Loss of power on a Chrysler 55 HP

[Aussie Ed]

Hi there everybody. My oldie 1979 Chrysler 55 has lost it's Mojo. Always starts okey, but since leaded petrol here in Australia was replaced for "leaded replacement petrol" with chemicals instead of lead, the spark plugs form carbon after 10 minutes running. I am using unleaded petrol now after changing it all and cleaning the tank and instaled NGKs BUHX. When I bought this engine 5 years ago in had normal electrode spark plugs but then I was told that this engine had to have the BUHX. The thing is that the engine has lost it's power, I can't get the boat to plane as it use to. Black box is new, both coils are new, wiring has been replaced to secure good and firm conecctions and spark plugs are new as well. Petrol/oil ratio is 1:50, spot on!.<br />Since the engine is old, should I use normal electrode spark plugs, what type? What would happen if I use Premium unleaded petrol, would I burn out the pistons? Thanks for all the advise yous can offer. Oih Oih Oih!!!! Cheers<br />Aussie Ed

 

[suzukidave]

Re: Loss of power on a Chrysler 55 HP

It might be the plugs but I doubt it's the fuel unless you guys have lowered the octane down under (or if it is the fuel, it's probably too late to reverse it without a rebuild). <br /><br />Easy enough to check if it's the plugs by buying a set of the old style plugs and popping them in for a trial run. A $10 diagnosis and if that's the answer to your power woes then start calling wrenches to find out what's the downside to carrying on with them. If that's not it, it is an old motor so maybe the powerhead is just worn out. What's your compression like? What's the variation between cylinders? Are you getting the same RPM you used to on the same boat with the same prop? Maybe the boat's heavier -- your foam could be wet or maybe the skipper had too many raw prawns and tins of foster this summer? <br /><br />Good luck

 

[Terry H]

Re: Loss of power on a Chrysler 55 HP

Aussie Ed...I would first check compression, it should be in the 140-150psi range on both cyls...check the spark...you may just need to change or reset points. Hi-speed jets may be a little dodgy. Those plugs should be fine, be careful with standard electrode plugs with those high domed pistons a little carbon and they can contact the plugs...when you get it running right you might think about decarbing...anyroad, just a few Thoughts

 

[oldboat1]

Re: Loss of power on a Chrysler 55 HP

Ed,<br /><br />I ran a 55hp Chrysler ('72 model) for about 5 years on unleaded premium, and had good performance. Other listers may want to contribute on this, but it's my understanding that the leaded vs. unleaded issue is essentially moot for two-cycle engines, since lubrication is provided by the oil that is added to the gas.<br /><br /> Curt

 

[sony2001]

Re: Loss of power on a Chrysler 55 HP

My 88 Force 125 had those NKG plugs but the mechanic moved me over to the Champs with conventional electrode. I use high octane unleaded<br />to replace regular leaded since the recommended timing is 32degrees BTDC. If that doesn't work and you are SURE you don't have a dead cylinder,Mercury recommended when switching to unleaded fuel to reduce prop size until you get WOT.

 

[Aussie Ed]

Re: Loss of power on a Chrysler 55 HP

Thanks everybody! or should I say: thanks mates Oih oih oih!!!, I'm on my way to a friend to borrow his compression gauge and I will test the compression, I reckon it should be alright because the head gasket was changed and the cylinder head was shaved recently.... but who knows, salty water can do damage fast sometimes. Sony 2001 please explain WOT remember I'm Aussie. If compression is okey, I'll try Premium Unleaded since it seems it won't do damage to the pistons. Thought 101, thanks for pointing out the high doom pistons it could be a problem. This engine has no points but I would like to know what the recommended timing is: degrees of BTDC. I've got ostroboscopic lamp for timing but I wan't to know if by using it I could burn out the black box. Ah Hahaha!! sponges are dry, no raw prawns on board..... and geee... we forgot the Foster's on the pier!!. <br />Thanks again

 

[DaleT]

Re: Loss of power on a Chrysler 55 HP

WOT=Wide open throttle<br />Took me sometime to figure that one out too.

 

[Aussie Ed]

Re: Loss of power on a Chrysler 55 HP

I've done my home work. Compression is okey on both cylinders 140 and 150+. I need the advance timing please, how many degrees BTDC?<br />I have it fully advanced where it seems to develop the most power but still not enough. Carbys both open fully as well.<br />Cheers