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7.5 1971 will not start after being run and then sitting for over 30 minutes unless u flood the carb

B

b521

Regular Contributor
I have had this problem since I bought the motor in 1977. It had only about 10 hours on it. The motor runs flawlessly under all conditions. Starts on the second pull after winter storage etc. I have (way in the past tried to fix this for 10 years plus by doing all the obvious) including talking to every Merc tech at every marina or dealer I ever pulled into. (Float settings needle valves, compression tests, hose inspection replacement, different fuel tanks etc etc . How it works, Go out on a lake, run it all day or for a short while, if you sit for say less than about an hour it restarts first pull. You sit for longer than that and it will not start all day no matter what you do unless you slowly keep squeezing the primer bulb till it spills gas out the carb. You do that and first pull it starts right up.
I have not used this motor in ten years and will be bringing it out this fall for one more try to see if I can stumble on the cause and use it next year. Would like to get it running well and then save up for a newer motor and keep it as a backup, if not i will sell or keep if for parts.
I must be missing something, simple or small, like a hairline scratch in an o ring or a warm headgasket leak that allows fuel pressure leak and replacing it with an air block.

Any input will be appreciated.
 
OK it did post.
to continue, what I probably do not have here is
a electrical problem
a choke problem
a dirty carb problem
a tank problem
a needle valve problem

The key word is "probably"
A lot of the above was covered in the past and replaced rebuilt and cleaned when just trying things just to try and fix the problem. But something may have been missed. It was even turned over to a Merc shop who couldn'f find anything. Problem there could be because they could not have the time to duplicate the problem like being out on lakes all day for over a period of years.
What we ended up doing was living with it for years and just flooding the carb. I even contemplated drilling hole in the cowl and inserting a tube into the venturi so I could give it a squirt of starter fluid. This not starting after you are out really gets to be a problem when you sit for awhile and a srorm blows in real quick.
 
papyson said:
are you siphoning your gas back into the tank while its sitting?
Click to expand...

Crap I just lost a long good answer to your question.
So if you don't mind i will just ask you how do you mean it could happen , siphoning it back.\
Interesting concept, that is what i am thinking is happening and then maybe causing some type air block but I can't figure out how or where.
Please give some detail
thx
 
''The anti-siphon valve can also be considered to be an anti-flow-back valve'' ....there are several ways this is done...some tanks have them..some motors have them...this site may sell them..i didnt check...i would order a moeler inline one if it will fit your tank and try it...its under 15 bucks on the web..some tanks have a ball type valve installed in the pickup....
these are one of the first things discarded when any fuel flow problem is suspected...there have been fuel pumps that would not lift enough gas with them...make sure your fuel line is 3/8 and not 1/4 inch..
another thing to consider is the position of your fuel tank to the motor...you want the fuel to flow ''up hill'' so to speak with no dips in the line...the tank lower than the motor..
please get back to us on this....we have several people on here that know more than i on the subject.











 
Last edited:
800-209-9624 is the number for this site for parts help....i have used this site and the prices are good and the delivery is prompt...
 
I will pull the motor out of storage next week and get back to you asap
I was also wondering if there could be a small head gasket leak that was not detected back then and when you start the motor the first time the waterjackets are dry, you sit out on the water for a while and they leak/drain into the combustion chamber. you combine that with the fuel siphoning back etc etc. So maybe my problem is a combination of two inter-related issues.

Whatever
Your feedback is great for a few reasons, one you may be right on the problem and two It will get me in there playing with other issues that will make me recheck a lot of things, rather than standing there looking at it and saying, well I checked that three times and I already replaced that twice etc etc.

Question, does it matter that you close the vent valve on the tank when we stop and are floating around, (my partner is particular about doing that, so we did do that most of the time.
 
i am 75 years old and been boating since i was a teen and i never ran into anyone that bothered to close the vent between runs in a boat...the gas expands with the heat of the sun etc...the air in the tank has to go somewhere...without giving it a hell of a lot of thought it seems to me the only place it can go is into your gas line if you got the vent closed..then when you open the vent and hear the air leaving the tank it will be assisting the start of a siphon effect...having said that some of the newer portable tanks are equipped with environment friendly gas caps with a vent...and some of those dont work....i have a name brand tank that i have to crack the fill cap...the other tank works well...
 
