carb cleaning/rebuild - idle problem

dajohnson53

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Hi: I did what I think was a thorough cleaning of my carb and it didn't seem to help much. Here's the facts:<br /><br />Merc 110 (9.8 hp), 1974. I bought it cheap last year and it ran OK, but not great - a little hard to start, tended to die at low idle. The only adjustment on this carb is the low idle rich/lean screw which would have no effect unless screwed in completely, at which point the idle seemed to even out a little.<br /><br />This weekend I disassembled and soaked all big and little parts in carb. cleaner for about 12 hours or more (1 gallon can with wire basket). Removed parts, and blew out every orifice I could find with air (small can; I don't have compressed air). <br /><br />Replaced all gaskets and fuel pump parts (diaphragm, gaskets). I didn't "rebuild" the carb because the rebuild kit costs $60 - local source as well as on-line price! However, in looking at the various small parts, I could not see any visible wear or defects. Especially the low idle needle - it looked perfect. <br /><br />Only glitch was that one of the small parts is a plastic venturi with two wings that fit into slots in the main throat. Unfortunately, I broke one of those wings off. Fortunately, I cleaned the parts up, dried off and repaired with a tiny amount of JB weld (with toothpick), and it seemed as strong as new and no intrusion into the actual venturi orifice. I really don't think this repair is affecting the function of the carb.<br /><br />Also cleaned tank pick up and the integral fuel filter screen was cleaned and blown out along with all the metal parts. I haven't actually replaced the fuel line and bulb from the portable tank, but they seem to work fine.<br /><br />So, I got it all back together and ran it in the tank. It seems that the starting and idling is again OK, maybe a "little" better than before, but not a huge difference. The low idle screw again does not affect anything until it's screwed completely in (not torqued in hard, just gently screwed in). When in the full-in position, the idle does seem to be better but not great.<br /><br />I know with an old 2 stroke, the thing isn't going to idle like a sewing machine, and it is working OK for what I need, but it seems rougher and noisier than a friend's similar Merc of the same era. <br /><br />The main things that have me thinking are the fact that the low speed adjustment doesn't have any effect full out to nearly full in - it's only at full in that any change is noticed. Also, it's hard for me to get it to idle at a low enough speed to smootly shift gears - it doesn't grind, but really sounds a little too high idle to me - but if I lower it the idle to where I think it should be, it tends to die (again, this is in a tank, not on a hose).<br /><br />I have no problem with re-cleaning the carb and will probably do it on general principles, because with the learning curve, it will be a very simple job the second time. Do you think that even though the small parts look perfect, there might be some defect that I just can't see (with my reading glasses on!)?<br /><br />Thanks in advance for any help you can give.<br /><br />Any other advice?
 

Laddies

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Re: carb cleaning/rebuild - idle problem

D, buy a gasket kit here on iboats or NAPA and a inlet needle if you want one. The problem could be the idle supply tube is pluged don't forget to clean it and reseal it after reinsallation. --Bob-- When you see the price you may have doubts about that dealer, also that venturie is availably as a seperate part from any honest merc. dealer
 

dajohnson53

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Re: carb cleaning/rebuild - idle problem

Originally posted by Laddies:<br /> D, buy a gasket kit here on iboats or NAPA and a inlet needle if you want one. The problem could be the idle supply tube is pluged don't forget to clean it and reseal it after reinsallation. --Bob-- When you see the price you may have doubts about that dealer, also that venturie is availably as a seperate part from any honest merc. dealer
Thanks Bob. I'll follow your advice except... The gasket kit is indeed available on line for a cheap price ($6), but checking with two storefront dealers and everywhere I could find on the net, there is nowhere that shows individual needles, etc. available except in the full rebuild set, which, again looking at both (honest) local dealers and the best on-line source I've found, is $50 - $60, if even available. I'll hunt again. <br /><br />
Originally posted by IBNFSHN:<br /> Recheck your float setting too.
Will do. <br /><br />Thanks to both of you - I'll give it another shot and see what happens.
 

dajohnson53

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Re: carb cleaning/rebuild - idle problem

