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75 hp Mariner 4 cyl.

F

fastbee

Member
New to this forum, hopefully I can get some assistance on my new to me engine. Today I picked up a used boat/motor: 2007 Crestliner CX17 with a 4 cyl. 75 hp Mariner engine (SN: A954549). Guy wasn't sure what year model the engine was (I later found out it is maybe a 1986 model?) but it ran great on the hose when I first looked at it earlier this week. We met up today at the lake for a test drive and final checkout. The motor was having a terrible time running and wanted to die alot. The guy indicated it does that for a while when cold (today it was about 30 outside). After a little bit it seemed better, and ran fine as long as throttle was up. Around idle speed it was difficult to keep running. Auto mix oil has been removed and it has an electric fuel pump. Both were this way when he bought it 3 years ago. I'm not so sure I like the electric fuel pump idea since if the key if left on it will keep pumping fuel. I'd like to return it to the original mechanical setup but upon researching some it appears that won't be possible if the engine had the triangle fuel pump that has been discontinued. I don't know what was there originally and neither does the guy I bought it from. Can the square pump be installed? What are my options? I got a pretty good deal and I think I'm beginning to see why. Any suggestions on a path forward?
 
racerone said:
Compression test would be step #1 on that motor.
Click to expand...
Thanks for the reply racerone, I've got that lined up for next week. Is there any way to tell which fuel pump was on my motor? I can buy the whole kit, lines and all for the square pump. I've located a used but good triangle one but only get the pump. I'd have to source everything else. I downloaded a "service manual" that covers a very wide array of motors, mine included, but it doesn't really have any pictures other than of the actual pumps. I don't have any idea where it mounts or how to plumb it. The electric pump might be fine, the issue could be something else but I would prefer returning to the diaphragm pump if possible. I'm not huge on replacing the auto-oil system as mixing is not a problem for me. Anyone else got any ideas?
 
Done or done right? You'd be surprised how many "carb rebuilding" consisted of spraying the fool thing with carb cleaner. Then there's the all important carb adjustments.

Jeff
 
No doubt...Guy said "his boat mechanic" but no idea on what was done or if it was done properly. I plan on spending this weekend tinkering to see what kind of improvements I can make.
 
Compression test complete...120-122 lbs. per cylinder. I found where the original fuel pump was and I had the triangle style. Found a used pump and ordered a rebuild kit. Should have them installed tomorrow. Removed the electric fuel pump today and made sure the key controlled choke was working properly. With any luck I'll be able to get this thing running right again. I've looked around and can't find anyone local that really knows much about a 30 year old motor. I looked through my service manual today, not sure about all the adjustments it talked about. Hopefully it will be OK once the original style pump is back on. I'm a pretty good mechanic, but I've always had someone else do carb work for me.
 
I got the mechanical pump installed Saturday. Engine runs much better than before. I haven't had it to the water yet, so there could still be adjustments needed but it was encouraging. The electric fuel pump was a 4 psi pump and the flow rate was about 3 times what the stock unit is. My guess is it was flooding (or close to it) at idle and low speed. Not sure about the limited top end yet until I actually run it. I'll update after more testing.
 
Be careful running only 4 psi fuel pressure. I fried a good PH doing that. You need at least 5 to 5.5 psi at WOT.

Jeff
 
I got the boat to the lake today. I just left it strapped to the trailer for the most part. Got it far enough for the motor to be in good and started work. It was a little hrd to start and would not idle at first. I made some adjustments to the idle mix screws on the carbs per the manual and got it idle pretty good for a bit then it slowly died. Got it started back up and as long as I was at about 1000 RPMs it was golden and would purr right along. Move control to neutral and it would slowly die. RPMs would drop off to about 800 or so and then it just slowly stops. I could mess around with it and get it started and in gear. Once in gear and moving forward it ran like a champ...so much better than before. Topped out around 35 MPH at 6000 RPMs. I think I need a little more prop as well. It was threatening rain, so I didn't get to work on it much more. The manual says it should idle at about 600 RPMs, right now there is no way it will do that. I'll try adjusting the idle stop next time and see what difference that makes. I'm not sure I can take on the timing and such since I don't have a tank and really don't want to try to adjust timing running down the lake. Also, my control lever has to be moved well over half way to full travel before I start seeing much change in RPMs. Is that normal? I might need to look at my control cables as well...this thing is just the gift that keeps on giving. I got a great deal, but there just seems to be a lot wrong here. I finished a total rewire of the boat Friday and all of that went as planned. Now if I could just get the motor running right...
 
