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79 Sanger Picklefork
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Discussion Starter · #1 ·
I have a 454 (mid 1970's) LS7..compression is 12 to 1, serious over lapping cam (no specs), tunnel ram with 450's, iron heads. The carbs have always been too small. I have an opportunity to pick up some near new Edelbrock 750's very cheap. The advantage of the Edelbrocks is that my fuel lines can stay as they are, just move to the other side of the carb...question is, is that too much carburator or am I making a big mistake. I don't want to use larger Holleys if I have to mount them sideways...thanks
 

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Some guy
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I have a 454 (mid 1970's) LS7..compression is 12 to 1, serious over lapping cam (no specs), tunnel ram with 450's, iron heads. The carbs have always been too small. I have an opportunity to pick up some near new Edelbrock 750's very cheap. The advantage of the Edelbrocks is that my fuel lines can stay as they are, just move to the other side of the carb...question is, is that too much carburator or am I making a big mistake. I don't want to use larger Holleys if I have to mount them sideways...thanks
What kind of rpm are you running that makes you say 900 cfm is not enough for that engine?
 

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I am running 450's on a 10.2 to 1 496 chevy spinning an "A" to 5500rpm. I think you should keep the 450's unless you want to get shitty fuel consumption. My jet gets about 5mpg at cruise speed!! And top speed is 80mph. Most are around 1-3mpg.
 

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79 Sanger Picklefork
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857 Posts
Discussion Starter · #5 · (Edited)
What kind of rpm are you running that makes you say 900 cfm is not enough for that engine?
RPM is about 5400..the problem I have with these 450's and I have never been able to resolve is the idle and transition slots. I have already drilled the throttle plates out for more air. This year I even drilled the secondary blades with holes. I've pulled off the metering blocks and cleaned them out with air. In order for it to idle at 1100-1200 (or it dies) I'm into the transition slots. I've even played with the secondary throttle blades by opening them a little or closing them. Air bleeds are clean. After running when I let off the gas it takes quite a while for it to finally idle down. It stays at about 2000 rpm and then finally when it does idle down it won't hold at 1200 rpm, it dies off. Or I have to have the idle set so high it's difficult in a no wake zone. Float level is correct and the fuel pressure is at about 6.5. Plugs are clean and dry. I would like to keep the 450's but I just can't get it to idle down and hold that idle.
 

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79 Sanger Picklefork
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857 Posts
Discussion Starter · #7 · (Edited)
I'm still of the opinion that your idle issue is in the mechanical ignition advance. Lock it out.
I know I'v asked this question before, but everything suggested I tried and has not worked.I have a Vertex mag and a couple of years ago it was rebuilt. That didn't help the problem. It is not locked and appears to work fine. It idles great on the trailer without a load. Put it in the water then I have to set the idle up and the problem begins. The motor revs fine on the trailer. That's why I don't think it's ignition. So my next thought is maybe I just need larger carbs...
 

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I've had a couple of tunnel rammed motors, and single carb set ups. they all idled high when out of the water ( about 1800-2000 rpm), when in water and in gear ( or turning a pump), I usually have idle set around 1200-1500 rpm, what ever it took to keep motor running with foot off the throttle and not not having to feather it to keep it from dieing
 

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79 Sanger Picklefork
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Discussion Starter · #9 ·
I've had a couple of tunnel rammed motors, and single carb set ups. they all idled high when out of the water ( about 1800-2000 rpm), when in water and in gear ( or turning a pump), I usually have idle set around 1200-1500 rpm, what ever it took to keep motor running with foot off the throttle and not not having to feather it to keep it from dieing
I understand that..but to get it to idle in the water it seems like I have to set the idle so high that were in that transition slot area. Then it just idles too fast...like maybe 1500-1600.
 

