Puzzling behavior after carb adjustment

[Baltimore Sailor]

I recently put the adjustable main jet on my 1-year-old carb, along with the extended gnurled adjustment screw for the idle mixture. I love both of the mods, as they make adjusting the idle and running mixtures a tool-free exercise.

Last week after the installations, I ran the engine in gear tied up at the dock until it was up to about 150 deg, and then made all my adjustments. When I was done she was purring like a kitten and would hold an idle in neutral all the way down to 400 rpm, and in gear at 800 rpm steady as a rock.

That being said, I'm puzzled by the behavior of my engine today.

Today I fired her up again to recharge the batteries for a bit, and I pulled out the choke and turned the key and again, she ran smooth as silk. I put her into gear and put the rpms at 1500 and just let her run. After about five minutes I figured I should push the choke back in, but when I did that she dogged down and tried to stall. I pulled the choke back out and she went right back to smooth running again.

Unfortunately, the boat owner just across the dock from me was at his boat with his wife, so I didn't want to run the A4 all the way up to 2200 rpms in gear to really heat her up and subject him to both the noise and the 6 kt current beating against his stern. I kept the rpms low, around 1500 which didn't seem to kick him around any more than the water was already, but I couldn't get the temp up above 125 or so either. it got up to about 140 once, but then I guess the thermostat opened up because the temp dropped back down to about 125 immediately.

So my question is this: what is a normal amount of time to run with the choke pulled out before the A4 is "warmed up"? Do I wait until the temp gauge is actually up around 140 or before I push it in? Is it a gradual thing where you have to adjust it in a little at a time as the temp climbs? With this cold Chesapeake Bay water, is it possible you might run for 20 minutes or so with the choke out before pushing it back in?

From the behavior of the engine I'd say it was suffering from fuel starvation, since allowing more air into the carb causes it to run rough. I'm tempted to go through the entire adjustment procedure again, just to make sure I didn't make a mistake somewhere.

[roadnsky]

Baltimore-
I re-read your earlier post (http://www.moyermarine.com/forums/sh...djustable+main) regarding installing the Indigo Kit and the Adjustable Main Jet and noticed you had to open it up more than the initial setting of 11/2 turns. "I cranked it open another whole turn, to 3 turns from the seated postion."
Also, I noticed you said, "That let the engine keep running, though it seemed to prefer having the choke partially closed, so I kept opening up the adjustable jet a little at a time, waiting a couple of minutes between changes to let the engine stabilize, and I finally got the best results somewhere around 4 1/2 turns."
It does seem like quite a few turns as well as a long time to keep your choke closed. I agree that it sounds like fuel starvation.
You might re-visit the Adj Main Jet setting as a start to your troubleshooting?

As a comparison, my engine starts 1st crank with the choke and I immediately open it and the engine runs fine with a small amount of throttle (800-900RPM) until it warms up (100º). Takes about 1-2 min and I back her down to 600-700 RPM. That's why I'm a little concerned you'd need choke after 100º...
-Jerry

[Kelly]

I'll just chime in with personal experience.

My engine is a hard starter, but once running, I can almost immediately release the choke. The engine doesn't need to warm up at all before running well without the choke (cold, northern France waters).

This behavior has been backed up by Don's comments on the forum stating that the A4 needs the choke to start easily due to the design of the carburetor, but after start-up, the choke shouldn't be necessary.

Good luck,
Kelly

[msmith10]

Ditto Kelly.
I have a stock carb and have cleaned it periodically but have never needed to adjust anything-- main or idle jet-- spring, summer, or fall. Maybe I've just been lucky.

[Marian Claire]

My A-4 starts like Roadnsky’s. Choke only to start. The only time I have had to use the choke to keep her running was due to crud in the carb restricting the flow, fuel starvation. I would pull the main jet and shot some carb cleaner in then reinstall. If that does not help: time to clean the carb. Hope that makes since. Dan S/V Marian Claire

[Baltimore Sailor]

The carb is brand new as of last year; I doubt if it has 5 hours running time on it. When I had it off to put in the adjustable jet and idle adjustment screw it was as clean as a whistle. My fuel tank is steel, not plastic, and I have a new Racor and polishing filter on the fuel lines, and the gas has been both stabilized and MMO'd. I'm not thinking there's a problem with the fuel or a clog in the carb.

I will revisit the adjustments, however. Back to step one with it, close down the idle adjustment and main jet adjustment and then back them out a turn, and do it all over again. It's so easy to do with the new setup that's not a problem.

I just wonder if I did something as dumb as make all the earlier adjustments with the choke still out! I wouldn't put it past me.

[roadnsky]

I just wonder if I did something as dumb as make all the earlier adjustments with the choke still out! I wouldn't put it past me.

Baltimore-
BINGO! In your earlier thread (INDIGO PCV) you describe making the main jet adjustments with the choke "partially" closed.
Also, I thought about this some more and wanted to suggest you double check that your choke cable is adjusted correctly so that your choke is FULLY closing when you pull it out all the way.
(ie. FULL CHOKE and FULL CHOKE OFF)
I suspect this is a 2-part issue that begins with the choke. THEN your idle and main jet adjustments.
Let us know what you find...
-Jerry

[Marian Claire]

Please correct me if I am mixed up. If you back the main jet out, you are increasing the flow of gas?? So if the choke is “ on”, air flow restricted, it seems that she would run best with the jet turned in to get the mix right. I like the idea of checking the cable. I have been surprised at how small a piece of crud can cause so much trouble. That’s what I like about this sight. I can be so wrong and learn from it. Dan

[Don Moyer]

I don't believe your situation has anything to do with your choke technique.

