TK wrote:
too high compression for low grade of fuel, timing?
I'm using BP Ultimate 98 RON fuel and timing should be good, I'll look at compression in the morrow.
Cheers
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| Engine Run-on After Ignition Cut Off? https://www.ausmini.com/forums/viewtopic.php?f=2&t=87640 |
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| Author: | Minimadmarty [ Tue Nov 04, 2014 6:08 pm ] |
| Post subject: | Engine Run-on After Ignition Cut Off? |
My newly built 1340 motor continues to run for a few seconds after ignition cut off. I always thought this was caused by excessive carbon build-up in the combustion chambers or piston tops which when hot act like little glow plugs! Any ideas? |
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| Author: | TK [ Tue Nov 04, 2014 8:17 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
too high compression for low grade of fuel, timing? |
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| Author: | Minimadmarty [ Tue Nov 04, 2014 8:20 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
TK wrote: too high compression for low grade of fuel, timing? I'm using BP Ultimate 98 RON fuel and timing should be good, I'll look at compression in the morrow. Cheers
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| Author: | 69cooper [ Tue Nov 04, 2014 8:47 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
What spark plugs are you running ??, I have the gear to cc a head if you need a hand. I would re check timing and even advance a couple of degrees to see if it makes a difference. My guess is that your carb mixture is to rich, what carb are you running. Mal |
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| Author: | Minimadmarty [ Tue Nov 04, 2014 9:05 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
69cooper wrote: What spark plugs are you running ??, I have the gear to cc a head if you need a hand. I would re check timing and even advance a couple of degrees to see if it makes a difference. My guess is that your carb mixture is to rich, what carb are you running. Mal Cheers Mal, My plugs are NGK BP5ES and look a tad lean if anything (the tips are black and the ground electrodes are white)! The carbs are twin 1 1/4 SU's I have a compression tester so I check that and post results tomorrow. |
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| Author: | Scoop [ Tue Nov 04, 2014 9:23 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
Not that kind of compression. Would involve removing head! |
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| Author: | Minimadmarty [ Tue Nov 04, 2014 9:29 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
Scoop wrote: Not that kind of compression. Would involve removing head! Oh bugger! Sorry, I'm still learning  Mal, the offer to give me a hand? Where abouts are you? When are you free? |
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| Author: | 69cooper [ Tue Nov 04, 2014 9:46 pm ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
Marty , I will send you a PM |
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| Author: | drmini in aust [ Wed Nov 05, 2014 6:36 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
On a well modified 1275 running 98 it's pretty normal, IMO. With an iron head, anyway. If it doesn't do it, your C/R is too low.  I doubt it's the plugs, you could try colder ones but they are more likely to foul in traffic. |
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| Author: | TheMiniMan [ Wed Nov 05, 2014 6:57 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
drop your idle down a tad &/or retard your ignition a little bit both of these will help reduce the chances of "run-on" |
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| Author: | drmini in aust [ Wed Nov 05, 2014 8:21 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
How does retarding ignition help, there is no spark when you've turned it off! It's either hot spots in the head, or red hot plugs... Mine does it when hot, even though the head is bathtubbed and has no beak. I just let the clutch up with the footbrake on, I've done it for years.
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| Author: | 69cooper [ Wed Nov 05, 2014 8:31 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
I am guessing if timing is to far advanced you will not burn all the fuel in the chamber, hot spot or very high CR would ignite it once ignition is turned off ? |
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| Author: | Minimadmarty [ Wed Nov 05, 2014 9:08 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
If compression is too high is it possible to reduce it? |
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| Author: | timmy201 [ Wed Nov 05, 2014 9:29 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
Minimadmarty wrote: If compression is too high is it possible to reduce it? More dish in your pistons, or get your head worked to increase the chamber size |
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| Author: | 69cooper [ Wed Nov 05, 2014 10:04 am ] |
| Post subject: | Re: Engine Run-on After Ignition Cut Off? |
Marty, that will mean head off and possible engine strip, do you have any details of pistons and or head work ? M |
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