Blower surge Make it stop
 

Ok Im sure this has been disused allot before/ I have a twin engine Nordic that Ive built two 509 tall decks with 871s 8.7% over driven with two holleys 4150 series 830 cfm and cant get them to idle smooth under 1000 RPMs
The engines
509 Tall decks
Brodix big brodie 344 cc runners
TBS 871 stripped
Chillers
Cam Comp solid lift fixed 114 grind lift intake .561 exhaust 569 Duration @.050 intake 234 exhaust 238
Lightning headers
Hardin Marine max volt ignitions
Timing locked at 34 advanced
Carbs 4150 830 cfm 4 corner idle dubble pumpers anular 88 primary jet 92 secondary 8.5 power valve primary blocked on secondary .067 air bleeds boost reference primary power valve
8.5 compression static
50 bottom pulley 46 top pulley 8.7% over driven

What I have tried/ had the carb shop rework my brand new carbs 1500.00 did nothing/ under driven 8.7 ( swapped pulleys ) nothing/ dropped timing back to 10 degrees advanced nothing/ tried a non stripped 871 blower nothing/ opened my idle air bleeds from .063 to .067 did nothing/ drilled holes in the butterflys nothing

So far ive tried everything under the sun to stop my surge idle and I feel like if I took a dump in the carbs while its idling it would keep surging. I can get them to idle smooth at 1050 rpms and as soon as I try and take it down below that the surge starts. The surge is pretty healthy hunts 600 rpms to 1500 rpms and pretty quick surge. Ive tried most every recommendation I have been told or found on the internet and still no change. Nate at BDS says my cams are too mild and that is the problem. Post vacuum is 20lbs to 12 lbs while surging and when steady at 1050 16lbs vacuum. Pre vacuum under carbs is 14lbs to 25lbs during surge and 20 steady at 1050. Looking for someone who can really answer the question of how to stop this. A real answer or info not just someone spouting what they don't know! Thanks

Oh almost forgot they made 850 HP @ 5500rpms on dyno and 1250 degrees exhaust temps 12 to 1 AFR

I would upgrade to Daytona sensors ignition, it has some pretty advanced tuning options like idle stabilization.

Funny story a friend just ordered his " name brand" 900 blower motors specifically WITH blower surge, the builder hesitated because he thought it might make him look bad! LOL

what sensors are you talking about I don't have EFI they are carbed!

http://www.daytona-sensors.com/CD1.html


unlocking your distributors combined with this should fix it if everything else is in order

In my original post is where I stated that Ive taken the timing all the way back to 10 degrees and it yielded no change at all. And that was with 8.7 over driven and tried that at 8.7 under driven and no change. So dumping the timing off did nothing so don't see how a timing retard would fix it. Timing retards are generally used to help start a locked set up!

Opening up the idle air bleed hole sizes leans it. Did you try smaller ones ?
Are your idle feed restrictions too small ?

I have done testing to see if its too lean or rich and it gets happy when you lean it out. So with opening up the air bleeds .004 made the mix better but still once you drop below 1050 rpms it wants to serge. When I get the mix nice I can get it to idle at 850 to 900 but then its way lean and dies as soon as you put it in gear and makes it next to impossible to start when its cold.

Ok. So, youre idling at 1000rpm with 34 degrees correct? And when you set timing to 10 degrees at idle, did the rpm drop down? It should have, without touching the carbs idle speed screw.

On to the mixture circuit. If you turn the idle mixture screws in, does the surge stop, and engine want to stall ? It should.

Where are the float levels set? Too high of float level, can cause overly rich fuel mixture , and not just from having them high enough to see a visiable fuel dribble. I mean, like 7/8 of the sight glass, to 1/2 of the sight glass.

It sounds to me, like you are simply giving it too much fuel at idle. With that small cam, and locked timing, shes drawing fuel from those idle circuits like crazy.

If you have adjustable idle feed restrictions in the carbs, going smaller can help that. They are much more effective than fuking with air bleeds.

When everything is working properly, the daytona sensors ignitions work beautiful. On the blower motors Ive tuned, i set them up so they idle around 15 degrees in nuetral at 950rpm. Once the rpm falls below 700, which would be when you shift into gear, the idle then kicks up to 36 degrees. It needs the timing in gear, but not when its unloaded in nuetral.

The reason it works, is the reduced timing, helps slow the engine down. When the idle timing is cranked way up, the vacuum goes up, and the engine is sucking on that carb like a baby sucking on his mothers nipple. To calm it down, you end up having to close the throttle blades off completely to get an acceptable idle speed. With the timing backed off, you can now actually fine tune the carb properly, and when its idling at the dock warming up, everybodys eyes arent watering from the raw fuel fumes out the tailpipes

Havasu, the Daytona sensors ignition alters timing quickly (Up and Down) in stabilization mode to keep the idle level. This feature is built into the unit. It also does many, many other things. You leave the carbs on it...

MT can post a video of before and after his Daytona sensors installation showing the improvement on his carbed blower engines. It is nothing short of dramatic.

Havasubill, what carbs do you have

Edit: jist reread and saw you have 830cfm holleys. Pretty sure those are the old school carbs. No adjustable idle feeds in those if i recall.

But, you can try experimenting with some small wire, V shaped, inserted into the restrictor in the metering block, to reduce some of the fuel flow.

with timing locked dont think any curve will cure it, just for grins try removing and plugging the power valves just to test and see what it does, might be enough vac fluctuation to cause them to act weird, also 8.5 ??? are they boost referenced carbs ?

I am looking for more surge. Wanna trade for a 177/Dominator setup?

