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#1795417 - 12/10/07 12:56 PM Mercruiser 170 I/O power problems, Sorry long post!
Toontroller Offline
deacon ogre

Registered: 01/18/06
Posts: 9677
Loc: Ennis, Texas
I need some help for a good friend @ Cedar Creek. 1986 Mercruser 170 I/O Same as the newer 470 or so I have been told. Ford product.

He bought the current engine from Jasper two years ago, ran great.
When the lake went down he got caught in his boathouse and could not get it out so it sat.

This summer it was running fine after the water came up. July he was pulling the Grandkids on toys when it started backfiring through the Carb when starting from idle. He rebuilt the Carb w/ no success. Took the boat to the shop and they rebuilt it, No success, Then they ordered a new Carb, Still backfiring. Took it back and they said the mechanic had put the accelerator pump on the wrong setting, said there were three notches and said it was on the right one now. Also while they were at it they installed new the following; Distributor (yes the whole thing), Dist. Cap, Rotor, points, Condenser, Wires & plugs & intake manifold gasket. Said they water tested it and it would cough some until it reached 150 degrees and then everything is ok and runs fine. Last week he got the boat back from the shop and put it in the water Saturday. Let it warm up to above 150 degrees just like they said and tried it out. NO LUCK, still backfiring though the carb when he tries to put the power to it. This time he can just ease the power and it will come up to speed and run well, however if he pulls it back down to neutral then punches it, it will cough and die! Any suggestions? Or would one of the TFF mechanics be willing to take a look at it.

He has spent close to 2 grand this year and it still does not run correctly. He wants to get his boat running right.

Oh he is out of town right now and is planning on getting the mechanics who worked on it out on the lake for a ride to show them the problem when he gets back but he is does not have a lot of confidence in them right now.

Tommy, are you familiar with these I/O's? or would you recomend someone in your area?

As always help is apreciated.




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#1796325 - 12/10/07 05:31 PM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: Toontroller]
Creed Offline

Registered: 03/10/03
Posts: 417
Loc: Rowlett, txusa
I had an 470 I/O, and the motor out lasted the boat, by far. This should be an easy fix, but I am not sure where to start. You have done everything I can think of. If it back fires though the carb, it has to be an ignition problem? Kinda sounds like it is jumping spark somewhere. Good luck and post keep us posted as to the fix.

#1796466 - 12/10/07 06:30 PM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: Creed]
waydon1 Offline
Pro Angler

Registered: 01/11/03
Posts: 821
Loc: central tx
Could be as simple as old/bad gas or water in gas.. Sounds like your friends boat needs to be checked out by a pro tech... Like opti says " if you think a pro is expensive wait til you hire an amature" shouldn't be that hard to fix...Good luck

#1796603 - 12/10/07 07:35 PM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: waydon1]
Toontroller Offline
deacon ogre

Registered: 01/18/06
Posts: 9677
Loc: Ennis, Texas
Agreed, However the engine has been to a "marine shop" twice since July Not sure of the name but it is in Cedar Creek. I do know that he put 15 gallons of fresh gas in before he unloaded. We have also run lots of Seafoam through the system since it first started acting up just to make sure that was not the problem.

Creed, your right the engine is a workhorse and should be running tip top with no more hours than it has. He keeps the boat under cover at all times and really goes above and beyond on maintanence. I have said timing or electrical the whole time but the "experts" kept saying Carb. When he told them to rebuild it they said a internal bolt hole was stripped and they could not garantee the rebuild. Thats when he laid out $500.00+ for a new one they said would be almost impossible to find, he found one through a out of State marine supply.

The shop will have one more shot to make it right then he will be through with them. I would like to try checking for an air leak at the carb base but the backfiring still does not make sense to me without it being a timing problem. Before it went to the shop we did inspect the valve springs just to make sure rocker arms were in good shape and no broken springs. I figured since it ran well at WOT when you could get it there a weak spring could be ruled out.

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#1797023 - 12/11/07 04:39 AM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: Toontroller]
gary purdy Offline
TFF Celebrity

Registered: 05/24/03
Posts: 8674
Loc: Littlefield Tx & Lake A. H. US...
You may want to check the valve train again. It is really hard to see a spring that has broken a bottom coil or a spring that has collapsed. Ford motors were real bad to break a spring in these year models. Pull plug wire one at a time and run it. When it stops backfiring go to that cylinder checking springs, pushrods, camshaft, lifters and compression. Have seen the top lock come out of a lifter and a or intake valve tuliping cause this, because the valves are nonajustable. Sounds like you have pretty well eliminated the fuel and fire because shurly the fuel pressure, gaskets, timming, coil, and ignition wires were checked allready. Good Luck
“The world will not be destroyed by those who do evil, but by those who watch them without doing anything”

#1797050 - 12/11/07 05:07 AM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: gary purdy]
Bullet[BS] Offline
TFF Team Angler

Registered: 03/18/03
Posts: 3125
Loc: San Marcos, Texas, USA
Toontroller, I would head over to O'Reilly's and get a ignition coil for that engine. They do offer a high output version of that coil in Borg Warner.
When in doubt SET THE HOOK!

#1797167 - 12/11/07 06:13 AM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: Bullet[BS]]
Tommy Yetts Offline
TFF Team Angler

Registered: 12/14/02
Posts: 3009
Loc: Rockwall, TX USA
Toon, Yes we are familiar with this motor. If they can't solve your problem we would be more than happy to look at it for you. Everyone that has responded has good input. I still believe there is a problem in the fuel system, carb. I would make sure that the replacement carb is indeed exactly the same as the old one.Some reman. carbs, as well as new, are not the same. Make sure the jetting is the same.

Tommy Yetts
Rockwall Marine
Rockwall Marine
Tommy Yetts

#1807487 - 12/14/07 09:08 AM Re: Mercruiser 170 I/O power problems, Sorry long post! [Re: Tommy Yetts]
Toontroller Offline
deacon ogre

Registered: 01/18/06
Posts: 9677
Loc: Ennis, Texas
Update 12/13

My friend and the owner of the shop took the boat out yesterday. I had kidded him about the classic won't do it again when the guy rides on it and it fired up and ran great! bang Well almost, after a few tries the engine started acting up and backfiring. The mechanic started adjusting the carb and timing and then disconnected the INTERUPTER SWITCH (which I had never heard of before) and the problem stopped, but with it disconnected he said you cannot get the boat to neutral or back in gear since the RPMs are too high. So the plan is to replace the faulty switch and they are going to replace the Throttle and shifter cables while they are at it to make sure there is no slop in the system.

After the repairs the shop owner has agreed to take another test ride just to make sure everyone is happy.

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