CT Rebuild 375 (295) Robin Engine Won’t Run

[trig123]

With this spark tester make sure you leave one plug wire on spark plug when testing. If it fires across this tester then you don't have a spark problem which then leaves making sure your plugs are not gas fouled.
I didn't realize you had messed with the carburetor while waiting on engine.
Let us know the results of spark then we can go from there.

[wingmanchris]

Originally Posted by trig123

With this spark tester make sure you leave one plug wire on spark plug when testing. If it fires across this tester then you don't have a spark problem which then leaves making sure your plugs are not gas fouled.
I didn't realize you had messed with the carburetor while waiting on engine.
Let us know the results of spark then we can go from there.

Ok thank you.

[JPonLKN]

Were you able to get both jets out of the carb when you cleaned it, or did you just spray carb cleaner in there? There are two. One on top, and one in the bowl. Also, look at the bolt that attaches the bowl to the carb There are passages in that bolt that allows fuel up to the main jet from the bowl. I've seen them partially clogged and often gets missed in clean up. If its clogged, adequate gas won't get to the main jet.

Since this carb worked days before the engine was sent off for rebuild, look closely at the carb gaskets and spacer/insulator as well. If they are leaking air, the mix will be wrong and it won't run right. These engines are finicky on fuel air mix. There isn't any adjustment, so the jets, ports, and air passages need to be right.

I guess we will se what comes of this as the new parts are added.

[trig123]

Originally Posted by JPonLKN

Were you able to get both jets out of the carb when you cleaned it, or did you just spray carb cleaner in there? There are two. One on top, and one in the bowl. Also, look at the bolt that attaches the bowl to the carb There are passages in that bolt that allows fuel up to the main jet from the bowl. I've seen them partially clogged and often gets missed in clean up. If its clogged, adequate gas won't get to the main jet.

Since this carb worked days before the engine was sent off for rebuild, look closely at the carb gaskets and spacer/insulator as well. If they are leaking air, the mix will be wrong and it won't run right. These engines are finicky on fuel air mix. There isn't any adjustment, so the jets, ports, and air passages need to be right.

I guess we will se what comes of this as the new parts are added.

I have never seen any passages in the bolt that holds the bowl. You sure you aren't thinking of another engine like a mower ?
The passages that usually need cleaning is under the main jet that is no longer available from ezgo and they are very hard to remove. Carb cleaner normally won't clean it. An Ultrasonic Cleaner will clean that.
Maybe I misread

[wingmanchris]

Well I picked up the spark checker as y’all recommended and tried it out. Both sides create spark. It still fired sporadically with only one plug, both right and left, while testing. I was not able to get a set of OEM plug wires. The videos show brief periods of no spark but it’s just the camera not picking it up, I watched with my naked eye extensively and it’s continuously firing spark on both sides.

Left (drivers) side plug


Right (passenger) side plug


I also picked up another set of NGK BPR4ES plugs, gapped to .030 and a set of Autolite 65 plugs gapped to .030 and tried both sets. No difference, still barely runs but backfires more with fresh set of plugs when I let off the throttle.

Update: right after posting this Amazon showed up with the aftermarket coil, I took the plug wires off of it and installed them and still no change, barely runs.

[JPonLKN]

Originally Posted by trig123

I have never seen any passages in the bolt that holds the bowl. You sure you aren't thinking of another engine like a mower ?
The passages that usually need cleaning is under the main jet that is no longer available from ezgo and they are very hard to remove. Carb cleaner normally won't clean it. An Ultrasonic Cleaner will clean that.
Maybe I misread

Trig, as always, you are correct. Gas enters the carb through the holes at the bottom of the carb pick up tube, not through the bolt as in other carbs. Been working on a bunch of engines...got em mixed up. There are holes down there that gas flows through, but don't clog like the bolts of other carbs. My mistake. Can you post the full blow up of the carb parts breakdown so WingmanChris can see all the components that need cleaning? That jet and tube you point to and the other jet and tube on top of the carb.

WingmanChris, Sounds like its carb related. Air fuel mixture. It has to be clogged passages or bad gaskets or maybe a crack in the carb to head spacer. Something else I noticed in the video, you aren't using choke when trying to start. Pre-MCI engines require choke to start when cold...Have you tried using the choke? Choke it till it starts, open the choke and it should run.

