93 Mercruiser 5.7 - No Power Under Load

Hello all, I am new to the forum, and would first like to thank everyone for the valuable information you provide through this forum. I have tried to solve my problem through reading current threads, but even after trying many things I have read here I am still having no luck, so I thought I might start a new thread and maybe get some more specific advice.

I have a 93 Maxum 22' Cuddy with a 5.7 Mercruiser Alpha Drive and Carb. The main problem is that when under load I have no power (runs and revs just fine on the hose or in nuetral while in the water). I can ease up to speed most of the time, but I am still not getting up to the speed I use to be able to before this issue started. My father was a mechanic by trade before passing in 2007 so I am somewhat mechanically inclined, but there is certainly a point in which I am better off leaving it to the pro's.

At first I thought spark, so I replaced the plugs, wires, coil, coil wire, cap, rotor, and module in distributor. No change. I did not replace the Thunderbold ignition on the back of the dist. because I was told that it either works or doesnt so if I have spartk at all it is fine. I then decided to rebuild the carb. The carb looked to have never been apart, was full of dirt, and the floats looked way out of adjustment (one lower than the other). I thought this has to be the problem. I soaked the carb in carb cleaner for two days with all parts out of it. Put it back together and tried it this past weekend. Well it seemed slightly better at first, but then quickly started the problem as if I never touched anything. At this point I am stumped. I have tried to take it to the local marina's but they are all backed up for 5-6 weeks. The only things I can think of to do is adjust the floats up a little (maybe it is still starving for fuel??), and do a compression check. Any ideas or suggestions would be greatly appreciated.

Tony

Re: 93 Mercruiser 5.7 - No Power Under Load

while i'm not the pro on these questions. i'll comment anyways..:facepalm:

I replaced the plugs, wires, coil, coil wire, cap, rotor, and module in distributor.

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that sounds good. imho, check elec. before fuel. one thing i don't see there is did ya set timing per the book on your rig?

I soaked the carb in carb cleaner for two days with all parts out of it. Put it back together

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that sounds mostly good. fwiw, the carb. cleaner i used said to soak for 20 min. or so. the clean w/soap and water. most importantly, air dry with compressed air being sure to blow out the small passages that can become clogged over time. i don't think ya should miss that step.

i also don't see where ya R&Red the fuel filters. that's always seems to be a 1st on the list of to do items.

and do a compression check.

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for sure. do that. assuming all is well. it'll at the very least give ya a reference for future use to be compared to. a compression test give the general health of the engine. if something is wrong with compression, all the tuning in the world won't fix it... ya gotta have a starting point.

now let the pros fill ya in..

Re: 93 Mercruiser 5.7 - No Power Under Load

Ziggy -I did used compressed air to blow our all of the passages. I did so when I first took it apart and just before putting it back together. The carb was nasty for sure and I felt that I got everything out of it. I really thought that was going to be my problem for sure. I also replaced the fuel filter/water separater during all of this, and the mechanical fuel pump. I have good pressure going into the carb. I have not checked the timing yet, as I cannot find my fathers timing light, may have to borrow one. I plan to do so this weekend along with the compression check. I am a little rusty on checking timing and do not have the Mercruiser Manual for my engine, so I am doing some reading on how to best check it. Also, as I stated, I was told that the Thunderbott IV ignition module either works or it doesn't, but after reading another thread, I am thinking that may not be the case. Thanks for the reply.

Re: 93 Mercruiser 5.7 - No Power Under Load

I thought I would add that I have the Weber #9665S 4 bbl carb in case that might make a difference. I know the rebuild kit for this carb was much more expensive than if I had the Rochester, but that doesnt mean its a better carb. Also, if I stay on the throttle long enough it will completely die out and occasionally back fire through the carb. Thanks again for any advice.

