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Engine runs ROUGH on Start-Up


DJ Todd B
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My engine has suddenly developed Rough Start-ups but smooths nicely after about 4-5 seconds.  I have pulled the prop through as normal prior to each starting and ONE time, It was very difficult to pull it past Top Dead Center... almost like Hydro Lock.  . Since it is a 2009 model, I opted for getting the NEWER modules with Soft Start but that did not solve the problem. Any Suggestions?   

BTW - The older modules will be listed on EBAY in the next few days.

My thoughts at this point are...

* Stuck Valve

*Fouled Plugs due to OIL in the cylinder (Hydro Lock)

SEE THE VIDEO

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I hear tapping and a LOT of it. And not the kind I would normally hear with an out of balance carb sync, it sounds like a tappet or two tapping. There is a section in the line maintenance manual to check for stuck tappets. Section 12 I believe.

Stop running the engine and do a compression check too. Do it cold if you have to. You're just making sure there's no damaged valves or anything like that.

These are probably overkill, but these are simple tests just to make sure you aren't damaging anything because the tappet rattle kind of sound is not normal at all it's just to verify what I'm hearing is not a tappet.

I'm leaning with tom, you have a fuel or vacuum issue.

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19 hours ago, Anticept said:

I hear tapping and a LOT of it. And not the kind I would normally hear with an out of balance carb sync, it sounds like a tappet or two tapping. There is a section in the line maintenance manual to check for stuck tappets. Section 12 I believe.

 

Is that the same procedure you use following an oil purge, where you take off the valve covers and push on the rockers to check for softness?  If so I have done that and it's pretty easy.

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In addition to choke travel, there's a small jet down a tube in each float bowl. It feeds the starting circuit (choke) and it easily clogged if there's any debris in the float bowl.

You can see it here:

51709720742_ba57673ff6_z.jpg

It's fresh in my mind since I didn't check to see if that jet was in place in a new float bowl I had installed. It wasn't, and I had horrible rough running with the choke engaged until I moved the jet over from the old float bowl.

As an aside, the other float bowl I got form Lockwood did have that jet installed. But I would generally assume its absence, since its listed as a separate part number in the Parts Catalog.

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THANKS everyone for your feedback.  This has given me a lot of insight on what to look for. SO FAR, I have narrowed it down to the floats.  Although they weigh under 7, the fuel is still seeping into the throat when I leave my Fuel selector ON  and the weight of the HIGH WING fuel may still be seeing into the OPEN cyl causing the Hydrolock "feel" and rough / rich starting. Over the last few days, I have SHUT the fuel OFF overnight and come back to start it iand the problem seems to have gone away. I still don't see the SOFT START doing anything thought. It should run "draggy" for a few seconds then smooth out but it just seems to run as normal as ever when I had the OLD modules in there.

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When you installed the modules, did you run the wires from the open 6th pin socket on the connectors to the starter solenoid control wire? They need the crank signal to charge the internal capacitors and trigger the "soft start" mode. There is also a corresponding flywheel with a different timing that goes with the softstart, otherwise you won't get the full effect.

If your carbs are flooding, its not your floats, its the fuel float needle or corresponding seat. The floats press on the arm, which presses on the float arm, which presses on the needle.

In the heavy maintenance manual, there is a carb section. In the carb section is a test you can perform to verify the seat and needles are sealing properly, where you turn the carb over and apply a few psi to the fuel intake port and see if it holds.

Edit: still hearing that clicking noise. Maybe its because of my phone speaker.

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Todd...

If you are still getting fuel seeping past with the fuel valve open overnight, and your floats are within spec as you mentioned, you might have some debris or another problem with the carb's conical valve seat.  If you can't solve this any other way, it might be time to overhaul the carbs and eliminate any internal carb issues.  It's not hard to do the overhaul, and I think Roger Lee still does them for a very reasonable flat rate with quick turnaround in your neck of the woods.

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You may only need to adjust the brass float armature height. It is 10.5mm from the edge of the carb outside rim up to the top of the float armature when the carb is held upside down.

I do lots of carb overhauls. Seems like Oct. & Nov. were carb overhaul months. I did a bunch of them.

Todd's carbs were overhauls in 2017. My best guess is that the float armature needs adjusting. The second guess is the needle valve isn't functioning correctly. His plane was starting rough partly because the carbs were flooded due to leaving the fuel shutoff on 24/7. Since shutting that off when done flying starts on another day are better, but I still think the carbs may need adjustment to bring the fuel level in the bowl down some.

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  • 2 weeks later...

Between Tom Baker's assessment and Roger Lee's guidance, I think we found the issue. Since I never take the key out of the ignition, therefore can't/don't turn off the fuel (my Bad), the "head pressure" of the fuel is always trying to force fuel into the carb.  I have weighed the floats and each pair are good at under 7 grams but we think needle is not seating properly and still allowing the fuel to enter the throat and into the open intake valve which would explain the feeling of a hydrolock sometimes.  Either way, ONE cylinder is always super rich and it takes a few seconds of VIOLENCE to burn itself out then runs fine.  Last week i started it every morning for 5 days but turned OFF the fuel after each run and the engine started perfectly. I flew about 3 hours last weekend and everything was normal.  The annual is due in April so I will have Roger rebuild the carbs.  Either way, just by changing my procedure seemed to clear it up.  THANKS for everyone's input and help!

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