Merc 7.5 Power Loss

[jmccartney@indy.rr.com]

I have a 1982? (s/n 5816301) 7.5 hp Merc that went swimming last summer. It was running went it went in and spent about 5 minutes underwater. We pulled it out and got it running right away. It starts and Idles fine but at about 3/4 throttle it starts to sputter and will not come up to speed. Plugs have been changed, a different carb was tried and still the same problem. It starts fine and runs good until about 3/4 throttle. When I leave it at 1/2 throttle and manually open the carb butterfly(?) it seams to want to run. <br /><br />The Carb has been rebuilt, sprayed 1 can of decarb(changed plugs again) , and checked the gas line(the bulb stays hard). <br /><br />What should the compression be? It is 90 on both cylinders.<br /><br />Any suggestions on fixing this would be of great help.

 

[Bear]

Re: Merc 7.5 Power Loss

7,5 5524660 - 5936300 1980/1981 <br /><br />Last summer, then there is no water left at the coils and so on I guess. Some components still might be damp. As you tried another carb there can't be water in the main jet.<br /><br />Are you sure about the links from throttle to ingition? Check this:<br />LINK, TRIGGER HOUSING TO THROTTLE LEVER<br /> http://www.dolleroffshore.com/parts.cfm?c=btp&m=1&pn=608&r=222 <br /><br />I what order did you do things?<br />Did you restart it BEFORE you removed the carb?<br />Or did you remove to clean the carb and THEN restart it?<br /><br />Do you have a manual? <br />Are you sure both carbs are ok? All parts where they are supposed to be? <br />Float level? And the float needle valve opens?<br />What do the spark plugs looks like after running WOT (Wide Open Throttle)? Dry or wet?<br /><br /> http://www.dolleroffshore.com/parts.cfm?c=bt&m=1&pn=608&bn=297

 

[jmccartney@indy.rr.com]

Re: Merc 7.5 Power Loss

Thanks for the reply...<br /><br />I am NOT sure about the links from throttle to ingition. It all looks good and move fine with no apparent damage. <br /><br />Sequence of events:<br />- Hopped of transom at about 1/2 throttle and died underwater. Spent about 5 min underwater. <br />- Got it started after about 10 pulls right after getting it out of the water. Starts, Idles and gets to about 1/2 - 3/4 throttle then starts misfiring or chugging or bogging down.<br />- Cleaned plugs<br />- Broke original carb while cleaning<br /> - Put on a used, poor conditioned carb, and had exact same same problem <br />- Rebuild used Carb, changed plugs, took comperssion test, checked all fuel line, put in test tank(at a marina) and spayed a bottle of Mecury engine tune-up to decarb the engine. Same Problem.<br /><br />Two other concerns:<br />The original carb had a clear tube connected from the the crankcase to carb(right where the carb connects to the engine). The replacement carb did not have this fitting, so I blocked off the tube. <br /><br />When running the engine I noticed some small white watery air bubbles coming from the bottom of the baffel plate/engine block - I tightened all bolts(some where slighlty loose)<br /><br />I am NOT sure I have the float adjusted right! I will re-adjust and try again. If I have the same problem I will try squirting some gas/oil mixture in the carb to see if it is a fuel/carb problem.