1972 Merc.800 Idles at 2000 RPM

[Gomer50]

Just got my motor up and running again,did a carb rebuild soaked them in Chem dip for about a week.Nice and clean installed them pumped up the bulb nice and tight no leaks.Had to prime the cylinders with 50:1 mix and she fired right up.But she will idle @ 2000 RPM and the only way I can get any lower is if I scew out the idle screws to about 2 1/2 turns out then she smokes like crazy.Can't find any air leaks or gas leaks.Any Idea's?? Thanks......

 

[Chris1956]

Re: 1972 Merc.800 Idles at 2000 RPM

It sounds like you need to check the idle timing pickup. The timing should be 4-6* BTDC, just as the finger on the distributor starts to open the carb.
Carbs idle mixture should be set aproximately 1-3/4 to 2 turns out. Smoking is good for it..,..

 

[Gomer50]

Re: 1972 Merc.800 Idles at 2000 RPM

Thanks Chris but 2000 rpm when the distributor is totally retarted (havent even touched the throttle yet).I put the timing belt on as per intructions TDC rotate the flywheel counter clockwise until my TDC mark,crankshaft and distributor pully/shaft are all lined up.Starts fine.I'll check tomorrow with a timing light where my timing marker on my flywheel shows up at Idle.Its usually the other way around I cant keep it Idling now I cant get it to come down.This motor is really messing with me anymore LOL.

 

[Chris1956]

Re: 1972 Merc.800 Idles at 2000 RPM

OK, So the dissy is all the way retarded and the carbs are closed, and you see 2000 RPM. That ain't right. Either your timing is set wrong or the tach is wrong. The motor should stall.

Stick a screwdriver into #1 cylinder and bring it to TDC, turning CW. Set it to the very beginning of TDC, as the piston is at TDC for a few degrees. Now recheck the timing belt and timing marks. Your timimg marks are on the cowl support? Merc went to an adjustable timing pointer in the newer models.

 

[Gomer50]

Re: 1972 Merc.800 Idles at 2000 RPM

Well Chris1956 went out this morning tore everything apart again and the timing is right on,so I decided to check out my carbs again and noticed my bottom carb there is gas coming out of the bottom where the spring/butterfly is attached to.It would run as if 2 cylinders were getting gas and the other 2 were not.I got these carbs off of ebay awhile back and they are a little different then the originals.These dont have the round screen on top of the floats there flat and have a tiny hose that goes over to the other side of the carb.So I am not really sure if these are for the 80 hp family (checked high and low cant seem to get any info on these) most all have the dome on top of the float for the filter.Anyway sorry for rambling on but I think my problem lies with the carbs.Thanks to all.

 

[Chris1956]

Re: 1972 Merc.800 Idles at 2000 RPM

Sounds like you got the backdraft carbs. They were on the newer inline 4/6 motors. Is it possible you got larger bore carbs than the originals?

if you have real trouble, I have some original carbs from a '73 Merc 850 that I will part with. They are non-backdraft.

 

[Gomer50]

Re: 1972 Merc.800 Idles at 2000 RPM

I was wondering about that because I couldnt seem to find much info in my year range for these carbs.PM me and we might be able to cut a deal.I had the orignals but they were so buggard up from someone trying to take them apart to clean that the screw driver is useless anymore.