Merc 170/470 backfires, dies .. please HELP

[jbwilson]

After warm-up, when pushing the accelerator fast, boat hesitates, backfires, dies. If I push accelerator slow and steady, no problem. After it quits, starts hard ... long cranking, runs rough and then steadies out. Bought the boat last year (it's a 1984). I rebuilt the carb immediately as it ran rough and had been sitting around for several years. Set everything to specs in manual. It's done this ever since the rebuild.<br /><br />Any help would be greatly appreciated! Thanks!

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

It would be safe to assume that this is a GM motor 3.7L/Merc 2 bbl Carb same as 165 4 cyl...<br /><br />Right... I would start with all specs as they do change... fuel filters, points, then timing... but it would be safe to say that you have accelerator pump problem which is causing fuel starvation which results in "POP"... which if not working properly will cause hard starting... NO GAS!!!<br /><br />Let me know...<br /><br />------------------<br />Good Luck!!!<br /><br />fone_man

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Update: replaced plugs, rotor, distributor cap. Timing ok, points set. Still have problem. Rebuilt accelerator pump at time of carb rebuild. Checked in carb after it coughed and died ... all surfaces wet with gas, some gas pooling in intake runners. Is this normal?<br /><br />Help! The skiers are getting pretty frustrated. Slow pulls out of the hole just don't cut it.<br /><br />Thanks.

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Any thoughts anyone?

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

Only thing I can come up with is accelerator pump??? It actually is "backfiring" through the carb... take off flame arrestor & tell me if black w/soot... I know its wet because fuel entering intake is being blown back out of carb... looking for the "dark stuff".<br /><br />Also, pump sits in gas all year even through the winter... they go bad... what kind of kit did you use & what type carb does it have??? When was rebuild... approx date (not last year)<br /><br />Auto are constantly using thier pumps... where boat only use theirs on acceleration & take offs... this is where I would start as they do dry out plus get out of adjustment/spring weak, etc.<br /><br />Let me know....<br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Fone-man, thanks for the reply.<br /><br />No black soot, so I guess it is not actually backfiring, but it does 'pop' loudly and it sounds like it's coming from the carb?<br /><br />Carb is a Rochester 2GC? I think (the boat/manual is a hour away, but I'll check dir sure this weekend). I rebuild the carb in May 1999. Don't know the brand of rebuild kit, but it was complete. I tore it completely apart, soaked the body and put back together with all new gaskets/float/needles, etc.<br /><br />It was better (not perfect) after the rebuild and has gone steadly down hill since.<br /><br />Thanks again for your help!

 

[clanton]

Re: Merc 170/470 backfires, dies .. please HELP

A 470 has aluminum block cast iron head four cylinder. Cooled with antifreeze, and heat exchanger. This your engine? Has the head been rebuildt? After you do the easy stuff and still have problem check for broken valve spring, maladjusted valves. The lifters are hyd with non adjustable rockers, adjustment by changing pushrod.

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Yes, it is a 470 engine. No, the head has not been rebuilt, at least not to my knowledge. Thanks for the info on the valves. If all else fails, I'll go there next.

 

[Walter]

Re: Merc 170/470 backfires, dies .. please HELP

Those paricular engines are all closed cooling...for the very reason described by Clanton: Cast iron head and aluminum block. The head is from a 460 Ford... These engines have never been known to idle smoothly, but have great pull.<br /><br />From what you describe...I'm inclined to agree with Fone_Man in believing your problem is most likely a fuel starvation issue. It sounds like your accelerator pump isn't providing the necessary fuel supply when you goose the throttle.<br /><br />I rolled over the plunger rubber on my accelerator pump when I rebuilt my Roch. 2GC earlier this year... had to pull it apart and reposition it. <br /><br />Walt

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

Thanks to the vote of confidence, Walt!!!<br /><br />I have worked on a variety of I/O's in my life & this is one of them plus hundreds of Rochester Carbs... & I don't like to brag but I feel like I should know their symptoms by now... but you never know when a new one will come up!!!<br /><br />I agree that this is a great little engine... plus the the idle issue.. rough... but you cannot beat for thie displacement & fuel economy!!!<br /><br />Weak spring, valeve, etc... would be more pronounced on acceleration plus more continous "popping" over various RPM's.<br /><br />Start with basics, elect, fuel, water & oil... I always say. Throw a dwell meter on it to watch during acceleration... plus I always use a dwell meter after gaping points... I have seen 'em MOVE & be off just a bit... perfect should be between 28-30 and DWELL does effect TIMING!!!<br /><br />Let me know what you found on Carb plus another pointer... I change points/cond like I change oil... plus I keep old set in boat (in plastic bag) for emergencies & other stranded boaters,... they do wear & this will affect timing. Water/Moisture is great for one thing... corrosion!!!<br /><br />Keep us posted on your findings.<br /><br />

