WOT only 3800 RPM
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=14520
Printed Date: June-05-2024 at 9:22am
Topic: WOT only 3800 RPM
Posted By: Excel94
Subject: WOT only 3800 RPM
Date Posted: July-18-2009 at 7:49pm
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I noticed a drop in engine performance this season, especially under load. In the mid RPM range it would run about 1 mile an hour for every 100 RPM. However, when I checked WOT it would only turn about 3800 at 37 MPH.
It's a 94 351 PCM reverse rotation in a V drive. I replaced the pro tech last year with the electronic ignition distributor kit from CC and that has functioned fine. Prop is in good shape and not recently dinged or damaged. From my search I saw some others had a firing order issue that produced a similar problem but I checked mine and it is correct. I checked my timing and it's about 10 at idle. When I gave it gas it advanced. I really could not read the numbers well, but it definitely advanced with the RPM. I did notice that the secondaries did not open when the RPMs increased. I took it briefly up to 3000 in the driveway and they still did not open. Is that an effective test of secondary opening or does it have to be under load to determine if they are functioning correctly? |
Replies:
Posted By: nuttyskier2002
Date Posted: July-19-2009 at 12:48am
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Check your spark plugs (clean and gap) or replace them. Next check your timing advance at 3000 RPM. If you do this at home don't hold the RPM that high any longer than necessary than it takes to get a reading. If you don't have a variable strobe delay timing light then get a timing tape label for your harmonic balancer. If you go this route make sure you get the right one for the diameter of the balancer. 3000 RPM with engine unloaded is not enough to get the secondaries to open. ------------- 95 Malibu Echelon w/Mercruiser 350 Magnum Skier Former boats: 88 Ski Centurion Tru Trac II 59 Chris Craft Capri (woody) |
Posted By: Excel94
Date Posted: July-19-2009 at 12:39pm
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Okay, I'll replace the plugs and try to get a better look at the timing when advanced. I will also replace my fuel water separator and check the anti-siphon valve.
Here are a few questions 1. My manual just mentions 10 BTDC at 600 PRM. What should the timing be at increased RPMs? 2. Other than running with the rear hatch open and the spark arrestor off, how do you check to see if the secondaries are working correctly? |
Posted By: Excel94
Date Posted: July-19-2009 at 12:57pm
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I just saw this by GottaSki
Aim for 10 initial, 36 final i like these numbers..I think its a little earlier than stock. I run my boat light for slalom, you may want to be on the shy side of these numbers. 10 at 700 21 at 1500 30 at 2k 34 at 2500 36 by 3k Now that I've got these numbers I'll look to see what mine does. Still would like to know how to check the secondaries. Thanks. |
Posted By: Excel94
Date Posted: July-19-2009 at 5:13pm
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Update:
I pulled the plugs and there were as black as can be, smelling pretty strongly of gasoline. In addition to putting in the new plugs I assume I need to make it run a little leaner. Is there a simple way to correctly adjust the air/fuel mixture on my Holley? |
Posted By: SNobsessed
Date Posted: July-20-2009 at 11:08am
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Sounds like your choke isn't opening up all the way. ------------- “Beer is proof that God loves us and wants us to be happy.” Ben Franklin |
Posted By: Excel94
Date Posted: July-20-2009 at 12:48pm
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I'll take a look at that too. FYI, the anti-siphon valve looked good.
Something interested I discovered while trying to set the idle mixture was that if I turned the two screws all the way in the engine kept running fine? I was expecting to hear the engine start to get fuel starved as I turned them CW but that never happened. That made me wonder about junk in the carb keep the needle valves from seating correctly. I put some sea foam in the tank and also took off the fuel water separator and filled it with 25% sea foam then started it. I hoped that would give it a high concentration to clear any junk. I will try and take it to the lake today and run it to see if there has been any improvement in performance. Somehow I think there is a carb rebuild in my future. |
Posted By: Excel94
Date Posted: July-20-2009 at 1:27pm
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SNobsessed, Good thought on the choke. I went out and checked it right away and after a minute or two the choke plate was vertical. So I guess that one is off the list.
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Posted By: nuttyskier2002
Date Posted: July-21-2009 at 1:51am
Something's causing your carb to run rich. Float level too high or leaky power valve come to mind. ------------- 95 Malibu Echelon w/Mercruiser 350 Magnum Skier Former boats: 88 Ski Centurion Tru Trac II 59 Chris Craft Capri (woody) |
Excel94 wrote:Posted By: Excel94
Date Posted: July-21-2009 at 12:43pm
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Yeah, when I had those needle valves all the way in and the engine was still running great I thought "this is odd behavior for a carburetor". I guess its the power valve or something in the metering body?
I've ordered the refresh kit and hope to rebuild it this weekend but it's been a while since I tackled that job. The last time I rebuilt a holley carb was 1978 and it was on my '68 Camero. Hope the instructions are good. I'll be posting any questions I have so stay tuned! Tim |
Posted By: SS 201
Date Posted: July-22-2009 at 6:50pm
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Go 32 degrees at 2500-3000, whats' left over at idle is your inital. This changes from boat to boat based on engine condition and other incindentials.Where it runs the best is your engine spec. |
Posted By: Luchog
Date Posted: July-23-2009 at 12:07am
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If the air mixture screws are not responding there's an issue with the carb for sure.
