Mercarb 7.5 float setting question....

[jbjennings]

Laddies, I read your info on the 7.5 carb needing fuel squirted into and have a similar problem. After the same squirting need, I decided to rebuild it. I noticed on the float where the needle valve sits that the top of the needle valve had either worn a little dimple in the float lever or was sitting in a dimple that was supposed to be there. I've cleaned the carb and noticed that when I filled the carb bowl with the primer bulb, quite a bit of gas spit out the little brass thing on the carb throat. It cranked right up with no help and ran GREAT for about 5 min. then died. The float valve was stuck closed (I couldn't squeeze the bulb), then it finally opened and wouldn't close (flooded out , I took off the fuel connector, got it to crank again, connected the fuel hose and it started spitting a big stream of gas out that brass nipple in front of the carb). I know I have the float adjusted wrong and am going to fix it, but first, I have a couple of questions:

1. Is this little brass nipple that is in front of the carb throat supposed to prime the engine when you pump the bulb?
2. Is the float lever the needle valve sits on supposed to have that dimple?
3. If it's not, can I fill the dimple and fix my adjustment problem or get a new float? ( I think it might be slipping down in that dimple)

Thanks,
JBJennings

 

[Laddies]

Re: Mercarb 7.5 float setting question....

1. The little brass tube is a float bowl vent
2. The float lever should not have a dimple in it but I think you should be able to overcome the problem with the adjustment.
3. If the carb is a KB then you turn the float bowl cover over and set the lever that rides on the float spring by bending the end of the lever that rides on the needle so it is even with the pin for the other lever. If it's a BB carb with the carb inverted the measurement should be 1/4" plus or minis 1/64" from the bottom of the float to the float bowl flange.

 

[jbjennings]

Re: Mercarb 7.5 float setting question....

I believe it said it was a tillotson on the carb body. I cleaned it good, it idles o.k., but of course will not crank after it's sat a while. There was no spring on the float needle. I saw your post on the other guys 7.5 and tried to set the float as high as possible with it still closing of the gas so the level in the bowl would be as high as possible. It has a low speed adjustment, I set it where it would idle fine but, still won't crank after sitting. It has me baffled just like everyone else.....Any other ideas. Also, I just ran the crap out of it about 2miles on the lake. It has a little insulation missing on 2 of the wires coming out of the box by the heads. I don't believe it's shorting out but will fix them. When running wide open, it has a slight miss like it IS shorting out but only at wide open. Oddly enough, if I back off the grip just a little without letting it slow at all it seems to help the miss. Any ideas on this craziness? I take it there is no high speed adj. on this carb from what I saw when I took it apart. One more thing about this "jewel". It makes tiny bubbles all around the powerhead where the 2 halves of the crankcase come together, but only at idle...... AAAAAAAAGGGGGHHHHHH!!!! Well, I guess that's about it...Ha Ha. I wish I could figure out the not cranking thing as I have a nice 9.8 '72 model that will crank cold after about 10 or 15 pulls but am scared to mess with the carb on it until I feel confident I can fix it and not mess it up worse. the dang things look incredibly simple but sure are ornery!
Sorry to overwhelm you but I suspect you have seen all this before!
THanks,
JBJ

 

[Laddies]

Re: Mercarb 7.5 float setting question....

The KB is a side bowl carb and the BB has the bowl underneith the carb a 72 engine should have a KB9A or 12A but some were also BB it makes it nice. If you can't identify the carb with a number goto the BAM Marine site and try to figure out with one you have and we can go from there, they both have differant type problems--Bob

 

[jbjennings]

Re: Mercarb 7.5 float setting question....

Well, the '72 9.8hp is the sidebowl model. I looked at the '76 7.5 hp and couldn't see a number with it on but here's 2 pics.
ANy ideas? It's like two different model carbs have the same exact problem.
Thanks,
JBJ

 

[Laddies]

Re: Mercarb 7.5 float setting question....

First thats a model BB carb, things that can make them hard starters are wrong inlet needle it should be one with the spring on it. The float level should be set at 1/4" plus or minus 1/32" measured from the bottom of the float to the float bowl mounting surface. The low speed pickup tube dirty or a slightly lean idle mixture. Some have a two piece choke butterfly that the spring lets 1/2 open when cranking and be sure the detent on the choke cable holds the butterfly completly closed.

 

[jbjennings]

Re: Mercarb 7.5 float setting question....

Thanks for the info Laddies,
I'll post you back when or if I figure out what the problem is. I'm pretty persistent. Judging by the amount of posts on this subject that never say what fixed it, maybe the solution will be helpful to someone else.
JBJ

 

[Cornell]

Re: Mercarb 7.5 float setting question....

Hi jbjennings. Thank you for being persistant about your problem. I am one of the other guys with "won't start without squirting fuel into carb when just getting onto lake or when carb is dry". I'm still hoping to fix my '73 7.5 hp and have been reading the threads, trying to get back into this. As laddies says this looks like my carb which is a BB2A. And yes there is a small spring that is attached to the needle valve. That small spring has made indents on the brass tang of my float but never felt that it would hinder it's performance as they are maybe .005". Mine looks good and have no reason to feel the float isn't adjusted right as I am the original owner and no one has taken this carb apart. However, I will take it apart the 3rd time and try to adjust it to allow more fuel and using Laddies specs. I will also buy gasket kit and needle valve for it as well. They sell them separately and are not too expensive for my numbers above.
Looking at your carb. picture on the right; (if like mine) you will find the carb number you need on the carb. 2 bolt flange that goes into the intake manifold. Look just to the right of the brass screw fitting in the picture, and on top of the flange is the carb number which you will need to order parts. Mine says BB2A 5. If you fix it and want to share what the problem was I would be glad to hear it as I plan to get back on mine. My email is thecruiseguy@comcast.net