LOL You might be 75 and so probably no one said this to you in a long time but as the saying goes "your momma didn't raise no dummy"..
I am older than dirt also. 62 I especially liked about the part of reopening the tank could actually assist a siphoning effect. and extra especially the part of no one ever closing the vent during the whole day. HAHA ,, you never met my good friend/partner ... great guy, and a one of a kind.

I can hardly wait to get my hands on that tank, It has been a long time ago but I do not believe we knew there was an anti-siphon valve in the tank. if someone mentioned it we may have thought the connection to the motor (the ball type schrader valve internal to the connector or I think we thought or their is a check valve in the primer bulb which there should be or it would not function as a pump we may have assumed these had some anti-siphon effects, or maybe our tank does not have an anti-siphon valve in the tank, or it was removed.
I think we ruled out siphoning for the reasoning of even if the line draining gas back in the tank, would we not still get the motor to start or sputter from the gasoline left in the float bowl. (maybe there is an orafice or a tube that goes to the bottom of the bowl or bouncing around drifting with engine off . don't know. But i did see somewhere just yesterday when googling anti-siphon in a marine application that you will have one h-ll of a time starting it, if at all.
He may have recommended or I may have assumed in these circumstances that disconnecting the motor connection and purging the line with say a screwdriver and a squeeze of the bulb could get you started.
don't know

You said to hurry up. n/p now I am anxious. I will have my hands on that tank and motor by Sunday.
Thanks again
 
Yes I am a seafoam proponent, and I come all the way back from in the late 60's when gumout in their original formula sold the kits where you could connect it directly into the fuel line into your carborator. The stuff worked fantastic, except their claim that it would eat rubber and not neopreme was wrong. That stuff would eat anything. (I think it was just lacquer thinner) A couple weeks later you were rebuilding your carb. seafoam seems really good. (does anybody know what is in it)?
Whatever seafoam is, it does a nice job and doesn't seem to harm anything.
-no never checked if the plugs were wet because the problem would only happen if we were out on the lake. I figure it was because the fuel line was draining only when the motor was not running and we were bobbing around, (drift fishing), did not want to open the cover an splash the motor, as our first boat was not very seaworthy for fooling around back there, (we were lucky it floated at all, seriously). We could get the cover off, but could not lean far enough to set all the gizmo's back on without bringing a lot of water in the boat. We did shortly graduate to bigger better boats and I think we just got use to living with the problem by then. and made sure we did not let it not run for too long of a time. (and then was able to afford a trolling motor which could get us to shore as a fail safe.
--ok check valves in the bulb and fuel pump, and your saying there is probably one in the tank, if not add one? also overnight soak in seafoam solution and not it letting it siphon back while soaking.
 
Does anyone know where I can find the weight of older 7.5 an 9.9 or 9.8 merc. I will weigh this 1971 model when I get it out of storage, (maybe Sunday)
The reason I am asking is this thing is heavy. If I remember correctly it is in the 94 pound range. A few years later they changed them and made them a lot lighter. Not sure when but I think they went from in the 90 pound range down to 65 pounds. The earliest spec I can find is on NADA but it only goes down to 1974 and it says 65 pounds. Either them or I am wrong. I don't think they got that light that early. Reason is i am refurbishing this 1971 model and successful I will keep it but will be always looking for one of those 7.5 or 9.9 mercs that are in the 65 pound range. Kinda like trying to upgrade a little and still have a spare or parts doner engine around. etc etc.
 
I ALWAYS close that vent after a run (and occasionally forget to open it). This is vital with ethanol ga.

Jeff
 
fastjeff said:
I ALWAYS close that vent after a run (and occasionally forget to open it). This is vital with ethanol ga.

Jeff
Click to expand...

I guess being I am re-entering into the outboard motor fishing hobbie, that I have some things to learn about the problems with ethanol.
The only thing I heard so far is you may have to change your fuel hoses to be compatable. Is this necessary, what do you do about the other hoses under the hood. does runing the motor dry after a run suffice.

I am assuming you close the vent because ethanol is more of a problem when allowed to mix with the air.
I also heard an additive can be mixed in with the fuel that neutralizes the problems with ethanol, true or false?
 
