July 2, 2020 at 10:49 pm #207517
Hello to all;
Yes, I still haven’t ironed all the bugs outta this motor. All but one bug, I think.
It seems to starve out when the throttle’s advanced much more than half way. The rpm’s will continue to climb, but not a lot. Acceleration is steady and strong until then.
And, when letting off the throttle, there’s a surge at about half way. The revs pick up a bit, and it surges forward a little. As the throttle is closing, at about half.
Only gets up to about 4,200 RPM. In a flat bottomed aluminum runabout with two people in it.
Tried 3 different props and maxed out the trim; no help.
Otherwise it starts up the first time you hit the key, and the link to me rope starting it w/ ease is https://youtu.be/ehm0GoSSo0Q
I’m starting to suspect a crack someplace or something.
Here’s what’s been done.
Carb’s been cleaned many times. like 10.
Venturis centered with a centering tool.
New gaskets, needles, and packings
New high speed jets, correct size, installed with a jet tool.
New fuel lines and clamps, from carb to tank.
New fuel pump diaphragm, (twice now).
New fuel hoses, CG compliant, new fuel fittings both ends. New pickle.
Tanks cleaned, screens clear, new tank fittings, orings, etc.
Tried two different tanks, and squeezing the pickle while Dad drove. No change.
Full tune up, including all new spark wires.
Checked linkage synch many times.
OK, I’ll poke my head around it tomorrow, looking for cracks or leaks, muttering darkly. Anything else I can try?
AlanJuly 2, 2020 at 11:30 pm #207518
I have to believe it is a belt timing or sync issue, but you’ve already denied that so I won’t argue. Still, it sounds like retarded timing. How about a sheared flywheel key?July 3, 2020 at 1:20 am #207520
Many thanks Frank R;
Agreed, this does sound like retarded timing, like it’s not advancing. I’ll check that thoroughly and try to look at it with fresh eyes.
If it looks right I’ll post pics to confirm.
Flywheel’s been off, twice, and key replaced. No concern noted. Also replaced the points cam, (right side up).
All opinions welcome.
US Member - 2 Years
Topics: 40July 3, 2020 at 5:55 am #207524
Sounds like you have flogged the fuel system pretty hard. However, the ultimate verification of your work would be to have somebody drive the boat while you take a pump oiler/ squirt can full of two stroke mix and shoot some down the throats of the carb, when the problem is occurring. If the speed picks up, you’d have a fuel issue. If it actually slows down, then your fuel system is probably okay. I am not exactly sure about the configuration of a ’67 80 but I seem to remember it has a belt driven mag, which rotates when advanced. Do you have a plug wire arcing out at full advance? Something like that?
Long live American manufacturing!July 3, 2020 at 9:24 am #207527
It is a belt driven battery ignition distributor. I was patting myself on the back (wrong), thinking a sheared flywheel key, but I guess he has gone everywhere with it already.July 3, 2020 at 11:00 am #207532
The RPMs actually surge up/increase briefly when you are retarding the throttle? If so, just seems like something with the syncronization is off…July 3, 2020 at 1:08 pm #207537
The RPMs actually surge up/increase briefly when you are retarding the throttle? If so, just seems like something with the syncronization is off…
That is exactly why I suspected the timing is retarded. Spark must be at full advance before the carb butterflies kick full open or it will bog when they do open. Back the throttle off just a bit to “cruise” position, and the butterflies close down some and it takes off again.
feetwin and I are on the same page with our thinking.
Alan, you do have the breaker points set at 0.020″, don’t you.
July 3, 2020 at 9:33 pm #207582
- This reply was modified 1 month, 1 week ago by frankr.
All replies appreciated.
First two pics are with the distributor advanced by hand to the stop. They show the throttle position at full advance (not very far open) and the view of the control shaft in relation to the diamond shaped projection, (they look parallel to me).
The second two are of the belt timing marks.
The only way I’ve ever been able to set the points is to rope it around with a multimeter attached, and watch for them to open when the red marks on the distributor wheel line up with the pointers on the housing. The way it starts so easily and runs so smoothly at low and medium speeds, I’ll be surprised if the gap is way off.
But I bet this is one small mistake that I keep missing, and I am very open to correction or speculation.
I very much appreciate the support.
Happy Fourth of July to all!
- This reply was modified 1 month ago by Alan.
You must be logged in to access attached files.July 3, 2020 at 10:25 pm #207594
Ok, you convinced me that I don’t know what’s wrong unless the flywheel key is sheared, and you assured me that it isn’t so I believe you. I realized that you know what you are doing when you said you used a venturi centering gauge. Not many people have one of those.July 3, 2020 at 11:32 pm #207596
Many thanks for your support and prompt replies, frankr.
I’m not feeling like the sharpest knife in the drawer at the moment. The centering tool was loaned to me by parts guru Dan Gano. He’s been a great source for NOS parts. Lots and lots of NOS parts.
