Twin Guys Question

dr gary turner · Oct 20, 2013

Do you use mixture control in your twin or just isolated needles?

If you use mixture controls are they mounted in the carbs or isolated, CLOSE or FAR from the carbs and WHY?

Do use a single mixture control or one for each motor and WHY?

For those that use one, Which motor inboard or outboard and why?

For those that use two mixture controls when you richen or lean the motors do the needles bring the motors richer or leaner, the same, ie still together at the new setting?

julianconde · Oct 21, 2013

Well I think I spew for the roadrunner team we all have the same set up and use the same needles maybe Jose and Jeff use a different needles but Joe,Ralph,chuck and I have identical twins down to the props.

1) we use 2 BVM mixture control needles

2) our BVM needle valves are mounted behind the engines away from the carburetors ( I assume by having them away from the carburetors like in our case behind the engines it has a little delay from the time you make the needle adjustment to the time it actually happens. Plus we don't have too much room in front of the RR Twin 101 engines.)

3) we use 2 needles one for each engine so when we test fire the engines we can tune each one individually after that we can lean and richen both engines at the same time.

4) Does not apply ;-)

5) when we richen and lean our engines both needles move together as a unit. We don't have individual needle adjustment for each engine.

Julian.

Bob Morton · Oct 21, 2013

I have two twins that have remote needles. I adjust them using the Boris meter. So they flow the same. Then if I need to

I can adjust as needed while under way. I have a twin with BVM needles mounted in the high speed side of the carbs.

I adjust them remotely. I have a twin setup that I use Ferretti needles the are manual I adjust on bench with the Boris

Meter. They all work very well. Evey perameter is even,props,needle settings, head clearance,etc.

The best data acquisition is the Eagle Tree system.

Nails

dr gary turner · Oct 21, 2013

When you adjust your needles while running do you think they remain in sink either richer or leaner? Also why do you Bob put the needles in the CARBS and Julian- RR Team mounts them WAY behind the motors?

Bob Morton · Oct 21, 2013

Hi Doc,

I mounted mine in the carbs because there is instant change in the engine rpm. Plus the manufactors put there needles in

the carbs. Less plumbing to worry about. Always trying differant ideas to make our motors run better.

Are they balanced when changing the needles? That's a good Question the answer to that is put some sensors on your motors to measure the RPM,Exhaust temps. We just flow our needles and hope

The motors are balanced !!!!!

Nails

Nails

julianconde · Oct 21, 2013

dr gary turner said:
When you adjust your needles while running do you think they remain in sink either richer or leaner? Also why do you Bob put the needles in the CARBS and Julian- RR Team mounts them WAY behind the motors?

yes our engines stay sync the whole time when we lean and rich they stay together

yes Doc we mount our needles behind engines towards the back of the engine compartment as shown in this Pic

dr gary turner · Oct 21, 2013

Why Julian???? . We know where you put them. Maybe they would work better mounted up front on the boom tubes or at the transom??????????

dr gary turner · Oct 21, 2013

Bob, I think you are right and honest. I am not sure the motors stay together and have the same flow changes when they ar both adjusted simultaneously.

If they do not flow the same with the changes, why have TWO mixture controls???????????

Joe Warren · Oct 21, 2013

Behind the Engine works on all monos applications. as far as the fuel is conserned There is Nothing different between a mono & a hydro. The Needle dont know the difference. plus a longer fuel ltubing acts as a fuel reservoir on the low side of the needle and the Pressure side of the needle........ B) B)

julianconde · Oct 21, 2013

dr gary turner said:
Why Julian???? . We know where you put them. Maybe they would work better mounted up front on the boom tubes or at the transom??????????

Doc I have ran the needles in the front of the engines and in the back. I have noticed no difference at all in performance or anything at all. He'll if anyone would know it would be you lol you been in the hobby since they invented little boats ;-)

The engines should stay together if they don't you have a fuel system issue

Jose Ortiz ran the needles in from of the engines mounted on the boom tubes so did Nub at one point as well. It's personal preference I prefer them in the back away from the engine that's just me.

dr gary turner · Oct 21, 2013

Joe has the answer on why to mount away from the carbs. I think a small actual reservoir between the needle and carb may work better. I tried this at the fall Nats on my single 101 and throttle response was the best I have had.

