SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: nolongergreen on June 06, 2014, 03:46:31 PM
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What do I need to change on my setup to get it to idle below 2000 rpms?
Tunnel ram with 2 600 holleys. It does not have 4 corner idle.
It revs crazy and seems dead on everywhere else but the idle.
If you try to bring it below 2000 rpms it just dies.
I wouldn't worry too much about it because everywhere else it's so clean and crisp but 2000 rpms is a little too much for a no wake zone and could prove to be touchy trying to load it on the trailer.
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My bad, 4 corner fuel mix screws.
I have the front carb vacuum large port hooked up to pcv valve, should I hook up 2nd carb to other side and run 2 pcv valves? Could just having to front carb hooked up cause an imbalance of vacuum between the carbs?
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Also they are now 1:1 linkage on the secondarys
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Also they are now 1:1 linkage on the secondarys
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This could be your problem. How was it done? Are the throttle blades closing enough to get you into the idle circuit?
Have you checked for vacuum leaks?
What is your timing set at?
I'd recommend plugging off the pcv while you do testing then hook it back up after you have it running good (monitor if you have a change at that point).
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I modified the linkage arms to look just like the linkage on my 850 dp. No vacuum leaks sprayed carb cleaner all over everything.
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Instead of the arms sliding and letting the secondarys open up with vacuum they are pulled open with the front
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Instead of the arms sliding and letting the secondarys open up with vacuum they are pulled open with the front
Nothing wrong with vacuum secondary carbs! Did you even try running the vacuum carbs with the original set up? Before you decided you needed to hack them up to make a half assed mechanical secondary :screwy:
If you want mechanical secondary carbs... get mechanical secondary carbs.
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All I have to do is pull a cotter pin out and take the arm off. The vacuum mechanism is still there I'm just bypassing it . Kind of force feeding it..
100% reversible. ..
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I'm a big fan of the KISS (Keep It Simple Stupid) method.
I'd recommend put the carbs back to original. Make sure the throttle blades are adjusted correctly (throttle stop on base plate is adjusted properly).
Figure out the idle issue, get it running decent throughout the rpm range then you can start making changes to see if anything helps with performance.
You've got to have a repeatable baseline before you can tell if you are making improvements.
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You are absolutely right it ran much better with the vacuum secondaries hooked up like it's supposed to. Had a huge bog in it when you nailed it just as you said.
Runs great now actually picked up 7 mph and that's even with relocating the tank to the front of the boat sitting about 1/2 full which means maybe a 10 mph gain if the smaller 8 gallon tank was still in the back...
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Also, once it was in the water I got it to actually idle down where it should be, still tries to surge a little but I'm damn close. Close enough to run it like it is.
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Glad to hear you're getting it sorted out.
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Thanks for your help. You were dead on with the whole vacuum secondaries thing.
Why would anyone run a tunnel ram on a basically stock motor?
7mph gain and like I said there's a 17 gallon tank in the front now verses the 8 gallon tank that sat right in front of the motor before.
It would definitely have gained another mph or two if I hadn't relocated the tank.
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dont vac secondary carbs not work very well with tunnel rams?
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Here is my advice, take it or leave it. Take out whatever you have to open the secondaries mechanically, and let the vacuum pots do their thing. If you really want mechanical secondaries, go buy a couple of 660 center squirters. My guess is that not only do you have idling issues, but it probably bogs when you get on the throttle quickly. If you don't know how to work on carburators yourself, take it someone who does.
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I'm sorry I wasn't clear. I ran it with the with the secondaries hooked up mechanically and it ran like crap.
It HAD a huge bog when they came open.
So I took the linkage off and let the vacuum secondaries do there thing and it works perfectly.
It has quick fuel adjustable secondaries with a screw to adjust how quick they open and I actually had to run the screw in to slow down how quickly they open.
So yes, I would say the vacuum secondaries works very well with the tunnel ram on mine.
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Instead of the arms sliding and letting the secondarys open up with vacuum they are pulled open with the front
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Won't work properly imho.
I would also lose the pcv.
Are the butterflies drilled?
Are toy trying to adjust the idle with the idle screws one at a time?
You may be able to get it to idle on one carburetor first....
GT
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Almost forgot my first thought.
It sounds like you are fighting power valves.
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All is well now. I ran it like described and it layed down when you got on it. I disconnected my linkage that I modified and let the vacuum secondaries do their thing and it works awesome. I even got it to idle down, I believe it had to to do with adjusting both even though linked together doesn't mean they close exactly the same time. The vacuum secondaries have the quick fuel adjustability to slow down how quick they open and I actually had to use that to slow it down a little because they came on so soon it still had a slight bog. I adjusted that out and now it comes on just as it should.