Originally posted by Laddies:<br /> D, buy a gasket kit here on iboats or NAPA and a inlet needle if you want one. The problem could be the idle supply tube is pluged don't forget to clean it and reseal it after reinsallation. --Bob-- When you see the price you may have doubts about that dealer, also that venturie is availably as a seperate part from any honest merc. dealer
Oops ! looking at the website diagram of this carb (see link below), I see that the venturi and some of the other small are indeed sold separately! I saw that some of the rebuild parts were not, and assumed (I KNOW!) that none were. Thanks for the heads up.<br /><br />Just thought of a couple more questions before I take it apart again (taxes first, outboard second today!)<br /><br />Is there more I can do to clean the passage that the idle mixture screw/needle goes into? Or any of the other passages? I soaked for around 12 hours in carb. cleaner and then blew it out as thoroughly as I could (exploring all apparent passages) with air. I didn't shoot spray carb cleaner through it. Is there a thin wire or something to clean it out with - if so, what thickness would a guy use (I have a micrometer so I could measure a wire), also, what material would you use to avoid damaging the passage?<br /><br />Second question - the idle supply adjustable needle or idle tube are these "generic" parts? Like I said earlier, I have looked far and wide and can't find some of the small carb. parts for this engine outside of the full, expensive rebuild kit. If it's a generic part, maybe I'll just take it in to the shop and see if they can match it.<br /><br />Final question (can you tell I'm procrastinating on the taxes?): What do you mean re-seal it after reinstallation? If you look at this diagram:<br />picture of this carb <br /><br />What should be sealed? I'm using a OEM shop manual and it doesn't mention any sealing when re-assembling. There's no way I can see to seal anything on the idle mixture screw. However, the part called "idle tube screw plug", which covers the "idle tube" appeared to maybe have some sort of red colored sealer on it when I took it off.<br /><br />Many thanks you guys. I'm actually enjoying this project and it's a learning experience for me. Later I'm going to rehabilitate the chain saw and lawnmowers!
 

dajohnson53

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Re: carb cleaning/rebuild - idle problem

Thanks again for the help. Latest report:<br /><br />Took the carb apart again. Didn't soak parts again, but I did very aggressively blast all orifices with spray carb cleaner and air. Re-checked float level. (was good). I also re-checked every fuel line connection, filter screen, pick up screen, etc. to try to avoid air in the system. Reassembled and ran in barrel. I think it idles quite a bit better. Again, it's no sewing machine, but it definitely responds to adjustment of the idle adjustment screw- which it never did before. I found a spot where the idle seemed best. So aside from the sheer learning factor (an accomplishment in itself), I improved the idle! Thanks. (see new post on mystery part)
 

dajohnson53

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Re: carb cleaning/rebuild - idle problem

Update:<br /><br />As described above - did the carb cleaning this spring.<br /><br />In another thread, I also found a bad coil and replaced that - good spark (per adjustable spark tester) both cylinders.<br /><br />After all that, the engine ran very well, idle to about 1/2 throttle, with prop, in barrel.<br /><br />Ran it for about 15-20 minutes idling and WOT in a lake a few weeks ago and it worked very well - easy to start, good idle, smooth power up to WOT. But, after a while it seemed to go bad - it died at idle and became difficult to start. Didn't have time to troubleshoot at the time.<br /><br />Took it out again last night: starts OK (3-4 pulls) with choke on. Will idle without choke for a few seconds, but after that, it will not idle unless the choke is about 1/2 closed (I had the cover off so could look at the choke plate). With 1/2 choke it idles real fast, and won't die. As soon as I open choke, it dies. This was the same after the engine warmed up. I tried adjusting the idle mixture screw both ways, but it didn't help. Bulb is firm - squeezing it has no effect. Fresh plugs, fresh fuel.<br /><br />This is definitely worse than when I started way back when. Then, it would work OK, but was pretty rough. Now it just wont' work without choke.<br /><br />I'm thinking that somehow it has picked up some crud in the carb so I plan to disassemble and re-clean as carefully as I can, re-adjust float, etc. I'll also re-check all fuel lines and connections.<br /><br />Can anyone give me any other words of advice? Is there any sneaky place that could be a problem - air leak or fuel restriction - that I'm maybe not thinking of?<br /><br />Thanks for any advice you can give.
 

dajohnson53

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Re: carb cleaning/rebuild - idle problem

Success!<br /><br />My theory was particulate clogging rather than gumming (since I'd recently very thoroughly soaked and blown it out). Took off carb, didn't soak, but disassembled and carefully, and thoroughly blew out all passages and parts with copious amounts of spray cleaner. Re-assembled with surgical cleanliness ;) <br /><br />Ran it yesterday for about 45 minutes pushing my big boat upstream at WOT and below WOT for about 25 minutes. Then I returned down stream at idle and/or trolling speed. Engine was smooth and trouble free. Stopped it a couple of times to see how it would re-start: first pull every time.<br /><br />Final 15-20 minutes were at very low speed because I wanted to see what the plugs looked like after this. Plugs looked perfect - moist with fuel, but no black crap. Some light brown toasting beginning to show.<br /><br />Thanks to all the advice given over the past couple of months.
 
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