Help - No idle

[hisoos]

Quick back story - Plane sat out of annual for a little over a year as I tried to find a new mechanic. Thorough annual completed December 2014, flew 2015, sat 2016. I would go out an start it from time to time. (Probably not frequently enough)

Found new IA, he came out recently to do the annual. I went out and drained the old gas out of it a couple of days before, added new gas, and started it up (used primer to start). It didn't want to idle. Seemed to run fine above 1000 RPM. Drop just a bit below 1K and it would quit.

We took the carb apart cleaned it out (didn't see anything to explain the issue). New seal kit for the carb, back on the plane. Same issue.

Tightened the nuts I could get to on the intake tubes (at jugs) and checked the hose clamps on the inner and outer intake tubes. Same issue.

Carb came off again. Went through it again. Paid special attention to tiny idle holes. Back on the plane. Same problem. BTW used the method of turning idle mixture screw out 3 full turns from closed as baseline. Then tried out and in a bit from there.

Now removed primer from the system. Couldn't even get it started as primer was needed to get it started before to get it to the 1K RPM throttle setting to keep it going. Keep in mind it would start with prime with slight throttle. So when it quits or won't start without primer at that throttle setting, it tells me it isn't getting idle fuel.

We haven't replaced the intake seals yet, but I purchased some in case it was necessary. Looks like it may be a little involved to do so.

I feel like we have addressed any low hanging fruit. What are your thoughts?

[hisoos]

Re: Help - No idle

One more thing. I went out and started it a few months ago (maybe a little more), and there was no idle issue then.

[hisoos]

Re: Help - No idle

Ok two more things. We did not adjust/move seat position. Left it alone. Just cleaned.

[Guest]

Re: Help - No idle

Did you check all the jets and clean them? Set float level?

[Guest]

Re: Help - No idle

You may need a manual to locate all the jets. There may be one in the tech section of this forum.

Dave R

[hisoos]

Re: Help - No idle

Looking at the diagram for NAS3A I have NAS3B, but looks to be almost the same. I think we got everything. Did not set float. Left that where it was since it was fine before. Seems to me that float would be more of a problem at higher RPM than lower, but I am no expert.

[Guest]

Re: Help - No idle

Idle ports in the throttle body clogged? Idle air bleed orfice/jet clogged?

[Guest]

Re: Help - No idle

My guess is that fuel gummed up somewhere in the idle ports/passages or jets. Brilliant I know but somewhere in that idle path I bet you find it. I forgot that you said it will run at 100 rpm or more.'
Dave R.

[hisoos]

Re: Help - No idle

We paid special attention to those ports the second time through. They are clear.

Not ruling out the carb, but after going through the carb twice, can't help but think it is elsewhere.

[Guest]

Re: Help - No idle

If you leave the primer unlocked and try to let it go below 1000 rpm will it run then? That will allow some leakage to compensate for carb and if it works it indicts the carb idle system.

Dave R

p.s. - I said unlocked by I meant unlocked and pulled back little bit

[hisoos]

Re: Help - No idle

I haven't done much reading about different primers out there on our planes, but I know mine is different than any other primers I have come across in my flying career. I understand what you are saying. On my T-craft however it is spring loaded, there is no lock. When I pull it back, it pulls in fuel then, let go, and the spring pushes the fuel automatically.

Perhaps I could have someone hold it barely open to simulate the unlock position.

[N96337]

Re: Help - No idle

Yep, Dave's right on. I'd say carb port isn't flowing. Did you clear the bowl vent as well? Those are a great little carb but can be picky!
John

[hisoos]

Re: Help - No idle

And now I see your edit...

[hisoos]

Re: Help - No idle

I agree that carb port isn't flowing, but I since we have been through the carb twice especially paying attention to those ports, I can't happen to think of some sort of vacuum leak at low RPM not pulling the fuel in.

Bowl vent? Please clarify. Other than the needle seat, and throttle butterfly, the carb was completely disassembled to the best of my knowledge.

[PA1195]

Re: Help - No idle

Sometimes removing the idle mixture screw and flushing the threaded hole with spray carb or brake cleaner will clear gummy stuff. I know nothing about Stromberg carbs so take it FWIW.

Edit: Power flushing the idle mixture circuit on carbs through the idle screw's hole is common practice on a variety of equipment subject to idle problems. Some circuits use the screw to admit fuel to the carb bore usually through a series of vertical holes placed opposite the nearly closed throttle plate. Sometimes the screw admits only air to the idle circuit, and sometimes it's an emulsion of air and fuel. Depends on the design. I'll assume it the first example for the Strombergs. Either way flushing it can sometimes clear a blockage in a variety of locations. If not successful. Disassemble the carb and flush any fuel circuits and jets. That may entail removing whatever jets are installed as sometimes they have cavities in the carb body that require cleaning as well.

Gary