One of the downsides to the adjustable main jet is that it requires somewhat cleaner fuel than the fixed jet. The reason for this is that the orifice in the fixed main jet is round and the orifice in the adjustable jet is donut-shaped (the annular space between the needle and the seat). Although the open area in both jets is essentially the same when the adjustable jet is properly set, tiny particulates that will be able to pass right through the round orifice of the fixed jet tend to get caught in the tiny annular space of the adjustable jet.

The fix is relatively easy; you simply back the needle out a couple turns until the engine runs very rich and then pull the choke fully out and push it right back in (if you're quick the engine will keep running and not stall out from being flooded). This little exercise will usually suck any particulates past the main jet and out of harm's way, after which the main jet can be readjusted to the original setting.

Don

[roadnsky]

Well, I'd certainly go with the sage advice of the expert!
Sometimes, when we have new or rebuilt carbs, it's too easy to forget that there can still be dirt that causes an issue.
After all, carbs don't make dirt...

[Dave Neptune]

Adjustments to dah carb

Baltimore, in my experience of working with "do-it-yourselfers" I have seen one common mistake. That mistake is that while doing the settings on a redone carb takes a while and the engine will be good and warmed up SO especially the idle will be set as lean as possible for smoothe running. If you talk to many mechanics they will almost always say once you have the idle set (especially if you are not concerned about fuel consumption) and the engine is all warmed up and working well--turn the idle screw about 1/8~1/4 turn rich and leave it!!! This allows the engine to work well while it is warming up because it has that little extra fuel needed for running a cold engine until it is all warmed up. When we adjusted "hi-speed jets" on old outboards against a dyno wheel we would do the same thing once max power was achieved, yes it does cost a little extra fuel but the engine will work better especially if you need it in a hurry and it is cold. With the adjustable jets you can "tweek" them back to lean for long passages to save fuel, then return back for easy starting and warm up for most usage.
On my A-4 I don't use a thermostat and she starts right up and I quickly disengage the choke allowing the engine to run at about 12-1300 rpm for a few minutes then back to an 800 rpm idle while the temp gage is still on the pin. When warm she runs between 120~130 degrees. I run at 1900 rpm with a 35 ft 13,000 pound boat, towing a 10ft rowing hard dinghy and the Indigo 3-blade while using about .8 gallons an hour. I have a 25ft waterline and cruise in calm seas at 5.8Kmh.
A lean engine is harder to start and rougher running until it is ALL THE WAY WARMED UP, then things are fine.
Side-bar last year I played with many jet sizes and float settings and found that if the float was a little low the engine was "MUCH" harder to start but once started all was well. I was surprised at how much a little raise-or-drop of the float affected the starting cycle.
Hope this helps some!

Dave Neptune
1970 E-35MkII original A-4 still ticking!!!

[Baltimore Sailor]

I'll give Don's technique a try, but I'm still dubious about clogs in the carb with fresh gas and both a Racor and polishing filter. I'm thinking "big dummy made adjustments with choke partially closed."

[Dave Neptune]

Choke

Baltimore, hopefully it was the choke, however unless it was just about completely closed it wouldn't have to much influence on base idle. However it would be drastic as far as running above idle with a load on the engine like against the dock lines. I had better luck adjusting my adj-jet before I removed it using the bay and the autopilot. I actually wound up needing a little more fuel while actually "reving" a little more underway.
Lots of luck!!
David

[Baltimore Sailor]

I got it running well again, but I'm still at a bit of a loss as to what was going on.

I figured I'd reset to the default settings and start all over again, but when I went to crank down the idle mixture screw it was practically all the way in as it was. That really puzzled me, since I was only able to get the engine running well since my last post by having the choke partially in. I know that putting the choke in closes the valve and enriches the mixture, but so does turning the idle mixture screw clockwise (closing it down).

So how does having the idle mixture way rich make it necessary to have the choke most of the way in as well???

Regardless, I closed the idle mixture screw down the rest of the way, then backed it out about a turn. The carb jet adjustment I left where it was for the moment.

The engine started right up, and after letting it run for a few seconds I pushed the choke in and she kept right on running, unlike the last time. I let her run for a few minutes more until the temp needle came up off the pin, then started making idle adjustment changes until it held steady at about 800 rpm. Then I put her in forward and throttled up to 1900 rpm and adjusted the main jet until I had max rpms.

Then I let her run for about 10 minutes to charge the batteries and see how hot she'd get (still in gear, of course). After about 10-15 mins she stabilized at about 150 deg., so I let her go another 5 minutes for the batteries' sake. For a test of the idle setting, I throttled quickly down to the stop (not an emergency stop, but a smooth, fast downthrottle), then pulled her out of gear before she could stall. The idle came right up to 900 rpms and sat there steady as a rock.

So I'm hoping this is it for the idle mixture/main jet adjustments. I'm hoping to get over on the weekend, and the test will be to see if she'll start right up and hold idle again as nicely as she did today.

[roadnsky]

Baltimore-
Well, good news is better than bad!
Let us know if she holds true this weekend too...