carberration problems

[nickster]

I have a mid 80,s 35hp mercury. The problem that we are having is in the fuel delivery. The motor runs fine at 3,000 rpm,s anything lower than that the motor doesn't want to rununless you choke it but on the other hand you can,t keep it choched or it will die. So you push the choke let off the choke and keep doing this repeatedly to keep the motor running. We have torn the carbs apart to clean them several times did not work. We dipped the carbs and rebuilt them twice seems to still not work. I have the secondary lever and the primary lever for the float where they are supposed to be set and this motor still doesn't want to run without choking. We have noticed if you let the motor idle down that it starts pooring gas out of the front of the carb. My boss seems to think that the carb is bad all together and i'm starting to think the same thing. I need some opions if you guys can help before I tackle this motor again.<br /><br />Thanks <br />Nick <br />Prop Shop Marine<br /><br />------------------

 

[JB]

Re: carberration problems

Hey, Nick. Have you inspected the reeds? Another possibility is an air leak into the crankcase.<br /><br />These symptoms seem to contradict each other: You need to choke it to get it to run, but it pours out excess fuel. <br /><br />I'm not a Mercspert. This is a 2 cylinder engine with 2 carbs, right? It seems that whatever is wrong is common to both jugs and that should eliminate a lot of suspects, but I am out of ideas for now.<br /><br />Let us know any new info.<br /><br />Red sky at night. . . <br />JB

 

[nickster]

Re: carberration problems

Jb I had thought of the reeds to but if it was the reeds it would have low comression and it would be spitting fuel out of the carbs. It does only have one carb. and what I was saying about the choking part if you was only at idle speed you have to keep choking it to keep it running but if you choke it to much at idle it will die. Now if you let it try to die as it starts to fall on it,s face fuel will start excessively pooring out the front of the carb. We are at a stand still till we find out the problem. Do you think it might possibillity have a bad carb all together.<br /><br />Thanks<br />Nick<br /><br />------------------

 

[nickster]

Re: carberration problems

I'm still not having any luck with this motor can anyone help THANK YOU!

 

[JB]

Re: carberration problems

Howdy Nick. Many people confuse crankcase compression with cylinder compression. They are not related.<br /><br />Your piston acts as a pump to draw fuel/air into the crankcase, then to pump it through bypass passages into the cylinder. This is when crankcase compression occurs. . . on the downstroke. If a reed is leaky or broken or a crank seal is blown crankcase compression will be low and reduced fuel/air will be pumped into the cylinder, causing reduced power. If it happens in the crankcase that operates the fuel pump less fuel will be pumped and fuel starvation will occur. <br /><br />Cylinder compression takes place on the upstroke.<br /><br />I don't know if that has anything to do with your problem or not. I've seen too many references to compression (cylinder) being affected by reeds or affecting fuel pumping and needed to set it straight.<br /><br />Now that you tell me it has only one carb I think there is something wrong there that your rebuild didn't fix; something in the float valving and/or the low speed circuit. It sounds like the low speed circuit is too lean, PLUS the float needle is letting too much fuel into the bowl.<br /><br />That is from an OMC guy. There may be differences in the Merc that make my guess wrong.<br /><br />Good luck, let us know what happens.<br /><br />Red sky at night. . . <br />JB

 

[nickster]

Re: carberration problems

J.B. Thank you for your knowledge! <br /><br /> I don't know if my local Snap On dealer or if my local Mac Tools dealer can get me one of these tools that test crankcase leaks but if I have to buy it special I will. Do you have an order number for this paticular tester? MUCH APPRECIATED<br /><br /> The worst of all of this and I'm shure we all have been there once before is that I am a mechanic at a very small marine comp. and we are all dumbfounded on this paticular problem. I will be shure to buy a tool to test crankcase and I just hope to be able to fix this motor <br /><br /><br />THANKS AGAIN!<br />NICK

 

[sony2001]

Re: carberration problems

Wouldn,t it be wiser to try a used carb than to buy a tool that your not sure will find the problem?

 

[nickster]

Re: carberration problems

Sony I will agree with you on the used carb but I don't have one. Now on the other hand if I get this tool and it comes in handy that I am using it frequintly it would be like the rest of my tools a very good investmentand it would eventully pay for itself.<br /><br />Thanks!<br />NICK

 

[Grant Ingle]

Re: carberration problems

Nick,<br /><br />Perhaps hooking a simple vacuum gauge to the fuel pump / crankcase line will determine the amount of vacuum being generated by the motor. Weakened reeds will lose a substantial portion of the available vacuum. The gauge can probably be found at a local auto parts store and require little or no modification to be used for this application.<br /> don't fret, it always gets better.

 

[Rex]

Re: carberration problems

IF YOU CAN FIND A USED CARB.<br />PUT IT ON AND DO NOT MESS WITH IT JUST TO<br />SEE IF THAT IT.<br />ASK THE OTHER MEMBER AND I THINK THEY WELL<br />SAY THE SAME. TRY IT FIRST.<br />LET US KNOW.

 

[JB]

Re: carberration problems

Hi, Nick. I don't know that anyone makes a tool for testing crankcase pressure/vacuum, and I don't know of an engine that has connections specifically for attaching one.<br /><br />Years ago I adapted an engine vacuum/boost guage from my turbo-Corvair to monitor these in my racing 2 strokes on a home-made engine test bench/dyno. That is when and where I learned how sensitive these engines are to reed sealing. A plain Vacuum guage wont do it because the critical value is pressure, when the reeds are closed. Just keep this theory on 2 strokes in mind when you have difficult fuel/air problems.<br /><br />Your present problem is a carburetor problem, not a reed plate problem. Don't get distracted by this new knowledge about engine theory. Focus on the carburetor.<br /><br />Why must you choke the engine to get it to run at low speeds, yet it dumps excess fuel in your lap? Are there 2 problems? Both in the Carb? It runs fine at high speed.<br /><br />I think so. I think your low speed circuit in the carb is too lean to allow it to idle without choke (after a respectable warm-up, of course). That may be adjustment or it may simply be still plugged up, in spite of your overhaul.<br /><br />Let's get that fixed first, and worry about the overflow later, after it is running.<br /><br />Red sky at night. . . <br />JB

 

[sony2001]

Re: carberration problems

Nickster Borrow a carb from your competitors<br /> Put on another merc carb same jet an<br /> work throttle with your hand.<br /> Buy a new carb and return it if you <br /> don't need it.<br /> Goodluck!

 

[nickster]

Re: carberration problems

I think that I might be real close on this carb . First I have to say that this is an 89 motor which I should have said something along time ago. Instead of beeing mid 80's like I thought earliear. I had contacted a friend of mine and he luckily has has problems very simular to this. I'm not shure on the carbs he did but it got me closwe enough on the ones i'm working on that I atleast got this motor to idle.<br /><br /> What I had did on this paticular carb there is a pressed in idle tube and a pressed in main nozzle. Now it did get a little confusing cause when we looked in midas for windows (Merc. micro fish for pc) it showed this main nozzle and idle tube srewing out. Some of them do not this paticular carb hell I spent awhile lookig for them when they was already in the carb. LOL So I found a very small piece of wire actually I think it was a bread tie an ran it truogh both of idle tube and main nozzle the idle tube did have some restrictions but finally got the wire to pass trough. Cleaned carb back up put it back on the motor purrrred like a kitten. Took the boat to the lake Idles fine got out past the no wake opened it up sounded great at first very short first then it died Primer bulb was limp as could be so now I beleive that I have to rebuild my fuel pump.<br /><br />Hey thanks guys I'm shure we will be back in touch with each other. <br />THANKS AGAIN!<br />Nick