Tony

Re: 93 Mercruiser 5.7 - No Power Under Load

from what i get. backfire through the carb. is lean. lack of fuel. maybe water mixed with fuel.

ya might try running it on an aux. fuel tank. plumb in right before the fuel pump. then run it. if the problem goes away, the problem exists prior to the fuel pump. then this article may be helpful. or maybe this one too. assuming ya can't obtain wot. both of those are from the adults only sticky at the top of the i/o fourm.

this could help too. at least it should have the procedure for timing your engine. won't help ya find your timing light though..

Re: 93 Mercruiser 5.7 - No Power Under Load

MstGT1 said:

I thought I would add that I have the Weber #9665S 4 bbl carb in case that might make a difference. I know the rebuild kit for this carb was much more expensive than if I had the Rochester, but that doesnt mean its a better carb. Also, if I stay on the throttle long enough it will completely die out and occasionally back fire through the carb. Thanks again for any advice.

Tony

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Ayuh,... For future reference, that Merc/ Weber carb is a carbon copy of the Edlebrock Performer carb...
All the pieces interchange...
Edlebrock parts are Way cheaper, 'n more available too...


Btw,.... I think it's an Easier, 'n probably Better carb....

Re: 93 Mercruiser 5.7 - No Power Under Load

Ziggy - Thanks for the articles they will be very handy on Saturday when I get to work on it. I have thought all along it was lack of fuel. When I took the carb apart I found the floats looked way low. I adjusted them up according to an edelbrock instruction sheet, and since the problem got marginally better, I plan to set them up a little further and try again. I will also try to come up with an alternative fuel source using a 5 gallon can.

Bond-o - I actually almost used an edelbrock carb kit #1477. My father-in-law had a box and instructions to one he used about 15 years ago and it all looked the same except for double pumpers on the edelbrock. I was afraid something would be marginally different and i guess I ended up paying double for the same thing.

My father-in-law has a timing light so no need to find mine now. I tried to find a downloadable manual but could not locate one. Dont mind paying for it just didnt want to wait for shipping but I plan on ordering one for future reference. I havent bought one yet because I was paying a local boat guy for repairs, but the problem started late 2009 and he never could get it right. I actually paid him close to $400 last year to rebuild the carb. It still didnt fix it, so I put a fuel pump on it. Three days later my wife gave birth to our first child and I never got to try it out, just had it winterized and put up for the year. I thought for sure it would work this spring, but when I found it didnt, I decided it was time to look at it myself. I found that the carb had never been apart, and began questioning everything the local guy did to it and ended up re-replacing all of the ignition parts he supposively already replaced. Again nothing in the dist. had been touched. I bought it in 2008 from the original owner and the boat is in really nice shape inside and out for a 1993 model. Anyway I have been screwed over on the repairs and just want to use my boat a few times before winter, so hopefully with the help you guys have provided I will be able to get it going.

Thanks again and I will post any progress.

Re: 93 Mercruiser 5.7 - No Power Under Load

Ok, so the last two weeks have been consumed with vacation and catching up on farm work, but last night I finally got to work on the boat. First thing I did was put a timing light on it. It read 4 degrees ATDC. I knew from the manual provided earlier in this thread that it should be 8 degrees BTDC. I adjusted it to spec, and it immediately sounded better, and began to fire everytime as before it was hit or miss whether it would fire, and mostly wouldnt fire when cold. I believe this will correct my problem, and according to the manual the timing should be checked annually. Hopfully I will get a water trial this evening or tomorrow. I will post back with the results. Thanks again for all the help.

Tony

Re: 93 Mercruiser 5.7 - No Power Under Load

Well the timing adjustment did the trick. My boat ran like a new one this past weekend!!! We can finally enjoy our boat again. Thanks again for all the advice and suggestions that helped figure it out. Hopefully I dont have any more problems for a while. Sure would like to have some of the money spent on parts I didnt need, but oh well it is going again and that is all that matters at this point.

Thanks Again

Re: 93 Mercruiser 5.7 - No Power Under Load

awesome, very useful thread and glad you got it worked out!! enjoy