Whats wrong with my engine?

davis · 11 December 2010, 19:41

Hi I am having a problem with a 4hp four stroke Yamaha , I had a job starting it up and it only goes with the choke out and runs very rough , when I push the choke in it cuts out , I took the carb off and blew it out with air and took the plug out and cleaned it. What else could be wrong, the fuel is getting to the carb. Can anyone give me any advice as to what it could be, thanks.

BogMonster · 11 December 2010, 20:33

It sounds like fuel contamination see my thread here similar problem though different engine: http://www.rib.net/forum/showthread.php?t=39133

Did you take the main and idle jets out and blow those through with an airline properly? If not, that's probably where to start.

outboardtech · 12 December 2010, 12:32

Hi , YES this sounds like a fuel issue . we do have issues on these all the time and 99.9999% of the time its fuel related.Igntion system on these are pretty good . YOU need to take that carb off again and carefully remove all the jets inside etc . I do a Carb , injector CLEANING SERVICE for outboard engines and charge £25.00 for small engine per / carb . I run this thru a ULTROSONIC Cleaning machine and set it all up after cleaning . You may aswell remove the fuel pump on this aswell and check the pump in working correctly with a vacuum pump , make sure the diaphrams inside are all ok .WHat is you MIXTURE SCREW SETTING ????

davis · 12 December 2010, 16:04

thanks for the replies , sorry dont know about screw setting. I had a problem before and carefully removed the carb as I had never done it before, blew it out with air ,reassembled and to my delight it went grand, now having it again so was wondering was it something else as it wasnt run much since I took it apart.
Is the fuel pump difficult , as I would like to learn but not f up the engine and have to bring it to someone to reassemble

BogMonster · 12 December 2010, 19:37

Personally I think you just missed some poo in the carb, how many jets did you take out? You need to take them right out and give each nozzle on each jet a toot with 100psi+ of compressed air to make sure they are all clear. Worked on mine anyway. Did you take the float chamber off and clean that out too?

T 15 · 12 December 2010, 19:38

Quote:

Originally Posted by davis

thanks for the replies , sorry dont know about screw setting. I had a problem before and carefully removed the carb as I had never done it before, blew it out with air ,reassembled and to my delight it went grand, now having it again so was wondering was it something else as it wasnt run much since I took it apart.
Is the fuel pump difficult , as I would like to learn but not f up the engine and have to bring it to someone to reassemble

where in Ireland are you ?

MOS · 18 December 2010, 16:09

Hi,

I know for a fact that the F4AMH Yamaha has 'Jet' issues... Yamaha replaced the jets & sometimes whole carburetor under warranty if the problem persists... If you can, contact a Yamaha dealer and see if they will help you with possibly a new carb...

www.mobileoutboardservices.com

davis · 18 December 2010, 19:46

I am in the south east, thanks for the advice MOS , stripped the carb again today cleaned and blew it out , changed the oil , put back together and it started and ran for a while then I turned it off. Tried to start again and no go so maybe what you are saying may be the problem , but the engine is not in warranty anymore so probably no hope of a new carb from them. I was going to try the fuel line and pump next to see if there is any dirt in there ,other than that I dont know , but the fact that it started and run it must be a fuel problem.
These engines are not easy to get at everything seems to be packed in around each other.

Chris · 18 December 2010, 22:09

I had this problem,

Make sure the tank does not have crud in as you can keep cleaning out the carb and the carb will keep getting crud in from the tank.

BogMonster · 18 December 2010, 22:15

When I did mine I took the tank right off, drained it out, and sloshed a bit of clean fuel around in it then drained that off, did it 3 or 4 times just to make sure. Nothing in the tank of the Merc, but when I had fuel problems with the old Johnson aux it was crap in the tank. Small engines tend to have the fuel pickup right more or less at the very lowest point rather than having any sort of sump, which is great until you get some crud in the tank then it is the first thing that exits via the pipe...

