# Starting troubles Mercury 7.5



## Insanity (May 1, 2015)

Finally bought a Mercury 7.5 for my boat. It's a 76 model. I replaced the empeller first thing. 
But can't get it to stay running. I cleaned the carb and had to replace the fuel pump. But it did the same thing it did when I first tried it. It tried to start on the second pull but died. Then got worse until it will only start in gear wide open. Runs fine wide open but when you turn the trottle down a little it dies in a few seconds like you hit the kill switch. No stubleing it just dies. 
Thinking I have two problems. Something with the carb. And maybe a coil pack going bad. 
Any ideas? 
How does one act when the plugs are bad?

Funny how it does the same thing as it did the first time I tried to start it. And got worse. 
I ran a little reg ethanol fuel just to try it. 
Which rinkled the fuel pump up ( along with the gaskets till they dry. Then they lay back down flat ) wondering if it messed up the new fuel pump again. I no it's not supposed to hurt things. But you should see the gaskets for yourself. I've done lots of car carbs and two boats. But I've never seen a gasket curl up like this before. Even the fuel pump screen gasket which is cork did it. 
This stupid ethanol fuel is some Hot stuff.


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## Insanity (May 2, 2015)

Well sence it still had the original spark plugs in it I went ahead and changed them. 
Wow what a deference in high speed. I don't no how many rpm she is turning wide open but I no its to much. :mrgreen: 

No change in running other wise. 

Also Checked the new fuel pump. It does still look good. 

It's looking like I'm gonna have to take it to the mechanic. Atleast three weeks from today when I have the money. Insert long sigh.....


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## Insanity (May 2, 2015)

Ok took the carb back off and cleaned the emulsion tube and idel air screw again. Per someone's suggestion on another forum. 
Still the same result. It will scream wide open but will not run any slower. 

Any ideas at all? 

Any web sites anyone could recommend?


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## TNtroller (May 3, 2015)

Throttle linkage ?? Just guessing.


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## Insanity (May 3, 2015)

Thanks for the guess! I was starting to talk to myself here. :mrgreen:


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## JMichael (May 3, 2015)

Have you gone through the steps to set the timing advance/carb linkage (link n sync)?


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## Insanity (May 3, 2015)

JMichael said:


> Have you gone through the steps to set the timing advance/carb linkage (link n sync)?



No I just kept thinking it had to be the carb. Humm
Il go read up on that on the net. I bet I own a Manuel as soon as I get the money.


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## nlester (May 3, 2015)

I just had my first carb apart 4 times before I traced down the problem. It was a frustrating week. Each time I started to take it to the shop, I thought about one more thing to try. Each time was quicker. I wish you the best of luck.


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## Insanity (May 4, 2015)

What would it do if it had sheared the key way in the flywheel? 
It starts and runs wide open but if you turn the trottle down in just cuts off immediately.
The carb is spot less you can see threw everything in it that matters. So it has to be something else.


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## JMichael (May 5, 2015)

If the key is sheared it could change the timing which could cause different things to happen. 

As for clean carburetors, I've seen them so clean you would think they were brand new but they wouldn't run an engine if your life depended on it. What you "see" with your eyes is only half of what needs to be clean. If any jets or the tiny passageways inside the carb get clogged, your carb is not going to work properly and you won't be able to see that sort of problem with your eyes.


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## Insanity (May 5, 2015)

I've blown carb cleaner and air threw everything. And even looked threw everything I could in front of a drop light.


