Replacement engine from Rapidomarine...

[redjmp]

Re: Replacement engine from Rapidomarine...

I also note that my secondary air valves are opening below 3000rpm's which from reading many posts here is a bad thing, this too could be a problem, but, ran fine prior to new longblock....I will get a new electric fuel pump if necessary, not a problem..
cheers,
Kevo

What kind of carb do you have?
Did you say you rebuilt it? Can't remember this thread is so long...
I'm sure it has mechanical secondaries doesnt it?
So if you have the controls at wot then the secondaries will want to open no matter what the rpm.
Seriously try my quick test before spending a minute more on anything to do with the fuel system.

My edelbrock 4bbl will only open 2 bbls even at wot if the choke isn't open.
But from the top, there appears to be 2 secondary valves that are part way open at wot. They are not the throttle valves though which are hidden underneath! ( and almost fully closed unless the choke is open)
These are airflow based choke plates which will open easily with minimal airflow
So maybe you are mistaken when you say your secondaries are opening.
Now if you rebuilt that carb, and you said you messed up with the choke linkage already, then it may be in there.
But it would be very easy to screw up the linkages and cams if it was ever disassembled....

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

What kind of carb do you have?
Did you say you rebuilt it? Can't remember this thread is so long...
I'm sure it has mechanical secondaries doesnt it?
So if you have the controls at wot then the secondaries will want to open no matter what the rpm.
Seriously try my quick test before spending a minute more on anything to do with the fuel system.

My edelbrock 4bbl will only open 2 bbls even at wot if the choke isn't open.
But from the top, there appears to be 2 secondary valves that are part way open at wot. They are not the throttle valves though which are hidden underneath! ( and almost fully closed unless the choke is open)
These are airflow based choke plates which will open easily with minimal airflow
So maybe you are mistaken when you say your secondaries are opening.
Now if you rebuilt that carb, and you said you messed up with the choke linkage already, then it may be in there.
But it would be very easy to screw up the linkages and cams if it was ever disassembled....

The carb is a Rochester Quadrajet with vacuum operated secondaries, and no, it has been meticulously rebuilt and nothing out of place, nothing in a bind and nothing misadjusted to create the problem I still have somewhere...I just read where my secondaries may be opening too soon creating a flat response due to the fuel not being atomized due to low air flow volumes with this engine below 3000rpm's, makes sense to me, due to check it out tomorrow to see if secondary AV's adjustment has slipped or is too loose.
cheers,
Kevo

As stated earlier many times, ran fine before new long block installed and does same thing no matter what I have tried....even though I am sick to death of working on this heap, I will not waiver and am in hot pursuit of the problem....lol....

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

7psi at idle is fine, and is within spec. Any higher and it will cause fuel to push past the needle. They don't list a wot spec. I can't say if 2psi is low or not. The pump would be providing more volume (needle open more often) and makes sense that psi would drop.

Boat Side Fuel System Tests: http://forums.iboats.com/showthread.php?t=283269

If the pump were not keeping up, this would have no psi reading at all?
Correct?

 

[choochooharley]

Re: Replacement engine from Rapidomarine...

Possible but if its just not pumping enough it will drop the psi....do you have a manual

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

I haven't read the whole post, but 22 degrees total advance ain't nearly enough advance! Get a timing tape, see what you're getting at 3000 rpms..should be identical to a 350..32 degrees or so TOTAL.

quadrajet air valve..5/8 to 3/4 turn on the spring.

Fuel pressure..it's not the pressure, but the flow. Quadrajets have small float bowls, but a steady 5 lbs should flow enough fuel for a little 4.3.

Manifold vacuum..I only get about 14 inches at idle on both my motors.

Compression..I got close to 200 lbs. on my 350 vortec truck..and it is identical to a 4.3.

 

[scipper77]

Re: Replacement engine from Rapidomarine...

Well I did a little web searching for you and found some things that have caused a lack of rpm's for other people (not all boats).

Poor spark at high rpm's: cracked coil, bad wires. Get a spark tester was the solution for diagnosing. "An inline spark tester is an inexpensive tool and it will let you check the spark while the engine is bogging."

Another guy replaced the flywheel and his problems went away.

I found a case where 2 wires were crossed on a 350 v8. It idled fine but for obvious reasons wasn't making power under load.

I don't know if any of this helps but It's driving me nuts that you have done so much and can't understand what's wrong. I can't imagine how you feel.

 

[redjmp]

Re: Replacement engine from Rapidomarine...

The carb is a Rochester Quadrajet with vacuum operated secondaries, and no, it has been meticulously rebuilt and nothing out of place, nothing in a bind and nothing misadjusted to create the problem I still have somewhere...I just read where my secondaries may be opening too soon creating a flat response due to the fuel not being atomized due to low air flow volumes with this engine below 3000rpm's, makes sense to me, due to check it out tomorrow to see if secondary AV's adjustment has slipped or is too loose.
cheers,
Kevo

As stated earlier many times, ran fine before new long block installed and does same thing no matter what I have tried....even though I am sick to death of working on this heap, I will not waiver and am in hot pursuit of the problem....lol....

Well something is wrong because to the best of my knowledge, quadrajunks have mechanical secondaries.
They also have the same kind of airflow operated butterfly valves above the secondary throttles as well like the edelbrocks. They control the metering rods so it is important that they are set up properly.

Now I think we might be getting closer to the root of the problem if you did indeed rebuild this carb and think it has vacuum secondaries. There should be a linkage that opens the secondary throttle and a cam that prevents it from opening if the choke linkage hasn't disengaged the lock out.

But before you mess around even more, just take it out and squirt some raw fuel down its throat and see if the ***** smartens up for you.

