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Boat Nut
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Discussion Starter #1
Im still battling a lean stumble on hard acell, seems to be related to boat attitude, and how hard the launch is. Im running dual side mount carbs, on a t-ram, and believe that the jets are being uncovered, when the fuel is tossed to the rear. I have the taper cut floats, power valves blocked, am I missing something? This is not happening intantly, engine reaches full power 5700 rpms, then loose 900 rpm. As the boat lays over it recovers and goes, then repeats. The cycles get shorter, each time..... usually it lays down three times on a run.
 

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Facing the rear of the boat.....
It take 1G to stack fuel on a 45* angle in a perfectly square chamber. A NHRA Pro Stock accelerates to 210 in a 1/4 mile, and has not problems with the bowls in a Holley dominator.
Where is your fuel pump. Can fuel flow on its own into the pump, or does the pump have to pull fuel in. Is the pump at the rear of the boat? How big is the line to the carbs? Regulators at the carbs? What regulator. What size needles in the bowls?

The angle of the engine in a jet is not helping your issue, but I think you have a delievery problem more than a stacking fuel problem.

If it laid down once, I could see it. But to lay down 3 times, you simply cannot be pulling that kind of Gs that late in the run. Unless this thing turns 200 MPH trap speeds.



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Boat Nut
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Discussion Starter #5
It take 1G to stack fuel on a 45* angle in a perfectly square chamber. A NHRA Pro Stock accelerates to 210 in a 1/4 mile, and has not problems with the bowls in a Holley dominator.
Where is your fuel pump. Can fuel flow on its own into the pump, or does the pump have to pull fuel in. Is the pump at the rear of the boat? How big is the line to the carbs? Regulators at the carbs? What regulator. What size needles in the bowls?

The angle of the engine in a jet is not helping your issue, but I think you have a delievery problem more than a stacking fuel problem.

If it laid down once, I could see it. But to lay down 3 times, you simply cannot be pulling that kind of Gs that late in the run. Unless this thing turns 200 MPH trap speeds.
It all happens in the first 100 ft. with the single carb deal jet extensions totaly solved the issue, but side mount dual carbs it's been tough. The float bowl is much wider than is deep or front ways, it would appear fuel stacking would be easier with the carb sitting sideways. The rpm lost is probly more, I never look at it, but sure can feel the boat stop pulling, till it gets fuel again. When it recovers it's intant, the cycles are short and quicker thru the first 100ft.


My fuel pump sits next to my sumped stack tank, there is an-10 feeding the pump, thru the filter to the aeromotive 4 port regulator. AN-8 feed the carbs, fuel pressure is 7 psi from what I see it's steady.

I was looking over the rigging, I could drop the motor some what in the front.
 

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It take 1G to stack fuel on a 45* angle in a perfectly square chamber. A NHRA Pro Stock accelerates to 210 in a 1/4 mile, and has not problems with the bowls in a Holley dominator.
Where is your fuel pump. Can fuel flow on its own into the pump, or does the pump have to pull fuel in. Is the pump at the rear of the boat? How big is the line to the carbs? Regulators at the carbs? What regulator. What size needles in the bowls?

The angle of the engine in a jet is not helping your issue, but I think you have a delievery problem more than a stacking fuel problem.

If it laid down once, I could see it. But to lay down 3 times, you simply cannot be pulling that kind of Gs that late in the run. Unless this thing turns 200 MPH trap speeds.
It all happens in the first 100 ft. with the single carb deal jet extensions totaly solved the issue, but side mount dual carbs it's been tough. The float bowl is much wider than is deep or front ways, it would appear fuel stacking would be easier with the carb sitting sideways. The rpm lost is probly more, I never look at it, but sure can feel the boat stop pulling, till it gets fuel again. When it recovers it's intant, the cycles are short and quicker thru the first 100ft.


My fuel pump sits next to my sumped stack tank, there is an-10 feeding the pump, thru the filter to the aeromotive 4 port regulator. AN-8 feed the carbs, fuel pressure is 7 psi from what I see it's steady.

I was looking over the rigging, I could drop the motor some what in the front.
What ignition r u using? Are u using a launch rev limiter feature?
 

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What ignition r u using? Are u using a launch rev limiter feature?
Excellent point Mike. If its a digital with rev limiter and retard features, you need to KNOW where they are set.
I've seen problems where guys will have a launch rev limit curve programmed to start off a full throttle switch mounted in the carb linkage. If you roll into the throttle the engine passes the lowest data point of the rev limit curve before u hit full throttle and activate the switch and program. So the motor reaches 7000 rpm and then program starts and tugs the engine back down to 5,000 or whatever that first data point is in the program. Not saying that's happening here but it's a pretty common mistake when guys use a box like an msd digital 7 or programmable 6 series.
 

