470 miss idle to 1500 rpm - still cant fix it

[darot]

The boat ran great and this happened during one outing and I can't figure it out.

it has a miss (runs rough) from idle to 1500 rmp, above that it smooths out and seem to have good wot. I can ski with it.

i have replaced: plugs, wires, cap, rotor. It has petronix ignition and i put the points back on with no change.

running at say 1300 rpm and pull any plug wire and it will run much smoother (does not matter which plug wire). The timing is set right at 8 degrees.

my compression test showed all cylinders pumping to 145-150 on 8 revs. each one had a min pump of 60 PSI on the first rev.

I don't know what else to do. the boat has a new fuel pump and lines also and a new coil.

 

[Don S]

Re: 470 miss idle to 1500 rpm - still cant fix it

Check the shaft in the distributor for side to side movement, check all directions. Worn shaft and bushings may be your problem.

 

[TowRoper]

Re: 470 miss idle to 1500 rpm - still cant fix it

this is a long shot but mine did the same thing and it ended up being the tac, just a thought.

 

[stonyloam]

Re: 470 miss idle to 1500 rpm - still cant fix it

running at say 1300 rpm and pull any plug wire and it will run much smoother (does not matter which plug wire). The timing is set right at 8 degrees.

That indicates whatever it is affects all 4 cylinders, at low rpm. You are set at 8 Degrees BTDC, the "book" says that it should be 4 degrees BTDC. Might possibly be it.

 

[darot]

Re: 470 miss idle to 1500 rpm - still cant fix it

stonyloam
my info says 8 degrees at idle (about 700 rpm), im in the drive on muffs and my idle is about 900 rpm. Maybe you thought I was 8 degrees at 1300 rmp?

my distributor does not seem to have any side toside play.

i'll disconnect the tack today and see what happens.

 

[darot]

Re: 470 miss idle to 1500 rpm - still cant fix it

took the signal lead for the tach off the coil and it had no impact, still missing.

Any ideas?

 

[darot]

Re: 470 miss idle to 1500 rpm - still cant fix it

bump

 

[ErieRon]

Re: 470 miss idle to 1500 rpm - still cant fix it

Darot,

In 1987 Merc changed the timing to 4 degrees BTDC from 8 due to fuel quality. It's Service Bulletin No. 87-17. Here's a link; (http://www.boatfix.com/merc/Bullet/87/87_17.pdf) I have a 1984 470 and changed my timing when I discovered it, and didn't notice much difference. I also installed the Pertronix set-up and have been very happy with it. Don't know if it's what your problem is, but you never know. Have you looked through the "Adults Only" sticky ? http://forums.iboats.com/showthread.php?t=288430



Good luck.

 

[darot]

Re: 470 miss idle to 1500 rpm - still cant fix it

thanks for the insight. i did reset my timing to 4 degrees and i think it helped a little. I still have a rough running engine from basically idle to 1500 rpm. over 1500 runs fine. I pull skiers with the boats as is.

i'm done messing with it, i'm going to ignore it and run it till whatever it is breaks. you know if you can't fix it . . . . .

 

[Bt Doctur]

Re: 470 miss idle to 1500 rpm - still cant fix it

Check #4 plug to see if it`s a lot whiter than #1, may have a leaking riser affecting #4 plug.

 

[bigbrownbuku]

Re: 470 miss idle to 1500 rpm - still cant fix it

im leaning toward leaky riser too.