[wingmanchris]

Originally Posted by JPonLKN

Trig, as always, you are correct. Gas enters the carb through the holes at the bottom of the carb pick up tube, not through the bolt as in other carbs. Been working on a bunch of engines...got em mixed up. There are holes down there that gas flows through, but don't clog like the bolts of other carbs. My mistake. Can you post the full blow up of the carb parts breakdown so WingmanChris can see all the components that need cleaning? That jet and tube you point to and the other jet and tube on top of the carb.

WingmanChris, Sounds like its carb related. Air fuel mixture. It has to be clogged passages or bad gaskets or maybe a crack in the carb to head spacer. Something else I noticed in the video, you aren't using choke when trying to start. Pre-MCI engines require choke to start when cold...Have you tried using the choke? Choke it till it starts, open the choke and it should run.

Yes sir, I’ve been choking it. In the first video, I choked it briefly to get it to fire then released the choke. In the last two vids where I was just checking spark, I didn’t bother because all I was worried about was the spark. I will disassemble the carb again and post pics of what I find. The gaskets are new, they came with the rebuilt engine. I’ll double check them and the spacer again. Thank you.

[trig123]

Originally Posted by JPonLKN

Trig, as always, you are correct. Gas enters the carb through the holes at the bottom of the carb pick up tube, not through the bolt as in other carbs. Been working on a bunch of engines...got em mixed up. There are holes down there that gas flows through, but don't clog like the bolts of other carbs. My mistake. Can you post the full blow up of the carb parts breakdown so WingmanChris can see all the components that need cleaning? That jet and tube you point to and the other jet and tube on top of the carb.

WingmanChris, Sounds like its carb related. Air fuel mixture. It has to be clogged passages or bad gaskets or maybe a crack in the carb to head spacer. Something else I noticed in the video, you aren't using choke when trying to start. Pre-MCI engines require choke to start when cold...Have you tried using the choke? Choke it till it starts, open the choke and it should run.

Here is the complete breakdown of whats need cleaning . I came home from my shop at 7 pm and fell asleep in my chair and just noticed this post :)
This is interesting on why it won't run. I didn't see but one video and I could hear it trying to hit. At least he now knows its firing now I hope.

[trig123]

Originally Posted by wingmanchris

Well I picked up the spark checker as y’all recommended and tried it out. Both sides create spark. It still fired sporadically with only one plug, both right and left, while testing. I was not able to get a set of OEM plug wires. The videos show brief periods of no spark but it’s just the camera not picking it up, I watched with my naked eye extensively and it’s continuously firing spark on both sides.

Left (drivers) side plug


Right (passenger) side plug


I also picked up another set of NGK BPR4ES plugs, gapped to .030 and a set of Autolite 65 plugs gapped to .030 and tried both sets. No difference, still barely runs but backfires more with fresh set of plugs when I let off the throttle.

Update: right after posting this Amazon showed up with the aftermarket coil, I took the plug wires off of it and installed them and still no change, barely runs.

Did you have a video of it firing with the new spark tester ? If it fires with the tester I mentioned then you fire would be eliminated .

This is a puzzle for sure.

You have fresh gas, fire , new plug wires, spark plugs and compression which I think is a little low for a rebuilt engine but it should at least run if the valve timing is correct.

Manual says to leave one spark plug in when testing compression so it won't spin too fast and maybe give a false reading. You did mention yours was not turning that fast to begin with.

Check that compression one more time and this time make sure you hold the throttle down with your hand to wide open and post back results for us. To be on the safe side I always reach over and unplug one of the small wires on coil when doing this.

[wingmanchris]

So I double checked compression this morning when the engine was cold from sitting all night. Removed (+) coil wire, fuel line from carb, and crankcase signal line to fuel pump. Held carb linkage wide open and tested.
Left (drivers) side 133psi
Right (passenger) side 145 psi

When I get home today I will check valve lash. I know .004 is what the manual states but I see some recommending .006, not sure how much difference it will make. Also the engine supposedly has new intake valves per the rebuilder.

I will also thoroughly go through the carb again. I also have an aftermarket carb showing up today that I can use to test if needed.

Question, if I use a spray bottle to spray gas in the carb with the fuel lines disconnected, or directly into the intake with the carb removed, while cranking the engine should it run? Would this be a legit test or no don’t bother?