Made some more adjustments today. Set primary pick up timing and max advance today while cranking it over on the hose. The primary pick up timing was WAY off from the manual spec. Got it to the ramp and the SOB wouldn't start. I had to take half of the primary timing back out just to get it started, not sure what the timing is anymore but it starts. I messed around with carb adjustments and idle stop and was able to get it to consistently idle around 900 rpms, go into gear and return to idle without dying. I was really wanting to run the boat today because I replaced the 17P prop with a 19P. Got it off the trailer and was able to idle in gear with very slight throttle. I buried the throttle control and it took off great and ran amazing. Problem is I still am turning 6000 RPMS with the new prop, which is very close to what I was spinning the 17. I did pick up 4 mph, so it improved there. I was able to come off throttle and basically idle in gear through a no wake zone with out issue. Shifted in and out of gear several times and it stayed running, so another improvement! Slowly got it on the trailer and when I advanced the throttle to push the rest of the way on the trailer it died. Had a hard time restarting, but finally got it going again and it idled fine but when put in gear it died again, repeatedly. By then it was getting dark so I cranked it on the trailer with the winch and headed out. I think I'm pretty close on everything right now. I did notice the #4 plug wire looked awful, so I might go ahead and replace those. I keep wondering if the PO was truthful about the carb work he had done. It just seems like it's still not just right. I might try to ask around to see if I can find anyone around that knows these engines. I can keep whacking at it a little at a time but I might be better off just dropping it off somewhere.
 
Pull all plugs and take a look, You mentioned only 6000 rpms,are throttle plates opening all the way,not to mention slop in throttle cable in previous thread,obviously a problem with timing advance at wot, fastbee i see no mention of water/fuel separator and/or filters inspected,lines, tank,fuel pickup,primer bulb,clamps& fittings, "air leaks"
 
If that's the engine I'm thinking it is, then 6,0o0 rpm is way above the recommended red line. That would indicate you need even more prop.

Jeff
 
A friend at work is bringing me a 23P prop to try. He's over-propped right now. Hopefully one of mine will work for him and his will work for me.
 
Been a while since I updated, but here's where I'm at now. The 23P prop worked great...I can cruise along at 37 mph and 5500 RPMs. Motor runs strong after I get it running. I've tweaked, adjusted and fiddled with nearly everything so far and am still not satisfied with where it is. The best I could get it to consistently idle is about 1000 RMPs but I have to start it with high throttle and let it run a bit and bring it down. After it's warmed up some it gets a little better in that I can usually start it in neutral at idle position and be ok. Shifting into gear is a little tricky from time to time. It wants to die when shifted into gear, I can give it a little more throttle and it will stay running. Today was the best its been since I bought it. I tweaked some stuff on the ramp before putting it in the water. I was able to start it and let it idle while I parked my vehicle. Got in and could low speed maneuver while shifting into/out of gear around the ramp. Pulled out and went full throttle, no hesitation at all and pretty quickly I was up to 5500 RPMs and 37 MPH. It ran great the whole run. Let out to idle into a cove and it behaved perfectly. I made several more stops, and each one the engine was very well behaved. Started right up, idled fine, shifted good, didn't die! Then I came back to the ramp...I pulled it up to neutral and tied off to the dock. Got my trailer backed in (boat was idling the whole time, maybe 2 minutes) and when I put it in reverse it died. I spent 10 minutes trying to keep it running enough to load the boat on the trailer. Finally ended up having to come in a lot hotter that I like to get it on there. I just can't figure out why it would do so good for 3 hours and then go to total crap all of a sudden. It was almost like it knew I was at the ramp! I've tried a couple of different procedures to link/sync. I've got new plugs, new plug wires, a new starter solenoid, new voltage rectifier (old one took a dump last weekend) and a new water pump (old one was only putting out 3-4 psi, new one is 5-6 not sure if that is enough or not). I ran all the old fuel out and refilled with non-ethanol gas and Amsoil premix oil. I haven't pulled the carbs yet, not sure I will. I haven't done much carb work before. I've checked around and can't find anyone within an hour of me that knows much about these older engines. I'm beginning to think I either need to expand my search area or try to find a reasonably priced used engine to trade on. I did have a though today, the control box looks to be older that the engine. I owned a 1988 Bass Tracker with a 75 HP Mariner 3 cyl and the controls were much different than these. Could they be causing some problems? The shifter seems to work OK but the cables look to be too long, not sure if that would matter or not.
 
