Honda gx200 mods for power and efficiency

O

oil pan 4

Joined
Feb 24, 2005
Messages
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Location
eastern NewMexico
I put a Honda gx200 on my air compressor, bone stock from the factory.
It was running so rich my eyes were burning form 50 feet away with ethanol free gas.
I opened up the carb, pulled the main jet and found it had a #75. Got into my jet collection and the next 2 smallest jets I had were a #69 and a #65. So I put the #69 in. While I had the carb off I made the air bleed adjustable with a Dremel, it had that limited 1/4 turn epa approved bs. Just grinding away the blocking tab allowed for full rotation of the screw.
Backed the screw off 4 turns.
I'm going to try the #65 jet just to see what happens. The #69 is still a bit rich, it starts first pull and I can turn the choke off right away and it stays running. The perfect tune I need to ride half choke for 10 to 30 seconds to keep it running.
Next mod, ignition advance. Since the "idle" is about 1,800rpm because it's always under load I'm thinking bump the advance another 6 to 8 degrees.
I forgot to check if this engine has the standard 1mm thic head gasket, if so I'll replace it with an ultra thin head gasket to bump compression.
I'm not going to mess with the exhaust or intake. Ideally I'll simply remove the intake cover for cold air in the summer and leave the cover on in the winter to trim the air fuel mixture.
 
oil pan 4 said:
I put a Honda gx200 on my air compressor, bone stock from the factory.
It was running so rich my eyes were burning form 50 feet away with ethanol free gas.
I opened up the carb, pulled the main jet and found it had a #75. Got into my jet collection and the next 2 smallest jets I had were a #69 and a #65. So I put the #69 in. While I had the carb off I made the air bleed adjustable with a Dremel, it had that limited 1/4 turn epa approved bs. Just grinding away the blocking tab allowed for full rotation of the screw.
Backed the screw off 4 turns.
I'm going to try the #65 jet just to see what happens. The #69 is still a bit rich, it starts first pull and I can turn the choke off right away and it stays running. The perfect tune I need to ride half choke for 10 to 30 seconds to keep it running.
Next mod, ignition advance. Since the "idle" is about 1,800rpm because it's always under load I'm thinking bump the advance another 6 to 8 degrees.
I forgot to check if this engine has the standard 1mm thic head gasket, if so I'll replace it with an ultra thin head gasket to bump compression.
I'm not going to mess with the exhaust or intake. Ideally I'll simply remove the intake cover for cold air in the summer and leave the cover on in the winter to trim the air fuel mixture.
Click to expand...
This is crazy. Your bone stock engine should run perfectly from the factory. If not, it should go back to the manufacturer or place of purchase. All these mods on a new Honda small engine are simply uncalled for, especially in this application. (maybe if you were running a go-cart, or minibike, that might be appropriate). Please trust me when I tell you that this old engine design has been noodled by Honda engineers to the nth degree, and you are diminishing value with your Dremel, your supply of jets, and your ultrathin head gasket.
 
TomYoung said:
This is crazy. Your bone stock engine should run perfectly from the factory. If not, it should go back to the manufacturer or place of purchase. All these mods on a new Honda small engine are simply uncalled for, especially in this application. (maybe if you were running a go-cart, or minibike, that might be appropriate). Please trust me when I tell you that this old engine design has been noodled by Honda engineers to the nth degree, and you are diminishing value with your Dremel, your supply of jets, and your ultrathin head gasket.
Click to expand...

For most people, that is very true, and for general use, Honda engines are world class best.

However, hot-rodders have known for over 100 years that improvements are not only possible, but can be significant. Having been involved in manufacturer based turbocharged engine camshaft development, along with 2 stroke racing outboard testing, I can clearly describe in gory detail, the large number of compromises made to provide a reliable, smooth running and emissions compliant product.

Way off topic here: A Ford 5.4L, 3valve, port injected V8 known to have dismal BSFC, is also unique enough that it is among the very few designs that can run quite well at Air/Fuel ratios as extreme as 21 to 1, providing a emissions noncompliant, high load, thermal efficiency north of 41%.

That little Honda is well known to "take well" to modifications and will tolerate 6000 RPM without issue. Higher compression and advanced timing are common tweaks here. Including a cylinder head from the 160cc version, which raises compression markedly.
 
TomYoung said:
This is crazy. Your bone stock engine should run perfectly from the factory. If not, it should go back to the manufacturer or place of purchase. All these mods on a new Honda small engine are simply uncalled for, especially in this application. (maybe if you were running a go-cart, or minibike, that might be appropriate). Please trust me when I tell you that this old engine design has been noodled by Honda engineers to the nth degree, and you are diminishing value with your Dremel, your supply of jets, and your ultrathin head gasket.
Click to expand...
Sit back, relax, and enjoy his threads. His oil filter one and the murder machine stump grinder was interesting, at least for myself.
 
I've modded a few Predator 212cc engines for mini bikes/gokarts for customers.

You can find billet flywheels that advance the timing, different cams, valve springs, etc. I will say they do run noticeably hotter than factory like this, so I'm sure longevity is compromised.
 
TomYoung said:
This is crazy. Your bone stock engine should run perfectly from the factory. If not, it should go back to the manufacturer or place of purchase. All these mods on a new Honda small engine are simply uncalled for, especially in this application. (maybe if you were running a go-cart, or minibike, that might be appropriate). Please trust me when I tell you that this old engine design has been noodled by Honda engineers to the nth degree, and you are diminishing value with your Dremel, your supply of jets, and your ultrathin head gasket.
Click to expand...
No I'm not. I'm un-EPAing the engine making it what it always should have been.
So eyes burning from the exhaust fumes from 50 feet away is "is running perfectly"?
 
Cujet said:
For most people, that is very true, and for general use, Honda engines are world class best.

However, hot-rodders have known for over 100 years that improvements are not only possible, but can be significant. Having been involved in manufacturer based turbocharged engine camshaft development, along with 2 stroke racing outboard testing, I can clearly describe in gory detail, the large number of compromises made to provide a reliable, smooth running and emissions compliant product.

Way off topic here: A Ford 5.4L, 3valve, port injected V8 known to have dismal BSFC, is also unique enough that it is among the very few designs that can run quite well at Air/Fuel ratios as extreme as 21 to 1, providing a emissions noncompliant, high load, thermal efficiency north of 41%.

That little Honda is well known to "take well" to modifications and will tolerate 6000 RPM without issue. Higher compression and advanced timing are common tweaks here. Including a cylinder head from the 160cc version, which raises compression markedly.
Click to expand...
I'm just looking for 3,400 to 3,800rpms.
For emergency war reserve power I might turn it up to 4,000rpm rarely.
 
With the HP lapse rate of 3% per 1000 feet, the OP is down nearly 15% in HP already. I understand why he wants mower powa!

The GX200 will easily take to the mods and won't be making any more HP than it was designed to. Reliability should remain 100%.
 
Cujet said:
With the HP lapse rate of 3% per 1000 feet, the OP is down nearly 15% in HP already. I understand why he wants mower powa!

The GX200 will easily take to the mods and won't be making any more HP than it was designed to. Reliability should remain 100%.
Click to expand...
Yeah being at 4,400ft will lower dynamic compression ratio by a full number. Going to a thinner head gasket and going up half a number of static compression will get back some of that lost dynamic compression.
 
Can't find my box of timing advance keys.
Plus I know I don't have a 8 degree timing advance key.
So I ordered an 8 degree advance key, the thin head gasket and some main jets.
 
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