HELP - 3.0L Stalls Upon Accel AND Rapid Decel

[Cherishher]

OK - I think I've read every thread on teh web about bogging and Mercarb rebuilds. I think my situation has an added element.

Let's see if I can relay all the pertinent details.

Three summers ago, I experienced the typial bogging and dieseling problems that the 3.0L is known for. Nothing I couldn't live with.

Two summer ago, I got the boat out only once and the engine wouldn't start - narrowed it down to lack of fuel.

I didn't get it out last summer.

This summer I started to look into the problem. First thing I did was check the fuel pump - no problem. Fuel is being delivered under pressure to the carb.

I dismantled the carb and did a partial clean/rebuild. The engine fired up and idled ok for the most part however, when I went to accelerate the engine would stall. If I feathered the accelerator, I could get it up to speed but if I rapidly decelerated it, the engine RPM's would drop and stall.

I figured it was the accelerator pump so I once again stripped the carb and got the accel pump working. I put it back together - same problem.

Wen I accelerate I can hear the air being sucked into the engine - I assume it's not getting enough fuel. Does this make sense seeing as the accelerator pump is functional? I'm not talking about bogging - the engine dies!

I have to VERY carefully feather it to get the RPM up but once running, all is OK. decelerating either stalls the engine or the idle RPM remain high (1200 -1500).

I have throttled the engine up to around 2,000 RPM but don;t see any gas being injected from the venturis - should I?

I have yet to check for vacuum leaks and will do so tonight...along with a complete strip, clean and rebuild. BUT - it there was a vacuum leak wouldn't I see problems even if feathering the throttle? Wouldn't I see it at idle?

So here are the facts....

engine idles (idle circuit ok)
idle mixture adjustment works as expected (needle valve ok)
accelerator pump circuit works (accel pump ok)
can get the engine up to speed (main jets ok?)

So, is it the transition circuit? What does it consist of? What does the power valve do?

Please help - I have a camping trip scheduled for two weeks from now and really need to get this thing up, running and water tested before then.

Thanks.

 

[Bondo]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

I dismantled the carb and did a partial clean/rebuild.

Ayuh,......... I Think that's the Problem,..........

The Carb either needs a Complete Rebuild,.............. Or Replacement..........

 

[Don S]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

hree summers ago, I experienced the typial bogging and dieseling problems that the 3.0L is known for. Nothing I couldn't live with.

Two summer ago, I got the boat out only once and the engine wouldn't start - narrowed it down to lack of fuel.

I didn't get it out last summer.

Please help - I have a camping trip scheduled for two weeks from now and really need to get this thing up, running and water tested before then.

Let's see here, you have had problems for 3 years, you couldn't get it started 2 years ago, and you let it set till now. And now you are begging for help to get it fixed within 2 weeks?????

Do you have spark at all? I'm talking now, not 2 years ago.
When was the last full tuneup?
IF if has spark, have you tried squirting some gas in the carb to see if it will start?

 

[Cherishher]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

Don,

I do have spark - I can run the engine. It starts fine, runs at idle and I can edge it up to speed but if I try to make any rapid throttle changes then the engine stalls. I hav everified that the accelerator pump works - I get two solid streams when moving the throttle forward.

Any thoughts on the transition circuit?

Thanks.

 

[Coors]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

Don, are you getting crankier in retirement?

 

[stug]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

head gasket problems or possible vavle seating problems or head cracks ?

 

[Cherishher]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

OUCH - I hope not!

If there was a head gasket problem or cracked head wouldn't I see water in the oil, white smoke or misfires? I don't see anything like that.

Any thoughts on how to troubleshoot this thing to figure out what's wrong?

What's most confusing to me is wh the engine would stall upon rapid deceleration from high RPM to idle......does the transiiton circuit come into play here too?

 

[Don S]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

Have you done a full tuneup, Spark plugs, cap, rotor, points, condenser, set DWELL, not just gap, set idle timing and check advance timing then carb mixture and idle speed. Do a Compression Test so you know the engine is good, do a vacuum check to make sure you don't have a vacuum leak from your partial rebuild.
There is a lot more to having a stalling engine than the carb, and it all has to work together.

 

[captainbri]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

sounds like carb is bad or float is sticking . I had same problem and it was the carb. Did have my head checked and valve job done and pressure tested. Do the carb first. Then if that doesn't work take head off and have it checked. do manifold to.

 

[Don S]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

sounds like carb is bad or float is sticking . I had same problem and it was the carb. Did have my head checked and valve job done and pressure tested. Do the carb first. Then if that doesn't work take head off and have it checked. do manifold to.

Sounds a lot like try this, if that don't work try that, throw greats amount of money at it and hope you hit on the problem.

Sounds to me like he needs to do some troubleshooting and save himself a valve job and carb if that isn't the problem.

 

[Cherishher]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

Quick update....

I checked for vacuum leaks - none!

I did notice that the choke was not closing when cold - re-engaged the spring (it was somehow disconnected) and I can now throttle the engine (with the usual bogging). After a few minutes however, when the choke heats up and opens fully, I am back to pretty much the same problem. Is there a way to check the choke resistance to determine if it still has teh appropriate tension/spring force?

I did re-adjust the float height (and checked the valve for proper seating)which helped but....

The problem still remains that; if I get the RPM up then decel, the engine dies. Why would this happen?

Will check dwell and possibly replace plugs, tomorrow.

It's better now but something's still not right.

 

[jimhen]

Re: HELP - 3.0L Stalls Upon Accel AND Rapid Decel

strongly suggest you follow dons advice. basic to any performance is running the proper sequence in tuning things up. You may have had a carb problem 3 years ago but after sitting a couple years other things are sure to be fouled up. ignition 1st carb last. If your carb is the big problem you will never get it right without the other stuff working correctly.