my Yamaha 70 is stuck at 3000 rpm underload ! idels ok!

[vcreation]

i got a 95 yama 70 HP, is 2 stroke, never had any problems.

today take it out and at high speed all of a sudden engine slowed down, i open the cover saw one spark plug coil felt off, they are lose, i plug it back it and engine won't go more than 3000 rpm, i stop at a beach and had passenger jump off, and i go by myself to test, it slowly get back to 4000 and 5000 and all of a sudden goes back to normal.

i try to drive it again, it drives normal, very powerful but after few minutes it stuck on 3000 rpm again, untill now.

@ neutral gear i can reve it to 5000-6000 no problem, but when under load, it stuck at exactly 3000-3100. there is no strange noise or chocking of any kind, engine completely normal and revs up to 3000 as normal. just won't go over 3000. got oil and fuel everything. donno what's wrong!

[99yam40]

Coils are not suppose to be loose and falling off.
Tighten up properly.
check to see if you are losing spark to a cylinder, a timing light should show if that is happening at the problem RPM.
If no problem with spark then check fuel pump to see if it is leaking and causing one cylinder to run too rich

[jb123]

Operate your Carb linkage by hand, sounds like a prob with linkage/butterflies

[vcreation]

UPdate, when engine is out of water (on house) and is in gear, it can rev easily over 3k.
today i changed in some fresh fuel, did a compression test found bottom cyclinder to be about 10 PSi below the top 2 @145psi. mechanic reckons not bad enough to cause lost of power.... took it out again and it did 4000-4500.

so it is pretty sure it only does it underload, 4 person = 3000rpm, 1 person = 4500..... before the problem it reves about 5700-5800. easily

[jb123]

Misunderstood your post, sounds like dirty carbs, fuel supply, non firing plug...

[sasko1980]

Hi ,

After a month, out of water, my Yam 70 2 stroke 1995 also started to act like this.
It gets around 3000 RPM and won't go above.
I tried to change sparks (new ones), but all the same.
New tank, new primer bulb, new hoses, fresh fuel.
I'm thinking on cleaning the carbs jets, and see if it works.

Is there a something that needs to extra careful not to mess around when cleaning the carbs ???

[ausnoelm]

UPdate, when engine is out of water (on house) and is in gear, it can rev easily over 3k.
today i changed in some fresh fuel, did a compression test found bottom cyclinder to be about 10 PSi below the top 2 @145psi. mechanic reckons not bad enough to cause lost of power.... took it out again and it did 4000-4500.

so it is pretty sure it only does it underload, 4 person = 3000rpm, 1 person = 4500..... before the problem it reves about 5700-5800. easily

Revving in neutral is no test, completely useless, as mentioned, have you tightened the coils?

[cpostis]

When you said "spark plug coil felt off", did you mean the actual coil, or the spark plug boot fell off. If boots, are they all still loose? Make sure all have good tight connections. What is the condition of the spark plug leads themselves? Have you checked/replaced the fuel pump?

Let us know how you do.

Good luck, Chuck

[TownsendsFJR1300]

Hi ,

After a month, out of water, my Yam 70 2 stroke 1995 also started to act like this.
It gets around 3000 RPM and won't go above.
I tried to change sparks (new ones), but all the same.
New tank, new primer bulb, new hoses, fresh fuel.
I'm thinking on cleaning the carbs jets, and see if it works.

Is there a something that needs to extra careful not to mess around when cleaning the carbs ???

**Guys, the coil falling off was from another Op FOUR years ago...

This op ^^, the engine just won't rev.

Sasko, it's best to start a new thread to prevent this confusion.

In any case, agreed, the carbs are likely plugged up with varnish. Clean and make sure you pull all the jets and can literally see light thru them...

[ausnoelm]

Jesus, you have to check everything, I usually have a quick look at dates, but this one slipped through....agreed, start a new thread rather than dredge up a years old one because it was the same motor or something.

[TownsendsFJR1300]

I blame 99yam, he shoulda caught this first!!!