70HP Johnson build date December 1999 Warm start problem

[Andos2009]

Hi everyone, I have a 1999 Johnson 70hp which will start beautifuly, idle and drive to my destination. On a warm start is where the problem is. I will turn the ignition and the motor will idle, then if I throttle into gear I will loose revs and the motor will die like it is being starved of petrol unless I get over 1500rpm. The VRO has been disconnected and I have changed the fuel lead. I have also checked the fuel pump and all ok. If I start the motor and then go into gear and pump the fuel bulb the motor will run perfect. Is this a problem with the power pack? The motor will only die when it is warm and this will not happen on the muffs. In all other respects the motor is perfect.

Any advice would be appreciated.

Thanks

Andy

 

[iang]

Re: 70HP Johnson build date December 1999 Warm start problem

There are two things you can check,one is make sure your float levels are correct and you have enough fuel pressure from the pump,should be around 4psi at idle.The other thing is to check your reed valves are within spec,the fact that you say it will run fine on muffs but not in the water is a typicle symptom of weak read valves.What happens is that when the leg is submerged it puts back pressure on the exhaust and therefore a weaker flow of gasses through the system.Check your fuel supply first and if that all checks out you will most probably be in for a set of reeds.

 

[tashasdaddy]

Re: 70HP Johnson build date December 1999 Warm start problem

what are your idle rpms, with the motor warm and in gear?

 

[James R]

Re: 70HP Johnson build date December 1999 Warm start problem

The following are suspect and it may be a combination.
Fuel pump,float levels, idle mixture set a little lean or the wrong plugs.

 

[Andos2009]

Re: 70HP Johnson build date December 1999 Warm start problem

Thanks, idle is around 900rpm cold in idle, 850rpm warm in idle and 800rpm in gear, I am thinking about including an electric pump in the line to increase fuel pressure. Would that be suitable? It might be a silly question but how can I check the fuel pump is at 4psi, is there a tool for this? Thanks

 

[Silvertip]

Re: 70HP Johnson build date December 1999 Warm start problem

DO NOT install an electric fuel pump in line unless you wish to go kaboom. Electric fuel pumps on EFI engines are controlled by the ECU which knows when the engine is not running (as in a stall condition). You engine has no such capability. In the event of a fuel leak, you pump fuel on yourself, the boat and the engine. Yes, the pump will quit when you turn the key off, but in an emergency you will not remember to do that. You also run the risk of pumping the engine full of fuel in the event of even a slight needle and seat issue. There is nothing wrong with the standard system where fuel is "sucked" through the line. There is absolutely no reason to pressurize that line with a pump that can't be shut off except with the key. This topic has been discussed in detail on this forum so do a search for the many reasons why this is not necessary or safe.