Papyson and anyone else who can input.
I was able to get hold of my 3 gal tank. (I am pretty sure it was the tank that was supplied when the original owner bought the motor) (not sure if that would make it a merc OEM part if each particular dealer supplies their own. I do remember the original owner stating that the 3 gal tank actually cost him more than a six gallon tank that came with the motor. (Maybe the tank is generic and intended for any manufacturer especially to be carried on a bigger boat as an emergency reserve)t there is no anti-siphon in the pick-up tube, nor in the top tank connection. (remember I am the second owner so don't know if anything has been altered. So the only place it could have been would be some kind of insert in the top tank fitting between the brass barb and npt threaded fitting. Tested everything there out, the hose through the primer bulb will a slow leak down. especially if the priner bulb is pointed downward or level and also vertical. (vertical takes less of a flow to activate the check valve in the primer bulb to close.) Do a little jiggle of the hose and the check valve must open again and it will enable back flow once again. And naturally, bobbing around a lake with the engine off will accelerate this intermittent condition.

Where eles could an anti-siphon valve be, The manual I have don't show it.
 
Kimcrwbr1
Great input , and thx for taking the time to do it, I understand the principal and can work with it. Hoses maybe a mute point, (I was hoping you would say that, but it is very important to know, and deal with on a secondary basis, so run it dry will minimize any effect.) I especially liked that incorporated natural drain in your barrel. LOL
 
how do you edit your own post after it is posted, I have one line I need to take out so I do not waste anyones time dealing with it.. That woulb be the line of where else would a A.S. valve be on my motor. I think the tank and the feed line are the only place so don't waste your resources on this aspect
thx B521
 
How do I edit my previous posts. I.e. on this thread I gave too much info in some cases as I was more or less in direct conversation with the other post member. That is wasted info and anybody looking for similar help in this topic will have to waste a lot of time reading irrelevant info.. I searched long and hard, and cannot figure it out. My permissions say that I am allowed to do this.
 
My wife is like that; endless explanation of a simple thing. (I sometimes fall asleep waiting to hear all she has to say, then get in trouble!)

That's a Phase Maker ignition motor, and they are troublesome. The 'kill
switch on those is wired assbackwards in that you ground the mag to RUN it; an open circuit kills the motor. Hope that helps.

If there's still a spark problem (bad or none) you need to clean and reset the points--a dog of a job.

Jeff

PS: After doing a few dozen of these dogs, I ended up converting them to Phelon magnetos. That requires changing the top bearing housing (easy job), a cam (it's different) the mag and the flywheel.
 
Hello Jeff
Thx for the info . Two things, I am not having an ignition problem yet. And now I am finding this motor is somewhere in the 1973 year. Ser No. 373-1914. (That serial number seems to fall into a 1973 7.5 hp and can also fit into the 1973 9.8. When I bought it used in about 1977 the owner had 6 HP stickers on it as he said he bought a 7.5 then bought the 6 hp stickers and threw the kit away but put the 6 stickers on the motor. I don’t even know how to tell if it is not the 9.8. It runs real strong and has pushed 3 people (600 Lbs) around fairly well. It would not surprise me if it was a 9.8, but I doubt it. Enough said.
So I started a thread for the wrong year motor. I am having a restart fuel problem. (I don’t want to take flywheel off and try and figure what type of ignition I have till I solve this fuel issue. Geeze I hope I don’t have the impossible pain in the rear ignition system.
So here is where I am at. Finally picked up motor, Started fine, It will not restart the next day with everything connecter after say 4 hours. Unless you steady hold and squeeze the bulb till gas pours out of the carb. You do that and do a 1/4[SUP]th[/SUP] pull and if fires right up. I disconnected the hose from motor hook up and took pick-up tube out of the tank.. I can force air down thru the line to where it comes past the primer bulb down to the pick up tube if a small amout of back flow is forced. Apply a little more back flow and the check ball/valve in the P>B stops the flow. So I put an in-line shut off valve at the tank. Ran the motor. Shut it off. Immediately Closed the fuel valve, . (all the fuel line goes up toward the motor, there are no dips . I waited like 2 hours and did nothing but re-open that valve, the vent valve was open on the gas cap and put the engine on choke and it would not start. I squeezed the primer bulb and It would not start. I then went to squeezing the primer bulb till gas runs out the front of the carb and then again as always it starts right up. There is no sign nor smell of fuel leaking in the engine compartment, But I must be getting a leak down somewhere from the carb down to the fuel like quicd disconnect at the front of the motor, do you think it is leaking internally say in through the fuel pump.
What are your thoughts on the fuel pump, I don’t think this motor has heck valves in the fuel pump, and it runs strong and smooth which makes it appear that the fuel pump is ok. But who knows, maybe there is a small leak.
 