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Some guy
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I understand that..but to get it to idle in the water it seems like I have to set the idle so high that were in that transition slot area. Then it just idles too fast...like maybe 1500-1600.
Not sure who you have in the north end of Idaho that might help with carbs,, you could call Kidd Performance in Twin Falls. I think he is pretty sharp with carbs, I ran an engine on his dyno earlier this year. If you were in So Cal there are a number of places you could try. I would think those could be made to work.

By the way, fuel economy is based on a given air fuel mixture at a given horsepower, so carb tuning has a lot to do with fuel economy, not to mention accelerator pumps and how the boat is being driven.
 

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79 Sanger Picklefork
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Discussion Starter · #11 ·
Not sure who you have in the north end of Idaho that might help with carbs,, you could call Kidd Performance in Twin Falls. I think he is pretty sharp with carbs, I ran an engine on his dyno earlier this year. If you were in So Cal there are a number of places you could try. I would think those could be made to work.

By the way, fuel economy is based on a given air fuel mixture at a given horsepower, so carb tuning has a lot to do with fuel economy, not to mention accelerator pumps and how the boat is being driven.
As always thanks for your help..I know someone who is good with carbs can make these work..Like you said I live in N. Idaho. I can't find a good carb shop up here. I hate to send them to someone, pay good money, put them on and I still have the same problem..I don't think there is even a good carb shop over in the Spokane Wa. area..
 

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Or Seth, either one
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I know I'v asked this question before, but everything suggested I tried and has not worked.I have a Vertex mag and a couple of years ago it was rebuilt. That didn't help the problem. It is not locked and appears to work fine. It idles great on the trailer without a load. Put it in the water then I have to set the idle up and the problem begins. The motor revs fine on the trailer. That's why I don't think it's ignition. So my next thought is maybe I just need larger carbs...
I'd pay $25-30 and lock timing out before considering $pending anything on carbs. 90+% convinced it will put a smile on your face. Gonna be chasing your tail if you don't.

Either way, I wish the best to ya :))THumbsUp
 

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79 Sanger Picklefork
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Discussion Starter · #13 ·
I'd pay $25-30 and lock timing out before considering $pending anything on carbs. 90+% convinced it will put a smile on your face. Gonna be chasing your tail if you don't.

Either way, I wish the best to ya :))THumbsUp
But if it revs and idles fine on the trailer, why would I have the problem only if I have to reset the idle while in the water to allow for load. I don't see how locking the timing out helps that issue...appreciate the help and answers..
 

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Give this a try...have the boat in the water, advance the timing 10 to 15 degrees. This will kinda simulate locking out the dizzy. Set idle back down to what you like to see and see if it idles correctly. DO NOT DRIVE IT WITH THE ADVANCED TIMING!!!! If it idles good that way, lock it out and set back to total advance you had it set to before moving it.
 

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Or Seth, either one
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But if it revs and idles fine on the trailer, why would I have the problem only if I have to reset the idle while in the water to allow for load. I don't see how locking the timing out helps that issue...appreciate the help and answers..
If I remember correctly, you have the lightest springs in there and your target idle is very close to, if not already slightly into the advance curve. So, when you initially start it, it idles fine. But, once you give it some gas it takes forever for the idle to return to it's desired rpm. The springs aren't strong enough to pull the weights back after the rpm has elevated. It wouldn't be an issue if you had a smaller cam and lower idle, but because you're on the edge, it's kinda a one way deal. I would imagine, if you cut power and turned it back on before it died that it may return to it's desired idle. I really don't think the answer is in the carburetor tuning/selection.

For the same idle setting on the carb, more timing will raise rpm. Once you give it any gas and return it to idle, the same throttle position has more timing and will idle higher than before, until the wimpy springs struggle to pull the advance back out of it. Which may never happen or just take a long time.

Again... 90+% convinced this is your issue.
 