Can you post a couple of pictures of it so we can see the linkages and cams?

 

[scipper77]

Re: Replacement engine from Rapidomarine...

How the heck did we get this far into this thread before a pic request was made??? lol.

I don't remember if you said you changed out the cam or not. Did you swap the cam?

 

[choochooharley]

Re: Replacement engine from Rapidomarine...

Have you checked the spark I know it was mentioned a few times but I can't find where u did check it. I know u checked the plugs but no comment in what kind If spark u have.

 

[John_S]

Re: Replacement engine from Rapidomarine...

Possible but if its just not pumping enough it will drop the psi....do you have a manual

Manual says 3-7psi, procedure says to measure at idle.

 

[John_S]

Re: Replacement engine from Rapidomarine...

I also note that my secondary air valves are opening below 3000rpm's which from reading many posts here is a bad thing, this too could be a problem, but, ran fine prior to new longblock

The air valves open at a certain engine vacuum, and not a rpm. You are holding the butterflies wide open, so not surprised the air valves are trying to open.

You could test by holding the air valve closed and see if rpms increase. I doubt they will.

 

[John_S]

Re: Replacement engine from Rapidomarine...

I haven't read the whole post, but 22 degrees total advance ain't nearly enough advance! Get a timing tape, see what you're getting at 3000 rpms..should be identical to a 350..32 degrees or so TOTAL.

Regardless of what you think a 4.3L can take in advance timing comparing it to the 350, the reality is he is running the stock advance, as he should. In the other thread where you thought that this was the issue, it turned out to be the wrong spark plugs. http://forums.iboats.com/showthread.php?t=446204 The marine 4.3L is fine with only 22 degrees of total advance.

Manifold vacuum..I only get about 14 inches at idle on both my motors.

That is on the low side for a stock carbed marine engine, unless your gauge is off, or you are at a few thousand feet of elevation.

Compression..I got close to 200 lbs. on my 350 vortec truck..and it is identical to a 4.3.

I know, the 4.3L is 3/4 of a 350, but if you take identicle mercruiser 350's except one has the stock flat hydraulic marine cam and the other has the roller, you get different psi ratings. (intake valve closes at a different point) So, just your truck cam will make a difference, let alone the other minor differences in chamber volume, gaskets, etc.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

I need to write a book.....
Bought new marine spec plugs and they looked great after the last trial on the water.
If I did replace the cam with the old one(big effin job with the engine in the boat), in theory, wink, wink, it runs exactly like the new cam, better on the bottom end, same rpm problem....so, no matter what cam comes with it, the problem exists still, in theory, wink, wink....(read into this what you will, its my game from this end, gotta keep things interesting, lol).
I have adjusted the secondary AV's to open later in the rpm range so we shall give this a try...Hey, at least it is getting a good break in period of no high rpm's, it is just costing me my sanity!
I/we have basically built this boat from a heap of parts this summer. You and yours have supplied me with the appropriate knowledge to make this heap into a running boat. It ran great, popped out of the water easily and zipped across the lake wonderfully for about 30 minutes when the oily froth started spewing out of the cracks in the heads. Each and every system that you helped me create, wiring, fuel delivery, out drive, etc. were functioning exactly like they should have just prior to installing the new block, zero adjustments were made to each and every system prior to the new reman engine, so, of course, I immediately blamed it for all my troubles, which, of course, cannot be logically explained by myself or anyone else here. I am of a very meticulous nature, I restore old Japanese motorcycles that almost always have electrical and fuel related problems that I handle with ease. I labeled each and every wire, marked everything so as to be certain of its needed location...it all makes me want to gag...
Check all of my posts for pics of the boat we have built this summer.....I still welcome comments, but please read this entire thread so we can be accurate in our postings, I am getting numb from the experience and want to get back to reproducing things I love to work on, not nightmarish, unending problems...
truly had enough,
Kevo

 

[FreeBeeTony]

Re: Replacement engine from Rapidomarine...

I'm totally confused........are you saying it ran good for 30 min then died?

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

I'm totally confused........are you saying it ran good for 30 min then died?

No, it ran great and then the oily froth was spewing from it and then it was decided that the entire block had to be replaced, further investigation led to the facts that the block as well as both heads were damaged beyond repair...It would still run fine in theory....and, the compression tests on the old engine were in the 150 to 180 ranges on all cylinders....it just would not hold the coolant in the correct places....

 

[billder62]

Re: Replacement engine from Rapidomarine...

Just curious , have you tried running it wth the orignal rockers and push rods that were sent from Rapido ?

 

[FreeBeeTony]

Re: Replacement engine from Rapidomarine...

Oh.....I thought you were talking about the Rapido replacement.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

I was reading all posts pertaining to the 4.3l engine that I am still having trouble with and ran across a posting that had this view of a knock sensor, my old block had one of these installed and I did not reinstall it on the new block as it was foreign looking and was not connected to any wiring, could this be my smoking gun? I have no idea how it may or may not affect my problem of no rpm past 2800 on the water, thoughts, suggestions..???
http://www.iboats.com/mall/image/view/3/6/9-33503_0.jpg

still on the hunt but failing fast..
Kevo

 

[redjmp]

Re: Replacement engine from Rapidomarine...

I don't think knock sensors were ever used with a TB IV ignition. Used only on fuel injected models with a computer. Don't think thats your smoking gun...

 

[Bondo]

Re: Replacement engine from Rapidomarine...

I don't knock sensors were ever used with a TB IV ignition. Used only on fuel injected models with a computer. Don't think thats your smoking gun...

Ayuh,... Agreed,... knock sensors are a T-bolt V thing...