Kimcrwbr1
Wow you put a lot of time in helping me thx much. I will check the carb for what I can get at tomorrow. Because I want to try a couple more tests, and they are right along with your reply, as you are following this issue really well, double thx for that. Years ago we had went through the rebuild the carb, new float , new needle valve etc. and nothing helped, (But maybe we missed something and or just re-duplicated the flaw/problem, who knows. What I am going to do tomorrow is start it and put the tank and hose higher (on a step ladder) let it run for awhile and just shut it off and check it all day for fuel leaks. I may have to just eliminate the primer bulb and just run a straight line down from the tank. If I do not notice anything I am going to make a tank out of something clear and hang it and see if the level drops after a couple days.
Question, how do I keep you interested and knowledgeable posters informed when I do an update, because with your help we may find a few things out that will help others down the road. I get an e-mail when you all reply but I think that is only cause I started the thread. As an example Papyson clued me in on the potential dual purpose of an anti-siphon valve. I have built a lot of cars and outdoor power equipment and had and worked on a few different marine applications ,, and I did not know jack about an anti-siphon val. And not afraid to admit it. These Mercs are tough to figure out.
 
my carb looks different, It has "MERCARB" cast on the side and the float bowl is on the bottom of the carb. (a very shallow floatbowl) It might hold a shot of whiskey if that. There are some other markings on the flange where it bolts to the intake, they appear to be in a foreign print like Japanese or Chinease, (they may have made the carb or just the casting for some of the carb. Duno.
 
you pump about three times till the bulb gets really firm and it still won't start, you go grab the bulb again and force the issur with a steady hard squeeze and then in about five seconds you will hear the gas squirting and it flows out of the venturi, then a slight pull on the roap and it starts.
 
kimcrwbr1 said:
The primary pickup (sync) is not adjustable as long as you didnt mess with the WOT timing it should be just fine.
Click to expand...

Doing some testing,(while I have it running ) before I go through the carb tear down. I think I noticed something. The plastic upright post that connects to the throttle shaft….. at lowest tiller handle throttle there is a big gap between it and the timing advance cam/finger. Then when you advance the throttle to the start position the advance finger moves as it probably should but the plastic upright rod does not contact it till the end of the travel and only moves it slightly. So I am wondering (to use an analogy of a traditional automotive car with a carburetor and an accelerator pump, circa: 1950’s, 60’s, 70’s and 80’s. If the outboard carb is set up the way it is now, It may be like trying to cold start one of those cars without pumping the gas pedal a little which squirts via the accelerator pump to shoot a shot of fuel into their venture and not depressing the gas pedal. Summary, one will have an extremely hard time starting that auto, and it has a much stronger vacuum going thru its venture.
So I let the outboard cool down put it into the start position, only firmed the bulb a little, did not force any gas through the needle valve, put I piece of wood between the plastic throttle shaft rod, thereby increasing the potential of a higher volume of gas flow ,, and one pull and it started right up.
I have to wait till it cools as I want to tes t this again a few times. Now I am not saying this is the actual problem or just a band-aid/work around as I was waiting to see what you had on sync the carb with the motor. But there is a set screw on top of the throttle shaft that looks like it can be loosened thereby allowing you to make an adjustment which would be the same as me making the adjustment with the wooden spacer.
 
