Plugged jet on carb, or... ?

[robshepherd]

Greetings all!

I have a new situation where my A4 will start fine and run all day at relatively low power (enough to push our Yankee 30 at 4 knots in a calm), but when I try to increase the throttle the motor begins to stumble. I can recover by gently decreasing the throttle, but if I raise it quickly she'll just die. At that transition between smooth running and stumbling, I can apply choke and that helps considerably. I hear the rpms come up and there is more power. It doesn't run perfectly, but much better.

Do these symptoms point to the high speed jet being obstructed? What else might I consider? I have a Racor, then a 7-10 micron filter before the mechanical pump. No filter between the pump and carb.

I have not taken anything apart yet, nor inspected the sediment bowl. Just now preparing to work on it this week.

I had the carb apart last year for a good cleaning, and everything was working great. I did leave a few gallons of ethanol gas in the tank over the winter.... Now ethanol-free gas is available here again.

I look forward to hearing any thoughts this fine group has to offer! Thank you. -Rob

[Marian Claire]

Do you have the adjustable main jet? Some issues can be fixed by adjusting it in and them back to original setting. How old is your exhaust system? You could try pulling one of the plug wires when it boggs down. ?? exhaust blockage and increased back pressure. This fits some of the symptoms. http://www.moyermarine.com//forums/s...ead.php?t=3369
Dan S/V Marian Claire

[robshepherd]

Thanks Dan. Yes, I've got the adjustable main jet, and it's easily accessible. Easy enough to try your suggestion. The exhaust hot section is less than a year old, and the rest was inspected at that time.

One thing I neglected to mention is that in neutral I can get the full range of rpms, and it's very smooth. The stall only happens under load. That's why I was thinking that *maybe* the stall happens at the point of the high-speed jet coming into play. Is it feasible that I could be getting enough power to motor at 4 knots on the low-speed jet alone? That's something I just don't have a sense for.... Thanks, Rob

[JOHN COOKSON]

If The Carburetor Maneuver(s) Don't Help.......

How clean is the prop?
Are the prop and shaft clear of obstructions?
Is the packing gland acting normal?

TRUE GRIT

[Trés 30]

I have an old Ford truck that had similar symptoms resulting from a clogged in-line fuel filter (gas tank had a lot of dirt & rust).
It was a fuel starvation issue FWIW.

[edwardc]

This sure sounds like a transition issue when going from the idle jet to the main jet. I believe this happens gradually in the 1100-1800 rpm range, but could be mistaken. Dave Neptune is the guy who would know. (Dave?...)

Remember that timing will also interact with your mixture settings. You might try advancing it a little and see how that affects it.

[hanleyclifford]

Sounds like your main jet is partially blocked. Could be a small particle being fondled intermittently in the orifice. Take the adjuster off, then get the jet itself out for a thorough cleaning/inspection. As mentioned above you could also rod out the two idle ports in the main body (one below and one above the throttle plate). You need a very thin wire for this.

[robshepherd]

Thanks!

Thank you all for the ideas. I feel like I'm on the right track.

Hanley, do you imply that if I remove the adjuster I will have access to and be able to remove the jet -- without taking the carb off the manifold?

It's been a year since I looked at it closely, so I can't be sure I understand you fully. I was planning to remove the carb and disassemble for inspection.

Such a great group of people and ideas here. Thank you! -Rob

[hanleyclifford]

Thank you all for the ideas. I feel like I'm on the right track.

Hanley, do you imply that if I remove the adjuster I will have access to and be able to remove the jet -- without taking the carb off the manifold?

It's been a year since I looked at it closely, so I can't be sure I understand you fully. I was planning to remove the carb and disassemble for inspection.

Such a great group of people and ideas here. Thank you! -Rob

Some might be able to get the main jet out without removing the carb but I wouldn't try it. The carb comes off so easily it isn't worth the risk or aggravation. Your plan to disassemble and inspect is spot on especially since the engine sat all winter with ethanol infected fuel.

[robshepherd]

Resolved!

Just wanted to complete the loop and explain the resolution to my issue.

It turned out that the top and bottom halves of my carb were slightly warped/deformed/bent. My friend was looking at it once I had it all cleaned up with a new bowl gasket installed. He said "something doesn't look quite right here...". He's got a LOT more experience with this stuff than I do. We took it apart, and sure enough, the surfaces didn't meet perfectly, and there was enough of a gap to cause a vacuum leak. It worked OK the past 6 years that I've owned it because the PO used silicone or something similar to seal it. That has mostly worn away, and that's when my fuel delivery problems started.

