...
Click to expand...

This will probably blow your local dealer techs mind.. that is if they are like all in my area... Have you taken a look at the plugs? Reading the plugs can help in diagnose a problem.. Keep it running the best you can till warm temp. and do a compression test..check those results... what type ignition system are you running?? What alternator?? Are there any electrical issues going on??
 
Trollhole said:
This one about 20 or 30. I'm serious I have never seen and engine do this.
Click to expand...

What about the exhaust?? does it seem restricted or plugged?? I have seen engines with exhaust restrictions so bad, that they would run for awhile until the pressure would build up, and when shut-down accurs.. the pressure flows backwards.. causing reverse rotation...
 
Last edited:
Personally I would be looking at the cam timing, valve clearances and valves themselves. Sounds like it is not fully exhausting.
 
I'm running a DUI dizzy, stock carb, stock intake and exhaust manifolds, stock exhaust system...

What makes everything so confusing is the fact that I was driving down the highway at 60mph, everything going just fine, then I got off the highway, and as soon as the engine went down to idle it cut off... I'm willing to try these suggestions, I just don't have all the tools that would be necessary to get into it... so, anyways.. yea, that's my situation.
 
Horsehead said:
What makes everything so confusing is the fact that I was driving down the highway at 60mph, everything going just fine, then I got off the highway, and as soon as the engine went down to idle it cut off... I'm willing to try these suggestions, I just don't have all the tools that would be necessary to get into it... so, anyways.. yea, that's my situation.
Click to expand...




So are you saying that the truck was not acting up in any way before it did this? That you have been driving it for years in this configuration and that it just started doing this?


How long has the distributor been in there?



Did you preform these modifications, or were they on the truck when you purchased it?



There are not any special tools that are needed for any of the troubleshooting procedures that have been suggested so far… Pulling spark plugs and looking at them…Adjusting the valves….


You probably know someone with a compression tester, or could rent one from an auto parts store…but warm the engine up and adjust the valves first, before checking the compression, since a tight valve can give you an erroneous weak indication on a cylinder.
 
Poser said:
So are you saying that the truck was not acting up in any way before it did this? That you have been driving it for years in this configuration and that it just started doing this?


How long has the distributor been in there?



Did you preform these modifications, or were they on the truck when you purchased it?



There are not any special tools that are needed for any of the troubleshooting procedures that have been suggested so far… Pulling spark plugs and looking at them…Adjusting the valves….


You probably know someone with a compression tester, or could rent one from an auto parts store…but warm the engine up and adjust the valves first, before checking the compression, since a tight valve can give you an erroneous weak indication on a cylinder.
Click to expand...

The truck ran fine for weeks before this happened. Only a few weeks prior to this happening I drove it 3 hours from my home in NC to my school in SC.

The DUI was installed 2 years ago by me.

I know that adjusting valves and checking plugs doesn't take special tools per say, all I was saying is that I don't even have a plug socket in my box (thought I did, but it appears that I don't)... So that's where things stand.. any more thoughts? Appreciate the help imensely!
 
This is very similar to what I had a few months ago. Mine started with the symptoms you describe , then eventualy ended with one bad backfire & wouldn't start at all. I have a stock 77 2F w/header & DUI. I checked timing, cleaned carb, replace intake/exhaust manifold, & all vacum hoses. I was starting to get pretty frustrated with what it could be. Then I was checking plugs & decided to crank the motor with a plug out to observe its' spark. The spark just didn't look right...looked real weak to me. So then I started focusing on the DUI. I checked all the multimeter readings of the coil, module, pickup, etc. from a DUI troubleshooting web site (sorry don't remember which one). The readings from the module were not quite what they said should be, but at this point I had no confidence in my ability to do this "right".

So, I went to my local parts place (not a chain one) & bought all new parts for the DUI. I explained to them that I just wanted to swap out one thing at a time till something/nothing happened & was hoping to return anything I didn't need for a refund. They went for it. Well, when it came to the module, I swapped it, closed up the DUI & hit the key. VROOOM...it fired on the first revolution & idled like an almost kitten (the timing ended up being off just a little bit). Actually, the truck has never run better!!! This all leterally hours before I was supposed to lead the TLCA/PMC McGrew Trail Ride (thought I was going to have to hitch a ride as trail leader)

The reason I went the long story route is that I thought you might benefit from what I tried as it relates to your plight. Good luck :)
 
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