It's probably running on the transition slots and not the iddle circuit. it seems like a good time for a carb rebuild. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-24-2009 at 10:18pm
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So far so good...
I took the day off and rebuilt the carb with my father-in-law. Neither one of us has seen the inside of a Holley in at least 30 years but between the two of us we got it back together and the engine started up pretty quickly. However, we could not adjust it well enough to get it running the way it should at idle and it backfired when you hit the throttle repeatedly. I check the timing and played with that for a while but still no improvement. Then it occurred to me that even though the plugs are only a week old this thing has been running so rich they may be fouled. Sure enough with 8 new plugs it now runs great! At least in the driveway. Tomorrow I'll take it on the lake and see how it performs in real world conditions and what the RPMs are now at WOT. I'll report back with the update tomorrow night, thanks for the help! Oh, almost forgot, how do I adjust the choke? When the engine is hot or cold? TIm |
Posted By: Excel94
Date Posted: July-26-2009 at 1:05pm
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I need some help here I'm running out of possible causes of the poor performance. Bit of a long post but wanted to provide you with the whole story.
After the carb rebuild the boat runs great in the driveway but this time it would not go over 3600 RPM? Granted the water was a choppy with an occasional white cap and we had 6 people in the boat but still it should turn more than 3600. I took a plug out when I got back and at least now no sign of it running rich, so that's good. So far here is what I have done/checked On the fuel side; can of sea foam in the tank, ran it through anti-siphon valve clean, spring compresses easily new fuel-water filter carb rebuilt On the electrical side checked timing confirmed firing order (18456273) new plugs Last season replaced Pro Tech with Mallory (kit from SECC) What I will check next... Secondaries opening (best way to check by raising hatch and using mirror to see if they open?) Poor Compression (will test that and report back) Prop (previous prop had a ding, current prop was a remanufactured version of stock OJ, ordered new ACME prop which was needed anyway and will eliminate prop as cause of problem) What else could be causing this poor performance? FYI, the original 351 HO was replaced by the previous owner with a Jasper long block. So I lost 40 or so HP due to that but even so shouldn't it still rev to 4400? I've wondered if the firing order stayed the same? I assume it did because the other version of firing order I've seen has 4 plugs in a different sequence. I assume there is if 4 plugs were firing out of order it would not run well at all. Ideas on what else I should be checking? Tim |
Posted By: eric lavine
Date Posted: July-26-2009 at 1:50pm
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I thought alot of those excels were bib block boats, losing 40 horse would definitely be in the cards, is your boat soggy possibly? all these factors add up to a 400 rpm decrease.....your chain could be stertched....you need to take some vacuum readings and do a compression test then figure out what needs to be fixed...your using the process of elimination but starting at the wrong end, obviously tune-up parts should be first...thats using common sense, but your at a point where you dont know whats happening and a 1/2 hour of your time will nail the problem ------------- "the things you own will start to own you" |
Posted By: Excel94
Date Posted: July-26-2009 at 4:03pm
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Thanks Eric,
Yeah, its time for a compression test, it's raining right now but hopefully I can do it tomorrow morning. I assume you do vacuum readings from the main port that runs to the PCV? I assumed the boat is not soggy since it does not have wood, although I guess the foam could still be soggy though, had not thought about that. I'll re placing the carpet at the end of the season and could look for some worn fiberglass on the floor. |
Posted By: Excel94
Date Posted: July-27-2009 at 7:34pm
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Here are the results of the compression test, I don't think that's the problem, which is good news.
#1 132 #2 132 #3 140 #4 142 #5 130 #6 135 #7 135 #8 132 I'm not really sure of the correct way to run a vacuum test so I just measured it at various RPMs. 600 14-15 (needle bounced quite a bit) 1000 17 (much more steady here) 1500 19 (very steady) 2000 20 (very steady) 2000+ 20 (very steady) So, check me out on my logic here. Most likely culprits for low power fuel electric (spark) compression prop 240 HP instead of 285-300 HP engine overwhelmed by wet foam, overweighting boat, etc. As mentioned earlier I have checked/replaced/rebuilt most of then fuel system including the carb. The carb definitely needed rebuilding and it no longer runs rich, but that did not restore the power. Also as mentioned, I replaced the pro-tech with the Mallory EI kit and checked the timing. Also replaced plugs again after carb rebuild. Mallory made it start easier and run smoother but not the culprit either. Prop is still a possible suspect, I've learned that the Excel came with a 14X16 prop only if it had the 351 HO or 454. If it had the 240 engine it came with a 15 inch pitch instead (thanks Woody at SouthEast for that bit of info). While my prop (14 X 16) technically is stock it is not the factory prop for my current engine. I have an ACME 328 on order. I should get some improvement from that but I'm still wondering if there is something else to this?? Any other ideas???? How would I know if the foam was wet?? Thanks, Tim |
Posted By: Luchog
Date Posted: July-28-2009 at 1:48am
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are you sure the secondaries are opening? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-28-2009 at 2:56am
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Luchog, actually I don't know if they are. I forgot about that one, thanks for mentioning it.
