Mercury 3.0 EST no spark

[alldodge]

Agree unable to find exact info. Its a Merc carb
Contact Mike's Carb Kits and he can advise, but my guess is he will say its PK112 because so far there is only one for all Merc carbs
https://www.carburetor-parts.com/
When rebuilding the jets and suck are not replaced

 

[Scott06]

Trying to do some more digging on this carb. In seeing S/N 15396A4, but I can't seem to find anything on this carb. My engine serial is 0F076166, but it's not listing this carb being on it. Am I reading carb wrong? Pic attached.

here is the link to the carb breakdown which is a mercarb https://www.marineengine.com/parts/mercury_marine_parts/sn/0F076166/430B0003S/1604_120

 

[Yz229]

Awesome, thanks!!

Still wondering if it's carb, not making much sense. I'll start it up , idles great, runs great, revs freely, goes back to idle (not good idle afterwards) and then it won't take throttle anymore, just bogs and dies, sputters a lot with backfiring. Start again, and seems to run ok again.

 

[alldodge]

Need to find out if its carb or something else, but sounds like carb. If it was electrical it would just run good, bad, good , bad

You said no spark at the beginning. Your compression gauge could be off but it would be way off with 170 psi. My guess is its flooding

Watch the carb down its throat to see if its flooding or something else

 

[Yz229]

Do you think it could be anti siphon? Looking at hooking external tank to see. Having a fun time trying to get rubber hose off tank. Doubt it's been off

 

[alldodge]

With current symptoms I would think No
The shutting off and restart and its fine rules that out.

Think you might have the throttle cable misadjusted, meaning it might have slop in it. Every time it goes to neutral position it should have same idle

 

[Yz229]

I actually adjusted that. But I took it off as well using throttle by hand.

 

[Yz229]

Going to order this and try again. I only cleaned it before. I think someone changed main jets before since it had 165's

 

[Scott06]

Going to order this and try again. I only cleaned it before. I think someone changed main jets before since it had 165's

Try mikes carb parts had very good luck with their kits over the years

if you look in that parts list it lists both 1.60 and 1.65 jets not sure if one is fir the 3.0l vs LX doubt it would make much of a diff in air fuel ratio

 

[Yz229]

Rebuilt the carb. Still stalling out and backfiring. Accel pump is working fine. I'll try to upload a video.

 

[alldodge]

What does the throat of the carb look like when its at idle?
Do you see any dripping of fuel or just a thin mist?

When motor shuts down is the throttle plates wet with fuel?

 

[Yz229]

I don't really see any mist, dry. Unless I open throttle, then I get accel pump. Looks dry on shutdown.

 

[alldodge]

If plugs are dry, then its lack of fuel
If plugs are wet then maybe water is getting in or bad gas

I just don't see an electrical problem or carb issue

 

[Yz229]

Idle

 

[alldodge]

Looks good, so what happens when it dies?

 

[Yz229]

Looks good, so what happens when it dies?

Usually it will diesel for a bit when it's up to temp (170-180f). In video I posted, it wasn't fully warmed up so it only sputtered once.

 

[alldodge]

I'm trying to find out if there was excess gas in carb when it dies. Dieseling is caused by incorrect timing, wrong firing order, idle to high, bad gas

Need to find out if when it diesels and shuts down hard are the plugs wet, did the carb spit. Might be the fuel pump is not keeping up or shutting off. When motor dies you still may be able to pump and get a shot of fuel out, but the bowl may be real close to empty.

I don't know, need info

 

[Yz229]

It doesn't really die on it's own but I'm sure I could make it do that if I tried to bog it hard enough. It diesels when I shut off ignition. Base timing and firing order is correct, but it's moot since I'm shutting it off anyways, there is no more spark. Float level is dead on.

I'll check the plugs again. I just put in new plugs, but the old ones looked good.

One thing I didn't check was timing advance

 

[Yz229]

All the plugs look good. Identical to this one.

Going back to timing, this is the module I picked up just to see if it would run...

https://www.oreillyauto.com/detail/c/masterpro-ignition/ignition---tune-up/ignition-module-control-unit-ignitor/9331d0e7f826/masterpro-ignition-6-terminal-ignition-control-module/mpi0/27031/v/a/3653/automotive-suv-1992-chevrolet-s10-blazer?pos=0

I wonder if this isn't advancing correctly.

 

[alldodge]

To recap

First no spark, and spark was fixed but motor runs crappy

Carb cleaned/rebuilt a few times and there are no issues currently with carb

Motor diesels when turned off. Idle is correct RPM

Timing and firing order is correct
Spark on all cylinders and no issues

Compression on all cylinders is between 150 and 170 (might be a gauge issue) and cylinders should be within 10% low to high. Assuming gauge is the issue, there is a 14% difference. No evidence of moisture in any cylinders

So everything works as it should but still runs bad. If valve or rings had issues there would be signs in the compression numbers.

I'm running out of ideas.
Even if there was intermittent plug firing of plugs there would be no dieseling.