1974 merc 850 doesnt want to accelerate past half way

[Awc9372]

Hi, a buddy and I have a 74' merc 850 serial# 3869102 that we've been working on for the last few weeks. We rebuilt the carbs, fuel pump, water pump, and replaced all the full lines. New plugs too. Anyways, got it running and it ran great with the hose hooked up to it. So today we went to the lake to test it for real. We navigated out of the launch and everything went great until we wanted to go fast. it would accelerate until it reached the point where the bottom of the distributor stops rotating and the top portion starts rotating, I think this movement is called the second pickup? past this point it doesnt accelerate anymore and just remains at the same speed. i moved the linkage by hand and witnessed the butterflys open all the way yet there is no apparent change.

question: is this a simple beginners mistake or is it a serious problem, and what do i need to do?
thanks much!

Andy

 

[kazek]

Re: 1974 merc 850 doesnt want to accelerate past half way

What hapens after motor hits second pick up,engine dies? Try pumpin primer bulb or aply choke when it happens again.Have you tried adjusting carbs.starting point carbs idle screw is 1 1/2 out from lightly seated and then keep outing the screw in 1/8 segments till engine starts to bog down.at that time screw needle in 1/4 turn.that should be about 2 turns out,some engines even more.

 

[Chris1956]

Re: 1974 merc 850 doesnt want to accelerate past half way

Did you set the max timing to 21*BTDC? With spark plugs 2-5 out of the engine, but installed in their wires and grounded to the block, set the throttle to full speed and put a timing light on the top spark plug wire. Crank the motor and adjust the max spark advance screw 'till the timing light reads 21* BTDC.

 

[Awc9372]

Re: 1974 merc 850 doesnt want to accelerate past half way

The engine continues to run after the second pickup, have adjusted carbs like you guys said, it just doesn't increase in rpms. We haven't checked the timing on the thing so we will find out.
Could it just be the timing is way off?
Is the timing for the primary pickup different then the second pickup?

I'm just a beginner so I'm trying to learn.

Thanks for the help!

Andy

 

[Chris1956]

Re: 1974 merc 850 doesnt want to accelerate past half way

Idle pickup timing should be 4-6* BTDC. As the distributor advances to 4-6* BTDC, the carbs should just start to open. There is a brass collar about 1/2 way up the distributor. That collar rotates to set idle pickup timing.

 

[Awc9372]

Re: 1974 merc 850 doesnt want to accelerate past half way

Ok great, Ill give it a try on Friday and let you guys know how it goes. On a side note I did a compression test 1.135 2.130 3.127 4.129, are these good numbers?

Thanks!
Andy

 

[Chris1956]

Re: 1974 merc 850 doesnt want to accelerate past half way

Those numbers are real good.....

 

[satanclause]

Re: 1974 merc 850 doesnt want to accelerate past half way

Mine mercury 500 acted the same way at test run, when i got home checked ignition and it was set at 43deg instead of 34. Will do another testrun this weekend. Ps i removed all sparkplugs and put the nr 1 to ground and got strobo to work. Easyer to pull without them

 

[Awc9372]

Re: 1974 merc 850 doesnt want to accelerate past half way

Well I figured it out! I went back and totally readjusted the timing, get on the lake and it's a no-go. So I do some inspecting and I see the carb to carb fuel line is pinched a little. So being as ambitious as I would ever be I decided to un pinch it and see what happened... So I had the thing tore apart, out on the lake, I pull off the starter and see the line, completely pinched shut, must have gotten caught somehow. Any ways I take the top off the float bowl in the bottom carb, it was completely dry inside! So I readjust the layout of the fuel lines a bit, and put the whole thing back together, and by now were at the boat launch having people watch us work on it, kind of nerve wracking, the thing fired right up! Got out onto the water and let her rip, she goes fast now!

Thanks for all the suggestions guys!

Andy