185 upgrade

[Garland Terry]

What about milling the head a little flatheads forever baby!!

Exhaust upgrade? I look at my int154 and the exhaust manifold has a reducer on it. What if you put a larger exhaust pipe/muffler on it? I wonder if we added the int154 manifold to an Fcub if the difference would be noticable to the operator and on the dyne too performance wise.

My int154 cub has the zenith carb and the PO says it also has the high compression pistons(184 setup) that were added when they rebuilt it. I just purchased an extra 154 exhaust manufold and an extra 154 hood to make the exhaust change and go vertical with the exhaust pipe/muffler too. Thats my plan right now.

I have a feeling when i refresh my fcub the motor is going to get ported too. I'm more interested in making it flow better over making the ports larger. Matching the ports to each other really matters too. I leave them rough too for mixing the gases nothing gets really polished. I even ported my log splitter engine years ago. I just took out the casting flaws inside the ports.

[b52c130]

ok. Thanks for the input. I have a brand new Zenith carb. And a lot of blowby. It gas knocks under a load real bad even on high octane gas. It starts great no choke even. But as grandpa said "it ain't got enough power to pull the hat ofn yo head."It pull a 4.5 foot disc ok but won't mow for nothin even in low range 1st gear. I am thinking timing or not advancing inder a load. Hep me.

Garland - the key to the power problem is "I have a brand new Zenith carb". With the symptoms that you describe - the new carb has too small a 'main jet'. If it does indeed have too small a main jet - you will either burn the valves or melt the aluminum pistons. (pull one of the spark plugs to see if you can see any 'tiny shinny metal splatterings' on the ceramic insulator tip surrounding the center electrode - if you do, this is pieces of 'melted piston').
To check and or fix the main jet: Turn off the gas at the the fuel strainer under the gas tank. On the lower rear edge of the carb - facing rearward toward the rear tire, there is a hex head pipe plug (1/2", I think). Remove plug, catching gas in a coffee can underneath. There is also a fiber washer seal that you don't want to loose - it seals the cap. Take a 'medium' tip straight blade screw driver and insert into the hole about 1" - 'feel around' until you find the 'slot' in the jet. Unscrew the jet. it also has a small gasket that should come with it. Now that you have the main jet out, look on the flat face of it and in very small numbers it should be stamped "21" - if it is, then you are OK - if it is a smaller number, then this is the source of your 'fuel knock'. The correct size jet for this 60 cubic inch engine is the #21 jet which corresponds to a .041" drill bit. If the jet is too small, your only practical alternative is to 'drill it out with a .041" drill bit (best done in a drill press - so that you keep it perfectly straight and don't 'oversize' it. (the preferred method is to just go out and purchase the correct #21 jet; however, don't hold your breath while your trying to find one!!). Blow the drilled jet out clean, put the small washer back on, find a screw driver that 'exactly' fits tight in the jet slot, and reinstall the jet.

'Replacement' Carburetors usually cover a wide variety of applications - so vary often the jet size is not right for your situation. The following was taken from a 'boat' carburetor tuning guide for a Zenith Series 68 (which yours is), but the procedure is the same.

To adjust the idle mixture screw, initially adjust the idle mixture screw (the upper adjustable jet with the slot for a screwdriver) clockwise (in) until it bottoms lightly, and then out 1 turn. Connect a tach to the engine, start the engine, run the engine until it is fully warmed up, then close the throttle and adjust the carburetor idle speed screw (the screw on the carburetor throttle arm that controls the throttle stop) until the engine is idling at 600 rpm, turn the idle mixture screw slowly out until the rpm drops noticeably, and then in again until the fastest idle speed is obtained. Readjust the idle stop screw to again set the idle speed at 600 rpm. Repeat the idle mixture adjustment again. Readjust the idle stop screw to again set the idle speed at 600 rpm.

[Garland Terry]

Thanks for the heads up. I have tuned and timed and adjusted everything else and it does run a lot better but I had better look into this right now! thanks Randolf, NJ.

ok. Thanks for the input. I have a brand new Zenith carb. And a lot of blowby. It gas knocks under a load real bad even on high octane gas. It starts great no choke even. But as grandpa said "it ain't got enough power to pull the hat ofn yo head."It pull a 4.5 foot disc ok but won't mow for nothin even in low range 1st gear. I am thinking timing or not advancing inder a load. Hep me.

Garland - the key to the power problem is "I have a brand new Zenith carb". With the symptoms that you describe - the new carb has too small a 'main jet'. If it does indeed have too small a main jet - you will either burn the valves or melt the aluminum pistons. (pull one of the spark plugs to see if you can see any 'tiny shinny metal splatterings' on the ceramic insulator tip surrounding the center electrode - if you do, this is pieces of 'melted piston').
To check and or fix the main jet: Turn off the gas at the the fuel strainer under the gas tank. On the lower rear edge of the carb - facing rearward toward the rear tire, there is a hex head pipe plug (1/2", I think). Remove plug, catching gas in a coffee can underneath. There is also a fiber washer seal that you don't want to loose - it seals the cap. Take a 'medium' tip straight blade screw driver and insert into the hole about 1" - 'feel around' until you find the 'slot' in the jet. Unscrew the jet. it also has a small gasket that should come with it. Now that you have the main jet out, look on the flat face of it and in very small numbers it should be stamped "21" - if it is, then you are OK - if it is a smaller number, then this is the source of your 'fuel knock'. The correct size jet for this 60 cubic inch engine is the #21 jet which corresponds to a .041" drill bit. If the jet is too small, your only practical alternative is to 'drill it out with a .041" drill bit (best done in a drill press - so that you keep it perfectly straight and don't 'oversize' it. (the preferred method is to just go out and purchase the correct #21 jet; however, don't hold your breath while your trying to find one!!). Blow the drilled jet out clean, put the small washer back on, find a screw driver that 'exactly' fits tight in the jet slot, and reinstall the jet.

'Replacement' Carburetors usually cover a wide variety of applications - so vary often the jet size is not right for your situation. The following was taken from a 'boat' carburetor tuning guide for a Zenith Series 68 (which yours is), but the procedure is the same.

To adjust the idle mixture screw, initially adjust the idle mixture screw (the upper adjustable jet with the slot for a screwdriver) clockwise (in) until it bottoms lightly, and then out 1 turn. Connect a tach to the engine, start the engine, run the engine until it is fully warmed up, then close the throttle and adjust the carburetor idle speed screw (the screw on the carburetor throttle arm that controls the throttle stop) until the engine is idling at 600 rpm, turn the idle mixture screw slowly out until the rpm drops noticeably, and then in again until the fastest idle speed is obtained. Readjust the idle stop screw to again set the idle speed at 600 rpm. Repeat the idle mixture adjustment again. Readjust the idle stop screw to again set the idle speed at 600 rpm.

[smigelski]

Exhaust upgrade? I look at my int154 and the exhaust manifold has a reducer on it. What if you put a larger exhaust pipe/muffler on it? I wonder if we added the int154 manifold to an Fcub if the difference would be noticable to the operator and on the dyne too performance wise.

I understand your theory. My question is back pressure. The more air and fuel in and out gives more power. So in order for it to work you need to make sure you can get more air and fuel. If you open the exhaust or intake uneven, you have a motor that runs like crap. I have a friend that runs prostreet raceing. They have several rules to stick by when building a motor. Balance is always the key