SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: SuperJet on June 11, 2012, 08:28:05 PM
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Hi all, I just put a new motor in my boat this season and when I run it it has a popping sound from the exhaust at idle. When idling for a while ( like through a long no wake zone) the boat acts like its loading up and wants to die. Tonight I pulled the plugs and they have almost no color to them, witch normally indicate the motor is too lean. The motor is a 460 ford with 73 heads, and an 800 double pumper mech secondary. Also running a Pertronix flame thrower billet dizzy. The plugs are Delco MR43T's gapped at .044. I am stumped and any help is appreciated.
RC
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Here is a pic of the overall look of the plugs.
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It can't load up and be lean. Run
It under the circumstances where it runs like like crap for a bit, the kill it without moving the throttle. Now pull the plugs.
Make timing/fuel changes accordingly.
The plugs will tell the story of the final condition under which they've been run. If you're fat at idle and lean at top, making a pass and idling
Back to the ramp, or even keeping it running till you come off plane will
not show you what you're trying to
see. Be damn sure the boat shuts down safely before killing it at WOT
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Those plugs don't look to lean, but you've gotta peak way down
The insulator to get any usefull info.
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It only pops at idle?
Any idea where the timing is?
If I didn't know any better I would say the lifters are pumping up and holding the valves open... :-\
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how did you break in the cam, does it do it on the trailer, has it always done it, how new is the motor? does it do it while on the plane, has the carb and dizzy been on another motor and if so did the other motor do this
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It only pops at idle?
yes
Any idea where the timing is?
if i remember correctly 12 initial and 32 total, but could be mistaken
If I didn't know any better I would say the lifters are pumping up and holding the valves open... :-
Thats what I tought too so I readjusted the valves(has 1.7 BBC roller rocker arms) and no change, when I adjusted them, I set them at half turn past zero lash. Too tight?????
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how did you break in the cam, does it do it on the trailer, has it always done it, how new is the motor? does it do it while on the plane, has the carb and dizzy been on another motor and if so did the other motor do this
Broke the cam in on the trailer 2500rpm for 20 minutes. So far yes it has done it both times Ihave had it out, and have not checked on the trailer yet.No, does not do it on plane, and the carb is one i had on the shelf(freshly rebuilt) and yes the dizsy was on my last motor and gave me no problem for two seasons.
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It can't load up and be lean.
I know thats what has me stumped
Run
It under the circumstances where it runs like like crap for a bit, the kill it without moving the throttle. Now pull the plugs.
Make timing/fuel changes accordingly.
The plugs will tell the story of the final condition under which they've been run. If you're fat at idle and lean at top, making a pass and idling
Back to the ramp, or even keeping it running till you come off plane will
not show you what you're trying to
see. Be damn sure the boat shuts down safely before killing it at WOT
got it, and yes the boat shuts down very solid and safe at WOT lol
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Update. Just ran it in the trailer and yes it does pop on the trailer. Can't figure out how to upload a video from my phone, but I have a recording of it.
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Worlds stupidest question........But have to ask.
Are you sure the firing order is...well....in order? :-\
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Worlds stupidest question........But have to ask.
Are you sure the firing order is...well....in order? :-
Haha yes it's been triple checked.
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not to get in this conversation late but have you thought about a lean burn at idle? that would cause popping and go away off idle.
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not to get in this conversation late but have you thought about a lean burn at idle? that would cause popping and go away off idle.
Thats what my Dad thinks, and I am starting to lean that way also.
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After thinking about this all day....You have an intake leak. Spray some ether starting fluid in the breather of a valve cover while idling...
Better yet, an unlit propane torch in the breather...Betting it goes away. :sly:
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After thinking about this all day....You have an intake leak. Spray some ether starting fluid in the breather of a valve cover while idling...
Better yet, an unlit propane torch in the breather...Betting it goes away. :sly:
Ill give it a shot. But, if the intake is leaking wouldn't it have the pop all the way through the RPM range, and not just at idle?
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Ill give it a shot. But, if the intake is leaking wouldn't it have the pop all the way through the RPM range, and not just at idle?
The popping is due to a lean AFR. As the RPM increases, the AFR fattens up. Basically because there is little/much less vacuum at a higher RPM than idle. This will "suck harder" on the potentially leaky gasket/broken manifold...
Did I mention you should inspect the manifold for cracks?. ;)
I guess it could also be a poorly fitting carb base gasket or an open vacuum port.... :sly:
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The popping is due to a lean AFR. As the RPM increases, the AFR fattens up. Basically because there is little/much less vacuum at a higher RPM than idle. This will "suck harder" on the potentially leaky gasket/broken manifold...
Did I mention you should inspect the manifold for cracks?. ;)
I guess it could also be a poorly fitting carb base gasket or an open vacuum port.... :sly:
Ok I understand now. And the intake is all good as far as cracks go. It has given me no problems the last two seasons, and was inspected before I put it on the new motor. As far as leaky gadgets going, I know what I am doing tomorrow night:D thank you for the help so far.
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