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Before you waste money on newer, bigger carbs Buy a vacuum gauge and check the secondary vacuum spring tension. This sounds like a vacuum issue with the secondary plates. As you stated the cam you are running may be have to large a lobe center to snap the secondaries shut thus holding the secondaries from closing and bringing the idle back to reality. As already stated 900 cfm is plenty for a 454 but the cam could be robbing vacuum for what is required for the carbs you have to operate properly. Mechanical carbs will help but I would get what you have tuned correctly first. First being check the color of the spring in the secondary can. the lighter the color the lighter the spring tension. You may be able to go to black spring and work backwards. JMO
 

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Simple fix

For a simple, "I love my boat again" fix, take the TR off and bolt on an open plane, isolated runner, high rise, single 4 brl intake with a good 800 DP... All these problems WILL go away. You'll be able to set the idle where it belongs, get much better fuel economy, better throttle response, and better performance... TRs are not designed to "cruise", they like WOT, or idle and very little in between...
Your issues are NOT in the MAG. It's ALL about the TR and the shitty vacuum signal the carbs are seeing... Go single, and go happy..
Ray
 

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Or Seth, either one
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For a simple, "I love my boat again" fix, take the TR off and bolt on an open plane, isolated runner, high rise, single 4 brl intake with a good 800 DP... All these problems WILL go away. You'll be able to set the idle where it belongs, get much better fuel economy, better throttle response, and better performance... TRs are not designed to "cruise", they like WOT, or idle and very little in between...
Your issues are NOT in the MAG. It's ALL about the TR and the shitty vacuum signal the carbs are seeing... Go single, and go happy..
Ray
Ray, you're one of the smartest guys here. I don't think you're looking closely enough at the situation with the mechanical advance.

Without changing any carb settings, if he locked the timing out and set timing at whatever the initial is now, it would maintain the low idle. But advance it to 34º or whatever his desired total timing is and the engine is going to idle at the "higher" undesirable rpm it get's stuck at. Retard it by hand and it will mellow down again. So, as it is, when it starts it's on base timing. But, once revved the timing advances and it get's the timing it wants. Even at the same carb settings it now has more advance which will keep the rpm's up. There is little chance the timing is going to return to it's retarded base setting once it's in the middle of the advance curve at an idle throttle position. Just not gonna happen, it's near impossible. It's stuck in the advance curve.

Once the timing is locked out, the carbs will be able to be adjusted without too much transition slot being exposed. Guarantee it. Unless all the mods made to them cause some headaches.

-Seth-
 

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Locked timing...

Seth, locked timing on a pleasure boat, a boat that gets started/stopped many times a day, will chew up starters and ring gears. He said the mag was "serviced" recently in an effort to cure the problem and the problem is still there.. I'm sure whoever serviced the mag would've seen any sticking advance problems... I've seen so many boats sporting TRs for the "look", when in reality, they would run much better with far less intake volume for a relatively low RPM application... I'm betting the power curve on the TR doesn't even start before he maxes out the pump. AND, he is dealing with vacuum secondaries that may very well be sticking, either open, or closed...
I would try the old "screw in the secondary slots" trick and spring load the butterflies closed just to see if anything changes... But again, dump the TR and learn to love your "turn key" boat again....
Ray
 

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79 Sanger Picklefork
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Discussion Starter · #20 ·
Seth, locked timing on a pleasure boat, a boat that gets started/stopped many times a day, will chew up starters and ring gears. He said the mag was "serviced" recently in an effort to cure the problem and the problem is still there.. I'm sure whoever serviced the mag would've seen any sticking advance problems... I've seen so many boats sporting TRs for the "look", when in reality, they would run much better with far less intake volume for a relatively low RPM application... I'm betting the power curve on the TR doesn't even start before he maxes out the pump. AND, he is dealing with vacuum secondaries that may very well be sticking, either open, or closed...
I would try the old "screw in the secondary slots" trick and spring load the butterflies closed just to see if anything changes... But again, dump the TR and learn to love your "turn key" boat again....
Ray
No vacuum secondaries..mechanical. Dual 450's..
 
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