SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: nolongergreen on June 02, 2014, 10:15:55 AM
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I'm getting closer on my boat but I'm needing info on the jets. We thought it was a little lean and wasn't getting enough fuel so we tried taking jets out of the 850 carb I had on there before which happen to be 80s and put them in the front carb. Ended up changing plugs and wires and it's running a little better so I figured let's put the 66s back in the carb.
Here's the problem.
We cannot adjust the idle down below about 15 rpms or it dies and it has a popping sound on the passenger side so I'm assuming it's running lean.
My idea is to put the 80s back in the front of both carbs and then I can idle it down where it needs to if it's lean. Does this sound right?
Are the jets mainly for the idle circuit?
This is on a tunnel ram with 2 600 holleys.
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I did just see a video online that shows the idle mixture screw under the threaded rod that holds the air cleaner on. Gonna try and adjust that tomorrow
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The jets do not influence the idle circuit at all. Changing the jets will not change the idle air fuel ratio.
The idle circuit is completely separate from the main circuit (jets). If you look at the bottom of the throttle bores, you will see a little slot (B in picture) in the throttle bore that crosses over the edge of the throttle plate when it is closed, this is the idle transfer passage. You will also see a small hole (A in picture) in the bore below the throttle plates; this is the idle discharge hole.
It is important to note that the idle circuit only functions during conditions of low throttle settings (nearly closed). When the throttle position is opened enough to provide sufficient airflow velocity at the venturi boosters, to promote fuel flow, the carb transitions from the idle circuit to the main circuit (jets).
Depending on which carbs you have, you may have either two idle mixture screws (most common) or you might have four corner idle mixture screws. Opening these screws (needle valves) only adds more fuel while at idle. Making adjustments to the idle does NOT change the air fuel ratio. It is probable, that you have carbs that were not originally intended for use in a dual quad setup and that your engine is already getting too much fuel at idle. The only way to change the air fuel ratio at idle is to alter the idle feed restrictions.
Is the popping from the passenger side coming from the exhaust? Do your carbs have 1:1 linkage or are they progressive linkage where the primaries open before the secondaries? IMHO, if not already, you should adjust your linkage to have a 1:1 opening ratio. Though some like the progressive linkage, I believe that it causes cylinders to operate under different conditions until WOT even though all share a common plenum. You may also find that you will end up with different size jets over each port to fine tune individual cylinder air fuel ratio.
I highly recommend Super Tuning and Modifying Holley Carburetors by Dave Emanuel to get you going. http://www.amazon.com/Holley-Carburetors-Dave-Emanuel/dp/1884089283 (http://www.amazon.com/Holley-Carburetors-Dave-Emanuel/dp/1884089283)
Regards,
Joe
[attach=1]
From http://www.crankshaftcoalition.com/wiki/Holley_4150/4160_tuning (http://www.crankshaftcoalition.com/wiki/Holley_4150/4160_tuning)
(A) Screw holes-
Four total, one in each corner used to fasten float bowl assembly/metering block to main body
(B) Idle downleg-
This passageway feeds fuel to both the idle discharge port and the idle transfer slot.
(C) Idle well-
Fuel from this well travels to the top of the metering block, then turns 180 degrees and mixes with air from the idle air bleed into the circuit.
(D) Accelerator pump passage-
This transfers fuel from the accelerator pump to the outlet nozzle.
(E) High-speed air bleed-
Air from the high-speed bleed enters the metering block here to be mixed with the fuel as it climbs the emulsion tube.
(F) Passage to booster-
This channel transfers fuel from the main well to the booster
(G) Ported vacuum passage-
This connects the ported vacuum source in the throttle body to the outlet where this can be routed to a source like vacuum advance.
(H) Parallel air well-
Air is introduced into the main well through these two holes.
(I) Main well-
Fuel collects here after passing through the main jet.
(J) Power valve port/channel restriction orifices-
This is where the power valve is located. The two small holes are the power valve channel restrictors (PVCR) that determine the amount of fuel added to the main metering circuit when the power valve opens. This valve determines when additional fuel is added to the main circuit.
(K) Idle restriction channel-
Fuel from the main circuit passes through this short channel and through a small brass restrictor (L) that acts as the idle circuit jet.
