1990 75bhp 2 stroke problem

hello,

me and my friend ave just got a little a speedboat which is fitted with a mercury 75bhp 2 stroke engine, which is around 20 years old.

The engine looks like it has barely been used, very clean.

We took it out on the river last night and a problem became apparent:

we let it warm up - it will crusie all day long at 2000rpm, but as soon as you give it full throttle it will rev to 4-5k then die back dow to around 2k and wont rev any further.

Its like its using all the fuel in the carb and isnt receiving an adequate supply for the higher revs.

It was sitting around for 7 years before last night, but we put some new fuel in, and plugs and it fired straight up.

I am not very mechanically minded but it definately sounds like a fuel supply problem.

Any help appreciated.

Dave

Re: 1990 75bhp 2 stroke problem

"Classic" post: awakenig a sleeping outboard

All great infos: get a manual, do the carbs, lower unit oil, waterpump, fuel pump, fuel lines etc.

Essential.

http://forums.iboats.com/showthread.php?t=158086

Re: 1990 75bhp 2 stroke problem

thanks for the reply

anyone know where i can get a carb rebuild kit for my engine?

Re: 1990 75bhp 2 stroke problem

Easy to get, but we first need your engine serial # (located on a sticker on the bracket or on a 1" round silver "plug" on the block, beside the sparkplug holes. Something like 0D123456 or 1234567.

Re: 1990 75bhp 2 stroke problem

okay,

I'll post the number up when i get home.

Im fully aware now that there are a lot of things need looking at before we take it back out,

From the symptons described, anyone a better idea of what the actual fault may be?

Re: 1990 75bhp 2 stroke problem

Dave_yd said:

okay,

I'll post the number up when i get home.

Im fully aware now that there are a lot of things need looking at before we take it back out,

From the symptons described, anyone a better idea of what the actual fault may be?

Click to expand...

Bad fuel pump diaphragm would do that. But don't skip the carbs cleaning.

Re: 1990 75bhp 2 stroke problem - update

Re: 1990 75bhp 2 stroke problem - update

Update:

a bit gutted to say the least - was meant to be taking out properly tomorrow.

I sent the carbs off to be professionally rebuilt, ive changed the fuel pump diaphragm kit - as per an exploded daigram i had, and put a new fuel tank and line on and cleaned the spark plugs properly.

We took the boat into the river tonight and its worse than before. it will start great, tick over ok. We then went to try and move it, put it in gear, applied upto 50% throttle - absolutely nothing no acceleration at all, then moved to 75% throttle and it just dies and cuts out.

It appears its still starved of fuel, appears to be on all 3 cylinders. doesnt smell rich at all. Carbs are all opening and closing together in sequence, no blockages at all with it being a new tank and line

It will start up again easily and do the same thing over and over again^

something i thought when i came home, the fuel tank was resting on the seat in the boat as a temporary measure, which is approximately the same height as the fuel entry on the engine?

any help greatly appreciated.

Re: 1990 75bhp 2 stroke problem

Anyone help?

Re: 1990 75bhp 2 stroke problem

Look like it'snt getting enough fuel. If it were me, i'd try to hook it to a portable fuel tank with a known good hose. The result will, at least, tell you if the tank-line-primer is in cause or not.

BTW, did you ever check the compression on your engine?

Re: 1990 75bhp 2 stroke problem

I tried to eliminate the possibility of a broken/blocked tank/line by buying a brand new tank and line, so im hoping that isnt a problem.

No, i havnt checked the compression, probably a good idea to check it.