Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

davids_1718

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I have 2 issues I'm dealing with. I have a 1974 7.5 HP Mercury Thunderbolt with a replacement carb. I previously had issues when I rebuilt the water pump but after months of trouble shooting I finally figured out that the length of the tube was too short. With that being said I ran the motor yesterday and water is flowing through the powerhead however..... My Throttle Linkage isn't properly connected. As I mentioned my carb is a replacement and when I rev up throttle the lever seems to not be connected to anything. Can anyone tell me what am I missing or how is it suppose to be connected? My second issue is how is the inside of the lower unit suppose to look. It appears that mine is cracked inside. Do I stand correct with that statement? Please help cause I dont know what to do with this throttle lever. I know it's definately something with the throttle lever / linkage. Any help is desperate and greatly appreciated. Thanks in advance.
 

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loogoman1970

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

My motor is also a 74 7.5hp. I'll send you some pics as soon as possible. The one thing I did notice was your choke wire has a spring at the end and mine doesn't. If you disconnect the choke wire does the choke close on its own with the choke shaft lever spring? Just curious.
 

davids_1718

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

I believe it does, I will have to confirm this when I get home after work today. I appreciate you helping me out. Would I stand correct by saying that I need help with the throttle linkage?. Reason I ask is because I have been looking this info up for quite some time now and I cannot find anything related. Once again thanks.
 

Texasmark

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

I don't see any throttle linkage. The throttle appears to be nothing more than the twist grip connecting up through some shafts to a swinging lever whose purpose is to move the black plastic arm (on the top rear of the carb) which is connected to your throttle butterfly in the venturi of the carb. Otherwise you have the spark advance rod that goes back and under the flywheel. Both look normal to me. Then there is the choke cable and it also appears normal to me.

If you don't think your throttle is working, open the choke butterfly and look down the venturi of the carb. Twist the throttle handle back and forth and look for the rear butterfly to open and close. If it does you're good to go.

HTH

Mark
 

davids_1718

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

Thats the problem I'm having. When I start the motor without any adjustments it takes a few pulls then runs real low till it stalls. When I adjust the plastic lever what I have to do is make sure the it's in shift, then turn the lever and lock it in a position that holds till the motor starts and when it does it revs super high. Once its strated I give it some throttle but nothing because I notice that something isnt properly connected because the lever does not move unless I do it manual. I'm at a lost with this I know their is something I missing that needs to get connected to the lever.
 

davids_1718

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

If you look at the second pic you will notice that the lever is not connected to anything. That is the main problem I am having is that it does not do anything unless I do it manually. I 've heard there are 4 different carbs for this dam motor and I'm hoping that when I purchased this carb thats installed that the linkage was not overlooked. Or perhaps I just dont have it installed correctly. Is there a problem with installation or am i missing a part to connect this. Diagrams dont show any real assembly of this other than seperate component breakdowns.
 

Texasmark

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

In picture #2 it appears that there is a roller on the end of a black plastic arm that appears to move as you turn the twist grip. Looking up from where the throttle butterfly is located in the carburetor appears to be a plastic adapter that has a relatively long vertical piece which appears to be in a position to be contacted by the roller and moved as the throttle is moved on the steering handle. Seems that the roller is right there to ensure that there is little to no friction between the twist grip linkage and the carb butterfly linkage.

Somebody else is going to have to help you man because from here, it looks like it ought to work.

Sorry.

Mark
 

davids_1718

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

Mark I appreciate it, thats the problem that i have. The roller moves as i shift or accelerate but it does not in anyway assist the lever to move. That is when i have to turn it by hand to get acceleration. Thats where i think i have my problem is finding the linkage that goes from the roller to the lever.
 

loogoman1970

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

I'm having a difficult time attaching the pictures. I can e-mail them to you if you want. Just give me your e-mail address, Thanks
 

loogoman1970

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

Did you get the pics?
 

davids_1718

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

loogoman sorry for the late response. Yes thanks I got them, it appears we do have the same set up however I a still unable to get my lever to catch the guide and open the butterfly as I turn the handle to shift. I am wondering if my problem lays on the fact that thre carbureator I have now is not the one that originally came with the motor. On the old carb it looks like it has some type of hook connection. Do I need to adjust the lever or something? I just dont get it and I want to go out on the water sooooo bad already.
 

MassillonBuckeye

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Jul 26, 2010
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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

The part that moves when you twist the throttle needs to be in contact with the black plastic part on top of the carb. If these aren't lined up, or in the wrong place, they wont make contact and wont work. I'm thinking its the wrong carb.
 

loogoman1970

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

What's the serial number on the motor?
 
M

Maxz695

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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

Do you still have the old carb if so try using the Plastic part from it on the new carb
 

Rmoore45

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Aug 4, 2011
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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

In the second picture http://forums.iboats.com/attachment.php?attachmentid=104146&stc=1&thumb=1&d=1311374052 you can see that the throttle lever isnt close to the throttle advance cam. As you twist the throttle it advances the timing as well as opening the the throttle. If you remove the set screw that holds the throttle lever, make sure the throttle on the tiller is set to no throttle, then move the throttle lever on the carb till it touches the throttle advance cam and then put the set screw back in. On my 9.8 there is a hole in the throttle rod so you can mess up, it appears that yours may be out 180 degrees.

Hope this helps
 

loogoman1970

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Jun 4, 2011
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Re: Please Help 7.5 hp mercury thunderbolt throttle assembly / inside of lower unit

Rmoore is correct. The plastic lever isn't positioned correctly. I used one of your own pictures to show where it should be located at low idle.
 

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