SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: The Chaz on February 06, 2008, 09:00:35 PM
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I was hoping someone could give me some pointers or literature on how to tune my new Holley carbs. In my haste to get a new set it appears I got vacuum secondaries which will have to do now. Is the amount of vacuum needed to open the secondary adjustable?
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You can get different tension springs for the vacuum pods that will adjust when the secondaries will open. There is also a set of vacuum pods that have a balance hose between both carbs so that they open equally.
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http://cgi.ebay.com/ebaymotors/Holley-Tunnel-Ram-or-2x4-Balanced-QC-Vacuum-Pods_W0QQitemZ370018865534QQcmdZViewItem?hash=item370018865534
Check this out
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Umm hose between? there are two vacuum lines coming off the base plate of the carbs. One is a lot smallerthan the other. Also The carbs came with the chokes removed, and
66 jets
6.5 power valve
.025 acc pump
is this ok to start with for my tunnel ram? The engine has a mild cam, maybe RV. .495 lift 299* duration on intake and exhaust ,468ci, 9.76:1 compression, deburred ports, and logs/snails
The large one opens next to the secondaries.
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Is this a must have or a performance enhancer?
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Its not going to give an increase in performance but it will help when it comes time to dial it in (I haven't done it yet, but I plan on it).
Before I put my boat on the water after I bought it I went through the carbs. Someone had disconnected the secondary diaphrams and installed a small bolt into the linkage making the secondaries come in all the time. I set them up with stock jetting, new 6.5 power valves and corrected the secondary operation. So far on a mild 454, low rise dual quad manifold my jetting seems to be very close.
Put them on and run it, once you have it running decent get some plug readings to see if it is over rich (not likely going to be lean).
P.S. I would have hated to see how much worse my fuel mileage would have been with the locked in secondaries :o
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SO should I plug the vacuum lines that come off the base? I have breathers on both valve covers so no need to route lines to the carbs. Also will a vacuum gague give an accurate reading off these lines or does it need to be off the manifold? The only way to check one off the manifold is to put a vacuum line plug in the 1 hole that is 1/2 way up the tunnel ram runner on the rear of the manifold...
Sorry for all the questions I will have, but I am determined to be more than a plug and play jet boater. I want to understand how my equipment works and how to properly tune it.
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SO should I plug the vacuum lines that come off the base? I have breathers on both valve covers so no need to route lines to the carbs. Also will a vacuum gague give an accurate reading off these lines or does it need to be off the manifold? The only way to check one off the manifold is to put a vacuum line plug in the 1 hole that is 1/2 way up the tunnel ram runner on the rear of the manifold...
Sorry for all the questions I will have, but I am determined to be more than a plug and play jet boater. I want to understand how my equipment works and how to properly tune it.
A vacum gauge anywhere on any of the base lines (except the ported vaccum which will pull 0 at idle) will reflect the entire manifold. For the longest time on one of my tunnel rams, I used an old fogger boss at the end of the runner far from the carb. When I changed it to under the carb, there was no difference.
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OK, I will let you all know how it goes tomorrow. Hopefully my timing is close enough to not cause a backfire :o
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The new carbs should have a blow out protection check valve to keep the power valves from being damaged if it does back fire.
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I found this site, very helpful
http://www.bob2000.com/carb.htm (http://www.bob2000.com/carb.htm)
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Vacuum secondarys are awesome!
The balance line crewchief mentioned is very important!! it is in the secondary part of the carb in the metering block.
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Opps primary side. It's been a while. ::)
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I took my whole tunnel ram to my carb guy , and when I got it back with the carbs rebuilt there was a metal tube connecting my secondaries. I get people asking me all the time how hard it was dialing in my carbs. I never had to dial in shit! They worked great fresh from the shop. The carb guy told me most people have trouble with their tunnel ram due to the carbs not being matched and the vaccuum secondaries not being in sync.
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Does this set-up have that tube for the vac secondaries sync thingy... :P ???
http://www.socaljetboats.com/index.php?topic=2691.0
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You can either modify the tops of your current vacuum secondary pods or you can get these guys to replace them. http://www.holley.com/20-28.asp
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HELP!!
What do I do if fuel is spraying out of one of the tubes on top of the carb? [attaching=#1]
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I would think float adj.
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I read that the needle may be stuck how can I check this? I removed the screw on top and tried adjusting the float up and down, but this did nothing. It literally sprays out of the tube at high pressure. The other 3 seem to be fine though.
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Sounds like maybe a stuck float, the last time I adj. a float it seemed backwards from what I thought, I kept turning it the wrong way. Also check your fuel pres. although I'd think all 4 would be gushing if that was the problem.
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Remove the lock screw and adjusting nut, then remove the needle and seat assemlby (count how many turns it takes to remove/reinstall same amount to get adjustment close), inspect the needle and seat for debris (small piece of rubber hose is common), clean and reinstall.
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OK, I fixed it ;D
It LIVES again O0
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Remove the lock screw and adjusting nut, then remove the needle and seat assemlby (count how many turns it takes to remove/reinstall same amount to get adjustment close), inspect the needle and seat for debris (small piece of rubber hose is common), clean and reinstall.
Will the assembly just come out after I unscrew the float adjustment screw? After I readjusted it and blew it out, it started leaking gas through the the secondary outlets and around the entire secondary assembly. I tightened the 4 bolts and it works now.
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The needle and seat assembly is the float adjusting screw. To adjust float level you loosen the top screw and turn the nut (up/down) which is turning the needle and seat assembly, but if you remove the top screw and continue turning the nut counter clockwise you will remove the complete needle and seat assembly.
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Thanks, ;D I will know what to do next time I have a problem like this
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On any new carb I recommend removing the bowls, inspecting the needle and seats, and double check the float level. The reason for this is the float level can be knocked out of adjustment due to bouncing around in shipping.
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Can those tall tubes that the fuel was spraying out of be removed? I was just thinking about how a flame arrestor or filter would fit on top of there... nevermind I just had a brain fart :o
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A lot of times that "problem" can be solved by whacking it with a screwdriver handle.
That tube is a vent for the floatbowls, you cannot plug it without the carb no longer functioning. What you can do though, is take a piece of 1/4 inch hose, put each end to the float bowl tube vents. Make sure you then cut a hole in the middle on the bottom so the vent tubes are still vented to the air, but any excess fuel bouncing out (or from a stuck float) will then go into the the carb rather than onto the outside of the carb and manifold.
If you aren't worried about that, then you can shorten the tubes, and many times you want it at an angle so the air filter / spark arrester doesn't block the tube.