MOS · 19 December 2010, 13:07

Quote:

Originally Posted by davis

I am in the south east, thanks for the advice MOS , stripped the carb again today cleaned and blew it out , changed the oil , put back together and it started and ran for a while then I turned it off. Tried to start again and no go so maybe what you are saying may be the problem , but the engine is not in warranty anymore so probably no hope of a new carb from them. I was going to try the fuel line and pump next to see if there is any dirt in there ,other than that I dont know , but the fact that it started and run it must be a fuel problem.
These engines are not easy to get at everything seems to be packed in around each other.

OK, It does sound like the issue is the carburetor. The dealer you should have bought it from should help as it is a known Yamaha fault... Even out of warranty. We used to just change the complete carb for a new one and it did solve running issues. I have also known people to drill the main jet out slightly which improves the engines performance as it allows for fuel to mix with the air.

Also, try this:

Try putting a brand new BR6HS NGK plug in.

Remove carb again, completly strip it down including top heat shield with white plastic dowel. Allow the carb to be submerged in fresh petrol for a good 24 hours. Then blow out with a 100PSI + Air line...

Thirdly, reset the pilot screw... Some F4 carbs allow you to change the pilot screw but others (newer models) had blanking plates so you couldn't. If yours is not blanked off then you will need to create a special tool (half mooned screw driver) to screw the pilot out 1.5/8 turns +/- 1/4 ...

Hope this helps

www.mobileoutboardservices.com

outboardtech · 19 December 2010, 21:17

Send me your serial number and I will log onto dealer system and see what I can do for you if you wish.I will even have a few carbs lying around. a ULTROSONIC CLEAN WILL SORT THAT CARB OUT.I run the machine every week in the test room and it does do the job

BogMonster · 20 December 2010, 01:38

I'm curious, what goes so drastically wrong that it makes fitting a new carb a regular fix?

I looked at a Yamaha for my aux, quite glad I didn't go for that option now!

ADI · 20 December 2010, 20:31

Fitting a new carb seems a bit extreme, A proper strip down and an ultrasonic clean should do the trick.

davis · 20 December 2010, 20:37

how is an ultrasonic clean done ,is there a special machine, if so I will need to bring it to a professional

ADI · 20 December 2010, 20:47

Its an ultrasonic bath the carb goes in, just like the jewler uses to clean jewellery, find a dealer who has one and post the carb to them or pop in if there is one close.

MOS · 20 December 2010, 22:06

Quote:

Originally Posted by BogMonster

I'm curious, what goes so drastically wrong that it makes fitting a new carb a regular fix?

I looked at a Yamaha for my aux, quite glad I didn't go for that option now!

It's because the small yamaha engines are made in MBK (France) and are not made as well and as close to the Japanese tolerances... If you put the Jap version against the French one you would be surprised on how much better the Jap one is!

The F6 is a smashing engine though...! And the two-stroke Yamahas are bullet proof... Just the F4 that's a little dodge!

You can try cleaning it again or allow it to soak for a lengthy period in a fuel / ultrasound bath... But, If it persists then easier to replace carb for reliability purposes. My customers like reliability

www.mobileoutboardservices.com

MOS · 20 December 2010, 22:07

Quote:

Originally Posted by BogMonster

I'm curious, what goes so drastically wrong that it makes fitting a new carb a regular fix?

I looked at a Yamaha for my aux, quite glad I didn't go for that option now!

It's because the small yamaha engines are made in MBK (France) and are not made as well and as close to the Japanese tolerances... If you put the Jap version against the French one you would be surprised on how much better the Jap one is!

The F6 is a smashing engine though...! And the two-stroke Yamahas are bullet proof... Just the F4 that's a little dodge!

You can try cleaning it again or allow it to soak for a lengthy period in a fuel / ultrasound bath... But, If it persists then easier to replace carb for reliability purposes. My customers like reliability

www.mobileoutboardservices.com

MOS · 20 December 2010, 22:09

I don't know why it has Posted twice... I do apologize!

outboardtech · 22 December 2010, 06:32

I would be more than happy to ULTROSONICALLY CLEAN that little PUPPY for you and set it up. I have all the special gear to do this aswell as a INJECTOR CLEANING SERVICE for Optimax Mercury ,Yamaha and the other brands.A ultrosonic clean should sort it.If you put it in the post to me I will do it FREE for you.Im away after christams and then off to London Show so I might only beable to do it after that.