HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

[kwikkar]

Hi newb to posting. Been watching the forums alot over the years. So never need any help before but this time i'm stumped! Heres what I have. 1988 Four Winns 160 Freedom w/ OMC (GM) 3.0 w/cobra o/d
Problem: Boat sat for YEARS before I bought it. Starts, idles great. The second I put it in gear in water or out of water it runs ok till I give it throttle. If i ease into the throttle it starts to break up between 2k & 4k rpms. If I just push through to WOT it will get up to plane and top out at 35. However its feels like it has more just wont go. then after 15 min or so it starts to break up worse, cut out, backfire through the carb and try to die out. If i throttle down it will stay running but mis like crazy. Shut it off sit for a minute and fires right back up everytime and will be ok for 5 minutes or so. (keep in mind even after sitting it will still break up in the 2k-4k range) 1 time I eased into the throttle and it accelerated with no mis?
What I have replaced:
1. Plugs (AcDelco)
2. Wires (NAPA)
3. Points
4. Condensor
5. Cap (NAPA)
6. Rotor (NAPA)
7. Coil w/external resistor
8. disconnected ESA? (shift interuptor)
9. Disassembled Carb 3-4 times 2 rebuild kits (back air/fuel screw makes no affect on the motor when running)
Whats left?
1. Anti-Siphon Valve
2. Dist. bushings( cap removed I can move the shaft enough to see the points gap get bigger?? enough to cause problems? I'd say it adds .10 thousands of an inch when I wiggle the shaft)
3. Carb

Any ideas here?

Points set to .25 in
Timing (base) 6 BTDC (did see the mark jump 10 back towards ATDC several times while idling, also missed at the timing jumps) Could this be from the dist?

Compression is 120 all 4

Any help I can get. Thanks

PS. I'm about to do the bypass my existing tank test with an aux tank to see if its the anti-siphon valve

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Fuel Pump (electric 6lbs)
NO issue with Anti-Siphon Valve
Pumped 3 gallons in 2-3 minutes no loss in pressure or volume


Soooooo......That leaves the some what sloppy distributor and the twice rebuilt carb right???

 

[Levinz11]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Points should be set initially to .017-.019. Then set dwell angle. I'm no pro but your dist. jumping around like that is no good.

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

What if I dont have a dwell meter? Dont really know anyone I could borrow one from?
I talked to local boat mech. and he said just convert the dist to electronic. $120.00 then the shaft movement wont affect timing (providing thats the issue)

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

OK..... Set (base) points to .17 in then used a multimeter with dwell setting set to 4 cyl and achieved the 29.8ish dwell
readjusted base timing to 6 BTDC fired up idles even better. Revved up smooth in neutral and revved pretty smooth in forward gear... However I did still hear some missing (didnt sound as bad but I'm also not under load in the water).
Currently I am readjusting the lower shift cable so I can get forward gear to engage in the water. Once I get that back together I will lake test and see if that cleared any issues up.

 

[HT32BSX115]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Sounds almost like your ESA is intermittently activating.....

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Sounds almost like your ESA is intermittently activating.....

ESA is not even connected...................pulled entire module from boat

Ok adjusted lower cable and reinstalled out drive. Problem still exists.

In neutral about 1500-2000 rpm range timing moves from 28-30 advanced HOWEVER it will occasionally jump time 10 degrees or so and go back to 28-30 range, it does mis hard everytime the timing jumps.

Problem still exists between 1800-4000 rpms range (and NO i'm not revving out of water to 4000) this was from yesterdays lake test.

In neutral I did accel to 2000 where it starts to break up and sprayed ether into the carb and it just bogged it down more, it did not help so that makes me think its not a FUEL problem.................

ANY MORE IDEAS????????????

(makes me just wanna yank the 3.0 and install my Fuel Injected 383 stroker. Much easier for me. I like computers. HA)

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Ok lake test went with little improvement. Still popping thru the carb. Misfires
???????

 

[HT32BSX115]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Ok lake test went with little improvement. Still popping thru the carb. Misfires
???????

Hmm. Well aside from valve timing issues and swapped sparkplug wires.... popping back can also be caused by ignition timing problems (screwed up dist advance) and burnt valves....

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Hmm. Well aside from valve timing issues and swapped sparkplug wires.... popping back can also be caused by ignition timing problems (screwed up dist advance) and burnt valves....

pulled dist apart advance seems to be working correctly weights ok springs good. Swapped plugs/wires
only issue i see in the dist is the shaft movement

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Bump
Hello anybody ????

 

[HT32BSX115]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Timing (base) 6 BTDC (did see the mark jump 10 back towards ATDC several times while idling, also missed at the timing jumps) Could this be from the dist?

I am thinking that this might be related to your problem.....

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

I am thinking that this might be related to your problem.....

Ok I'm gonna order the electronic conversion for it today since that is a tad bit cheaper than replacing it and see if that takes care of any issue.

Thanks

 

[bruceb58]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Before you do that, measure the dwell with a dwell meter to make sure its steady. You should be setting dwell with a dwell meter anyway.

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Before you do that, measure the dwell with a dwell meter to make sure its steady. You should be setting dwell with a dwell meter anyway.

I used a multimeter that has a dwell setting. The dwell moves between 29.0 and 29.9 not much in my opinion.
I'm gonna try to get out and lake test it and watch the timing under full load tomorrow.

 

[bruceb58]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

If that's the case, I doubt making the switch to an electronic conversion is going to help you any. The conversion is basically an electronic version of points.

If your timing is jumping around like that, its going to be caused by something else like sticky weights/springs or cross fire on a spark plug wire.

Is your dwell steady over all RPMs? By the way, it should be between 31? and 34?.

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Talked to a carb rebuilder in Cali today and he says my carb is wrong. It's for a v8 not a 4cyl. So I ordered one for $278 should b here Friday or Saturday. While I had some down time I pulled the plate off the dist and greased the weights. Swapped out plug wires for another new set. So I guess I'll see what happens once I'm running the right carb setup.

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

Installed new carb last night and WHAT DO YA KNOW!!! Runs GREAT!! Lake tested great for 30 mins the acted like it was running out of fuel. made it back to dock with nothing more than idle. Replaced fuel filters (and eliminated the stone filter) added 1 more clear inline. and runs again. Still misfired a little bit but prob due to water in the carb as I can see water on the throttle plates. Removed carb and now waiting on base gasket. Then I will try again tonight.

 

[kwikkar]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

If that's the case, I doubt making the switch to an electronic conversion is going to help you any. The conversion is basically an electronic version of points.

If your timing is jumping around like that, its going to be caused by something else like sticky weights/springs or cross fire on a spark plug wire.

Is your dwell steady over all RPMs? By the way, it should be between 31? and 34?.

Dwell is now steady at 32 degrees. I did however get shocked by my coil wire when testing this. Soo guess its on to set 3 of plug wires

 

[bruceb58]

Re: HELP!! '88 OMC 3.0 Missing/Backfiring in gear!!

added 1 more clear inline.

You are going to want to remove that. Not allowed for marine use in an enclose bilge.