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Jun 07, 2021, 10:31 AM
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rc gasoline engines


sachs 3.2 engine. good compression rcexl ignition good spark, external pulse working. hook up fuel lines and turn over 4to 6 times fuel is drawn to carburetor. timing at 28 degrees btdc. will not start will not even fire? as you can see i need some help. any suggestions will be appreciated.vipers
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Jun 07, 2021, 10:58 AM
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koppterX's Avatar
could be bad cap.
Jun 07, 2021, 11:04 AM
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Or a cracked plug: Sparking when atmospheric, but not (or at least not between the electrodes) when under compression.
Jun 07, 2021, 11:59 AM
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ignition


the ignition is new. tried several new plugs. how can i tell if the cap is bad? vipers
Jun 07, 2021, 12:09 PM
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Power supply checked as well?
Jun 07, 2021, 12:33 PM
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SeismicCWave's Avatar
Quote:
Originally Posted by vipers
sachs 3.2 engine. good compression rcexl ignition good spark, external pulse working. hook up fuel lines and turn over 4to 6 times fuel is drawn to carburetor. timing at 28 degrees btdc. will not start will not even fire? as you can see i need some help. any suggestions will be appreciated.vipers
Sachs 3.2 has been around for a very long time. You said the engine has good compression, is the engine new? Has the engine been sitting for a very long time? Are you trying to start the engine by hand flipping or with a starter?

If the piston ring is a little stuck from the engine sitting around for too long the engine may not like to start by hand flipping.
Jun 07, 2021, 02:54 PM
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ignition


i used two 18650 cells showed 8.4 volts on the meter. turned it over using a home made starter in a cordless drill. i tried using a sullivan starter at 27 volts it just chewed up the spinner. the engine is new. it started last year after i found a crack in the fuel line inside the tank. i just wanted to put it on a 89inch chipmunk. how can you tell if there is no spark if it is on the engine?thanks again.vipers
Jun 07, 2021, 03:33 PM
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SeismicCWave's Avatar
Quote:
Originally Posted by vipers
i used two 18650 cells showed 8.4 volts on the meter. turned it over using a home made starter in a cordless drill. i tried using a sullivan starter at 27 volts it just chewed up the spinner. the engine is new. it started last year after i found a crack in the fuel line inside the tank. i just wanted to put it on a 89inch chipmunk. how can you tell if there is no spark if it is on the engine?thanks again.vipers
I test for spark by taking off the spark plug and grounding it against the engine. The danger of that is overloading the ignition module of the plug is not grounded enough like if you hand slip while flipping over the engine. Plus you run the risk of zapping yourself if your body provide the ground.

I like to use a Sullivan Dynatron on 4 cells lipoly and a BIG cone to start 30cc or larger gasoline engines.
Jun 07, 2021, 04:13 PM
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DGrant's Avatar
Quote:
Originally Posted by vipers
the engine is new. it started last year after i found a crack in the fuel line inside the tank. i just wanted to put it on a 89inch chipmunk. how can you tell if there is no spark if it is on the engine?thanks again.vipers
Didn't you say in your first post it has good spark?... and now you're asking how to tell..?... LOL

With a modern electonic ign... like RCExcel, you should be able to simply toggle the engine, near TDC(near the point the ign sensors pass each other), with a spark plug in the cap, resting/grounded on the engine block. That should produce a visible/audible spark every time. Some proprietary EI's don't work like this, but the RCExcel unit will....

... but now I'm wondering, since you said the ignition is new, did you get an auto-advance timing ign, and disable the mechanical timing advance on the engine?... or exactly which ign box did you get?... and exactly how is your engine set up?...

There are a few options with these.
Jun 07, 2021, 04:19 PM
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SeismicCWave's Avatar
Quote:
Originally Posted by DGrant
Didn't you say in your first post it has good spark?... and now you're asking how to tell..?... LOL

With a modern electonic ign... like RCExcel, you should be able to simply toggle the engine, near TDC(near the point the ign sensors pass each other), with a spark plug in the cap, resting/grounded on the engine block. That should produce a visible/audible spark every time. Some proprietary EI's don't work like this, but the RCExcel unit will....