<br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[ODDD1]

Re: Merc 170/470 backfires, dies .. please HELP

J.B, how many idle mix screws on this carb??? about this time merc went to a NON rochester carb called a mercarb...made by nippon on japan....it only has ONE idle screw versus rochesters two...the first mercarbs only had a 2cc accelpump, unlike rochesters 3cc...it was ok on a 3.0 liter motor, but was inadequate on a 3.7....nothing to do but replace with a later mercarb with a 4cc pump...<br />the puddled fuel is another problem...these carbs like to flood over at idle /after shut down...the book specs are TOO HIGH and if this carb drips fuel from the booster venturis after shut down, it must be lowered..<br /> by the way, if you have a sympathetic mercruiser dealer, ALL THIS HAS BEEN COVERED BY SERVICE BULLETINS....

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

Yes... I agree with Merc Carb post... one idle screw but pretty much constructed/built similar to Rochester. Idle Screw is the tell-tale to the identity.<br /><br />I repaired a 1987 18' FourWinns 165 HP 3.7 / Closed Cooling System with Acelerator pump/Carb rebuild with same symptoms in 1996.<br /><br />Just waiting for post back from JB<br /><br /><br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Thanks, guys. It only has 1 idle mix screw, so must be a Mercarb. How do I tell if mine has the 2cc pump? and What need's to be lowered? The float? lowered to what? <br /><br />I do not have a sympathetic dealer, does anyone have access to these service bulletins?

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Replaced points today. Much better, but still hesitates, pops, just not as bad. Will get into the carb (float & accelerator pump) next weekend.<br /><br />Thanks again!

 

[Walter]

Re: Merc 170/470 backfires, dies .. please HELP

Was it ever determined which carb we're talking about here? Roch. 2GC or MerCarb??<br /><br />Walt

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

Walt.......<br /><br />A couple postes up!!!!<br /><br /><br />jbwilson<br />New Member <br />Posts: 7<br />From:geneva, ny<br />Registered: Jul 2001 <br /> posted August 04, 2001 09:41 AM <br />--------------------------------------------------------------------------------<br />Thanks, guys. It only has 1 idle mix screw, so must be a Mercarb. How do I tell if mine has the 2cc pump? and What need's to be lowered? The float? lowered to what? <br />I do not have a sympathetic dealer, does anyone have access to these service bulletins?<br /><br /> <br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

Hey JB...<br /><br />When you do float... replace with brass not synthetic/plastic... worth the money!!!!<br /><br /><br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[ODDD1]

Re: Merc 170/470 backfires, dies .. please HELP

hey, fone man, what you got against plastic/foam floats????of the hundreds of carbs i have done in the past 20 years, I have seen just 2 heavy/saturated floats....have seen alot more bad brass......

 

[fone_man]

Re: Merc 170/470 backfires, dies .. please HELP

I have done so many rebuilds... with synthetic/plastic/foam floats that have been saturated... the problem occurs with a slight saturation, which then affects all settings of carb... by the time you disassemble, fuel has evaporated & float is OK!!!!!<br /><br />I have certain things that I do when I have the option & this is an option when rebuilding Rochester/Merc carbs... eliminates problems down the road or should I say "water"!!!!<br /><br />Also, JB... I have come up with certain Merc Service bulletins for you on Carb issues over the last few years that I need to forward to you... Need email address for delivery plus you will have to have "Adobe Acrobat" as they are .pdf files. Tell me what you need... It has the corrrection for Merc's terminology "BOG"ging down on acceleration!!! Let me know when ready......<br /><br />

<br /><br /><br /><br />------------------<br />"Keep It Between The Bouys" & "Good Luck"!!!<br /><br />fone_man

 

[jbwilson]

Re: Merc 170/470 backfires, dies .. please HELP

Great fone_man... my email is jwilson9@rochester.rr.com<br /><br />Thanks, if I can get rid of this "bog", I'll be a hero!