2.4 200 carb tuning issue

[90 5.0]

Ok, this one has me pulling my hair out. I'm open for ideas on what to try next.

Basics
2.4 200 83 block
wh22 carbs
holley red pump
aeromotive regulator

at high rpm, exactly 7k it seems every time it falls flat on its face, boat noses over. If you keep your foot in it a moment later it will snap back to life an pull clean to 72/300immediately. Fall over again, snap to 75/600 immediately again and fall over. I get out of it at this point because I don't want the boat nosing over going even faster.

This is a recent issue that has come up once I started testing with shorter props and race gas. The first time it nosed over at 7 I suspected had jetted down too much and never stayed in it. I kept going up in jet sizes until I got back to my fat cruising pump gas jets and it never changed. That's when i decided to keep my foot in it and see what happens.

This was with a 20p drag prop. The same boat has turned a 30 to 7800 and was still pulling when I let out.
I have not put a big wheel back on to see if it does it with it again or not. I suspect it would, I had some mid speed stumble that was starting to show up every now and then before. I suspect what ever is causing this was causing that.

But it could be perhaps its accelerating so much harder with the short wheel the fuel demand can't keep up.

Anyway in testing I have also developed an off hit stumble a few moments after you punch it, not when you punch it but right after its up, and it's very quick. Nail throttle, pulls out of hole hard, stumbles for a fraction of a second and pulls clean to 7k the. Stumbles again.

I have changed jetting from 78/80 all the way up to 84/86 with the Same stumble everywhere. No difference

raised float bowl height thinking it might be draining the bowl too fast, no change

cleaned and inspected fuel filters no change.

Checked compression and leak down, all good.

Checked stator, switchboxes etc all good.

It has become extremely hard to start for the first time of the day, after that look at the key wrong and it barks off, was never this hard to start before

cleaned and inspected carbs, rebuilt with new gaskets, new needles and seats.

I suspect a fuel dilevery issue at this point but I'm out of ideas.

10an from sumped tank to 10 micron filter, 6an from filter to pump, pump to reg reg to motor and reg to return

adjusted fp from 3-7 at 1/2lb increments. No change.

The pump is new, but I'm starting to suspect it. I have a blue I can swap out to eliminate that issue.

Any other thoughts?? Seems like I've tried all the things I can think of at this point??

[John Jackson]

IF it's a fuel supply problem, increasing jet size will make the problem worse while at the same time making less HP. It's possible carbs are starting to flood if you fuel pressure is too high, blowing the float off the seats. Raising the floats could make this worse.
If you don't have the late fuel line, the fuel line could be collapsing internally. Also, the pickup in the tank could be clogging. Many of the older tanks had a screen that would get clogged. Blowing it out backwards would fix this for a while. Also, if your tank vent is clogged, it could be making a vacuum after some running. try running with the gas cap loose to make sure your venting is not clogged. I'm sure some other may have some other possibilities. I might too after thinking about it for a while.

[90 5.0]

IF it's a fuel supply problem, increasing jet size will make the problem worse while at the same time making less HP. It's possible carbs are starting to flood if you fuel pressure is too high, blowing the float off the seats. Raising the floats could make this worse.
If you don't have the late fuel line, the fuel line could be collapsing internally. Also, the pickup in the tank could be clogging. Many of the older tanks had a screen that would get clogged. Blowing it out backwards would fix this for a while. Also, if your tank vent is clogged, it could be making a vacuum after some running. try running with the gas cap loose to make sure your venting is not clogged. I'm sure some other may have some other possibilities. I might too after thinking about it for a while.

Talking to another buddy he told me he had dirt dobbers stop his vent up and do some weird stuff, I remembered then that when I put gas in it there was a vacuum on the tank and I just thought it was weird and nothing else about it.

I also realized that on the old reg it was non return style and where our return was it was open to atmosphere with hose fouled up, this problem has showed up right about that same time.

I bet you are right and we had been going down the same lines of thinking. I ordered all new fuel line too, just realized the line we were using was jegs pushloc, looking at the specks it's not for fuel. I think the weird stuff in my filter was prices of the line.

Will change that all out when the new fuel line gets here tomorrow or w dnesday.

If you think of anything else id love to hear it(especially if this doesn't fix it!!)

thanks!!

[John Jackson]

The crumbling fuel line is very common and can collect almost anywhere. So check both before and after all filters. (Some filters have pressure overrides), might even want to drop one of the carb bowls just for verification.
I've seen more EFI and carb motors blow in the past 3 years than in the preceding 20 years. Most of them due to the fuel lines and crappy fuel with ethanol in it.

Keep us updated.

[JOE54]

???plugs look lean or rich, ^^^^^^ amen to blown mtrs

[90 5.0]

Item hard to get a real good plug read on an Allison drag because you can't just kill it at wot , but they never looked overly lean except for with the 78's and never looked too rich even going to 86's.

[John Jackson]

Of course you can kill it at top speed. And it will stop very quickly. And maybe even cool you off in hot weather.

[90 5.0]

Of course you can kill it at top speed. And it will stop very quickly. And maybe even cool you off in hot weather.

It almost cooled me off earlier in the year when my steering broke. My shoulder still hurts from the hook

[EuropeanAM]

I was thinking along the lines of the pump, lines, regulator or combination of the above.

If possible, go back to known-working jetting and fuel after you've addressed the suspects... for a closer comparison without as many variables.

[90 5.0]

I was thinking along the lines of the pump, lines, regulator or combination of the above.

If possible, go back to known-working jetting and fuel after you've addressed the suspects... for a closer comparison without as many variables.

Thats where I ended up, went all the way up to my pump gas river jets and no change.

My fuel lines are new less than a season old but didn't realize till now they aren't rated for fuel. Who the heck would have thought any AN sized line would not have been fuel comparable?? Anyway live and learn.

Im gonna drain the race gas, put it back to river timing replace all the lines and pump , look at the vent and try and make a pass with the cap off the tank and see if it turns up like it was before

[90 5.0]

Update gas cap vent wasn't venting at all.

Cleaned vent and installed a second big 6 an bulkhead fitting , line coiled up open to air.

Better but not perfect, would probublay be perfect on pump gas. Had a friend help with testing and we ended up leaning down even more and pulling more fuel pressure out of it.

Motor comes on like crazy again now. Need to tweak motor height and props now but at least it's making power again now and will pull clean the entire 800' now to 82/300

[John Jackson]

Glad you found it. Sometimes the simplest things can cause tough to diagnose problems.

[EuropeanAM]