Actually picked up 7mph going from the single carb. Would probably be more than that since I went from an 8 gallon tank in front of the motor to a 17 gallon tank up front in the bow. I know that cost be some speed there but I'd rather have the ability to run a larger tank.
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I figured out the idle problem. Just by putting in the water tamed it down alot.
However I believe the problem was is that I linked the carbs together without checking to see that the idle screws were all the way out on both. So either way if you ran the screws all the way out after they were tied together if one wasn't set to zero that one would still hold open with the adjustments all the way out. Once they were linked one would hold the other open just a tad.
I believe this is going to be my final adjustment to get it complete. I'm gonna disconnect the carb throttle linkage tying them together, run idle screws all the way out on both, then reconnect linkage, then try and set the idle once they are both closed completely together.
I got it close but I believe this will get it dead on.
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Almost forgot my first thought.
It sounds like you are fighting power valves.
This is a great suggestion that didn't cross my mind because I was trying to press the point about altering the carbs.
If you are still running the 6.5 power valves, you should consider changing them to a 4.5. It'll help delay how quickly the added fuel comes in.
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Question: when you nail WOT from idle, the engine is effectively running off of the accelerator pump shot and fuel is not yet flowing through the main circuit (jets and boosters). Wont delaying enrichment via the power valve add to the bog until the main circuit catches up with engine demand?
Respectfully submitted,
Joe
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I've got to be honest with you. I have never nailed it from idle. Not sure why but just never have since I bought the boat.
I just always got it up on plane before I nailed it.
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Question: when you nail WOT from idle, the engine is effectively running off of the accelerator pump shot and fuel is not yet flowing through the main circuit (jets and boosters). Wont delaying enrichment via the power valve add to the bog until the main circuit catches up with engine demand?
Respectfully submitted,
Joe
I am hoping this is a general question, because I am going to treat it as such.
The idea behind the power valve is that when the vacuum level drops, it effectively makes the main jetting much larger. Having "too high" of a power valve size allows the fuel level to increase at much too high of a vacuum level. By reducing it (numerically) you are holding the enrichment out to a higher throttle setting (lower vacuum level) and effectively increasing the fueling when the jet starts to really pull some HP...
I am seriously hoping that helps clarify, if nothing else, at least causes more questions.
In all honesty, I would rather see the PV's eliminated and different jetting on a dual carburetor set up, it just makes tuning that much simpler. Maybe just me.
GT
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I've got to be honest with you. I have never nailed it from idle. Not sure why but just never have since I bought the boat.
I just always got it up on plane before I nailed it.
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I am betting that with the linkages locked together on the primary and secondary it would have fallen on it's face like a fat kid with his sneakers tied together...
No offense intended fat kids... ;)
GT
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Next time on the water I will nail it from idle and I'm sure all the re tuning will begin. Lol
Seriously though it's perfect how I run it but the thought of a perfectly tuned from idle holeshot sounds very addictive.
Might even get the same slingshot feeling I get when I leave the line on my crotch rocket. ☆
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I am hoping this is a general question, because I am going to treat it as such.
The idea behind the power valve is that when the vacuum level drops, it effectively makes the main jetting much larger. Having "too high" of a power valve size allows the fuel level to increase at much too high of a vacuum level. By reducing it (numerically) you are holding the enrichment out to a higher throttle setting (lower vacuum level) and effectively increasing the fueling when the jet starts to really pull some HP...
I am seriously hoping that helps clarify, if nothing else, at least causes more questions.
In all honesty, I would rather see the PV's eliminated and different jetting on a dual carburetor set up, it just makes tuning that much simpler. Maybe just me.
GT
Thanks GT, I don't think I could have explained it that well.
The other problem, and probably the main reason to lower the power valve starting point is due to the reduced vacuum caused by large cam profiles causing the PV's to blubber or start adding fuel at idle.
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So are you saying that the power valves are kinda rattling around causing the idle issue?
Like I say it's really close but I have noticed it kinda takes it a while for it to settle down sometimes close to idle.
It's on and off throttle great but it kinda acts like downshifting a manual shift car when you let out of it close to idle.
I don't mean like downshifting at 4000 rpm, it's like about 1500 rpms to 800 rpms.
It kinda wants to hang up for a second or two before it settles back down to idle. Not every time though.
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So are you saying that the power valves are kinda rattling around causing the idle issue?
Like I say it's really close but I have noticed it kinda takes it a while for it to settle down sometimes close to idle.