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I heard of programmable digital boxes getting freeky on the timing too.
Maximus had a blown hat injected E85 deal on Carson Brummetts dyno and it kept giving erratic pulls. Which is extremely unusual for Carson's dyno! Carson finally kept a running eye on the timing and it would go south for no reason. I think Ben told me they just took out all the programmed retards and timed it straight up.
But my understanding was it was erractic and unstable. This sounds much more consistent. More like you said, a rev limiter. From what I know, rev limit issues tend to me user caused, where as the timing retard issues tend to be ignition caused.



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I heard of programmable digital boxes getting freeky on the timing too.
Maximus had a blown hat injected E85 deal on Carson Brummetts dyno and it kept giving erratic pulls. Which is extremely unusual for Carson's dyno! Carson finally kept a running eye on the timing and it would go south for no reason. I think Ben told me they just took out all the programmed retards and timed it straight up.
But my understanding was it was erractic and unstable. This sounds much more consistent. More like you said, a rev limiter. From what I know, rev limit issues tend to me user caused, where as the timing retard issues tend to be ignition caused.

Chuck,
Interesting you're posting this issue. At the UMPBA race in Menomonie, WI. I was sitting in my boat adjacent to the start area waiting for my class to run, I watched (and listened to) your boat go several rounds that day. It sounded to me on each 'leave' like it hit the rev limiter and stuttered there until the pump hooked up and pulled the revs back down. Every run it sounded the same. Do you have a playback tach? If so, that would tell you if the rev limiter is the culprit. I may be way off base here, but that's what I heard. Jocko
 

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Boat Nut
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Discussion Starter #12
Chuck,
Interesting you're posting this issue. At the UMPBA race in Menomonie, WI. I was sitting in my boat adjacent to the start area waiting for my class to run, I watched (and listened to) your boat go several rounds that day. It sounded to me on each 'leave' like it hit the rev limiter and stuttered there until the pump hooked up and pulled the revs back down. Every run it sounded the same. Do you have a playback tach? If so, that would tell you if the rev limiter is the culprit. I may be way off base here, but that's what I heard. Jocko
Dave I took out the rev limiter at KOSH, still the same deal. When it lays down it's not pulling, tach never exceeded 6000 rpm.
 

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Boat Nut
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Discussion Starter #14
Chuck,
Interesting you're posting this issue. At the UMPBA race in Menomonie, WI. I was sitting in my boat adjacent to the start area waiting for my class to run, I watched (and listened to) your boat go several rounds that day. It sounded to me on each 'leave' like it hit the rev limiter and stuttered there until the pump hooked up and pulled the revs back down. Every run it sounded the same. Do you have a playback tach? If so, that would tell you if the rev limiter is the culprit. I may be way off base here, but that's what I heard. Jocko
Dave one other thing, I towed thru rain to get there, lots of carbon dust, and some moisture was found after post race tear down of the distributor.
 

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Boat Nut
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Discussion Starter #16
Thats a tough one. If you said it was one time, I go with the accel shooters, cam or pump size. But not 3 times without lifting.

I think I would try raising the float level to upper portion of the sight glass. Maybe even as high as the top of the glass and try it. It will richen your AF slightly, but not enough that you can't tell if it works.

Thats thing must leave pretty hard.
This would be easy enough to change, and change back. Was considering the push on extension tubes, with the crushed ends, this may keep some fuel at the jet.




Chuck Nuytten
jetext-2.jpg
 

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Highaboosta
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Chuck, with your background in aircraft and wiring you would be a natural at EFI anyways.
You just need a push over the edge. :hmmm: :thumb:
 

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Dave one other thing, I towed thru rain to get there, lots of carbon dust, and some moisture was found after post race tear down of the distributor.
no question if the center post in the cap is going away a little bit, it'll act and sound like it's hitting the rev limiter. been there done that, and is why i ALWAYS carry a new cap and rotor with me. that said, this distributor ran just fine winning several races looking just like this. big difference between minor corrosion under the rotor and on top of it with streaky cap... not suggesting anyone let there's get this bad, just the point that it still worked just fine.

 

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Boat Nut
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Discussion Starter #19
Chuck, with your background in aircraft and wiring you would be a natural at EFI anyways.
You just need a push over the edge. :hmmm: :thumb:
No doubt Mark, some of the graphic engine anaylizers, have complete digital pictures (number) of what happening and where, Each graph has a color asigned to indivual cylinders. They record in real time, so finding the issue is easy to find on the spread sheet. The only problem is I don't make enough play money to fund this :no:
 

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No doubt Mark, some of the graphic engine anaylizers, have complete digital pictures (number) of what happening and where, Each graph has a color asigned to indivual cylinders. They record in real time, so finding the issue is easy to find on the spread sheet. The only problem is I don't make enough play money to fund this :no:
Exactly. I run a JPI EDM800 on a TIO-540-S1AD and would love to run one on EVERYTHING. You feel blind after being able to see each cylinder EGT and CHT all at the SAME TIME and in REAL TIME. At $3000-4000 a whack, they're a bit hard to justify for street cars and lake boats.
 
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