3.0 timing issue???

[copelandcf]

Hey guys,

I've been fixing up my 88 Chris Craft with the 3.0l 4cyl mercruiser engine. I finally got my dwell set to 34* (took a pretty large gap of .028) and went on to try and adjust timing. The timing was around 0*tdc to maybe even 2* retard. It ran great but the idle was a bit high, maybe 1100rpm, I dunno exactly my tach is pretty quirky and jumps alot. So when I adjusted the timing to 6* advance (factory recommendation) it would not idle. It got real rough and died. With a little gas to keep rpms up it would run but it did not seem right. What should I do? It seems to run best with retard but I know this is not right. I tried lowering the idle on the carb with the retarded timing and it seems ok, better than the alternative but I know something is off for it to run like that. Any help is appreciated. Thanks.

 

[Don S]

Re: 3.0 timing issue???

It ran great but the idle was a bit high, maybe 1100rpm, I dunno exactly my tach is pretty quirky and jumps alot.

Get a shop tach to do the test so you know what you have. It's a must have.

So when I adjusted the timing to 6* advance (factory recommendation) it would not idle.

You should be setting it at 6?BTDC at idle rpm (650-700 rpm). Not sure what you mean by 6* advance.

Have you checked for a vacuume leak? Done a compression test? Checked for spark on all cylinders? Adjusted idle mixture?

 

[copelandcf]

Re: 3.0 timing issue???

I thought before tdc is advancing the timing, and after tdc is retarding. Either way when at 6* btdc it doesnt run right. I am new to all this so I havent checked the vacuum lines, not sure how to I suppose a vacuum gauge?? I have not messed with idle mixture either. I did check all the plugs and replace. I have checked them since and all seems well. I have not run a compression test either. But it ran fine for a while on the muffs many times with a slightly rough idle. Took it out on the water and it died suddenly while cruising. Figured it was spark or fuel since it was very sudden and ran fine before that. Replaced all fuel filters and cap, coil, points, and condensor. That seemed to do trick and have been trying to get it tuned since it started running again. I got the dwell set in range and now am at timing and idle. Any help is appreciated. Thanks again.

Edit: I read a way to test for vacuum leaks is spray starting fluid around base of carb around vacuum lines, is that the best way?

 

[chiefalen]

Re: 3.0 timing issue???

Sir: do you have a manual? If not here is a link that Don S posted and i am reposting. I don't think he will mind.



http://forums.iboats.com/showthread.php?t=251571&highlight=4.3+merc+service+manual+05'

 

[copelandcf]

Re: 3.0 timing issue???

I do have that manual. Thank you though. Any thoughts? Has to be vacuum or compression??

 

[achris]

Re: 3.0 timing issue???

Treat the engine the same as you would a car engine... The vacuum gauge is used as a diagnostic tool. Engine manifold vacuum can tell you a lot about how it's running. When you buy a vacuum gauge it (usually) comes with a sheet of paper to indicate the different conditions.

Chris.............

 

[JustJason]

Re: 3.0 timing issue???

starting fluid has a low flashover point... and i wouldn't recomend using it. I use a 6-1 oil that foams up when sprayed. if it get's sucked in then you have a leak.

either way you can't trust a boat tach. you need to get a shop tach that does dwell. You said you set dwell.... with what meter/tool did you do that with? I don't know of a dwell meter that does not have a tach as well.

 

[copelandcf]

Re: 3.0 timing issue???

I used an actron digital multireader with dwell. I dont think it has tach.

I did run a compression test and everything was around 120-125psi. I also did buy a vacuum gauge, but I dont see anywhere to hook it up except the valve cover hole from the flame arrestor. However my guage did not have any fittings for that size hole

After resetting and tinkering with idle and mixture I did get it running for a bit and the timing set correctly. However it seemed like it was flooding. I saw a lot of fuel in the carb. Had a lot of backfires and a couple little fires in the carb while trying to get it running. Pulled plugs and they were black and a little wet. Cleaned them up. Reset the idle and idle mixture and got it running for about five minutes. Still seemed rough, idle was below 1K but still dont have a shop tach for exact reading. Turned idle mixture to try and find an optimal range like the manual says, but I really couldnt tell a difference in roughness whether I turned it full lean or rich. It eventually died when I put it close to full rich and could not get it started after that. It would backfire while cranking so I gave up for now. Also when I did have it running, it would only idle, any increase in throttle would kill it. Thats where I am at.

Also a dumb question, when they say to turn idle screw two turns, is a turn 180* or 360*? I assume 360* and thats what worked for me, just making sure. I really need to vacuum test, but am not sure what to do since it wont fit valve cover. Is there any where else I should check?

Edit: After some searching it seems the consensus is there is no place to test vacuum on the 3.0L merc/gm. Anyone have a different opinion/answer??

 

[achris]

Re: 3.0 timing issue???

I think you'll find a pipe plug just aft of the carb, on the top of the manifold, that is for a vacuum gauge. Use that....

Have you checked that the plug leads are on the right plugs and posts on the distributor cap? You sounding very much like you may have a firing order problem....

Chris.............

One turn of the idle mixture screw is 'one full turn', 360 degrees.

 

[chiefalen]

Re: 3.0 timing issue???

Heres another thread for the vacuum gage.

http://www.secondchancegarage.com/public/186.cfm