Need help with chasing down an air leak

[freestylegeek]

OK, I thought I had my air leak problem taken care of (I didn't JB weld my second pulse line fitting into my cases :banghead. But, when I rode yesterday, it often acted like it was still there. Case in point: I did a big bronco (nose stab) and sunk it in pretty deep. I came back up, and obviously, the engine was starved for air. Well, even after the hood finished draining, it still felt like it was starving for air. It was basically running on one cylinder. If I kept on the gas long enough, it would rev to a point where they both would kick in, and pull my arms off. But, as soon as I let off the throttle, back to one cylinder. It would do this for about 30-45 seconds, then it would be running fine.

Now, annother thing that concerns me is that when I try backflips, and land upside down, it revs to high heaven (air leak). Then, when I roll it over and load the motor, it dies. Then, it takes about 30-45 seconds before it will start again.

Also, when it's on the trailer, it will idle fine, but when I brap it, it doesn't really rev back down. Every time it does that, I can hit the kill switch and it dies. That's what makes me wonder if it's an air leak or not?!?! If it was an air leak, the kill switch shouldn't really kill it. That's what it was doing when I had the air leak in the pulse line fitting - I ALWAYS had to kill it by pulling the throttle. After I sealed that fitting up, I did a leakdown test, and basically passed (just barely over 1 psi/minute - about 50 seconds to go from 2 psi - 1 psi)

I'm dissecting my carbs now, and seeing if there's anything suspicious in the internal filter, or in the circuit somewhere. Anyone have any ideas where else I should look? When it's working right, this thing is a monster! I'm hitting rolls just off of idle :barrel:. Toss out some ideas people!

 

[freestylegeek]

... and i'm also gonna put a T in my pulse lines...

I've heard of people putting an "H" in their fuel lines, and I wonder what effect that would have in the pulse lines too?

BTW, if anyone is wondering, my carb (dual 48 Novi's) settings are:

High - 100
Low - 115
N/S - 2.5
Spring 65g

 

[waterfreak]

Sounds like your too lean. Here's a set up that Malone's mechanic Mark told me to use on the Novi maxiflows for my 815cc 10mm
Start with these specs
Pilot Jet- 130 L.S. 1.0
Main Jet- 145 H.S. 1.0
Valve Seat- 2.5
Spring- Gold 110 Gram
He uses the same carbs on those EME 1000's !

 

[waterfreak]

BTW, try putting like 10 psi for your leak down test. When I did mine, it held 10 psi for 10 minutes! Now that's leak proof!

 

[freestylegeek]

Sounds like your too lean. Here's a set up that Malone's mechanic Mark told me to use on the Novi maxiflows for my 815cc 10mm
Start with these specs
Pilot Jet- 130 L.S. 1.0
Main Jet- 145 H.S. 1.0
Valve Seat- 2.5
Spring- Gold 110 Gram
He uses the same carbs on those EME 1000's !

Hmm, that's an interesting set-up (more traditional). I'm only at 783cc. With my ridiculously low pop-off (13 psi - measured), I don't think I'm too lean. Also, I can't get it to hesitate off idle, or off plane. Chuckie's known for tiny jets and loooooow pop off for freestyle motors.

I'm wondering if I just didn't pump enough in the cases during my air leak test. Your 10 psi for 10 minutes is perfect! :hail:

 

[freestylegeek]

Well, after dissecting the carbs last night, I found that the rear carb had a 95g spring and the front had a 65g spring. How the heck did this thing even run? I doubt that was the cause of my air leak, but I'm sure it was causing some sort of problem. I'll probably do a leakdown test again tonight or tomorrow and see if I can hold more pressure.

 

[Matt_E]

Always ALWAYS check your popoff pressure with a gauge. I am running two identical 48 Full Specs on two single carb motors. Ed advised to run 22psi popoff, with a 2.3 N&S and 115 g spring.

Two "115g" springs I had gave me 26-27 psi. Another 115g gave me 20psi.
One of my 95g springs gave me 21psi.

If it was an air leak, the kill switch shouldn't really kill it.

Not necessarily so. The kill switch will have no effect if the air leak is severe enough to make the plugs glow. If it is not that severe, it will just rev high and still shut down if you shut down spark power.

Btw, I just tracked down an air leak myself. Shoddy second pulse fitting.

 

[yamaslut]

I had a similar issue and it was the pumps on the carbs, but you don't have them right??? Yours is an external pump???

 

[freestylegeek]

I had a similar issue and it was the pumps on the carbs, but you don't have them right??? Yours is an external pump???

Nope, internal pumps. I went through those last night, and they're in fine condition.

 

[freestylegeek]

OK, finally found the air leaks. Yes, leaks - plural. I didn't want to yank the motor and go searching, but I didn't have a choice. I'm glad I pulled it out though. The first air leak was one of the bolts that holds the reed cages to the manifold. I cut two identical gaskets using the reed spacer as the template, and never thought about the fact that the bolt holes for the cages thread all the way out through the manifold. I had an extra stock f/a gasket laying around, so I cut out 4 individual bolt gaskets. problem solved there.

