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Engine not getting WOT rpm/Stalls at idle

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proav8tor

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Hello Everyone. This is my first post but I have found tons of useful info on these forums in the past...so here is my problem...

I have two Crusader 305s (manufactured in 1979 - installed in 1980 Silverton) with Rochester 4 barrel carbs one of them runs great the other has a weird problem that's been going for two seasons now.

1.The motor starts fine and even idles fine for quite a while...

2.After running the boat for varying lengths of time at different power settings about 90% of the time when throttling back to idle it will quit.

3.After it quits it starts right back up but won't stay running if I put it into gear (forward or reverse).

4.The same motor is not getting the WOT rpm only about 3400-3800 rpm (should be 4400 rpm) and the carb is getting full travel from throttle linkage.

Both motors have about 150hrs and both have rebuilt carbs that have about 30hrs on them. I have replaced the plugs, checked the timing, replaced distributor cap, replaced points, and replaced ignition coils.

Everything I did I did to both motors at the same time and as always the port engine runs great yet the starboard is stuck with this problem.

I'm at a loss...I haven't replaced advance springs/weights in distributor, haven't replaced fuel pump and haven't checked for vacuum leak...

Those 3 things aside does anyone have any ideas what could be causing this to happen?

Thanks in advance!
 
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Does "...checked the timing..." include the advance curve or just the 10 deg BTDC at idle?

Verify the point gaps with a dwell meter?
 
makomark said:
Does "...checked the timing..." include the advance curve or just the 10 deg BTDC at idle?

Verify the point gaps with a dwell meter?
Click to expand...


Yes as far as I can tell it is advancing properly and I didn't have access to a dwell meter so I just gapped the points while on the high part of the cam lobe...
 
I had a similar problem and it turned out to be the dwell. I ended up borrowing a dwell meter. I though I was pretty good a gaping the points but as it turned out even though it was gaped to spec I have to bring the points closer.
 
Great article on tuning I found here

I just mentioned in another post that I picked up a dwell meter (multimeter with tach and dwell) for about 20 bucks. Looks like the current one is about $35 from Harbor Freight

Back to your problem. I had some wiring issues last year. One engine would cut out when I throttled down and would intermittently start then die, usually when put into gear. In my case, it was a bad connection in a spliced wire to the ballast resistor. Just enough movement from the boats momentum(and me poking around the wiring while scratching my head) to open/close the circuit. Just food for thought, it could be unrelated to the WOT concern. Maybe a faulty neutral safety switch if present?
 
makomark said:
So, how are you assessing it is advancing properly?
Click to expand...

I just used a timing light and during engine acceleration I can see a smooth advance on the timing marks...then compared it to the engine that is working okay. I'm sure that this isn't the technical way of doing it....
 
I just went through the same thing and it turned out to be crud in the carb. She would run great at high rpm's but stumble and die at idle. Check your filters and if need be pull the top of the carb off and give it a cleaning. Good luck.
 
So what you have is some timing advance but you haven't measured it. Your approach is fine, I'd suggest investing a few dollars for a "timing tape" and then you can accurately assess what is going on.

Dwell angle controls spark quality as well as initial timing. To make the engine perform up to spec, it must be well tuned (all systems clean, working properly, and adjusted correctly).

I'd check or replace the spark plug leads and then do the vacuum tests and verify the fuel pressure too (same gauge can do both tests if you buy the right gauge). Complete the full tuneup and then proceed with the troubleshooting.

When was the last time both engines achieved the rated WOT rpm?
 
proav8tor said:
1.The motor starts fine and even idles fine for quite a while...

2.After running the boat for varying lengths of time at different power settings about 90% of the time when throttling back to idle it will quit.

3.After it quits it starts right back up but won't stay running if I put it into gear (forward or reverse).
Click to expand...

OK, i'm going to go against the flow a bit here. These 3 symptoms do NOT tell me that the timing, dwell, or even the ignition is bad. It COULD be crud in the carb; but do an easy test first. The next time it stalls, take off the flame arrestor and see if gas squirts into the bore when you open the throttle. THe symtom hints at a major lack of gas inside the carb.
 
Dave,
When I went through this last week, I could pump and see plenty of fuel. It was while I was trying to idle that it would stumble and fall on its face. I am lucky that my kid brother is a GM tech with carb experiance and I just took it to him and he cleaned it all out. He blew out everything useing carb cleaner and compressed air. She is running good now. (he say's as he knocks on wood)
 
Hook up a vacuum gauge, do the timing (don't think that's it, but the best "sweet spot" with the vacuum gauge) and also adjust your carb mixtures and idle. Bet you'll be fine.

Plenty of info how to do this with such gauge on the net.
 
Sounds to me like yiur carb is flooding. Try this:

1. Warm the motor and idle it down, giving it enough gas to keep it running if it doesn't want to idle

2. Turn the idle mixture screws in (clockwise) and see what happens

3. If the motor keeps running, or picks up speed, the carb is flooding. If it slows down, it isn't

Try that and get back to us.

jeff
 
I think you need to make sure its running on all 8 cylinders. At a cold start the choke will enrich the fuel mixture enough so that it won't stall when put into gear. So off you go, but it won't turn up to anywhere near its rated RPM. Now its warm, chokes off, and it stalls at idle when put into gear, behavior consistent with a bad plug or bad wire or dead cylinder.
 
Good advice! (Wish I'd thought of that....)

Try this: Warm the motor and get it to idle in neutral at 1,500 rpms. Using insulated pliers and gloves, remove one wire at a time from the distributor cap, listen for an rpm change, then put it back. If a cylinder does not respond there's your problem. If TWO cylinders don't respond, try swapping the plug wire positions and see if that helps. (It's damn easy to mix up wires on these engines with that dopey way they stuffed the wires between the valve cover and manifold.)

Jeff

PS: You'd be surprised how well that engine will idle on 6 cylinders! Mine would even plane off that way, though it backfired above 2,500 rpms.
 
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