carb adjustment

[ryanc]

Hello again, 1973 merc 200 20 hp<br /><br /> Just rebuilt carb and changed out foam float to a plastic float. Started up motor but she is still coughing at idle. Adjusted idle mix 2 turns out and fiddled with it but no major difference.<br /><br /> At idle she coughing then spits then shuts down. I squirted gas-oil mix into carb throat while at idle and she runs smoothe as long as I keep spraying her.<br /><br /> Is this a problem with float adjustment? which way do I adjust float to feed more gas at idle??? Thanks again for help

 

[RICKRICK1]

Re: carb adjustment

Have you tried adjusting the idle up slightly.

 

[ryanc]

Re: carb adjustment

Thanks rick for your reply. This particular carb (intergral fuel pump) Has a factory set carb. The only adjustment is the idle mix and the throttle linkage which both have been adjusted.<br /><br />This motor had a lower crank bearing blow out.<br /><br />The bearing and seals replaced as was the rings and cyclinders honed. The cdi was replaced and the electrical system gone thru.<br /><br />The motor during break in ran fine from 1/4 throttle to WOT but at "START" level down to "IDLE" level she would spit and sputter and finally die out.<br /><br />Did find a leak in primer bulb and replaced the whole fuel line. A Marine mechanic looked at it for an hour and figured that the carb needed to be rebuilt again. It had been rebuilt less then 20 hrs running time.<br /><br />ANyway, I tore it down and replaced all gaskets as well as the float and idle needle and spring.<br /><br />Still it is runnig terrible at low rpms as well now at higher rpms, spitting and sputtering.<br /><br />I am beginnig to think at this point that perhaps a reed on reed valve got messed up when bearing blew apart. I didn't inspect valve that closely. ANyway, thanks for your comments

 

[shelbert]

Re: carb adjustment

I found a really nice web page the other day that helped me alot with my carbs on a motor I am rebuilding, it might help you its at <br /><br /> http://www.maxrules.com/carbindex.html <br /><br />Alot of onfo on carbs there.

 

[Yepblaze]

Re: carb adjustment

When internal parts come apart, pieces of those parts can find their way into the crankcase and then through the transfer ports into the combustion chamber then through the exhaust ports. <br /><br />If so they will many times momentarily catch between the edge(s) of the port and piston. This can gouge this very intricate port timing effecting motor operations. Most noticeably at low RPMs. You may want to go back and double check cylinder diameter(s)and ring fit-up, especially around ports.<br /><br />Now I'm not saying this is the case with your motor, but, if you had pieces/parts coming apart "in there" this may be an issue.<br /><br />Now, back to carbs. I have noticed many a time that an idle mixture adjustment screw is in effect an idle "air bleed adjustment", and by backing the screw out leaning the mixture. If it is an air bleed screw it would require turning inward to richen mixture. <br /><br />Sorry, no definate corrective suggestions, just a bit of insight that may or may not be applicable.