Top carb sucks hard, bottom less...

[fishnfiend]

'88 40 HP Evinrude, E40ELCCS<br /><br />Compression checked a week ago (before problem occurred) was 150, 149.<br />Carbs rebuilt, cleaned out.<br />Reeds inspected - none broken, no debree<br />New fuel pump<br />New OMC fuel line<br />Clean tank, clean fuel filter, new plugs<br />Linked and synched. Pickup timing 3 degrees BTDC<br />Both plates closed tight at idle<br />Both plates horizontal and parallel at WOT<br />Timing base engages the stops at idle and WOT<br />Haven't messed with WOT timing - ran great recently<br />Does have old floats in carbs (saturated???)<br />Idles smooth, trolls well<br /><br />Ran like a scalded cat all summer, then began surging and losing rpms at WOT. Priming helped. Cleaned some crap out of high speed jet, bottom carb. Haven't been on the water yet to test WOT.<br /><br />Last nite, I was "de-carboning" with Sea Foam, and found a noticeable difference in the amount of suction in the bottom carb versus the top carb. Top would suck my hand in, and motor would slow almost immediately. Bottom had less suction, and less effect on runnning (just above idle). <br /><br />Would insufficent spark to bottom cylinder cause this symptom? Tonite, I'll test the spark at idle, but can't get to lake until Sunday.<br /><br />Any info greatly appreciated.

 

[CATransplant]

Re: Top carb sucks hard, bottom less...

Best check the compression again. I think you may find your problem there.

 

[fishnfiend]

Re: Top carb sucks hard, bottom less...

Thanks for the input.<br /><br />Will do. I'm hoping I didn't cause damage running the boat for an hour or so after the performance started to decrease. Sounds like you might be guessing piston damage.<br /><br />I'm going to run home at lunch and test the compression. I'll post the results afterwards.

 

[CATransplant]

Re: Top carb sucks hard, bottom less...

Yeah, let us know. You might have broken a ring or something like that. One of the symptoms of very low compression is a lack of vacuum to suck air through the carb. It could be something else, certainly, like a broken reed, but the cylinder is the most likely cause.<br /><br />The compression test will tell you. Let is know.

 

[fishnfiend]

Re: Top carb sucks hard, bottom less...

Checked compression again. It's "around" 135 in both cylinders. O-ring on the engine end of the guage was fubar, so I just tightened it in as best I could. Also, this time the check was motor warm, throttle open, post Sea Foam. Two weeks ago it was engine cold, throttle closed, pre Sea Foam. I'm hoping these factors account for the 10+ pounds of compression loss in both cylinders.<br /><br />Spark plug appearance. This summer while running well, they were a nice dark even tan. After the loss of power, surging, BOTH plugs had a black (carbon?) streak down the porcelain on the side away from the bent electrode. Just now, after idling to warm up, both plugs were wet and mostly tan (same plugs).<br /><br />On the carb suction test: maybe I need to get more objective. I had half of the air box still on, and maybe I just wasn't positioning my hand identically on both carbs (e.g. leaving a gap between my fingers.) Tonight, I'll take the rest of the airbox off and use a piece of paper or cardboard on both carbs. <br /><br />Thanks again for any information.

 

[CATransplant]

Re: Top carb sucks hard, bottom less...

OK, that could be. The compression sounds fine. The drop was probably because of the bad o-ring. So, you get a pass on internal damage, I'd say.<br /><br />Stuff a pair of new plugs in there and take it out on the water and see how it behaves. You cleaned the carb. Now put in new plugs and go run it. You may have already solved your problem.<br /><br />Your compression's fine. Now, if it doesn't run right, report back and we'll see what else it could be.

 

[fishnfiend]

Re: Top carb sucks hard, bottom less...

CA, I will do just that. I have also learned from this that if you can't get the rpm's up at WOT, don't keep running the motor! Scares the bejeebers out of me to think that I could've cooked the innards by running lean too long.<br /><br />Thank you, and I'll report back on this thread after return from the lake Sunday.

 

[CATransplant]

Re: Top carb sucks hard, bottom less...

Great! Let us know how it turns out. I'm betting that you had crudded up carbs and maybe some marginal spark plugs in there.<br /><br />Happy boating!

 

[umblecumbuz]

Re: Top carb sucks hard, bottom less...

Er ... yeah!

crudded up carbs

You learn summat new every day! I've had cruddled eggs, and a long cruddle in the cuddy ... but I've never had cruddled carbs before!<br /><br />Better go and check 'em right away.

 

[fishnfiend]

Re: Top carb sucks hard, bottom less...

Sunday - back from lake.<br /><br />Sad to report that I lost my good fishin' hat. <br /><br />Thrilled to report that I have no motor problem at this time. Dang thing runs so well it blew my hat clean off.<br /><br />I retested the compression yesterday (with new o-ring on the guage) and it was 145 in both cylinders. Both carbs would hold a piece of cardboard over them at idle, although covering the top carb still affected the engine more quickly and drastically.<br /><br />Test at the lake indicated all power and speed are back!!!!!!!!!!!!!! Don't have a speedo, but let's just say we had to slow down when coming up on several skiers. Motor was smooth and strong. <br /><br />Thanks, CA, for the sage advice.

 

[CATransplant]

Re: Top carb sucks hard, bottom less...

Good deal! I'm glad you didn't have to do anything more to your engine. Sometimes things just work out!<br /><br />By the way, I've lost four fishing hats this season. I'll learn someday.

 

[fishnfiend]

Re: Top carb sucks hard, bottom less...

This was an Aussie-style hat - even had a chin strap which I sometimes put down in the wind. Had it for years - doggone thing was 'seasoned' just right.<br /><br />Funny thing, my wife does not share my sadness in the loss of my good ole' hat.<br /><br />In any event, the stars are apparently in line again and the universe can proceed. Never felt quite right while the motor wasn't running well.<br /><br />Thanks again.