Mercruiser 3.0 'Deadband'

[sevans0579]

Hi,

I am new to these forums and i thought this would be a great area to gain some knowledge from varied experts out there. I have a sea ray 175 speed boat (1995), with the mercruiser 3.0 litre alpha engine.

I have a problem. I recently serviced the engine and after having to replace the starter motor (worn nylon brush) and all the filters (fuel filter pain in the arse securing arrangements) i am having a few problems with the timing. I have adjusted the idle mixture srew as per the manual and it ticks over sweet at around 900 rpm. So at idle the engine sits nicely.

However when i put it into gear (out of the water with flooding ears) i have a 'deadband' in the throttle where it goes from idle straight up to at least 1600 rpm. The throttle arm does nothing until it suddenly shoots up to that speed as if it is missing out a range of 400 - 500 rpm. Therefore when i want to go from around 2000 rpm back to idle it cuts out (then starts up first time). Also when i set the throttle it begins to creep up on its own about 100 rpm??

I have put new plugs in and the throttle cable has been changed. This leads me to think it is the carb, the filter in the carb is clean but maybe i need to overhaul the carb?

Am i heading in the right direction?

Any ideas would be greatly appreciated.

Kind regards
Scott

 

[fishrdan]

Re: Mercruiser 3.0 'Deadband'

Sounds like you need to rebuild the carb, paying special attention to cleaning it very well.

 

[sevans0579]

Re: Mercruiser 3.0 'Deadband'

Sounds like you need to rebuild the carb, paying special attention to cleaning it very well.

Thanks, might have to get the rebuild kit and overhaul it, just wanted to make sure that was were i needed to focus my attention on

 

[Oshkosh1]

Re: Mercruiser 3.0 'Deadband'

Yep...
Have had similar problems with snowmobile carbs in the past...pulled them, tanked them, made sure EVERY little passage, orifice, and jet was pristine, then put them back together with new gaskets. Problem solved.

 

[sevans0579]

Re: Mercruiser 3.0 'Deadband'

Hi, many thanks for the help. I have stripped and rebuilt the carb with new parts and it sounds great, the only slight issue at the moment is a bit of creep in the throttle. When i set the throttle the engine gradually continues to power up sometimes a further 200 rpm. Not sure whats causing this delay. so far nearly all the perishable components have been changed??

Any ideas would be greatly appreciated?

 

[Oshkosh1]

Re: Mercruiser 3.0 'Deadband'

Make sure you have a good seal on the manifold. Spray some carb cleaner or starting fluid around to check for any vacuum leaks. Oh...and when you do the final adjustments, ensure the flame arrestor is tightened also.