Carb Flowbench Testing

[Andy Brown]

Seem to have found back an older topic,

anyway I couldn't help myself......very interesting

Am I reading this right? Is the Zoom carb the only one that makes the mid-range richer? Is this an accident...... or just maybe it is designed this way to give it better driveability under different throttle settings, hmmmmmm...........

Charles

They all get leaner in the mid-range.

According to my math....

CMB 67 --- 10.67% leaner

Stk OS ---- 11.53% leaner

Mod OS----12.40% leaner

CMB 91 --- 12.77% leaner

Zoom 67-- 13.33% leaner

 

[Charles Perdue]

Seem to have found back an older topic,

anyway I couldn't help myself......very interesting

Am I reading this right? Is the Zoom carb the only one that makes the mid-range richer? Is this an accident...... or just maybe it is designed this way to give it better driveability under different throttle settings, hmmmmmm...........

Charles

They all get leaner in the mid-range.

According to my math....

CMB 67 --- 10.67% leaner

Stk OS ---- 11.53% leaner

Mod OS----12.40% leaner

CMB 91 --- 12.77% leaner

Zoom 67-- 13.33% leaner

According to the figures AND the graph, the Zoom carb has a richer midrange than the other carbs that was tested. The CD went from .720 beginning to .752 midrange then back down to .743.

Charles

 

[dwilfong]

Very interesting................................................would love to see a MAC .550 on the flow bench.......................

 

[Andy Brown]

Seem to have found back an older topic,

anyway I couldn't help myself......very interesting

Am I reading this right? Is the Zoom carb the only one that makes the mid-range richer? Is this an accident...... or just maybe it is designed this way to give it better driveability under different throttle settings, hmmmmmm...........

Charles

They all get leaner in the mid-range.

According to my math....

CMB 67 --- 10.67% leaner

Stk OS ---- 11.53% leaner

Mod OS----12.40% leaner

CMB 91 --- 12.77% leaner

Zoom 67-- 13.33% leaner

According to the figures AND the graph, the Zoom carb has a richer midrange than the other carbs that was tested. The CD went from .720 beginning to .752 midrange then back down to .743.

Charles

The CMB 67 remains flat at all points. The Zoom gets richer at the middle point. The others get leaner at the middle point. (Middle point = 12" H2O.) They all get leaner at the lower point.

Not one of those scenarios is a good thing or a bad thing in general.

I'm sure all of those test were made at full bore, meaning these tests have nothing to do with throttle position and "Drivability".

Would like to take a trip back to the Thread of origin for more answers...because mixture strength curve is important at different engine rpm and load.

No one carb design can provide the perfect curve for all boat/engine/pipe set ups.

 

[Charles Perdue]

I agree to disagree. A carb designed with a richer mid-range in our toy boat application provides better driveability. This is not a theory or just an opinion, it is a fact. It has been proven over and over with back-to-back testing.

No carburetor is perfect, but some are better than others. AND a bigger carb bore is not always better, if it were then anyone could make a great working carb, just make it with a larger bore. Beyond a certain point a larger bore is actually detrimental to driveability and overall performance.

A carb that is good for SAW does not mean that it is also good for heat racing.

This is my story and I am sticking to it.

I am through.

Charles

 

[Andy Brown]

I agree to disagree. A carb designed with a richer mid-range in our toy boat application provides better driveability. This is not a theory or just an opinion, it is a fact. It has been proven over and over with back-to-back testing.

No carburetor is perfect, but some are better than others. AND a bigger carb bore is not always better, if it were then anyone could make a great working carb, just make it with a larger bore. Beyond a certain point a larger bore is actually detrimental to driveability and overall performance.

A carb that is good for SAW does not mean that it is also good for heat racing.

This is my story and I am sticking to it.

I am through.

Charles

"I agree to disagree. A carb designed with a richer mid-range in our toy boat application provides better driveability. This is not a theory or just an opinion, it is a fact. It has been proven over and over with back-to-back testing."

That is because all of your Blue marbles lined up with your Green marbles on those back to back tests. If you tried to match your Blue marbles with Red marbles your Zoom carb could sag lean and take out the plug at the top end.

There are many more parameters involved with mixture strength at various rpm ranges than just the carb.

Just a side note on BIG carbs.~

My .640" bore carb throttles and drives perfectly on my .90 engine. Strong launch, slow mill, great acceleration and top end rpm. Has run on Zero % nitro, 50% nitro, 60% nitro and 70% nitro. Have yet to take out a plug using this carb!

Big Speeds coming from Andy Brown in the near future. Watch for it!

 

[lohring]

When we ran a Quickdraw in a heat racing rigger, the engine wouldn't run with a standard cowl. It took a cut down cowl with a lot of clearance that mostly acted as a spray shield.

Lohring Miller

 

[RaceMechaniX]

It would have been nice to flow test the carbs with various throttle openings when I had the chance, but now that flow bench is 2700 miles away.

I still have the fixture, just need to find a kart shop that has a small flow bench.

Lohring, I know you tested straight methanol and low percentages of nitro. Did you use a standard carb or a larger version? Todd set-up a WJ75 for methanol for me although I have never tested it. I believe the stock bore is around 3/4".