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It's not the control box. You're still having carb problems. I suggest a thorough rebuild and cleaning, followed by new hoses AFTER the fuel pump. I've seen older hoses degenerate with ethanol fuel to let small black rubber particles get into the carbs (and plug things up).

Jeff
 
I'm beginning to think the same thing. I found the carb rebuild kits and they don't look too bad...I'm a pretty good mechanic and maintain all of my other vehicles and equipment myself. I guess I have just been fortunate that I've never had any carb issues over the years so I haven't had the opportunity to get experience. I might order them up today and see how it goes.
 
In looking at the kits available I've become a little confused. I think I might have the WM-14 carbs but don't know that for sure. The pictures in the repair section of this site of the WM-14 looks like the ones in be engine, but I don't know what the WM-17 looks like. There is a big difference in the kit prices between the two. Also, would I need the full repair kit or not? I've found a couple of places that sell the stuff broken out to smaller packages, like a gasket kit, needle kit, then full repair kit.
 
I really like doing an ultrasonic cleaning to the carbs when they are all apart to get all the crap out. Make sure you run a tiny wire through every little port in the carbs. Would would be surprised how often one little hole is clogged up that you would swear was good. Take your time and run compressed air through everything too to make sure it is super clean. It will be a completely different engine with a clean carb. If they supposedly rebuilt the carbs last year you may not need any parts, just take the thing apart and see what you find. New gaskets will be pliable and still good. Old gaskets will be obvious. These other guys giving you advice are much better and experienced than me. Just my two cents.

Don't forget to sink up those carbs too with a set of vacuum gauges. Makes a world of difference too.
 
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Well, I found a guy to take a look at my engine. I thought he had quit working on them, but he still takes on some work here and there. Dropped it off last Monday and described the problems. He felt confident it was a carb issue and said he'd check a few things and then probably do a full ultrasonic clean and rebuild of both carbs. He called me today and said he found the problem. It appears that the reeds for #3 cylinder are broke. When he told me that, a finding on my initial compression test made sense. #3 cylinder would fluctuate when cranking it over...the others ran up to 120 and never moved. I guess I know why now! Any way, he said it would be pretty expensive to repair and that I should look at finding another motor to trade for. I asked him to get me a solid quote on the repair and I'd go from there. I've saw complete reman'ed power heads for less than 2k, but have no idea what this repair will cost. Maybe I'll call around and see if I can find a good used motor that is newer for a fair price.
 
You may look on ebay and see if anyone has reeds listed or a powerhead. Sometimes you can pick them up really cheap. Goodluck!
 
I've found complete re-manufactured powerheads around $1800 or so, just not sure I want to go that route. I'll still have a lot of things that are nearly 30 years old on there. I can still rebuild the fuel pump and carbs, but can't buy either new. Several parts are obsolete or getting hard to find (read expensive). I'd like to get a motor closer in age to my boat, with more current parts and something more shops are willing to look at but that might be more expensive than I want to go too.
 
Can I use a later model 3 cylinder power head? The later models seem to have better part availability, but I don't know if it will mate up or mess up the cowl fitment.
 
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