(M) Idle transfer slot discharge-
Idle fuel exits the metering block to deliver fuel to the transfer slot.
(N) Idle fuel discharge port-
Idle fuel exits the metering block and enters the carburetor main body for carb idle fuel below the throttle blades.
(O) Dowel pins-
Two pins locate the metering block on the carburetor main body.
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I did just see a video online that shows the idle mixture screw under the threaded rod that holds the air cleaner on. Gonna try and adjust that tomorrow
Please post a link to that video if available.
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Youtube search" how does a holley carb work" it's a black and white video.
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It pops out the exhaust
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Also the carbs are 2 corner idle
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When you say 1:1 are you meaning removing the vacuum secondaries and make them open all together?
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Are vac secondaries even applicable on a tunnel ram?!
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I ran a 10 second 64 Cuda with a 440 and a tunnel ram with two vacuum secondary carbs ran great .
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Pretty sure there's a bit of difference from a obviously built car motor to a near stock Jet boat motor, different type of loads and friction not to mention a gearbox and other factors, JMO it's always seemed worth the extra $ to find a decent set of mechanical secondaries, a lot less variables due to the vacuum needed and the tunnel rams
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Pretty sure there's a bit of difference from a obviously built car motor to a near stock Jet boat motor, different type of loads and friction not to mention a gearbox and other factors, JMO it's always seemed worth the extra $ to find a decent set of mechanical secondaries, a lot less variables due to the vacuum needed and the tunnel rams
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why would anybody run a tunnel ram on a stock motor?
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why would anybody run a tunnel ram on a stock motor?
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my thoughts exactly
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When you say 1:1 are you meaning removing the vacuum secondaries and make them open all together?
Ohhhhhhhhhhh, vacuum secondaries!!! I missed that. Yes, 1:1 linkage would be mechanical and require replacing the vacuum actuation with mechanical linkage. With vacuum secondaries, it is difficult to get the secondaries to open at the same rate as the primaries and to open all the way, even with the softest spring. But that wouldn’t affect your idle. It might give you some full-throttle blues. Ideally, you want each cylinder to receive the exact same amount of air and fuel. Every dyno operator that I have worked with has told me that when running vacuum secondaries, you are leaving some horsepower on the table.
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I thought I remember seeing pics of your tunnel ram install, but I can’t find them right now and I don’t remember if you have them mounted sideways or inline. If the carbs are inline, might you have a small exhaust leak in your passenger side header?
You might consider upgrading to secondary metering blocks with a kit like Holley 34-6, which will give you greater tunability. There are also metering blocks available with adjustable idle feed restrictions. Your vacuum secondary carbs will have secondary idle circuits built in, but are not adjustable. To adjust secondary main enrichment, you will need to change metering plates like you would change jets in your primaries. Switching to a secondary metering block, that utilizes jets, gives you more choices and jets are cheaper/easier to change than metering plates.
I think you are way too rich at idle and that the popping you are hearing is raw fuel exhausting and being ignited in your headers when exposed to oxygen. Raising the RPM above 1500 will help the engine digest the extra fuel being force fed and it will also open the throttle plates into the transition between the idle circuit and main circuit, thus reducing the affect of the overly rich idle circuit.
Regards,
Joe
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Ricky Racers and even the automotive engineers do all sorts of crazy things. At one time Edelbrock offered a dual quad setup where the engine operated off of the rear carb only until about half throttle. IMHO, the AFR between the front and rear cylinders wasn't even close and in practice, the engine didn't like it.
I built a '66 medium riser 427 Ford with dual vacuum secondary 450s that ran real hard and was very streetable in a Cobra replica. You just have to spend some time playing with it.
My thoughts regarding 1:1 secondaries are for an optimized cylinder-to-cylinder AFR once everything is said and done.