It's on and off throttle great but it kinda acts like downshifting a manual shift car when you let out of it close to idle.
I don't mean like downshifting at 4000 rpm, it's like about 1500 rpms to 800 rpms.
It kinda wants to hang up for a second or two before it settles back down to idle. Not every time though.
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Do you know what makes a power valve work?
Not being a snotbag, just curious.
If at a slower idle you are only making 6 or 7 inches of vacuum, the power valve will be on the edge of open, which is like jumping three or four jet sizes in a matter of seconds.. I am starting to think this is the issue....
GT
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Guys, as I said in the beginning, I own a carpet cleaning company. I have never and will never claim to be a mechanic. That is why I come here, a forum full of mostly knowledge. I am doing the best I can and would say I have come pretty far from where I started. If you research out my history here I came here with a hull and a pump which I just rebuilt myself also.
No I do not know the complete purpose of a power valve but I have an idea. Maybe rattling around was not the right phrase but we'll say low on vacuum enough to let it leak.
I have gotten a lot of useful info from alot of people here and I appreciate all the info and help I have recieved, especially the ones who have taken time with going the extra mile and using private messages to explain so I can understand.
Anyone need advice on carpet stains or repairs, feel free to ask. I do have 20 years exp. With that.
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Guys, as I said in the beginning, I own a carpet cleaning company. I have never and will never claim to be a mechanic. That is why I come here, a forum full of mostly knowledge. I am doing the best I can and would say I have come pretty far from where I started. If you research out my history here I came here with a hull and a pump which I just rebuilt myself also.
No I do not know the complete purpose of a power valve but I have an idea. Maybe rattling around was not the right phrase but we'll say low on vacuum enough to let it leak.
I have gotten a lot of useful info from alot of people here and I appreciate all the info and help I have recieved, especially the ones who have taken time with going the extra mile and using private messages to explain so I can understand.
Anyone need advice on carpet stains or repairs, feel free to ask. I do have 20 years exp. With that.
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Well now you're making me feel bad... I was not criticizing, not even a little bit. I was just trying to put information out there for you and potentially anybody reading this thread, how this circuitry works.
I was not calling you out, which is why I asked a question, then followed it up with an explanation.
I apologize if you read it that way.
Moving forward, I would not recommend trying to adjust it any more without a vacuum gauge hooked to base plate (or manifold) vacuum. I believe you are fighting a power valve issue.
Pick up some 4.5" power valves and some metering block and bowl gaskets. Don't forget to coat them with Vaseline before putting the carburetor back together....
And lose the PCV. If you need a reason, because I said so. :sly:
But seriously, you are making too much crankcase pressure for a PCV to even do anything. A PCV is a SMOG device and doing you no good at all....
JMHO..
BTW, my goal is not to make everybody a mechanic, but to provide input based on your questions...
If at any time you feel disrespected by comments made here, not just from me, but anybody, speak up. That is one thing that makes this site different... In a good way. :thumbup:
GT
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Thanks GT, I don't think I could have explained it that well.
The other problem, and probably the main reason to lower the power valve starting point is due to the reduced vacuum caused by large cam profiles causing the PV's to blubber or start adding fuel at idle.
Thanks crew, that means a lot coming from you... :thumbup:
GT
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The reason it ran like shit with the mechanical conversion is because you've got no pump on the secondaries...can't slam 'em open like the primaries.
Power valves should be OK...even 6.5s. Unless you've got a stupid lumpy cam in it, you're making much more vacuum than that at idle....probably over 10".
Power valves are held closed until vacuum drops below the rated level of the valve you're using. They make tuning a bit more tricky, and since in a boat, you never really have low load conditions, they're mostly open unless you're idling. Like GT said, I'd plug the power valves and jet it up about 6-8 sizes.
At idle, the blades need to be closed enough to cover the transition slots. It needs to idle
On the idle circuit. Sometimes with stupid big lumpy cams, you can't move enough air without introducing a leak while keeping the throttle angle out of the transition circuit....that's when we drill holes in the blades or in a pinch, make a small vacuum leak and fatten up the idle fuel to compensate.
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Like GT said get a vacuum gauge and see what vacuum you are pulling at idle IN THE WATER. Take that number and divide it in half and that will be a good starting point of which power valve to use. Example : vacuum is 13 at idle IN THE WATER, use a 6.5 power valve. I had this issue with my 460 and lots of people told me with a tunnel ram you don't pull much vacuum 7-8 so I based my PV selection on that :banghead:. Well until I actually measured it and found out it was 13, I used the divide in half method and now the engine runs great.