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Ford 351 Backfiring Above 2000 RPM.

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    Posted: June-19-2006 at 6:10pm
Hello. What a GREAT resource. Thank you!

I知 a newbie boat owner and I知 looking for some advice on diagnosing a backfiring problem I知 having. I bought the boat this spring. It痴 a 196鋳 inboard with a Indmar 351 Ford motor, and a holley carb. It痴 not a Correct Craft but was hoping you guys might still lend a hand. ;o) It痴 1986 Ski Eliminator (Eliminator is mostly a custom boat manufacturer) that made a Tournament Ski Boat for a couple of years.

Anyways I致e put about 20 hours on it so far this season with no major problems. Until today. I got to the launch. It started, idled, and warmed up fine. Then as I gave it throttle it started to backfire thru the carb at about 2000 RPM and above.   If I backed off the throttle it would clear up. But as soon as I would throttle back up to the 2000 range it would start again.

At first I thought maybe I got some bad gas and put some dry gas in on advice of a friend. No difference. Occasionally I could coax it up to 2500 to 3000 but not for very long before it started sputtering and backfiring again.

The distributor is the points style. I致e changed plugs recently. Have not touched the timing, nor adjusted the carb. I致e read thru many of the threads on this subject but I知 still not sure of the best order to get to the bottom of this problem.

Any advice on where to start? I don稚 have a lot of mechanical experience but can follow instructions very well. And unfortunately due to a family member痴 illness I知 not in the financial position to pay a marina mechanic to diagnose this problem. Any suggestions would be greatly appreciated. Thank you.

Joe

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Bradley950 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bradley950 Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 6:40pm
That's a nice looking boat! Have you checked the point gap? How old are the points? We can start here.
Brad Miller
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joed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 7:00pm
Hi Brad,

Thank you for the quick response.

No. I have not checked the points. And I do not know when they were last replaced. I am planing on taking the cap off tomorrow. I will check it out. Would that be something that would happen all of the sudden? From running fine to major backfiring within one outing?

I've also read about an advance spring... but cannot find any clear documentation on how to check that.

Can replacement points be bought at an autoparts store? I am planning on upgrading to an electronic ignition as soon as I scrape together $$$ for it, plus coil, and new wires.

I would like to get back on the water ASAP before I go in for hernia surgery next Tuesday.

Thanks again for the reply. I'll keep ya posted.

Kind regards.

Joe

PS. Any knowledgeable, friendly mechanics near Fenton Michigan on this board?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 7:09pm
If the rotor can flop around, an advance spring has corroded and failed. IF the rotor can't move agaist spring pressure, the advance mechanism is stuck from lack of lube.
There could also be crossfiring under the cap from moisture.

Another cause could be a lean condition, one of the primary jets are clogged. peer down the carb but keep your head away to view any disproportionate flow from the venturis. If there is junk in there, its only a matter of time before it clogs the idle circuit too, so search for the root cause else you'll re-re-rebuild the carb all summer.


"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."
River Rat to Mole
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 7:24pm
Hey GottaSki... thanks.

And just to make sure I'm clear...

To check the rotor... I just need to pop the cap without running the engine. Twist the rotor a bit... and if it moves too easily (without any resistance or return) then the spring is broke. And if it moves hard... the spring is stuck and needs cleaning /lube? Is that correct?

Next on the carb... can I perform that check on a fake a lake in neutral? Will fuel flow thru both venturies at idle? Or will I have to rev it up for the second jet to kick in?

Sorry about all the *dumb* questions... but like I said I don't have a lot of mechanical experience so I want to take this slow and methodical. Thanks again.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 7:31pm
Yes.
Yes.
And beware this will only show a gross clog. If fact the clogged main jet can sometimes free itself on the trip home to clog again someother time, so its not foolproof.

Check your point gap while you are at it, and don't delay the electronic conversion.

Questions are good.
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."
River Rat to Mole
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joed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 8:07pm
Hey Guys,

Here's a link to some video I shot today of my 10 year old son wakeboarding when the backfiring happened. It's a little over 2 minutes long, and you'll hear the backfiring start about halfway thru.

Just thought it might help with troubleshooting. If nothing else I learned how to upload video to the web.

Thanks again for all the help so far.

Backfire

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tim D Quote  Post ReplyReply Direct Link To This Post Posted: June-19-2006 at 8:09pm
That boat looks like a malibu sunsetter.
Tim D
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bradley950 Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 9:20am
Joed,
Any luck? I figured alot of good info would flood the post! Keep us up dated!
Brad Miller
bradley950@yahoo.com
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79nautique View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 9:37am
get a new 6.5 power valve and primary bowl gasket and replace the power valve in your holley carb.

