Merc 7.5 - Carb

[goinhungry]

I'm doing a carb re-build on an 81 Merc 7.5 (as it idled fine, but then dies out once it's put in gear) and in doing so noticed that the throttle shaft linkage coming off the top of the carb isn't connected to anything above - it doesn't make sense to me, as this is what opens the flap, but it's the first time I've worked on this motor, so I'm looking for help. When I took the carb off I noticed that the linkage had turned on the shaft, so that the flap was only opening 1/8 of the way (probably the cause of the problem, right?), but when I put it back in, should it connect to something on the top end - otherwise the flap won't open when it accelerates? I notice that there's a plastic arm that's attached above, near the flywheel, and on the left side of the powerhead (when facing the front of the engine) which has a hole in the bottom and would seem to be what the linkage connects to, but that too isn't attached to anything, and it almost seems like it's twisted around and stuck to the left (it's hitting on the underside of the pull handle case, which is why I can't just swing it over and connect it to the linkage, but I don't want to force it over and potentialy break something if I'm off base. Any thoughts/advice is greatly appreciated!! Thanks

 

[Silvertip]

Re: Merc 7.5 - Carb

While I'm not familiar with that engine, twisting the throttle lever does a couple of things. Towards the top of the engine, protruding from under the flywheel area you should see an arm. That arm controls the engine timing and a rod may connect it to a cam. The cam is also connected to a linkage that moves when you twist the throttle. As the cam moves, it opens the throttle plate in the carb. Looking into the carburetor, you will see two flaps or butterflies. The outside one is a choke. The inside butterfly is the one that should move with application of throttle. At wide open throttle that butterfly should lay horizontal. Twisting the throttle then advances the timing and opens the throttle butterfly in precise synchronization. You should have a service manual for your engine to properly perform whats called a "link & sync".

 

[goinhungry]

Re: Merc 7.5 - Carb

Thanks UIS - I've got a manual,but it isn't 100& clear - I'll have to investigate it further, but it sounds like what you're saying is what I've suspected. As it stands now, that throttle linkage arm isn't doing anything (i.e. opening the throttle butterfly), although I do see that the timing advance (small shaft at right side of engine with cable around it) is moving when the throttle is turned. I'll research the "link n' sync" (sounds like a new boy-band) further in he manual (SELOC) and thanks a bunch!!

 

[Laddies]

Re: Merc 7.5 - Carb

The plastic linkage that opens the carbs break quite often on those engines and have to be replaced

 

[goinhungry]

Re: Merc 7.5 - Carb

Thanks Laddies. Hopefully I can find one, or if fixable, do it. I don't see anything that looks like it's snapped/broken - maybe just separated and needs to be reconnected, but we'll see. Thanks again to all, I really appreciate it.

 

[goinhungry]

Re: Merc 7.5 - Carb

Anyone know what that plastic linkage is called? I tried finding it, but so far am striking out. Any one have a link to some place that does? If it breaks frequently, you'd think it would be available somewhere, but i dont' know... thanks!

 

[goinhungry]

Re: Merc 7.5 - Carb

Well, I looked through the Seloc manual and searched on line last night, but was unable to come up with the name for the above part or locate on. I rotated it around under the pull handle, so it looks like it's in the place it should be, but it's still pretty far away from being close to any contact with the throttle arm linkage. I did notice that there is a sharp edge on one side of the arm, so maybe there was something there that snapped off, but even if there was, I'm at a loss to see where it would hook up to anything. It basically looks like a elongated "z" with the end of the bottom leg having a hole in it (I'm assuming that this is what mates with the throttle shaft on the carb, then the center of the "z" is attached to the flywheel cover and has a spring on it. The upper leg of the Z is flat, has no holes, doesn't appear to attach to anything. I'm at a loss - any thoughts? Thanks, you guys on this board have always been a big help and I really appreciate it!

 

[Laddies]

Re: Merc 7.5 - Carb

Get your serial number and go to BAM Marine.com they have a great parts site

 

[goinhungry]

Re: Merc 7.5 - Carb

Thanks Laddies! I had tried the merc site, but they didn't have parts avail. when I entered my serial No., but BAM does!!! The part(s) I'm talking about are no's 32-36 on this diagram:<br /> http://www.mercruiserparts.com/Show...7&bnbr=10&bdesc=TOP+COWL+AND+STARTER+ASSEMBLY <br /><br />but everything that's shown there is exactly what I have, nothing broken or missing. Other than connecting the bottom arm to the top of the trottle linkage, I don't see where this connects to anything else that would allow it to affect the throttle butterfly when the throttle level is turned, or am I missing something? HELP & THANKS!!!