1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP!!

[fallautumn2]

Hi guys,
I have a 1985 Mercury 45hp (Classic 50). This has been a fantastic motor, yet has now developed a crippling problem. When you push the throttle down to try and get full speed you only seem to get about maybe 1/2 throttle (ie 1/2 speed). If you leave the throttle on full it will, after maybe 10 minutes or more, suddenly surge forward to its correct full speed.

Strangly, when you do a fresh water flush of the engine it seems to accelerate normally. I have no idea what is causing this very long accelaration lag.

This is now a consistent problem. I would greatly any suggestions that you may have re this problem.

Thanks for your help in advance.

PS: I have changed all 4 spark plugs and have installed a new fuel filter. The tank has fresh high octane fuel.

Kevin.

 

[jerryjerry05]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

Start with a compression/spark test.
Then the fuel system:check for water.Then the fuel pump:rebuild/replace.The hoses:check for soft/mushy lines.Replace with new.The tank vent make sure it's not clogged.
Clean the carbs.J

 

[CharlieB]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

Carbs, idle circuit is dirty, order complete carb kits, total tear down and thorough cleaning will restore the performance.

Pay very careful attention to the idle mixture screws, turn them in to 'very lightly seated' while counting so that on reassembly you can set them to the SAME position. Write them down. It will save you a lot of time on adjustment once back on the water.

 

[fallautumn2]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

Hi Jerry & Charlie,
I will do a compression test on the weekend, the fuel pump and teh carbs have already been rebuilt and, sorry I should have mentioned that before.

I have noticed that when there is fuel coming into the fuel filter there are some bubles in the filter - is this normal, or does it indicate an air leak, if it is an air leak where should I be looking for that ??

Thanks again for your assistance in advance, I really apprecaite it.

kind regards,

Kevin

 

[CharlieB]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

If you suspect air sucking into the fuel system, substitute a clear section of hose just before the carbs, start the motor and watch for any air bubbles passing thru. Just remember to remove the clear hose afterwards, it is not rated and possibly unsafe to remain in use other than for testing.

Idle mixture is critical to acceleration. Idle must be adjusted richer than 'Best idle' to provide the additional fuel for crisp acceleration. If the carbs have recently been cleaned and adjusted it may still need to be adjusted correctly to 'Best idle' while IN Forward gear and IN the water as exhaust back-pressure on the hose is non-existant and increases greatly once launched.

After adjusting to 'Best idle' the mixture must be further enriched almost 1/8 turn out, make very small adjustments to each carb, only the width of the screwdriver blade slot, test acceleration, any bog, hesitation indicates a need for yet more idle fuel. Repeat adjustment until perfection.

 

[fallautumn2]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

Hi Charlie B,

I'll check with a clear PVC hose as suggested this weekend, I'll also try to achieve best idle per your instructions as well.

PS I'm emailing from Sydney Australia - thus my seemingly very early morning responses.

Again thanks for your online help, its great to see people who have never even met each other coming together like this.

Kind regards,

Kevin.

 

[fallautumn2]

Re: 1985 Mercury 45hp (Classic 50) very long accelaration lag to full throttle - HELP

Hi guys,
the problem is now solved. Unbelievably, it turned out to be a faulty (cracked) fuel tank to motor connector - this was allowing air to be sucked into the motor, thus running lean and not allowing full throttle.

Thanks to everyone for your suggestions and help. Kind regards.