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## Insanity (May 5, 2015)

Dang it ! I'm starting not to like this motor. 
I finally found a syringe like you give a shot with. Loaded it with some gas and shot a little threw the throat of the carb. Guess what it fires. :evil: 
So it is the stupid carb dang it. I took it off and completely striped ( removed everything) and cleaned it again. Um I've lost count was that four times I've striped it completey. It's been off about 9 times. 
Even took out the main that the Manuel says not to.( thanks Jim for the Manuel!) Boy is it fun getting the Venturi back in place. 
The hole is not cloged in the motor side or front of the carb. 
All jets cleaned and you can see threw them. All passage ways let carb cleaner and air threw. There are no tiny ones on this carb. 
Fuel pump is new. 
Intake gasket looks good. 
Air tube um I forgot what you call it. But it's clean and you can see threw it. Barely. Man that's a tiny hole. 
Air fuel screw is clean and adjusted. 
Dang this thing should run. 
If I get board i might strip it again. But as of now I'm ready to let a mechanic have a go at it. Hope he has better luck. [-o< 
Oh and the key way is fine and linc n sync is good best I can tell.


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## JMichael (May 5, 2015)

OK, if you got air and cleaner through all of the passageways and jets you should be good to go on that part. Have you tried disconnecting the fuel line from the carb and verify the fuel pump is actually pumping?


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## Insanity (May 5, 2015)

It's the dia fram typ build into the carb.


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## nlester (May 5, 2015)

Did you pull your needle valve To clean it or just blow cleaner through it?


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## Insanity (May 6, 2015)

I pulled it.


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## JMichael (May 6, 2015)

Insanity said:


> I pulled it.


Did you notice whether the float bowl was full or not when you got it off?


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## Insanity (May 6, 2015)

Yep it was full and the float is set correctly best I can tell. It's going to the shop tomorrow if I get off early enough. Hoping they can figure it out before the cost gets to high.
I've cleaned or rebuilt a lot of car carbs and this thing is so simple in comparison its pitiful. It's killing me to take it to the shop.


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## onthewater102 (May 6, 2015)

sounds like the carb is out of tune - did you check the plugs to see if they're loading up and getting wet or if it's running lean?


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## Insanity (May 7, 2015)

I took it to the shop today but they are running behind. Said it would be two weeks before they could get to it. 
Heck il rebuild the hole thing before I wait two weeks. The fish are biting now. 

So! I ran the snot out of it wide open when I got it back home. Trying to figure it out. And noticed it does something funny every so often. It screams way above what I think the max rpm should be. Air leak maybe? I thought when it did it before it was just kicking up to much air around the prop sense it will only start and run in gear. But it doesn't do it all the time. 
It also gets harder to start and run as it warms up. 
Wouldn't an air leak make it not want to run low rpms and hard starting? ( like its doing) 
Someone mentioned the seals could be bad. The motor has barely been ran but they might be dry rotted. Any one think so?
Trying to figure out a way to vacuum test it. Il have to buy a new tester. If you guys think that will work.


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## Insanity (May 7, 2015)

onthewater102 said:


> sounds like the carb is out of tune - did you check the plugs to see if they're loading up and getting wet or if it's running lean?



New plugs and there wet every time Ive taken them out. Can't keep it running long enough to check to see if there reading lean or rich. It stumbles while running wide open and is still smokeing so I'm betting it rich enough. 
Less it does as I mentioned above. No dought its lean when it screams rpms like that. Problem is what's causing it the carb or a leak. I've done lots of carbs. This thing is so simple Compiared to others I've been in. I don't see anything wrong with it. It should run. So I'm guessing I've got and air leak somwhere. Now how to find it.


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## onthewater102 (May 7, 2015)

From what you'd described prior to me posting I was thinking you're running too rich, based on you're able to get it to run @ WOT but not any slower it sounds like you need that much air to keep it going, and that it's loading up on you at lower RPM's where the air is slightly restricted. The wet plugs are consistent with it being too rich as well. I'd get it ripping on the water and start tightening the mixture screw until you start losing RPMs @ WOT then ease off it a smidge (~1/8 turn) until they rebound then a smidge more so you're not running too lean WOT. You've got fuel and you've got spark, if it isn't an adjustment then you've got to pull the carb again & thoroughly clean it and snake the passages through it.

