Mercury 1500 77 model Hardly Accelerates

[old-misery-guts]

Hi, I know that this subject has been done many times on this forum and I've read them all but still would like some advice. I recently bought a 77 1500 inline 6. When I bought the boat there wasn't much info available as the previous owner had moved overseas. Anyway it wouldn't start unless you moved the throttle off the stop then it would start and idle but stall if you put the control into the neutral position. If you managed to get it into gear without stalling it went like a rocket. So I checked the manual and forums and you tube and sync and linked it. Now it will idle at about 5 degrees btc but with the butterflies slightly cracked open, but if you give it full throttle it dies. If you feed the throttle on slowly it will move but only gets up to a couple of thousand rpm and won't go any faster. I double checked the timing 21 degrees at full advance. The butterflies open fully and it idles ok (at 5 degrees btc). Reading the manual etc it seems that the idle should be controlled by the retard and says to set idle timing at 0 degrees.

So I'm a bit lost. I can't get it to idle at 0 degrees or without the butterflies open slightly. It won't rev and accelerate under load. Previous to my fiddling it wouldn't idle but did accelerate very well. Also I have the idle jets set about 1 3/4 turns out but turning them in the whole way makes no difference and turning them out more than 2 and a bit turns the engine dies.

Any Ideas? Thanks
Steve

 

[Bosunsmate]

Re: Mercury 1500 77 model Hardly Accelerates

Whats your compression like?
have you cleaned the carbs?

 

[old-misery-guts]

Re: Mercury 1500 77 model Hardly Accelerates

Compression within 8psi over all cylinders 3 is the lowest around 131. Haven't cleaned the carbs though. I figured that if it ran ok on WOT before the adjustments they would be ok. But then again I could be wrong, I often am.
Thanks

 

[Bosunsmate]

Re: Mercury 1500 77 model Hardly Accelerates

Running ok at wot means your pump and high speed jets are ok but if its not idling then your low speed jets/ channels can be blocked, they are much more little and convoluted so get blocked first normally

 

[old-misery-guts]

Re: Mercury 1500 77 model Hardly Accelerates

Thanks, I'll clean them up sometime in the next few days. It's starting to get cold here and I'd like to sort it out before winter.

 

[old-misery-guts]

Re: Mercury 1500 77 model Hardly Accelerates

Still not sure why it won't run on full throttle when it did previously. I can see how the carbs may cause the idle problem. But I have 21 deg BTC checked on the move under load and the dizzy opens the carbies full after full advance reached.