Half power
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=42506
Printed Date: April-29-2024 at 10:40am
Topic: Half power
Posted By: thump3r1337
Subject: Half power
Date Posted: March-16-2018 at 2:17am
|
I have a 1973 correct craft martinique with the 351W. The boat has been running great, and I have slowly been fixing issues. Last summer I replaced the points with electronic ignition, new coil, new plug, and it ran great. Until the last day, then it seemed to have half the power, and not the same hole shot. My thoughts it is fuel related, seems like the holley carb has issues (one thing I haven't worked on or rehabbed). I can manually open the secondaries, no extra boost of power, but I did do the hand pump to verify the secondary diaphragm isn't blown. A friend of mine suggested it was the power valve causing the issue? I am clueless when it come to carbs. After the season I cracked opened the secondary to verify it was fine. It will start and idle fine, will run all day, but feels like a 120 hp instead of 255 hp that it should be cranking out. I plan on taking it to a mechanic, but am open to anyone that might have suggestions. |
Replies:
Posted By: KENO
Date Posted: March-16-2018 at 8:49am
|
From your description it sounds like it runs smooth at any speed, just a lack of power or does it spit and sputter and run lousy at higher speeds? What kind of distributor do you have in it and what's your timing at idle and every thousand rpm increment? How many RPM do you get at full throttle with this problem? On another note, why don't you go back to your water pump impeller post in 2015 and update it so the next guy with the same issue knows what your solution was. |
Posted By: thump3r1337
Date Posted: March-16-2018 at 11:10am
|
The distributor is a Mallory, I don't have the timing because the degree gauge is missing. There is just a pin, that I marked the timing when I had points in the system. Then I timed it to match with the electronic ignition. I verified it was still set the same from the beginning of summer. The electronic ignition ran great all summer no hesitation, started right up. Then the last day the boat just had half power. I wasn't at the lake when my bother-in-law reported the problem started to happen. What I experienced, is the boat starts fine, idles fine, rev's fine. But under load just half the power. Still runs up to normal RPM's, no back fire's or hesitation, just no power. The weird thing is it is still burning through the same amount of gas. As for the water pump post, I don't show that I have any posts on my account, if you can send me the link I will take a look it the post and close it out. |
Posted By: 8122pbrainard
Date Posted: March-16-2018 at 11:43am
|
Robert, http://correctcraftfan.com/forum/forum_posts.asp?TID=36140&KW=&PID=468507&title=73-martinique-351-impeller#468507" rel="nofollow - Here's the link to your RWP thread. Regarding the power problem, I highly recommend get a timing light on the engine. Also have you checked that the mechanical advance isn't rusted up? Who's brand of EI conversion did you use? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: thump3r1337
Date Posted: March-16-2018 at 12:10pm
|
I updated my past post, thanks for the reminder. I used the PerTronix ML-181 Ignitor for Mallory 8 Cylinder: %20" rel="nofollow - https://www.amazon.com/gp/product/B000JUXGK2/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 I hadn't thought about the mechanical advance, because it is hidden under the electronic plate.  I will have to find somewhere to buy the timing marks for a counter rotating 351w. The previous owner really rednecked together the boat. After the first season I blew out the transmission connector, to find out they had used an automatic flex plate instead of a weighted fly wheel, and no. 10 sheet metal screws.. Luckly I had parts from my 65 mustang.  It's finally starting to warm up here in Kansas City, so I should be able to pull the boat from storage and take a look in the next few weeks. |
Posted By: GottaSki
Date Posted: March-16-2018 at 12:52pm
|
After checking the above, all valid tests. it could be one jug isn't firing. Soon after a cold start, check the exhaust ports for uneven heating, might be able to verify they are all firing or one cold. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: shierh
Date Posted: March-16-2018 at 2:05pm
| scale for timing is on the balancer.. |
Posted By: thump3r1337
Date Posted: March-16-2018 at 4:15pm
|
Not on mine, the harmonic balancer just has the score line, there is a pin on the timing chain cover, but no scale. A normal 351w timing chain cover won't work, since it is counter rotating. |
Posted By: 63 Skier
Date Posted: March-16-2018 at 5:22pm
|
Not sure I see it being possible that you have the same WOT rpm with the "half power" symptom you describe. I'm with Pete on looking at the mechanical advance, that distributor base looks a bit knarly in the picture. Having a light that will read timing at idle and total timing is a must, and first place I'd start on this trouble shoot. ------------- '63 American Skier - '98 Sport Nautique |
Posted By: TRBenj
Date Posted: March-16-2018 at 5:25pm
Wat |
thump3r1337 wrote:Posted By: MrMcD
Date Posted: March-16-2018 at 5:29pm
|
Odd for sure. Could be fuel supply or ignition. Since it runs smooth and quiet it does not seem to indicate an internal issue. I would put a timing light on the engine and watch what it does as you rev the engine up. You should see the timing mark smoothly and steadily advance as you increase RPM slowly. It should continue to advance till you get to 3,000 maybe 3,500 and then stop at that point even if you increase RPM to 4,000. If it does not advance you found the issue. Advance is what lets your power increase as the RPM increases. Assuming it is getting air and fuel properly. Fuel supply could be restricted, bad pump, plugged filter in the lines, carb or at the tank and cause similar issue. ------------- |
Posted By: shierh
Date Posted: March-16-2018 at 5:50pm
|
Sounds like you need a timing mark. You can use the TDC on #1 and install a scale and align it to the mark on balancer. I believe the pencil in the plug hole to find TDC would be accurate enough as long as its done on the up stroke of the piston. |
Posted By: bwinn
Date Posted: March-16-2018 at 5:56pm
|
Posted By: shierh
Date Posted: March-16-2018 at 6:10pm
| Yes but what I mean is that if you have to adjust the crank back and fourth some at the top make sure that you take final reading on the up not the down. no clue how much slop you may have in an old engine. Basically piston needs to be treated as if it was under load of compression. |
Posted By: KENO
Date Posted: March-17-2018 at 8:27am
|
Here's a picture of a 351w reverse rotation harmonic balancer. Like people have said, the timing marks are on the balancer (probably buried under years of rust ). Clean it up a little like this one and you'll have something to go by Since you don't think anything changed, you'll have to figure out what did change since the power loss is a result of something. It's easy enough to check the distributor internals and after you dewinterize it do a compression test, and check vacuum with it running. By the way that picture of the points probably got Pete all hot and bothered just looking at a set of points.  
|
Posted By: KENO
Date Posted: March-17-2018 at 9:22pm
|
Something else you might want to look at is your timing chain and gears. Back then there were a lot of camshaft gears made of aluminum with nylon coated teeth. The teeth eventually get brittle and break and this wreaks havoc on your camshaft timing resulting in symptoms like you describe. You could read about checking timing chain slack, but with your issues and the age of the motor, I'd get a look at the gears/chain There's some work involved in getting to the gears/chain but unless you're sure what's in there, you might as well pull the timing cover and inspect/replace with a new set with either double roller chain or silent chain with all steel teeth. A timing gear gasket set should come with the gears and chain. You can do it in the boat without dropping the oil pan but................If a lot of teeth are missing, they're laying on the bottom of the pan and the only good way to get them out is taking the engine out and removing the pan. Here'a a picture of a gear with a severe lack of teeth 
|