... but now I'm wondering, since you said the ignition is new, did you get an auto-advance timing ign, and disable the mechanical timing advance on the engine?... or exactly which ign box did you get?... and exactly how is your engine set up?...

There are a few options with these.
I am actually wondering the OP's idea of "new".

Here is what the OP said in a subsequent post:

"the engine is new. it started last year after i found a crack in the fuel line inside the tank."

If the engine is new but it was "started" last year.........so that meant the engine is at least over 1 year old.

The last time I owned a Sach's 3.2 was back in the 80's and Sach's has been out of business for a long time. I very much doubt you can just go out and but a brand new Sach's 3.2 anymore. Maybe a new old stock on eBay or the classifieds. That's why I asked how new was the engine.

Something is not making sense here.
Jun 07, 2021, 05:26 PM
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Thread OP

ignition


wave, isaid the engine was new. a 10 year old engine thats never been run is a new engine to me. as far as spark is concerned some said a plug may fire out in the atmosphere but will not fire under compression. thats why i asked how to tell if a plug is firing when you cannot see it. the pickup wire was broken when i got the engine, thats why i put on the rcexl unit. it seems to me i am not the only one that cannot figure out the problem.vipers
Jun 07, 2021, 05:30 PM
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If you have spark, and you have compression, I would squirt fuel in the carb and see if it'll fire on its prime. New engines don't like to suck fuel.
Jun 07, 2021, 05:33 PM
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ignition


grant you are not reading the previous posts.
Jun 07, 2021, 05:40 PM
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koppterX's Avatar
There is no need to ground the cap against the cylinder. The way to test is to try a different ignition.
Jun 07, 2021, 05:43 PM
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SeismicCWave's Avatar
>>wave, isaid the engine was new. a 10 year old engine thats never been run is a new engine to me.<<

I can understand that. However you did say the engine started 1 year ago meaning the engine actually started. So what has changed in that year?

A 10 year old engine may be new to you however with the engine sitting you can have some compression issue. Especially with a large displacement gasoline engine. The "felt" compression can be very different to different people. I have a Zenoah G23 that will refuse to start no matter how hard I pull the rope starter. It felt like there were a lot of compression. However the piston ring was stuck in the groove. As soon as I changed the piston and ring the engine started right up and is running perfectly fine right now.

A 10 year old engine could have some congealed oil and the piston ring could very well have been stuck.

>> as far as spark is concerned some said a plug may fire out in the atmosphere but will not fire under compression. thats why i asked how to tell if a plug is firing when you cannot see it.<<

That is a possibility but an unlikely situation. If the plug fires when you have it out of the engine with a decent amount of spark you are most likely going to have a good spark under compression.

>> the pickup wire was broken when i got the engine, thats why i put on the rcexl unit. it seems to me i am not the only one that cannot figure out the problem.<<

Then the engine had issues before. Maybe because it is 10 years old. You need to take that into consideration.

Everyone is trying to help but being online with you not feeding enough information no one can truly help you trouble shoot by speculating. We don't read minds. If you need help you need to spell out as much information as you possibly can for other posters to help. Otherwise every one is only grabbing at straws.

You also mentioned you "turned over" the engine 4 to 6 times and fuel is drawn to the carburetor. What if you have flooded the engine? My chainsaw will not fire once I flooded the engine when I push the primer bulb one time too many.

On the other hand maybe you did not prime the engine enough for it to fire.

"hook up fuel lines and turn over 4to 6 times fuel is drawn to carburetor."

Then another situation is that your power drill may not be spinning fast enough for the engine to fire.

Everyone is trying to help you but you are not helping by antagonizing posters trying to help.
Last edited by SeismicCWave; Jun 07, 2021 at 05:52 PM.


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