Mecury 4hp 4 stroke 2009

[richgrayson]

I hope someone can help. I have the above engine and it will just not start. I have replaced fuel filter, cleaned and dried fuel tank and lines, new fuel, new spark plug, new fuel pump, cleaned carb and all jets, compression is around 150psi. I have turned fuel air screw in and tried numerous times to start every 1/4 turn until 3 full turns out. Checked its not in gear. There is fuel in the carb bowl. I have tried internal and external tanks. Made sure cut off is fully out. The spark plug has a spark. The engine will start if I spray carb cleaner in air intake but cuts out as soon as that's burnt off. Any advice would be much appreciated. I do have a spare carb and its exactly the same.Thanks in advance.

 

[airshot]

Test spark gap with a gage, UT needs to jump a 1/4" gap at least. Sounds like a fuel delivery problem. There are a number of very tiny little passages going thru a carb and a tiny little spec of dirt can cause issues. When a carb is cleaned, A factory rebuild kit should be used so new gaskets are used, the entire carb needs taken apart and soaked in cleaner over nite with a vibrated if possible. Then all passages must be cleaned with wires and compressed air. If you don't already have an inline fuel filter, add one !! My OB has three filters before fuel reaches the carbs.

 

[QBhoy]

Hi...with a fair degree of certainty, I would suggest that it's the carb needing cleaned...or at least something related to it. I had a similar aged 3.5hp engine ages ago...it was a nightmare for needing the carb cleaned often. The gasket for the carb was also a weak point too. But more than everything else...these things were infamous for having their oil find its way up and into the carb, after being sat on their side in storage or transport in the car. Just to be clear, this happens even if played on the correct and recommended side. well known to do this. I might also suggest that the oil level can have an influence on this too. If the sight glass is showing anything close to or above the high level, then it's an issue for sure. Good to know that the oil can work its way to a high or over high level, by means of fuel dilution too.
Simply put, they are just very sensitive to the above. I can almost bet you that if you clean the carb properly, new plug, make sure oil level is about 3/4 level and set the mixture to 1 and 1/2 turns out...she will fire up just fine.
keen to hear how you get on.

 

[richgrayson]

Hi...with a fair degree of certainty, I would suggest that it's the carb needing cleaned...or at least something related to it. I had a similar aged 3.5hp engine ages ago...it was a nightmare for needing the carb cleaned often. The gasket for the carb was also a weak point too. But more than everything else...these things were infamous for having their oil find its way up and into the carb, after being sat on their side in storage or transport in the car. Just to be clear, this happens even if played on the correct and recommended side. well known to do this. I might also suggest that the oil level can have an influence on this too. If the sight glass is showing anything close to or above the high level, then it's an issue for sure. Good to know that the oil can work its way to a high or over high level, by means of fuel dilution too.
Simply put, they are just very sensitive to the above. I can almost bet you that if you clean the carb properly, new plug, make sure oil level is about 3/4 level and set the mixture to 1 and 1/2 turns out...she will fire up just fine.
keen to hear how you get on.

I will get a new carb and spark plug. Thank for your help, I just hope I can get it going. Cheers

 

[airshot]

Just buying a new carb may not be the answer, it still needs setup for your motor !! Carbs are designed to fit on a number of different engines so each one needs adjusted for your particular motor. Get a factory rebuild kit for your carb based on serial number. All the necessary adjustment info will be in the kit along with new gaskets and diaphrams if needed. You will get float settings and idle adjustment settings as well. Gotta be sure all the teeny tiny holes are clear and open.

 

[QBhoy]

I will get a new carb and spark plug. Thank for your help, I just hope I can get it going. Cheers

Easy as anything to remove and clean. God knows, you’ll soon be an expert at it, should you keep her for long. I ended up getting a little fed up with that 3.5 of mine. Any time I took it off the auxiliary (kicker you guys call it) bracket, back home and between use..then take back to the boat next time. If I ever needed to use it on the dinghy or bracket. It would hardly start, take ages to or not at all. Soon went back to my old trusty Yamaha 2 stroke. You simply can bet your life and know that it will just fire up after the second pull…whether it hadn’t been ran for a week…or a few years even. Sure…the Yamaha Malta 3hp might use more fuel that the 3.5hp mercury 4 stroke…but at that kind of size and use…it’s almost not even worth a thought. To be fair…the wee 3.5hp did well as an auxiliary and pushed my 19ft cuddy to about 4mph flat out…and a comfortable 3-3.5mph at 2/3 throttle. But so did the 3hp Yamaha Malta and with less worry over mechanical sympathy too. The hood removed from both of them side by side..revealed a very different and gulf in build quality and materials for sure. Don’t make em like they used to I suppose.