If you do not have a holley carb then there are other things to check before you rebuild the carb.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 1:54pm
Here's the update guys.

Cap, rotor, points, and gap... all in good working order.

Springs were a little rusty. Cleaned and lubed. Rotor advanced and returned well.

Drove to launch. Started, idled, and warmed up fine. Throttled up to about 2800 RPM, popping, and backfiring started again.

Pulled flame arrestor. Watched venturies. As my wife gave it throttle... a quick spurt of gas was evident in both venturies. But the duration was very short if that means anything.

I tried some carb cleaner. But each time I brought her up to 2800 or so it would pop again.

If a idled down for a few minutes I could get her back to about 2800. But once there the popping would continue even if I backed off the throttle a bit. Only bringing it back to idle for a minute could I throttle back up to that range.

Make sense?

I have read about backfiring ruining the power valve... so I guess my next step is to change that per 79's suggestion. And 79... it is a holley carb. Sound like the next logical step?

Next newbie question... can I pick up a powervalve at an autostore, or is it a marine part?

Thanks so much for all your help.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 2:01pm
O'Riely's carries them and they are all the same just ask for a 6.5 holley power valve at any auto parts store and get a gasket too incase you tear the old one taking it apart.
quite running the boat until you get it replaced, your going to foul the plugs and screw up the motor if you don't.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 2:32pm
Any good documentation around on replacing the powervalve. I'm picking one up tomorrow morning.
I have zero carb experince. I searched the forum but did not find any specific instructions.

Thanks again.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 2:40pm
there should be some with the power valve.

Basicly your going to deconnect the fuel line, remove the four bolts holding the primary fuel bowl, front, and then unscrew the power valve from the metering block. Go slow and pay attaintion to the float so you don't bend it and change it's setting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-20-2006 at 3:42pm
Thanks 79,

I'll keep ya posted.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Topher Quote  Post ReplyReply Direct Link To This Post Posted: June-21-2006 at 1:25pm
I'm having the exact same problem with my 351.   The boat was running great and then just died.

So I put a new cap, points, condesor, plugs, 10 degrees BTDC, check compression, new power valve, check the fuel filter. Ran a hose from the fuel pump to fresh fuel and it spits and sputters when you give it throttle and pops coming up through the carb. what can i do next???
Sticky valve?

Runs great at idle

Thanks in advance
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-21-2006 at 3:23pm
Got the 6.5 power valve and bowl gasket but nasty weather in Michigan is preventing me from from working on it today. I'll post an update tomorrow. Thanks again for all the help.

Trying to sell some toys on eBay to get money for electronic ignition set-up. Anyone looking for a Sumo Tube? Personally I don't like my face that close to the water.

Hey Topher... good luck getting to the bottom of your problem. I hope I have better luck. I'm guessing electronic ignition upgrade is going to be the next suggestion.

Cheers.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tommer12 Quote  Post ReplyReply Direct Link To This Post Posted: June-21-2006 at 5:52pm
Not sure if this helps, but on my old 84 nautique I had.. I found it backfiring and it turned out that my mechanical advance springs were bad... if you pop open the distrubtor, remove the points, look underneat at the weights and there they are... two cheap looking springs.... one, rusted off.. which cause the timing to go off whack
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-22-2006 at 3:23pm
*#$%^&*! #$*!!&^! ARGGHHH!

What's next gang?!?

Replaced the power valve. Took her out. Slowly but steadily throttled up. At about 3800 RPM'S (35MPH) she started popping again. I quickly throttled down and went back to launch.

Here's a recap:

The other day:
- Cap, rotor, points, and gap... all in good working order.
- Advance springs were a little rusty. Cleaned and lubed.
- Watched venturies. Gas eveident in both.

Today:
- Replaced power valve (6.5)
- Pulled plugs, 7 were light tan/gray. 1 was oily. See photo below.
- Tested fuel delivery. About 10ozs in 5 sec crank.

So what's the next step guys? Also I went looking for the fuel filter/water seperator. Don't have one that I can see. The only thing i found was what looked like an inline filter of some sort between pump and carb. See blue thing in photo below.

I've got about $150 saved up... do I have carb rebuilt or order electronic ignition, coil and wires? Or try something else?

I have to say I've kinda enjoyed the tinkering and learning, but I ready for some success!