Mild Thunder thank you do much for your advice, its nice to see some have positive input on a post. Im just exhausted trying everything to cure this. So when I dumped the timing to 10 at idle and lean it out I can get it to idle at 850 but as soon as I put a load on it, it will die. So Im wondering if a different profile of cam will help this at all? Ive done over 40 blower engines and have never had one that I cant tune the surge out of. So just pulling my hair out as Ive spent lots of hours and never get anywhere with it stopping. So some what in a nut shell ive tried the lower timing and adjusting the carbs for that and it still reacts the same.

Eliminated thanks for the info on the Daytona I went and checked it out and looks like some good stuff to have even if I didn't have this issue.

So Mild thunder your stating that if I had the timing come back in gear they wouldn't die when shifted? Curious as to once I would do that I would be back to surging and hard to get out of gear?

Eliminated572 I would love to see that video please if you can find it. Im wanting to find something that will blow me away with a fix!

79Formula have you got two of them or one? I would need two. Before I end up in a rubber room making surge noises! LOL

EZstriper been there and done that blocked off. They are boost reference and for sure they are not opening as the vac never drops below 11 pounds. They are defiantly closed!

I only got one. I cant pump up the power anymore anyways. Id have the broken bravo blues with anymore power.

79Formula Im having to be careful as Im 850HP @ 5500 and Im bravo ones with Imco shotys! That is why I want the surge gone so I can drive the stupid thing! Thank God its not a customers boat LOL

Heres with timing locked, before uploading the custom timing map I made. I could have leaned it down , but the idle speed would have had to been around 1100-1200rpm to keep her running. https://www.youtube.com/watch?v=O-fTA0JA36Q&feature=youtu.be

Later that day, mufflers installed, timing map uploaded, carbs fine tuned. https://www.youtube.com/watch?v=2nHvNQD13o4

MT thanks

The power valve opening, won't affect the idle. A power valve opening, simply adds fuel to the main well. The same well, that the jets pass fuel thru. It be like swapping from 82 jets, to 94 jets, no effect on the idle.

Being able to idle at a lower timing setting in nuetral, and higher timing setting in gear, makes for a much larger window of tuning your idle setup.

So, when you backed the idle timing down to 10*, and she was at 850rpm, she'd stall when putting in gear. What if, you were to try that again..back it down to 850rpm with 10*, and back the mix screws out slowly, till it just begins to surge., then, crack the throttle blades just enough, to get it idling at 950-1000rpm. Ill bet the situation, will be much better.

What kind of advance setup do you have? Weights and springs?

What`s going on there at :42?? :whistle:

MT thanks for posting the videos very cool. So if I start to back them out at 850 @ 10* it will take off and surge as soon as I touch the first idle air bleed an 1/8 of a turn. It is way sensitive big time. This is the issue Ive been having with it. There is no curve the distributors are locked. So when I back it down to ten thats all the timing all the way as you would know!

MT im not a rocket scientist (did paint all the parts on the Hubble how ever) but that sounds like way more than 850 RPMs in the second video?

It was around 1000-1050rpm in that video if I recall. once i got boat in the water, I was able to turn it down to about 950.

I think this might have been best idle at 26*
https://www.youtube.com/watch?v=rwE6eEf92p8

At 16* I think we were able to get a little lower rpm and still idle nice and better AFR`s but in the boat I had to richen it up a bit to mid 12`s and add have it idle at 900.

https://www.youtube.com/watch?v=hDqAawtfF0g

From what you're telling me, you're idle feed restrictors, are simply, too large.

Those 830 holley double pumpers, are like most double pumpers. They were designed for race cars, with big cams, and poor idle vacuum. So they opened the idle feeds up a bunch, to compensate. You are running TWO of them, atop an engine, with a fairly mild camshaft. There lies your problem.

Before we go nuts. Try this. Close the rear mixture screws off completely . On the secondary side on both carbs. Try using only the front ones.

Also, make sure your floats aren't too high. The higher the float level, the more head pressure you get, which will push even more fuel thru the restrictors, making this even worse. I lowered my floats down to where they needed to be this summer after my first ride last summer. They were a bit high. Just by lowering the floats, my Air fuel ratio at idle, went from 11.5, to 13's, without even touching the mixture screws.

Remember in loto when we dropped your "nuetral timing" to around 16, we were able to get it idling around 900-950, and still idle at what, 650-700 in gear if I recall? Rather than idling at 1100 in nuetral with 26*?

Those 900's idled like 454 mags around the docks :coolcowboy:

nice exhaust you have there on your run stand btw. Those stellings or CMI?

Icdedppl Great clip thanks. Im still wanting to know how all of you shift in and out of gear at those RPMs???

Transmissions. We don't have bravo's.

Although, I don't think 900rpm, should be an issue for a bravo drive. Im not super up to speed on the bravo stuff, so maybe someone else can chime in

MT that is one thing I thought about trying ( closing off the secondary idle screws )and havent yet but I will. Those Idle feed restrictors look small I haven't put my # sizers in them yet to see what size they are? Have you had any experience with moving the restrictors to the top of the tube inside? Ive read that helps with the emulsion in the tube??

Bravos don't like 900 very much and are hard to get out when at 900 under load

Dam if I had trannys I wouldn't worry about it LOL

Transmissions. We don't have bravo's.

Although, I don't think 900rpm, should be an issue for a bravo drive. Im not super up to speed on the bravo stuff, so maybe someone else can chime in

Must be an east coast thing ( Transmissions ) LOL!

I had solid roller setups with 35 degrees locked in timing idling around 1000 in neutral. In and out of gear was no issue on bravo's... FWIW

Looks like some kind of Mythical Blower Fairy.