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Crusader 270 bogging - still puzzled

J

junior4597

Contributing Member
Even though I've hauled my boat this past weekend I have an existing issue that I thought I'd bring up so I can prepare to address it during the off season. In the past I had posted about an issue with a Pertronix conversion kit from points to electronic ignition. Short version I put the points back in with no continual issues. The boat ran great the rest of the summer until a few weeks ago where the stbd engine decided to bog down or lose power at exactly 2k rpm. If I push it the tach needle will just dive and I can feel and hear the engine bog and lose power. Up until 2k rpm there are no hickups at all. It will present itself at EXACTLY 2k rmp, kind of ironic that it happens at the same revolution. I re-checked the timing and the dwell and its spot on. Things to point out - boat has 1 fuel tank, fuel has an additive, sprayed gum-out in carb, fuel filter was not checked but had been a few months ago when I first had my points issue, engine turns right over every time and runs just fine up till 2k. Anyone have a thought on this? Fuel delivery? electric? other? I'm at a loss and am at least looking for clues to move in any particular direction.

Looking for any suggestions
 
Check your fuel filters, I had this happed once and it was a case of the fuel filter being plugged up. Got enough full for the low speed run but starving at the upper end. I assume you have a seperate filter for each engine even though you have a single tank?
 
Junior, I am not a fan of the Pertronix kits.


These are Hall Effect. There's nothing intrinsically wrong with Hall Effect until we understand how Pertronix does this.
Their magnetic triggering units are cast into a plastic housing. IMO, this process lacks the precision of what a Reluctor or Photo-eye wheel offers.
Also, these can be sensitive to incorrect alignment with the corresponding sensor unit.

There is also a dwell contrary to what many think. The dwell is a result of the gap or distance between the magnetic unit and the sensor.

Add to this that the kit does ZERO to correct any inherent OEM distributor issues, such as worn vertical shaft bushings, excessive Up/Down play, and/or a worn and malfunctioning advancing system, etc. etc.

Due to lack of knowledge on Joe Users behalf, Joe doesn't consider these rather negative aspects.

IMOO......, this is a Cheezy way to create an ignition triggering system.
But because they are inexpensive, most will function, and they are simple to install............., we love the idea! ;)


Bottom line:
All ducks can be perfectly alingned (fuel delivery, compression, BASE timing, etc), but if our ignition systems are not doing what they are suppose to be doing, we will not get any performance from our Marine Engines.


.
 
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Just to be clear I do not have any of the Pertronix kits in the distributors. I went through that mess earlier this summer and removed them and re-installed my point setup. That said, one more thing to mention - at idle and not under load i can push that throttle past 2k rmp with no issues at all. So in thinking about this if I can throttle up and my tach advances the needle past 2k rpm and I have no bogging issues would it still be a fuel delivery issue? This "bogging" only happens under load and under way. Unfortunately I cannot really do any further testing as she is on the hard and already winterized but I thought I'd reach out for some thoughts here so when the spring rolls around I have a path to lead into. My thoughts are (at least for now) remove the can fuel filters for Racor ones with a fuel seperator and possibly replace both distributors alltogether, just to get them out of the mix. I timed those puppy's to the dime and the advance was working up to about 28* at 3k rpm or so. What else would cause the engine to bog down and drop rpm other than the mechanical advance, fuel delivery or faulty carb - when under load?

thanks
 
if the timing advance starts when it should and goes to full advance when it is supposed to (staying steady as it climbs its curve) then you are likely to have a fuel issue...you can monitor that at the fuel inlet with a pressure gauge. If the gauge shows adequate pressure as you increase rpm, that points to a carb issue. if the gauge pressure drops with increasing rpm, you need to find the problem in the delivery system.

Do it matter if you walk the throttles up vs just hammering them wide open?
 
until a few weeks ago where the stbd engine decided to bog down or lose power at exactly 2k rpm. If I push it the tach needle will just dive and I can feel and hear the engine bog and lose power. Up until 2k rpm there are no hickups at all.
Click to expand...
Assuming that this in neutral with no load........ does the tachometer take a dive on it's own......., or does the tach take a dive along with actual engine RPM?
I know that may sound odd, but I'm trying to learn if you could be experiencing kettering system (points) float, as in the contact points spring will not keep up with the points cam speed.
IOW, a weak spring that is messing up the dwell, throws the tachometer off, but still allows for 2k rpm in neutral!

BTW, your testing should be done under actual engine loads...... not in neutral.

I timed those puppy's to the dime and the advance was working up to about 28* at 3k rpm or so.
Click to expand...
Well, that certainly sounds within reason. Often it's lack of spark advance that will hold an engine back while under load.


