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-   -   Fuel in vacuum modulator line (http://www.hotrodders.com/forum/fuel-vacuum-modulator-line-200584.html)

Yegster 06-19-2011 01:25 AM

Fuel in vacuum modulator line
 
About 3 months ago, I pulled my vacuum line off my Turbo 400 modulator and noticed fuel in the line. I drained it, and now during a rebuild, the tech noticed the line had fuel in it again.

I'm pulling the vacuum from the base plate on the rear Holley carb (near the secondary rod). Running a tunnel ram with no factory vacuum ports.

If the solution is to tap a hole in the manifold, I'm fine with that, but where and why would it make much difference than being sourced at the carb, if the entire vacuum supply is full of air/fuel mixture?

http://i634.photobucket.com/albums/u...t/DSC00098.jpg

Crosley 06-19-2011 07:11 AM

in the old daze when transmissions had vacuum lines on new cars... you often would notice a u shaped loop that went 'up' near the hook up to the vacuum source at the manifold.

That loop 'up' , then down towards the trans , prevented fuel from traveling down the vacuum line tube. Any fuel would drain out of the vacuum tube because of that loop

delawarebill 06-19-2011 07:25 AM

vac line
 
i had the same intake, single 4 brl... nice offy too.. but anyways i'd drilled/taped the hole between the carb's on the side for my tranny line..

Yegster 06-19-2011 01:53 PM

Great ideas guys. I'm wondering if a right angle off the carb (or new tap point) that would send the hose (or stainless line) upward before it heads down would do the trick. How many inches above the tap point would be enough to keep the fluid from traveling down the line? I need to keep this line decorative as it isn't hidden under an air cleaner. I have a smaller diameter line that would tolerate a tighter bend then what is on the engine now.

2old2fast 06-19-2011 07:39 PM

Yegster, how'd you make out w/ your intake problem?


dave

Yegster 06-19-2011 10:36 PM

Hi there Two Old,

Thanks for checking in on intake leak. After milling the sides .070 and the front/rear .030, the ends still weren't providing enough of a gap at the china walls. They did another .045, and we set the manifold down and it maybe had .010 of a gap for the silicone. I was out of time to get the car back on the road, so we glued both sides of the gasket and put it on.

I ran a screwdriver down the plenum and it seemed like there was a nice transition at the lower port to intake runner. No way to get a feel on the upper side. Thought we had it fixed, but in a hundred miles the problem was back. I haven't pulled the carbs since to run a screwdriver wrapped with a paper towel to see which runners are leaking. Very easy to check, so I'll be curious to see what the scoop is.

On July 16th, the car heads to Superior Automotive here in the LA area for a chassis dyno run. As they were the ones to do the mill work, I'll be interested to see what they think now that the engine will be there in front of them to view.

I'm running out of room on the china wall ends of the manifold to cut much further, but I would still feel more comfortable knowing the manifold was truly wedged between the sides as evidenced by a large gap at the ends.

In the meantime, the TH400 (who knows hold old it was) let go under the torque of the new engine, so last week was a rebuild. Can't believe what a difference there is from before. The car is just plain a rocket ship off the line with the 4:30 gears, and way too fast for any type of street use (in terms of performance). I think the plan will be to take it down to something like a 3:55 over the winter and get some decent highway rpms out of it.

So for now, time to have fun hitting shows through the summer, and we'll just keep feeding it oil until I get a break in the action to cut the manifold ends again.

Appreciate the follow-up. Come on out and visit here in LA. We'll have a ball!

2old2fast 06-23-2011 08:28 AM

Yeg, well keep me informed as to what you discover. I have an edelbrock street tunnel ram ,w/ the plenum removed, using a mirror & lite ,I can look at the joint between the man.& heads, maybe this is something you could try.


dave

Yegster 06-23-2011 05:15 PM

Hi Dave,

Actually had the two pieces apart when the millwork was done, and like yours, you can see pretty well in there. Didn't try a mirror though - good idea. I almost fell like running an extra bead of silicone from the inside just for some extra insurance. I know it won't hold up to continued exposure to fuel, but anything would be better than the situation I'm having now. Since the leak is always on the bottom, that would be pretty easy to apply.

I will be curious the next time the carbs come off as to which side or which ports are leaking. It will be easy to tell from the top.

One difficulty I'm having is finding the gaskets on my old Weiand ram. My local speed shop ordered them over a month ago after the confirmed the pattern, but nothing back yet. I used a little silicone to seal up a couple of small gaps that came about from the original brittle material breaking off. I don't really want to separate the two pieces again until I have the new gaskets in hand. The odd shape of them don't make fabricating a new set an easy task.

Saturday is the Barrett-Jackson auction in Costa Mesa, so will have my car on display there, and then Sunday I will have time to play with getting the secondaries working (removing the balls in each chamber to see what that will do. I just want them to open too much, and then work backwards to adjust them. No luck so far with even the lightest spring in there. Just a little movement.

Was somewhat thinking about taking my carbs down to 450's. I see the Holley's with no choke, mechanical secondaries, etc. that seem like an interesting option.

http://www.jegs.com/i/Holley/510/0-9776/10002/-1

It looks like they have a metering plate instead of a block, and hopefully I can pull those off my existing 600's along with the longer transfer tube, and bolts to make it a simple swap. Not too excited about the gold color, but I think I can polish them to silver and match my existing carbs. I also don't think they operate like a true double pumper - no second accelerator pump - at least not that I can see. It just may be simpler to go this direction instead of tangling with the vacuum secondaries. I don't need a choke in my climate.

Ever see these carbs before?

2old2fast 06-23-2011 07:07 PM

Yeg, the 450 mech. sec carbs is what I'm running, but mines a 388 stroker small block,Ireally like these carbs, jetted just like they came out of the box-58 pri. 70 sec. yea you can change the sec. but why bother if they work o.k.? Iwould think that these would work allright for you , but thier's guy's on here alot smarter than me....


I hope that your manifold was milled at the correct angle ..

get gskt. material from napa, make your own, that's what I did...

dave

Yegster 06-23-2011 07:20 PM

Thanks!

Before I do anything with the carbs, the leak has to be corrected. Otherwise I might head in a different direction than the tunnel ram. We didn't change the angle on the cut as the heads matched the intake perfectly. We did the cut to lower the manifold which did smooth out the transition between the two parts.

I mentioned this earlier, but the only thing that concerns me is the china wall area. I don't think they milled it enough to let the manifold sink to its lowest point - and leaving a gap at the ends. There was a small gap, but nothing like we thought it would be - after two cuts. On the 16th, the car is going to the shop that did the cut, so we'll see what opinion they have.

Curious what kind of hp and torque we are putting out before playing with anything.

We'll see!


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