 

[richgrayson]

Update, i have bought a new carb and spark plug and still nothing, i have checked compression and kill switcg. I hope someone can help. I have the above engine and it will just not start. I have replaced fuel filter, cleaned and dried fuel tank and lines, new fuel, new spark plug, new fuel pump, cleaned carb and all jets, compression is around 150psi. I have turned fuel air screw in and tried numerous times to start every 1/4 turn until 3 full turns out. Checked its not in gear. There is fuel in the carb bowl. I have tried internal and external tanks. Made sure cut off is fully out. The spark plug has a spark. The engine will start if I spray carb cleaner in air intake but cuts out as soon as that's burnt off. Any advice would be much appreciated. I do have a spare carb and its exactly the same.Thanks in advance.

 

[QBhoy]

Hi. Is there a gasket both sides of the carb ? One at air box and one going onto the face that carb seals to on engine side ?
Other than that…have her one and a half turns out on the mixture screw.
Open the throttle all the way. Choke on for a couple of pulls. Then choke off with full throttle.
Despite your carb clean…I’d also never rule out having to do it again. Happened to me with the 3.5 I had. Same carb set up. Ended up having to strip every single part of it down and put it all in an ultra sonic bath. That did the trick after that. And also after finding the gasket or one of them wasn’t good.

 

[richgrayson]

Hi. Is there a gasket both sides of the carb ? One at air box and one going onto the face that carb seals to on engine side ?
Other than that…have her one and a half turns out on the mixture screw.
Open the throttle all the way. Choke on for a couple of pulls. Then choke off with full throttle.
Despite your carb clean…I’d also never rule out having to do it again. Happened to me with the 3.5 I had. Same carb set up. Ended up having to strip every single part of it down and put it all in an ultra sonic bath. That did the trick after that. And also after finding the ga

sket or one of them wasn’t good.

There are 3 gaskets on one side a plastic 1 sandwiched between 2 fibre ones. There isn't one on air intake side, never was from new. Should there be one ? Probably stupid question but what would a gasket do on that side as the only thing that could get in is air and its all open to the air anyway?

 

[QBhoy]

There are 3 gaskets on one side a plastic 1 sandwiched between 2 fibre ones. There isn't one on air intake side, never was from new. Should there be one ? Probably stupid question but what would a gasket do on that side as the only thing that could get in is air and its all open to the air anyway?

Apologies. What you have described is the way it is. Sorry. Yeah. No need for a gasket on air box side. But should be 3 somewhere further up. Remember that much. Think I maybe also mentioned earlier or in a similar post about the oil that can get taken up into the carb. Even if it’s laying on its correct side in storage or transport. Very temperamental to the oil level being right too. If it’s actually at or above the high mark on the glass. It will certainly take oil back to the carb. Needs to be a level clearly seen in the glass. With also some air visible at the top of the glass. Hope that helps.

 

[QBhoy]

I’d also check the fuel line exit from the tank and the shut off valve. There is a strainer in there somewhere if I remember right. Sure there is. But I’ve had that many of these things in bits, I could be describing another engine. But worth a check for sure. Empty the tank and carb completely if the fuel is in any doubt whatsoever too. Make sure it’s very very fresh.

 

[richgrayson]

Apologies. What you have described is the way it is. Sorry. Yeah. No need for a gasket on air box side. But should be 3 somewhere further up. Remember that much. Think I maybe also mentioned earlier or in a similar post about the oil that can get taken up into the carb. Even if it’s laying on its correct side in storage or transport. Very temperamental to the oil level being right too. If it’s actually at or above the high mark on the glass. It will certainly take oil back to the carb. Needs to be a level clearly seen in the glass. With also some air visible at the top of the glass. Hope that helps.

Thanks I will check the oil again to make sure.