I'm not sure how to test them other that to bring a mirror and lift the hatch enough to look and see if they open while my son drives the boat. I hope to go out tomorrow and find out. |
Posted By: Luchog
Date Posted: July-28-2009 at 12:49pm
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how old is your son? if not old enough to drive have someone else drive and hit the gas while you watch for the secondaries mechanism to open. If they dont, You could try to manually open them once you reach your limited wot to see if that gives you the lacking rpms.
First thing to check is the mechanism was correctly put together after the rebuild... then you should check the secondarie's diaphgram. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-28-2009 at 8:06pm
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I think you hit the nail on the head. I went out today and at WOT the secondary linkage did not move. Unfortunately I did not think of trying to open them manually and didn't see your response until I got back.
I will take a look at the linkage but I think its right. At least when I open the throttle all the way (engine off) I can move the secondary linkage and open them. I know I put that little "BB" sized ball back in place with a new diaphragm. I will take a look for anything obvious and if nothing is found I will take the secondary bowl off and look at the secondary plate. I know the metering block had junk in it maybe I missed some in other places? Any other thoughts on diagnosing exactly why the secondaries are not opening? |
Posted By: TRBenj
Date Posted: July-28-2009 at 8:25pm
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Check to make sure the shaft isnt frozen as well. You should be able to turn it by hand. ------------- |
Posted By: Luchog
Date Posted: July-28-2009 at 8:59pm
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the little ball is on the primaries, the secondarie's diaphgram is a big dished housing at the side of the secondaries bowl. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-29-2009 at 6:06pm
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Thanks guys,
TRBenj, when I opwn the throttle all the way (engine off) I can lift the diaphragm linkage and the secondaries open easily. Luchog, There is a small vacuum opening next to one of the 4 screws that hold on the cover for the secondaries diaphragm. According to the exploded view a small "BB" goes in that general area. It's called the "diaphragm housing check ball" on the parts list. I put it in the small vacuum opening since it fit and I didn't see where else it would go. Should it go somewhere else? Tim |
Posted By: Excel94
Date Posted: July-29-2009 at 6:14pm
| One more thing. I looked once more at the exploded view and I honestly can't remember if I put in a new O ring between the housing and the secondaries body. I will take off the carb and check that. I would still like to know if I put the "diaphragm housing check ball" in the wrong place. |
Posted By: Luchog
Date Posted: July-29-2009 at 9:31pm
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I stand corrected, there's a checkball on the secondarie diaphgram too.
There's a nice carb rebuild procedure on the 302/351 service manual on the reference section. I think you want to check it. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-31-2009 at 7:29pm
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Okay, secondaries now working, at least on the bench.
I also learned a cool way to bench test the secondaries. I found the vacuum passage opening in the primary venturi, the one that draws the vacuum to open the secondaries. Then I shot compressed air over it to produce enough flow to create a vacuum in the passage. Sure enough the secondaries opened right up (while holding the throttle linkage open) May be hard to understand so I'll post a video of it. I think the problem was the small housing gasket that goes between the body of the carb and the secondry housing. If it was incuded in the rebuild kit I missed it. I had left the old one in there when I did the rebuild and it looked pretty good but I found a new one and installed it. Now they open right up. I have to wait to test it on the boat because the damper plate started making a racket now that I have the new prop in place. Should know somehting next week. |
Posted By: Luchog
Date Posted: July-31-2009 at 7:35pm
have you checked if the problem is while at iddle? what's rpms while iddling around? I have found that these newer props with more surface area and less slip put some more load on the engine dropping the rpms while iddling. maybe you just need to bump up the iddle a little bit, mine's set at 750. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: July-31-2009 at 8:47pm
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HI Luchog,
Yes, I did have to bump the idle up a little bit to keep it from stalling when I put it in gear. I wasn't sure why but your explanation makes a lot of sense. Asside from that, it make a noise which I have heard described as shaking a "can of nails". I made it when putting it in gear and stoped around 900-1000 ROM. I assumed it was a spring from my damper plate but now you have me wondering because I did increase the idle and later noticed the noise stopped, but I did not connect the two. Just to double check, if that noise went away with an increased idle it may very well not be the result of a problem with the damper plate? |
Posted By: Luchog
Date Posted: July-31-2009 at 9:30pm
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the problem is there indeed, but the urge to take it apart might depends on how much you need to bump your iddle to keep it silent.
How many rpms at iddle, and when iddling in gear? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: Excel94
Date Posted: August-01-2009 at 1:15pm
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Hmm, tempting. I plan on doing an engine upgrade this winter and will have to pull the engine anyway to swap cams (unless someone can tell me a way to R/R the cam on a V drive without pulling the engine).
Due to my work schedule I only expect to put another 25 hours or so this season. I'm thinking if it stays quite to leave it until after the season. As it is about 800 RPM keeps it quiet. Sound crazy? |
Posted By: Excel94
Date Posted: August-01-2009 at 3:08pm
| To continue my side discussion. I went out and looked. I think it may be possible to swap cams without removing the engine on ym V drive. |