Sitting in the back of the boat at near full throttle, with the motor cover off, spraying fuel into the carb sounds sketchy when I say it out loud. But I see the wisdom and appreciate the suggestion. I would love to narrow down to either a spark or carb issue.
I sat in the back while Dad went from idle to top speed, repeatedly. I’ve pressed on the exhaust housing and didn’t see any transom flex or movement. Lund makes solid boats; I doubt it’s flexing. Hook, rocker, or whatever. The gearcase and driveshaft seem quiet and smooth, and there were no metal pieces on the magnetic plug when I changed the gear oil.
If anyone sees any issues with my synch or timing, I hope to hear those. Also love to hear any improbable or unlikely issues. Wrong part installed at some point? Upside down? Backwards?? A hairline crack someplace? Bizarre or improbable? Let’s hear it.
Thanks again, and very happy Fourth of July to all.
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US Member - 2 Years
Topics: 40July 4, 2020 at 5:37 am #207604
If it makes you feel any better, I have been squirting gas and oil into carburetors for probably almost 50 years and have never had an incident. Reed valves make it pretty unlikely that you will have a blow back. I didn’t make the technique up. It was taught to us by OMC. In small boats where I can both steer and reach the carb, I do it without assistance. Frank has been around longer than I have and has worked on those big old fuel black holes more than me. I am not disagreeing if he says it’s linkage. All I am saying is that the fuel spray test will eliminate any doubt you might have left about fuel supply.
Long live American manufacturing!July 4, 2020 at 6:25 am #207607
Bill’s technique is tried and true, and easy enough to do on this engine, no funky air box/hardware to remove. That being said, safey is key here. You will need an assistant to drive the boat and you must be securely “perched” close enough to the engine so you can spray the carb throats easily. Just put some 50:1 mix in an oil squirt can and spray the throats one at a time at the problem throttle position. Like Bill says, one of three things will happen when each throat is sprayed:
RPM will decrease indicating the fuel system/carb is functioning OK
RPM will pick up indicating something is restricting the fuel supply in either the delivery or carb
RPM will not change indicating those cylinders aren’t firing for some reason
I think it is safe to say that option three isn’t occurring, but who knows. Keep in mind that you can get different results on both throats. RPM might pick up when spraying one throat, while it might decrease in the other throat. If this occurs, there is some sort of fuel restriction in the carb barrel that increases RPM when sprayed.
Needless to say, do not perform this operation if you don’t feel relatively safe doing it, perhaps the transom restricts easy access to the carb throats. Have a fire extinguisher ready, although there is no big fire risk here. Backfiring is extremely unlikely.
I am not that familiar with the sync process on the older V4s like yours, but Frank sure is. I’m pretty sure that the carb has a stop on the throttle shaft that prevents it from going past fully open position but it is worth a look…Perhaps the roll pin is out of the shaft, or the stop boss is broken off the carb body. The symptom you describe sounds like what happens on the newer engines when the sync is off and the carb butterflies can go past the full open position….But again, I’m pretty sure your carb has a stop on the throttle shaft that prevents going past the full open position.
The only other thing I can think of is that perhaps incoming air is restricted to the engine, or perhaps there is an exhaust leak under the cover. But, I’m pretty sure you have run it with the cover off with the same results….July 4, 2020 at 9:00 am #207614
Wouldn’t it be nice if you could beg, borrow or steal a correct test prop for the motor? Then you could run it WOT without going anywhere.
EDIT: Since writing that, I got to remembering how scary it is to stand next to a four or six cylinder motor running at 5000 or 6000 RPM. Downright terrifying, actually. I once had a V4 Fat Fifty toss a rod on me at only around 2000 RPM or so. I also knew a man that had a flywheel explode in his face.
July 4, 2020 at 10:11 am #207624
- This reply was modified 1 month ago by frankr.
I guess I know a big reason I can’t hear anymore as well….Those engines are loud with the air box off…July 4, 2020 at 11:39 am #207638
All replies very much appreciated.
Wow, pretty exciting to stand next to a motor that threw a rod, or had the flywheel fly apart! Nightmare. Glad nobody got hurt.
Squirting fuel into the carb while running it sounds like a solid way to narrow down the problem, which would sure help. Although, after 6 unsuccessful attempts, I am running out of people who want to go to the lake with me!
I’d love to run it in a test tank; that way I could check timing with a light AND give a shot of fuel, without a lake trip. But no dealer in town wants to deal with old motors, or the liability of letting me play in their shop. Which I understand. One time I only made it about 10 steps down a driveway, with a (merely) 15 year old Merc in one hand, and my checkbook in the other before the guy started yelling at me. “Get that thing outta here!!!!!” All red in the face and PO’d.
I have run it with the cover off, without any improvement.
The carb does not seem to be opening too far, from what I can see.
OK, I’ll check the flywheel key today, and look for something loose or cracked.
Still open to all ideas and wild speculation.
Much thanks and happy 4th!
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