Now Joe, team Captain, do you think that the needles stay in sync with adjustment once they are set? IE with one number change on the transmitter changes the flow change is the same in each individual needle?

Any thought on one mixture controlled motor and the other with just an isolated needle?

Many years ago a guy by the name of Jerry Devay and his son each ran twins of his own design. His motors were ALWAYS TOGETHER AND BAD FAST without todays flow meter. He had the most consistently running twins I have seen run. HE USED ONE MIXTURE CONTROL NEEDLE THE OTHER NEEDLE WAS JUST AN ISOLATED NEEDLE.

Ray Sametz · Oct 21, 2013

Question from a newbie playing with a twin? If both needles are set the same do you tweak the right prop to handle the extra load????

julianconde · Oct 21, 2013

Stu bar runs one remote mixture needle on the inside engine and a non adjustible needle on the left engine you might want to ask him.

Ray this is just me I have ran 2 different size or pitched propellers on my twin. Turn fin side being less pitch and a little smaller than the non turn fin side it worked just fine and helped unload the inside motor on the turns.

I'm a newbie when it comes to twins as well I learn new things every time I test or race my twins. Record trials is a good way to tune and set up your twin. No radar guns just you against the clock you will see results based on your time and speed as well.

Tim Kish · Oct 22, 2013

The last two twins that I have raced I removed the remote needles and replaced with isolated O.S. needles in Don's blocks.

Very consisitent and easy to tune.

Tim

Tom Foley · Oct 22, 2013

Ray Sametz said:
Question from a newbie playing with a twin? If both needles are set the same do you tweak the right prop to handle the extra load????

I have been using isolated "floater" needles in my 80 Extreme twin for years with 80's and 91's with success . they are Webra needles and adjust a little more slowly than the OS needles in my other twin . I start out with both needles flowing identical then adjust based on plug condition . It's been working well . Fuel tubing length to the carb is about 2 " of Large fuel tubing . flow meter is checked and filters backflushed off the boat after every run . It has been working well . Needles are flushed with oil before storage .

Chris Wood · Oct 22, 2013

Many years ago a guy by the name of Jerry Devay and his son each ran twins of his own design. His motors were ALWAYS TOGETHER AND BAD FAST without todays flow meter. He had the most consistently running twins I have seen run. HE USED ONE MIXTURE CONTROL NEEDLE THE OTHER NEEDLE WAS JUST AN ISOLATED NEEDLE.

doc i remember racing him at indy.. you are right he was always fast and consistant..

the one thing i will say in regards to the needles away from the motors.. i used to do that in my 67 boat.. had the needle back by the bulk head where the cable come thru.. after 2 laps and tank pressure dropped comming out of a turn EVERY TIME. boat would just hickup and die.. i fought it and fought it.. mounted it right next to the carb.. no more issue.. last time i ran that boat we had it mounted TO THE CARB. with the g-forces and banging around the big boats have my own opinon the closer the better.

just my 2 cents though

chris

dr gary turner · Oct 22, 2013

Ray Sametz said:
Question from a newbie playing with a twin? If both needles are set the same do you tweak the right prop to handle the extra load????[/quote. Yes

dr gary turner · Oct 22, 2013

dr gary turner · Oct 22, 2013

Chris Wood said:
Many years ago a guy by the name of Jerry Devay and his son each ran twins of his own design. His motors were ALWAYS TOGETHER AND BAD FAST without todays flow meter. He had the most consistently running twins I have seen run. HE USED ONE MIXTURE CONTROL NEEDLE THE OTHER NEEDLE WAS JUST AN ISOLATED NEEDLE.

doc i remember racing him at indy.. you are right he was always fast and consistant..

the one thing i will say in regards to the needles away from the motors.. i used to do that in my 67 boat.. had the needle back by the bulk head where the cable come thru.. after 2 laps and tank pressure dropped comming out of a turn EVERY TIME. boat would just hickup and die.. i fought it and fought it.. mounted it right next to the carb.. no more issue.. last time i ran that boat we had it mounted TO THE CARB. with the g-forces and banging around the big boats have my own opinon the closer the better.

just my 2 cents though

chris

dr gary turner · Oct 22, 2013

I placed a small reservoir between my carb and the needle and did great wit the issue you mentioned

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