Carb question

« **on:** June 06, 2014, 03:46:31 PM »

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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« **Reply #1 on:** June 06, 2014, 03:51:07 PM »

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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« **Reply #2 on:** June 06, 2014, 03:52:00 PM »

Also they are now 1:1 linkage on the secondarys

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« **Reply #3 on:** June 07, 2014, 09:20:30 AM »

Quote from: nolongergreen on June 06, 2014, 03:52:00 PM

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).

« **Reply #4 on:** June 07, 2014, 01:33:24 PM »

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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« **Reply #5 on:** June 07, 2014, 01:35:34 PM »

Instead of the arms sliding and letting the secondarys open up with vacuum they are pulled open with the front

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« **Reply #6 on:** June 07, 2014, 02:26:35 PM »

Quote from: nolongergreen on June 07, 2014, 01:35:34 PM

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

If you want mechanical secondary carbs... get mechanical secondary carbs.

« **Reply #7 on:** June 07, 2014, 04:26:04 PM »

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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« **Reply #8 on:** June 07, 2014, 04:39:16 PM »

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.

« **Reply #9 on:** June 08, 2014, 04:03:18 PM »

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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« **Reply #10 on:** June 08, 2014, 04:04:49 PM »

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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« **Reply #11 on:** June 08, 2014, 04:15:05 PM »

Glad to hear you're getting it sorted out.

« **Reply #12 on:** June 08, 2014, 09:10:49 PM »

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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« **Reply #13 on:** June 09, 2014, 12:26:22 AM »

dont vac secondary carbs not work very well with tunnel rams?

« **Reply #14 on:** June 09, 2014, 01:40:51 AM »

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.

« **Reply #15 on:** June 09, 2014, 05:38:38 AM »

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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« **Reply #16 on:** June 09, 2014, 09:28:13 AM »

Quote from: nolongergreen on June 07, 2014, 01:35:34 PM

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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« **Reply #17 on:** June 09, 2014, 09:29:42 AM »

Almost forgot my first thought.

It sounds like you are fighting power valves.

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« **Reply #18 on:** June 09, 2014, 09:35:21 AM »

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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« **Reply #19 on:** June 09, 2014, 10:09:58 AM »

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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« **Reply #20 on:** June 09, 2014, 05:41:05 PM »

Quote from: GT Jets on June 09, 2014, 09:29:42 AM

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.

« **Reply #21 on:** June 09, 2014, 06:25:03 PM »

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

« **Reply #22 on:** June 09, 2014, 08:29:20 PM »

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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« **Reply #23 on:** June 09, 2014, 08:36:56 PM »

Quote from: Flusher on June 09, 2014, 06:25:03 PM

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

« **Reply #24 on:** June 09, 2014, 08:38:34 PM »

Quote from: nolongergreen on June 09, 2014, 08:29:20 PM

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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