Cheers,
Joe
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All the max wedge Chrysler were all vacuum secondary on both the long ram and the short ram double carbed engines
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Not trying to be argumentative, but the Ram Chargers are altogether a different configuration than a tunnel ram setup that attempts to place one carb venturi directly over each cylinder. The carbs on the MoPar long ram and short ram engines are turned sideways which minimizes fuel distribution issues between front and rear cylinders caused by the primaries and secondaries opening at different rates. Tunnel rams actually shares more common with a four Webber manifold than it does with a cross ram. Granted a tunnel ram has a common plenum that will tolerate a certain degree of non-synchronized throttle positions, it does allow individual cylinder tuning (should the OP choose to take it to that level). At this point, for his current configuration, I say run with the vacuum secondaries. He just needs to learn how to tune it.
From one MoPar fan to another, I am sure you are aware of the extensive modifications to these cross-ram manifolds performed by the likes of old Dandy Dick et al to tune individual cylinder AFR. I am not saying that they don’t run hard (with vacuum secondaries) or that I wouldn’t love to have one, but these were street cars that were expected to have a hint of gas mileage compared to their race counterparts.
Cheers,
Joe
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Not trying to be argumentative, but the Ram Chargers are altogether a different configuration than a tunnel ram setup that attempts to place one carb venturi directly over each cylinder. The carbs on the MoPar long ram and short ram engines are turned sideways which minimizes fuel distribution issues between front and rear cylinders caused by the primaries and secondaries opening at different rates. Tunnel rams actually shares more common with a four Webber manifold than it does with a cross ram. Granted a tunnel ram has a common plenum that will tolerate a certain degree of non-synchronized throttle positions, it does allow individual cylinder tuning (should the OP choose to take it to that level). At this point, for his current configuration, I say run with the vacuum secondaries. He just needs to learn how to tune it.
From one MoPar fan to another, I am sure you are aware of the extensive modifications to these cross-ram manifolds performed by the likes of old Dandy Dick et al to tune individual cylinder AFR. I am not saying that they don’t run hard (with vacuum secondaries) or that I wouldn’t love to have one, but these were street cars that were expected to have a hint of gas mileage compared to their race counterparts.
Cheers,
Joe
there's no argument here I whole heartedly agree with you im just saying you can do it , it just takes good carb work, that being said why not run some good old center squirters and call it a day unless your racing. On another note I use to work on Dick Landys cars back in the day ( his personal cars not race cars) his brother Bobby was the brains behind that operation.
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there's no argument here I whole heartedly agree with you im just saying you can do it , it just takes good carb work, that being said why not run some good old center squirters and call it a day unless your racing. On another note I use to work on Dick Landys cars back in the day ( his personal cars not race cars) his brother Bobby was the brains behind that operation.
I didn't mean you, I meant me. Not trying to come off like an Adam Henry. I just want brother man's boat to run good and if I can help so that he make the parts he has work.
Cheers,
Joe
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I did just see a video online that shows the idle mixture screw under the threaded rod that holds the air cleaner on. Gonna try and adjust that tomorrow
You got me on that one, I've never seen that one before. Must be some of that random MoPar engineering from back in the day.
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Kinda funny too, my carb didn't seem to have that adjustment after all
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Glad to hear the vibration issue is resolved. Where do you stand on the idle now?
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Well ,left the shop today and damn she runs good. It revs crazy fast no bogs, backfires, or pops. Only thing is if I idle it down below 2000 rpms it dies.
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By the way it's now set up as 1:1 on the secondarys
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Great to hear that you're making good progress. I still think the idle circuit is way rich. Is it smoking at idle? Is it sooting the transom? Did you get to take any plug readings?
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By the way it's now set up as 1:1 on the secondarys
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how did you convert a vacuum secondary to 1to1 your going to get a huge bog without an accelerator shot to mask the time the throttle opens and the fuel flows out the venturi
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It does not smoke at idle, no soot at all. I haven't taken any plug readings because I have not had it in the water.
I modified thelinkage to where it's pulling the secondarys open just like they are on my 850 dp.
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It does not smoke at idle, no soot at all. I haven't taken any plug readings because I have not had it in the water.
I modified thelinkage to where it's pulling the secondarys open just like they are on my 850 dp.
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by the linkage on yhe side I take it , you're still going to get a stumble by doing that because you don't have an accelerator shot of fuel on the secondarys
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Well its not like it's not reversible by pulling the arms off (cotter pin) and letting the vacuum mechanism do the work. That's still hooked up, I'm just force feeding it.
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