The second air leak was MUCH harder to find. I sprayed soapy water all OVER this motor, while pumping 10psi into it. Finally on the 3rd or 4th time I was checking my epoxy on the bottom, I accidentally sprayed some solution up into the voids near the side of the cases. Instant bubble. It was a tiny little pinhole. SWEET! I found the air leak!!:cheer: But then, CRAP! It's in the cases!:banghead: So, I thought I would just rough it up, and epoxy it. Well, during the rough up, I found out why there was a pinhole there. It's about as thick as tinfoil there! I ended up cutting a gash into the thing while trying to rough it up. So, time to split the cases.

After a thorough rough up and cleaning, I epoxied ALL the voids in the crankshaft area. Some advice to anyone building an 8mm or bigger stroker: EPOXY EVERYTHING!!! When I had Paul cut these cases, I asked him if I should epoxy there, and he said there's plenty of material in that area there, so only worry about the bottom two areas (where the tightening sequence numbers are). Well, he had to cut an additional 0.025" because the big ends on my rods are just that - BIG! The end result is thinness on a grand scale.
Hopefully, the problem is solved, and I'll be back on the water this weekend.

 

[ATS_Scott]

Have you tried the old, fill the hull with water trick? Give the cases a couple psi positive pressure and any leaks will be easy to spot.

 

[yamaslut]

damn.... nice work...

 

[SuperJETT]

Have you tried the old, fill the hull with water trick? Give the cases a couple psi positive pressure and any leaks will be easy to spot.

Read his post up there, he has already pulled the engine out, found the leaks, and repaired.

 

[waterfreak]

OK, finally found the air leaks. Yes, leaks - plural. I didn't want to yank the motor and go searching, but I didn't have a choice. I'm glad I pulled it out though. The first air leak was one of the bolts that holds the reed cages to the manifold. I cut two identical gaskets using the reed spacer as the template, and never thought about the fact that the bolt holes for the cages thread all the way out through the manifold. I had an extra stock f/a gasket laying around, so I cut out 4 individual bolt gaskets. problem solved there.

The second air leak was MUCH harder to find. I sprayed soapy water all OVER this motor, while pumping 10psi into it. Finally on the 3rd or 4th time I was checking my epoxy on the bottom, I accidentally sprayed some solution up into the voids near the side of the cases. Instant bubble. It was a tiny little pinhole. SWEET! I found the air leak!!:cheer: But then, CRAP! It's in the cases!:banghead: So, I thought I would just rough it up, and epoxy it. Well, during the rough up, I found out why there was a pinhole there. It's about as thick as tinfoil there! I ended up cutting a gash into the thing while trying to rough it up. So, time to split the cases.

After a thorough rough up and cleaning, I epoxied ALL the voids in the crankshaft area. Some advice to anyone building an 8mm or bigger stroker: EPOXY EVERYTHING!!! When I had Paul cut these cases, I asked him if I should epoxy there, and he said there's plenty of material in that area there, so only worry about the bottom two areas (where the tightening sequence numbers are). Well, he had to cut an additional 0.025" because the big ends on my rods are just that - BIG! The end result is thinness on a grand scale.
Hopefully, the problem is solved, and I'll be back on the water this weekend.

Wow, that's some thin cases! I think you should add some kind of aluminium plate there. I added a 1 inch think T6 aluminium plate to the bottom of my cases to accomodate the 10mm. the machining went right thru the cases and into the plate. but it is leak proof! now:woot:

I'm ready for 12MM!!:brap:

 

[yamaslut]

Wow, that's some thin cases! I think you should add some kind of aluminium plate there. I added a 1 inch think T6 aluminium plate to the bottom of my cases to accomodate the 10mm. the machining went right thru the cases and into the plate. but it is leak proof! now:woot:

I'm ready for 12MM!!:brap:

holy crap.... didn't know you guys were taking it that far...
:bigeyes::bigeyes::bigeyes::bigeyes:

 

[WaveDemon]

is epoxy enough with a case that thin? I would be tempted to have it filled with aluminum.

 

[freestylegeek]

is epoxy enough with a case that thin? I would be tempted to have it filled with aluminum.

Epoxy will be plenty. Running pressure in the case is usually 7psi. It's not so much about strength as it is about sealing.

 

[WaveDemon]

Epoxy will be plenty. Running pressure in the case is usually 7psi. It's not so much about strength as it is about sealing.

I wasn't thinking about pressure more about a crank running 8k RPM being supported by a paper thin case. I'm sure it's thicker at the journals but I would think the integrity of the case is compromised. They don’t make cases out of epoxy for a reason.

 

[Matt_E]

Yeah, metal is cheaper. :biggthumpup:

 

[freestylegeek]

I wasn't thinking about pressure more about a crank running 8k RPM being supported by a paper thin case. I'm sure it's thicker at the journals but I would think the integrity of the case is compromised. They don’t make cases out of epoxy for a reason.

The strengthening ribs are all still intact, and they are what primarily takes the load. The filled in epoxied areas will actually provide more rigidity than the aluminum did.