The Parker/RACOR fuel filter system is great. I can't say enough good about RACOR.

Check your fuel tank dip tube bottom screens. See if these are clean and open.
Perhaps replace the anti-siphon valves.
If you've not replaced fuel pumps in a while, may be good to do so.

Since you have twin engines, swap carburetors and test again. Cost is two new base gaskets.


.
 
Rick/Mark

Thanks for the input. I guess the issue all points back to either fuel delivery or spark distribution. That said I was contemplating replacing the distributors and installing the Racor filters anyway. I think I'm just going to go that route - would have done this regardless of the existing issue. I'm just hoping that when I do that the issue doesnt present itself again. I don't think it could be anything else IMO, do you?

To answer some of your questions:

Does it matter if you walk the throttles up vs just hammering them wide open? - No difference, if I move up the throttle ever so slightly it takes a dive at EXACTLY 2k rpm, every time. I wonder what happens at 2k rpm? more fuel introduced? but then why not 2500 rpm or 1800?? DOesn't make sense.

Assuming that this in neutral with no load........ does the tachometer take a dive on it's own......., or does the tach take a dive along with actual engine RPM? - It only happens under load and under way. In neutral the tach and engine just hums past 2k as it accelerates, no issues at all. Under load at when you get to 2k it just takes a dive and boggs down.

I guess at the end of the day if I replace both Distributors and install new fuel filters do you think it will resolve the issue? Guess it couldn't hurt.

Good winter project!
 
junior4597 said:
Rick/Mark
- No difference, if I move up the throttle ever so slightly it takes a dive at EXACTLY 2k rpm, every time. I wonder what happens at 2k rpm? more fuel introduced? but then why not 2500 rpm or 1800?? Doesn't make sense.
Click to expand...
Are these Rochester Quadrajet carburetors?
If so, the Q-jet secondary throttle plates are mechanically linked to the primary throttle plates.
The secondary throttle plates are rather in-effective until the air door above them opens via manifold pressure (vacuum).
The secondary air door may be wanting to open at/near your 2k rpm mark.
If there is a secondary throttle bore fuel metering problem, this may explain all or part of your "dead-spot" issue during the transition between priamary to secondary fuel/air metering.

I don't know..... just a thought!

Like suggested, you could swap carburetors and repeat your test.


.
 
If the air valve is opeing up at 2000 rpm, he's got serious issues...I'd rule that out since he has the effect with the throttles advanced in small increments. I'd also rule out the power system. Since it is consistent, I'd continue to lean towards an ignition problem vs a fuel issue.

No data in the intermediate points of the advance curve...may have a tight pivot that delays the advance??? Don't know but I've seen more bizzarre stuff.
 
Mark, you are very likely correct regarding the air door @ 2k rpm.
I just ran the calcs, and a 5.7L @ 2k rpm requires only 202.5 cfm.

It may be ignition related like you say.
The OP needs to plot out the progressive advance curve and post the numbers.

Junior, if you plot this out, do so in increments of at least 500 rpm or less.

IOW, first check at 750 rpm.
This will be BASE advance.
Follow this at: 1k rpm, 1.5k, 2k, 2.5k, 3k, and again at 3.5k rpm.
Better yet: 1k, 1.3k, 1.6k, 1.9k, 2.2k, 2.5k, 2.8k, 3.1k rpm.

Plot this out on graph paper, and see if the advance curve is linear or not.

You will be looking for something that ressembles this.
However, your actual numbers will include BASE advance, whereas this curve chart does not include BASE.

171135.jpg
 
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The air valve is controlled initally by vacuum....until the vacuum level is reduced sufficiently, the air valve can't open so even it its spring is busted, it can't become a factor. secondary metering is in proportion to the air valve opening....at 2000 rpm; it can't be a lean fuel issue as the root cause.
 
are these engines using Quadrajet carbs? either carb been rebuilt or replaced?
I have always had to mess with the spring on that secondary "door".. adding tension to force it to stay closed a bit longer to get rid of that bog at mid rpm's

Jetting and everything else has to be right too.
 
It's fuel pressure related. Replace the anti-siphon valve, be sure there's no filters finer than 30 microns BEFORE the fuel pump, and check the tank vent for blockage (insects). Then wait 'til next year with the rest of us!

Jeff

PS: I HATE winter!
 
I had a similar problem. Ran perfect until under load. I ran through the fuel delivery problems and after many weeks of trouble shooting I went back to basics and did a compression check to find I needed to rebuild the top end and now the boat runs great! This may not be much help but I tend to think too fast and not start with basics.
 
We are ALL guilty of that, myself especially. I tend to lock in on the "obvious solution", waste a bunch of time "fixing it", then trip over the real reason later on--MUCH later on.

Jeff
 
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