I don't know what type of seal you think could be leaking - on a 2 stroke you've got the head gasket, the reed valve assembly and the gasket between the carb and the intake...that's it on the vacuum side of the system.


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## JMichael (May 7, 2015)

I'm no expert on motors but I think a 2 stroke draws fuel through the crankcase so the oil can do it's job of lubricating things. So I would think that any gaskets that seal the crankcase could leak and cause a lean condition.


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## onthewater102 (May 7, 2015)

yeah - but you're looking for a leak substantial enough to impact the engine @ WOT with all that fuel...my engine really only has the cylinder block cover (i called it a head gasket, but as there ins't a true head that's not correct terminology) yours isn't too much different:







not a lot of options in there...intake cover gasket?


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## Insanity (May 8, 2015)

Perfect! Onthewater part number 21,s gasket was weeping oil out the bottom not to much just a couple of drops. I'm hoping that was it. The pistons are behind it. I was told it was a transfer port cover. Whatever that is. :mrgreen: 
But the Pistons come past the opening of the ports so I'm guessing it would suck against it pretty good. 
I couldn't get a gasket for it from the shop today so I cut one and sprayed the heck out of it with High Tack permatex gasket sealer. Waiting for it to cure over night maybe it will run correctly in the morning figures crossed. [-o<


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## Insanity (May 9, 2015)

Well I tried starting it this morning. Got the same results. I may shoot holes in the dang thing before I get it fixed. 
Someone on another forum is walking me threw One step at a time of things To check. I'm thinking the crank seals are next. ( I hope they no what they are doing ).


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## nlester (May 10, 2015)

I hope they can help you. Someone's check list worked for me.


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## Insanity (May 11, 2015)

Well I gave up and took it to a shop Sunday. He called this afternoon to ask what the problem was. It was peering like a kitten. Starts first pull every time. :shock: he didn't do anything to it. 
Only thing I can think of is that gasket I put in was one I cut. And the material was pretty thin. Maybe for some reason the high tack gasket sealer hadn't set by the next morning and it still sucked air. I did spray it thicker then a normally do. Because I figured it had a ton of vacuum plus gas/ oil in contact with it. 
Maybe by Sunday and Monday it dried. 
Anyway I'm taking him the boat tommorrow so he can run it and make sure it's rite. Because I had only took him the motor before sense it was 30 miles from home.


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## Triple obsession (May 11, 2015)

Did you take him your fuel tank & hose along with the motor or did he have his own?


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## Insanity (May 12, 2015)

I took him mine.


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## nlester (May 12, 2015)

I hope you are getting ready to get on the water in your next post.


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## Insanity (May 13, 2015)

Purs like a kitten my foot. :evil: 
Took the thing to the river today. At first it started right up ran a about ten seconds and died. No problem it's cold natured rite. Wrong. It just kept getting worse till it wouldn't start at all. So I shoved it off in gear wide open. :mrgreen: it starts fine like that. 
Ran it around for about 15 mins anytime you get to low on the throttle it will die. And forget about it idling unless it's wide open. And not to long then. It will die all of a sudden like you hit the kill switch. 

The guy said the carb was set. And I asum he played with it. Starts awful good when you first start. His compression gauge read the cylinders at 125. And it ran fine for him. My farther in law took him my boat and watched him run it. And it ran fine. 
So what would make it act like that? Fine one min and crazy the next. 
It run the same way in my water barrel as before. But acts better in the river with less turbulent force in the prop. 
Atleast it didn't rev to the moon today. 
Any ideas guys?


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## JMichael (May 14, 2015)

If the mechanic checked it out and it ran fine, I'd take it back to him and have him show me "fine". Then find out what he's doing differently than what you are doing. Either way, one of you is going to show the other one something.


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## Insanity (May 14, 2015)

I've got a good mechanic rite up the road from the house. There just running behind rite now. Il be taking it to them next. 
The guy that worked on it this time is just to far away to keep messing with. And he didn't charge enough for me to worry about.


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