 

[dwilfong]

Ripples in trough make good fish ladder................................Confucius say

 

[lohring]

I don't seem to be able to post significant attachments. The fuel tests on Quickdraws ran a WYK carb with a .610 bore that had the pump and pressure regulator section replaced with a plate with a fuel input nipple. In other words it became a normal nitro barrel carb. We tried standard boat fuels with glow ignition. We didn't find any plugs that would hold up so we switched back to the standard ignition. The engine ran fine on up to 15% nitro fuel, but we melted the plug electrodes on 40% nitro fuel, The ground strap put a nice dent in the piston on the way out. If we wanted to spend more time, we would have played with the head button, but we were after gasoline records. Spark ignition isn't allowed in the open fuel classes in any case.

Our fuel tests with various gasolines and other fuel blends was done in a standard M&D 26 cc Zenoah. We used the Walbro carb as it came on the engine and only adjusted the needle settings for the various fuels. We ran up to 75% methanol in 87 octane non ethanol gasoline and up to 15% nitro in 92 octane gasoline that contained 8% ethanol. Nothing really helped the power because we didn't play with the really important things like compression ratio, ignition timing, and especially the pipe. I bet the exhaust gas temperature was different with the various fuels. That alone would require a different pipe length.

Lohring Miller

 

[Andy Brown]

I don't seem to be able to post significant attachments. The fuel tests on Quickdraws ran a WYK carb with a .610 bore that had the pump and pressure regulator section replaced with a plate with a fuel input nipple. In other words it became a normal nitro barrel carb. We tried standard boat fuels with glow ignition. We didn't find any plugs that would hold up so we switched back to the standard ignition. The engine ran fine on up to 15% nitro fuel, but we melted the plug electrodes on 40% nitro fuel, The ground strap put a nice dent in the piston on the way out. If we wanted to spend more time, we would have played with the head button, but we were after gasoline records. Spark ignition isn't allowed in the open fuel classes in any case.

Our fuel tests with various gasolines and other fuel blends was done in a standard M&D 26 cc Zenoah. We used the Walbro carb as it came on the engine and only adjusted the needle settings for the various fuels. We ran up to 75% methanol in 87 octane non ethanol gasoline and up to 15% nitro in 92 octane gasoline that contained 8% ethanol. Nothing really helped the power because we didn't play with the really important things like compression ratio, ignition timing, and especially the pipe. I bet the exhaust gas temperature was different with the various fuels. That alone would require a different pipe length.

Lohring Miller

"Nothing really helped the power because we didn't play with the really important things like compression ratio, ignition timing, and especially the pipe."

....and MOST importantly, the fuel delivery.

 

[lohring]

Actually, we did adjust the carb for best power. Again, I'm not able to post the graphs, but the alcohol containing fuels had noticeably less power at the same needle settings as gasoline. From the article:

With the exception of E10, there was no real difference in the fuels. The alcohol containing fuels need a richer mixture than standard gasoline. Also, Walboro carbs are designed to meter gasoline, so the mixture variation over the rpm range probably is not the best for fuel with significant (remember the E10 was 32%) alcohol. Later tests where we changed both the high and low mixture settings brought the power of E10 back in line with the other fuels.

Lohring Miller

 

[Andy Brown]

Actually, we did adjust the carb for best power. Again, I'm not able to post the graphs, but the alcohol containing fuels had noticeably less power at the same needle settings as gasoline. From the article:

With the exception of E10, there was no real difference in the fuels. The alcohol containing fuels need a richer mixture than standard gasoline. Also, Walboro carbs are designed to meter gasoline, so the mixture variation over the rpm range probably is not the best for fuel with significant (remember the E10 was 32%) alcohol. Later tests where we changed both the high and low mixture settings brought the power of E10 back in line with the other fuels.

Lohring Miller

Lohring wrote: "Actually, we did adjust the carb for best power."

Lohring,

I should have been more specific. ....and MOST importantly, the fuel mass delivery.

Certainly we always want to adjust the needle to achieve the correct stoichiometric mixture.

But just as critical is the correct fuel mass delivery for a given set of conditions in an engine.

Too much mass delivery of a stoichiometricly perfect mixture and the engine will run and sound rich.

Too little mass delivery of a stoichiometricly perfect mixture and the engine will run and sound lean and/or even melt down. (Did I read Melted electrode? )

 

[Marty Davis]

Terry- Funny how modelers are now getting 'it' about tuning motors using a low speed needle-

The biggest reason I stopped offering the RPM carbs was the endless tuning problems that came up with them.

The average boater most often failed to (Could?) understand the tuning with both hi & low speed needles & how much you can move the torque curve with different settings- sorta like NASCAR left turn only deal-

Surprising how much supposed 'experts' don't know about carb /engineering tuning- I sure found that out-

In recent times the advent of gas carbs/motors use has forced this learning curve-

Nitro is easier to tune I think- think of it as being a crutch to cover many bad ideas for most tuners-

Once past the carb now you get to a tuned pipe- getting it to work right with the carb- now we have a whole new game over & over again tween the carb & pipe-

I'm no quitter but had to stop the carb deal to stay sane & healthy-

Retirement is great-

Be well-

Dave Richardson

Ackerman and our crew did a lot with your carbs and even more with your Rods. we do miss them a lot. I agree on the low speed needle. I use them on any carb that came with them and NEVER cut them off.

 

[dwilfong]

Just figured I would share a pic of the newest carb booster design for Holly Dominators.

Look familiar???????

 

[julianconde]

I don't use low speed needles on none of my engines 45's and 101's . Most of my boats are twin hydros so we don't mill to slow