Could the fouled plug be a clue to the problem?

Thanks again for any suggestions.

Joe



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Post Options Post Options   Thanks (0) Thanks(0)   Quote nuttyskier2002 Quote  Post ReplyReply Direct Link To This Post Posted: June-22-2006 at 11:30pm
What do the rest of your plugs look like? Have you put a timing light on and checked your timing advance up to 3000 RPM? Also have you done and fuel pressure and volume check. Fuel pump should deliver about 1 pint in 30 seconds cranking time. Now if all of that is okay, try running the boat hard until it starts to backfire, then shut it down immediately and pull the plugs. Unless most of them are white (on the tips) you are getting plenty of fuel. The porcelin around the center electrode should be dark tan to brown if the air/fuel is right.

Now.... here's something you might want to look at. Not sure how often this happens with Ford motors but it's quite common on Chevys. Remove both of your valve covers. With them off have someone crank the engine over while you watch the valves open and close. Watch each one of them. Make sure they all open and close and that none of them only open partially. If you have an exhaust valve that is not openning, this will cause popping back through the carb especially when under a load or at higher RMPs. The motor will otherwise idle normally. The popping is because the burnt gases can't exit out the exhaust as normal. So it exits out the intake the next time the intake valve opens. This is the result of a wornout cam lobe. Hope you find your problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 5:16am
Thanks for your reply nutty.

** What do the rest of your plugs look like?**

All other plugs looked good. Light tan/gray.

**Have you put a timing light on and checked your timing advance up to 3000 RPM?**

No. I'm going to try to get my hands on a timing light today.

**Also have you done and fuel pressure and volume check. Fuel pump should deliver about 1 pint in 30 seconds cranking time.**

I did a volume check... got about 10 ozs in 5 secs. Is that too much fuel? I am trying to get my hands on a pressure guage today as well.

**Now if all of that is okay, try running the boat hard until it starts to backfire, then shut it down immediately and pull the plugs. Unless most of them are white (on the tips) you are getting plenty of fuel. The porcelin around the center electrode should be dark tan to brown if the air/fuel is right.**

I will check out the above and post results.

Thanks again. Have a great weekend.

Joe

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 5:17am
Good suggestions nutty, and while its open look for a broken valvespring.
It happened to my mustang and sounded somewhat like that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 5:22am
Quote The porcelin around the center electrode should be dark tan to brown if the air/fuel is right.


NO that is way too rich by large margin. Combustion temps are too low, the plug is not self-cleaning itself. Carbon burns off above 400C so brown is wasting fuel and power.

White is good, and 1.5-2mm soot ring on the base of the porcelin.

GREY is bad, very bad. It means you are sputtering aluminum off the piston.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 5:44am
Here's what my other plugs look like. However this is not right after the backfiring. I took this after idling back to launch.



Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 6:24am
the one plug is oil fouled and that's most likely causing your miss, and it's not good news.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 6:39am
Yuck ... that didn't make my day. Should I check compression on that cylinder or what? According to some info I read...

**
Oil fouled plug. Indentified by wet black deposits on insulator and electrodes. Cauesed by too much oil entering combustion chamber thru worn rings and pistons, excessive clearance between valve guides and stems, or worn or loose bearings. Can be cleaned. If engine is not repaired, use a hotter plug
**

So perhaps I need a rebuild aye? Could that hotter plug thing work to get me trhu the season?

Thanks.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 6:53am
You can give it a shot it cann't hurt, did the wire come off real easy or did the plug seem like it was loose?
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No... plug and wire was snug. Thanks 79.

Joe
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 79nautique Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 7:05am
there's a few possibility what's causing the problem, shot rings, valve guide seals, or flat lobe on the cam. A compression test checks the rings, or a bad valve. You'll need to pull the valve covers and make sure that the oil returns are not cloged and the oil is pooling and leaking pass the valve guide seal. While it's off you can turn over the engine and watch the valve movement to detect a flat lobe.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote joed Quote  Post ReplyReply Direct Link To This Post Posted: June-23-2006 at 9:22am
Well I'm gonna try some hotter plugs and see what happens for a possible short term fix.

The PO said he would give me a one year warranty, so my next step is to contact him. I should've got that in writing.

He is a mechanic. I just didn't want to run back to him at the sign of my first problem. But it sounds like things could be getting serious so it's time to get him involved.

Thanks for ALL your help. I'll keep ya posted.

Have a great weekend.

Joe
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