To quote you as follows...”adjust the primary pickup the lever on the carb to where it is just touching the throttle cam”... I can’t seem to do that, but I did not try everything yet. I am assuming you may mean the vertical shaft offset on top of the carb that is attached to the top part of the throttle shutter rod, which would have to hit the throttle cam that is connected to the advance system. If not then I could be lost, but lets assume I just confirmed the correct part you are alluding to. If that is it lets call that vertical shaft the primary pickup. .
The primary pickup attaches onto the top of the throttle shutter rod which protrudes above and out the top of the carb housing. How it attaches is a set screw that goes through the primary pickup . I tried loosening that set screw to enable the primary pickup a closer tolerance to the beginning of the throttle cam. I was able to get a little adjustment, but could only move the primary pickup small amount (maybe a 1/16[SUP]th[/SUP] inch. Did not want to take that screw all the way out and drop it down to the gear case etc. So my question is , is there a flat spot in that throttle shutter rod (a milled cut/groove) whereas I cannot force the issue of adjusting it there as that would make it a fixed foolproof connection. (I did not want to screw it up as I would rather take the carb off and do it on a bench. To figure it out. But don’t want to take carb off yet till I finish testing cold starts without disconnecting fuel line.
Another thing that I was looking at is maybe the gear on top of the system that comes from the tiller handle system. It is a gear on a splined verticle shaft and the center of the gear is splined (Like a Torx screw. And maybe if it is not foolproofed or doesn’t have an index mark than it may have been installed a click off at the factory. Could be a reason the former owner sold it to me after only using it ten hours. . I looked around and cannot tell if it is Fool proof or indexed.
 
don think so but will try .
Yes I have that to check further down the list, Don't look like I am going to get any play there , never know, will try. I can only see from peeking up under the fly wheel rope starter mechanism to slightly see the exact hook up that you have accessed in the above post (post 43) (Incredable, you have a picture for everything ) I have been looking and I need to see a parts diagram of the top of the throttle shutter rod to see if it is grooved, and there is the other thing where one of the gears in the hand throttle mechanism may have been installed a click off.
This mornings test. last night I was able to get a very small amount more of throttle opening (very small) by loosening the screw on the primary pick up lever, then tightening it, I have the tank on a step ladder higher than the motor. (did not use the spacer on the PPL), and just a quarter squeeze on the bulb , and 4 hard pulls and it started. Keep in mind that is with the hose constantly connected and thats when this problem would arise. so now Making progress with the tank highet (which might not actually make a difference and a little more throttle . so those are the changes that count so far and it is acting more positive.. (going to not be on this problem again till evening)

ttl
 
I found the problem. Stay tuned I will write a post shortly. ( a 30 year old problem. how embarrasing)
 
http://www.ebay.com/itm/1973-Mercury...a889cb&vxp=mtr
Can you loosen the two bolts for the throttle cam and move it to touch the throttle butterfly lever.​

That is it . when you look at the throttle cam in the picture and all the other stuff it attaches to as it works its way up to the rotating ignition advance plate, you don’t see anywhere in any of the connections that you would have a slot or an oval hole for an adjustment. I had most of throttle connections apart and they were all indexed and foolproof. Was ready to give up and looked at that throttle cam attachment. You can’t see it all that well as I don’t have the rope starter and flywheel apart .so Kimcrwbri you nailed it. I said why the heck would an engineer put two screws there, and why the extra metal on the cam around the right screw. But it does not look like there is an elongated hole there allowing adjustment.
WELL THERE IS AN ELONGATED ADJUSTING SLOT THERE AND IT AIN’T OBVIOUS AND IT AIN’T MUCH BIGGER THAN THE BOLT SIZE…. BUT BEING IT IS LOCATED CLOSE TO THE FULCRUM OF A LONG LEVER THE LEVER IT MOVES THE OTHER END OF THE CAM FINGER A LOT.
Talk about excited .. my hands were shaking so much I could hardly put all the other stuff back together.
JUST A LITTLE FIRM OF THE BULB, ENGINE WAS QUITE COLD. STARTED RIGHT UP, LOT MORE RPM,S W THROTTLE IN THE START POSITION CAUSE CAM CONTACTS THE CARB THROTTLE LEVER SOONER AND OPENS IT MORE.
Now I still may have a contributing problem as during this testing the gas tank is higher than the motor.
Will start this a few more times as is then lower tank see if everything still works etc etc. (in the event of a contributing leak down or back siphon etc.
Then I will access what type of ignition I have as I see I may have one of those 75 pound paper weights. So I will have to keep an eye open for a donor motor. So will get back to you all on some of that.
I will thank you all in next post cause I am hoping this problem/fix helps somebody else. It may sound simple but like I said I must have talked to a gazillion boat techs over the years and they never even came close to pointing in the right direction. Because this problem caused systems that would easily mislead you. Matter of fact if you get a chance as I have to go there was this other fellow in another thread Merc 9.8 who said he could only start it in reverse at a lot of throttle, Maybe if he adjusts this mystery cam he can get closer to his real problem.
Ttul
God Bless
 
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