Talked to Ken in parts, and ultimately decided to buy a new carb. Got it installed today, and the motor has not sounded better or had as much power as long as I've owned it. She idles down to what sounds like 400-500 rpms, and the acceleration is smooth up to full power in gear. Couldn't be happier!

Thank you to everyone who chimed in with ideas for me to look at!

Best, Rob

[keithems]

similar problems with almost new carb

i'm glad to hear rob's problems resolved.

unfortunately, his fix [new carb] is not going to work for me.

i installed new carb last summer and motor ran great all summer long -- even on regular auto gas with 10% ethanol. unfortunately this winter i got lazy so did not fill the tank -- and then left the fuel cap off for a few weeks. so when i launched, motor would not run. i eventually got her to do so by draining fuel tank, changing filters, draining main passage plug, replacing fuel line and tightening all clamps, etc. tightened the breather tube as well -- i have the pcv kit installed. i have a groco 375 water separator [2-5 microns] and the mmi polishing filter before the carb.

as of now, she starts fine and idles well...even without the choke. like rob's she will go up to speed fine in neutral, but very little speed in gear. i have the idle set about 1 turn out -- 1.5 turns is too lean..that was true last summer as well, but she ran fine then. i've cleaned the fixed main jet also.....

i get it that i had a fuel problem..so that's where i have focused. seeing as nothing was touched since she was put away last fall when running fine, i've been reluctant to mess with the 1 year old carb, the mechanical fuel pump, or the ignition system [plugs and/or timing].

any ideas? i'm all ears...

[Clucas]

...as of now, she starts fine and idles well...even without the choke. like rob's she will go up to speed fine in neutral, but very little speed in gear...

Please clarify -- are you getting higher rpms in gear, but not speed (as in through the water)? That's most likely a fouled prop. If you're not getting high rpms while in gear, I'm guessing a gummed up passage in the carb (thank you, ethanol). I'd remove the carb and give it thorough cleaning using carb cleaner, and fine wire to clear passages (watch your eyes with spray carb cleaner). Did you have the pcv valve last summer also? If not, that would affect your idle adjustment setting.

[keithems]

Please clarify -- are you getting higher rpms in gear, but not speed (as in through the water)?

>>> no...much lower rpms in gear than in neutral...

That's most likely a fouled prop.

>>> no -- boat was just launched with clean prop

If you're not getting high rpms while in gear

>>> i'm not

I'm guessing a gummed up passage in the carb (thank you, ethanol). I'd remove the carb and give it thorough cleaning using carb cleaner, and fine wire to clear passages (watch your eyes with spray carb cleaner).

>>> did that without removing...did the main passage plug and main jet and also where the idle mixture screws in -- took it out and sprayed carb cleaner in there

Did you have the pcv valve last summer also?

>>> yes

If not, that would affect your idle adjustment setting.

>>> everything was the same, which is why i'm reluctant to f w i....

>>> except for the fuel contamination..but by now i've drained the tank, changed filters, and the fuel looks fine

>>> looks like i may have to remove and clean the entire carb or at least get an adjustable main jet...but hard to believe since the carb is only a year old...

[Clucas]

>>> everything was the same, which is why i'm reluctant to f w i....

>>> except for the fuel contamination..but by now i've drained the tank, changed filters, and the fuel looks fine

>>> looks like i may have to remove and clean the entire carb or at least get an adjustable main jet...but hard to believe since the carb is only a year old...

Someone may tell me I'm wrong, but yeah, I suspect you need to take the carb apart and give it a thorough cleaning. With fuel sitting in it all winter, I imagine some of the smaller passages are gummed up and are the source of your problem. Your winterization procedure should including draining the main passage on the carb.

[keithems]

Someone may tell me I'm wrong, but yeah, I suspect you need to take the carb apart and give it a thorough cleaning. With fuel sitting in it all winter, I imagine some of the smaller passages are gummed up and are the source of your problem. Your winterization procedure should including draining the main passage on the carb.

latest update:

i actually decided it was running ok in idle but not in gear -- like it has in the past when one cylinder wasn't firing. so i removed the plugs....they were all dirty and gaps too large...regapped and reinstalled them...and now it won't run at all!!

one of the plug wires is bad...so i'm gonna go get new plugs and wires if i can today and install them...hopefully it will at least start....if problems continue, doing the carb rebuild and installing the adjustable jet will be next....hope it's noting worse like a stuck valve on #1 [rearmost] or points, condenser, or coil, but i'll see.

thanks for your ideas