Fuel System: air and fuel too lean?

[am not r2]

I have a 64 hawk R1 power brakes , and steering. stick. I was in heavy traffic the other day and the engine started hissing....then the brakes were hard...I figured I had lost the brake hose and indeed it did come off the carb end. It ran poorly at idle but ran better at high demand. When I noticed this I waited for an opening and then I jumped on it...WOW. Suddenly I had more power...lots more. What can I do to keep that? How can an intake leak give me that much more power.... Is the filter that restrictive? Is this lean out dangerous? I was thinking it might be as I put the hose back on and finished my drive home. Any thoughts???

[altair]

lean mix

I have a 64 hawk R1 power brakes , and steering. stick. I was in heavy traffic the other day and the engine started hissing....then the brakes were hard...I figured I had lost the brake hose and indeed it did come off the carb end. It ran poorly at idle but ran better at high demand. When I noticed this I waited for an opening and then I jumped on it...WOW. Suddenly I had more power...lots more. What can I do to keep that? How can an intake leak give me that much more power.... Is the filter that restrictive? Is this lean out dangerous? I was thinking it might be as I put the hose back on and finished my drive home. Any thoughts???

A lean mixture will give you an increase in power, however it could be at great expence. An excessive lean mixture will burn very hot and could melt a piston or crack a head. I have had chain saws with loose carbs and the mixture is therefore lean, the little single two stroke was just humming with lots of power but it was short lived. In an aircraft engine at higher altitudes it is usual to lean the mixture to a point where the rpm increases at that point the vernier throttle is returned to just below where the rpm increase occured to avoid overheating.

[Dan Timberlake]

"Modern" automotive carbs only have a bowl vent into the air cleaner area. If done well This means the pressure in the bowl is the same as the carb inlet, so filter restriction (by design, or after many miles filling with junque) have relatively little effect on air/fuel ratio.

Was the "lots more power" over 3000 rpm?
Stock R1 Carb?

[Mike Van Veghten]

am not -

Interesting comments...to be sure.

A "lean" mixture, or fuel to air ratio (no big words here..!) will "not" produce more power..OR...more power thAn what..!? The proper or "book" ratio of fuel to air is 14.7 to one of fuel to air going into your combustion chambers. In real life conditions, a slightly richer mixture of 14.9/15.0 is normally more productive, makes the engine happier. Then you need a "much" more rich condition when you step on the gas pedal hard (the "accelerator" pedal), normally upward of 19-1, fuel to air, that ends up back down at your cruse ratio.

So, to not make this into a classroom lesson, all your experience prooves is that you have a carburetor that's setup too rich and maybe ignition timing that's set too low. I'm assuming your'e not overly experienced in this type of tuning, I'd sugest that you search out a "tuneup shop" nearby that has a "chassis dyno". Pay the man to tune your engine. You'll be MUCH happier, your wallet will be happier for the better milage, your butt will be happier because of the increase in power and drivability will make you like a school kid again...!

If you want to know/learn more, there are many books on "how to tune an engine".

Mike

[Dwain G.]

Maybe it did feel more powerful to you because of the way an AFB carburetor works. When the throttle is opened wide, manifold vacuum drops, allowing the metering rod springs to overcome the vacuum pull, so they rise and admit more fuel. The manifold leak may have helped the high speed circuit to open quicker, in turn activating the secondaries earlier also. It may have felt good, but as Mike sez, you don't want to run it that way.

[StudeRich]

I have a 64 hawk R1 power brakes , and steering. stick. I was in heavy traffic the other day and the engine started hissing....then the brakes were hard...I figured I had lost the brake hose and indeed it did come off the carb end./Cut/

Is this a miss-statement, typo or was your Power Brake Booster actually connected to your Carb.?
It is supposed to be connected to the Fitting in the Intake Manifold.

[EssexExport]

What I've done with mine (won't go into running problems):

1.) Started using Lucas Oil Safeguard.

2.) Replaced the fuel filter with a Napa Gold 20 micron (old one was full of particles).

3.) Adjusted the carburetor (plenty of videos online & You Tube explaining how).

My GH is now running very good.

[Dan Timberlake]

I think 19 to 1 is "leaner" than the stoichiometric just right 14.7.
Richer would be 12 or 13, which is the direction "power valves" and economizers etc move the mixture ratio when the throttle is opened and more than cruising HP is requested.

http://content.answcdn.com/main/content/img/McGrawHill/Aviation/f0044-01.gif

[bosshoss61]

I like just saying that word "stoichiometric" or theoretical. Every fuel has a stoichiometric A/F ratio at sea level to help oxidation. The gentleman is from NY. Hey-- am not r2 --how far are you above sea level?

[gordr]

Having worked with chainsaws a fair bit, I can tell you they will rev really high when set too lean, but put a load on them that way, and they will dog right out. You want to set the high speed jet so they run a bit rich under no-load conditions, almost to the point where they start "four-stroking". Then, when the chain gets a bite in a log, they smooth out and pull strong under load.

[Dan Timberlake]

stoichiometric is mass or weight based.
The chemistry is the same at sea level or 5000 feet.


Changes in elevation require changes in jetting ( leaner jetting at high altitudes) because the air density is generally less at higher altitude, but the density of the fuel doesn't change much, and pressure drop in the venturi is not linear when the air mass changes.

the direct approach for accurate tuning is to use a Relative Air Density meter.

http://pitstopusa.com/c-131738-pit-equipment-air-density-gauges.html

[bosshoss61]

Thank you Dan, you have good posts

[am not r2]

No, I am not too well versed in tuning but I can use a timing light and vacume gauge. I know it was set rich. The power was over 3000rpm, yep it hooks tothe fitting on the manifold, I live at about 300 feet elev. or so.
I have thought about going to get a dyno tune locally but I have some reservations. I never have been given strong positive feedback from the locals. I know it would be worth it. The carb is correct and original. Rebuilt a few years ago by pony carbs in NM. Thank you all for your input. R

[Dan Timberlake]

I'd think at 3000 rpm with a significant amount of throttle my carb has transitioned from the idle circuits (which is what the external mixture screws can change) to the intermediate or even power circuits which are controlled by jets and whatnot deep in the carb's gizzard.

I'd take off the air filter and have a peek around.
Maybe a plugged air filter would not make a big theoretical change in "richness" (except on carbs with vents outside the filter) but a choke that is not straight up when warm sure would.

As others said, a real tune up ( as detailed in the shop manual, not plugs-n-points for $39.95) sometimes finds a lot of lost horse pressure.