2 stroke 70 Yamaha dramas

Hi have to say this site really seems invaluable. I hate to go over ground thats already been covered but bear with me. I've got a 70 hp Yamaha 2-stroke about a 93 model i think. Engine starts fine and runs perfectly, problem is when i back off the throttle then go to accelerate again the engine will only run at an idle speed while in gear. In neutral the engine can be revved as normal but with the load of the boat on it, it wont respond. If i let the engine cool for a half hour or so it returns to normal operation until i back off the throttle again. I've installed new water/fuel seperator, fuel lines and plugs but problem persists. There is one segment of line i didnt replace and probably should, but i cant understand why it would run perfectly until i return it to idle. i should point out too that when it does play up and run at minimum revs any further attempt at acceleration will cut the engine, yet it will start again no worries. It may just be coincidence but the problem started when i had to slow down for a 3ft wake of a yuppy vessel. Ironically it was a big Riviera and i quit working for them the previous week..thats karma i guess. Any thoughts appreciated thanks

Simon

Re: 2 stroke 70 Yamaha dramas

when was the last time you changed the fuel pump?

Re: 2 stroke 70 Yamaha dramas

I've never replaced the fuel pump do u think that may be the problem? I just dont know why it will run perfectly and then play up. A fuel pump is a good call, if it was my car thats probably the first thing i'd look at.

Re: 2 stroke 70 Yamaha dramas

Long shot here but takes no effort to try. Leave the gas cap loose. If you have one of the newer sealed tanks like I do, the venting is done thru the cap. FRED

Re: 2 stroke 70 Yamaha dramas

A model number would help.

Next time it happens, try pumping the bulb. If it accelerates without dieing, fuel pump problem.

I had similar symptoms to what you are describing, Two of my coils would crap out when warm. In the genuine manual there are very easy test procedures for coils (and everything else). i would suggest performing those test procedures both cold and hot (a hair dryer is perfect for warming up electronics).

Re: 2 stroke 70 Yamaha dramas

Thanks for your help guys, i'll put it through its paces and try and isolate the problem, the engine is a 70BETO. A few other thoughts are really good to realise how many things a motor relies on to function properly. Sometimes its hard to differentiate between electrical and fuel problems. I've got a Valiant Charger, an Aussie Chrysler and been having engine problems....after replacing heaps of bits to do with fuel and electrics i finally isolated the problem (with the help of a few friends)...the oil pump, unfortunately that means pulling out the old hemi. i wish i'd been a mechanic..

Re: 2 stroke 70 Yamaha dramas

Where are you located (in aus)?

Re: 2 stroke 70 Yamaha dramas

I'm on the Gold Coast mate, got a nice spot, boat ramp's only a stones throw away

Re: 2 stroke 70 Yamaha dramas

Bottom right hand corner of your id plate is a solitary letter, that letter is the year code, what is that letter?

Do you have an analogue tach with the 3 oil warning lights?

Re: 2 stroke 70 Yamaha dramas

I have the letter "A". i think its about a 93 model. When i bought it i thought it was a later model it's in pretty good nic, been well looked after. I've had it a couple of years now and until this current problem its been excellent. I've got the analogue tacho with the three lights i havent used it for a few weeks but i'm pretty sure those lights were not lighting up while i've had troubles. They did work until recently. I put it down to a loose wire or something but kept an eye on the oil level, perhaps i should have put 2 and 2 together. Thanks for your interest too mate

Re: 2 stroke 70 Yamaha dramas

Thanks guys for your assistance, i pulled the 3 carbies off, dismantled them and gave them a thorough clean and blow out. Gaskets were good and reusable. I found quite a bit of gunk and crusty bits particularly in the lower carb. I drained the oil and the fuel, cleaned the fuel pump and somehow managed to put everything back together without any dramas. Took it for a test drive tonight and what do u know....she runs absolutely perfect. Sounds nice and throaty, just runs like a dream..better than ever. Just goes to show even if u only have half a clue what youre doing..there's only one way to learn and thats pull out the tools and have a go...might even save u a few hundred bucks. Cheers

Re: 2 stroke 70 Yamaha dramas

Dunaruna said:

Bottom right hand corner of your id plate is a solitary letter, that letter is the year code, what is that letter?

Do you have an analogue tach with the 3 oil warning lights?

Click to expand...

Dunaruna-

I just bought a Yamaha 70hp outboard, early to mid '90's model, but I do not know the actual year. Am I able to tell with the solitary letter / year code? Where can I find the codes to determine the year. I do not have the motor at the moment to read the ID plate and the letter.

Mahalo!

Re: 2 stroke 70 Yamaha dramas

The question now is where did the gunk come from? Have you emptied your tank and cleaned it? Also your fuel pump may have some in it as well which may end up in the carbie.

Re: 2 stroke 70 Yamaha dramas

Ian, this is the letter in question (bottom right hand corner).



Capt. Cooper, you have a PM.

Dunaruna said:

Re: 2 stroke 70 Yamaha dramas

A model number would help.

Next time it happens, try pumping the bulb. If it accelerates without dieing, fuel pump problem.

I had similar symptoms to what you are describing, Two of my coils would crap out when warm. In the genuine manual there are very easy test procedures for coils (and everything else). i would suggest performing those test procedures both cold and hot (a hair dryer is perfect for warming up electronics).

Click to expand...

Dunaruna, I would like to thank you for the hair dryer tip. I have been working on a yammy 2-stroke that I can't get to run long enough to get everything hot. I have suspected bad coils but runs great at idle and I am using water hose so it always has nice cool water to keep it from getting cold. I will try the hair dryer and test the coils hot and cold to see if there is any difference in readings.