Carburetor jetting question

[dualitymike]

I had a look at the Carb 101 topic which answered a lot of my questions. One thing that was mentioned is that it's best to run the motorcycle up a slight incline when doing your jetting runs. My question is - is it necessary to run the bike under load like that or can the rejetting be done in a garage on the center stand, so long as you're still running it at the required throttle positions?

Probably not important, but I'm running Stock Keihin carbs on a 1977 CB550F Super Sport, the carbs are rebuilt with 98 mains and 32 idle. The reason I'll need to rejet them is that I'm using K&N pod filters.

Mike

 

[AlphaDogChoppers]

Yeah, go ahead and hold your throttle wide open with no load on the engine. Let us know how long it takes for chunks of engine to come flying out through the cases.

 

[minibike69]

take her for a spin around the block to get accurate results.

 

[teazer]

ADC is expecting you to think about your original post and then to realize that WOT on the stand in neutral would be be smart. He's providing an opportunity for a learning experience.

Or you could ignore his input and just try it and see what happens as the motor tries to rev to a gaziillion revs just before it melts or disintegrates. Load is essential first to act against the forces generated inside the motor and secondly to get the appropriate running conditions.

 

[AlphaDogChoppers]

ADC is expecting you to think about your original post and then to realize that WOT on the stand in neutral would be be smart. He's providing an opportunity for a learning experience.

ShudDUP! I want him to do it and then post pictures! :

 

[mydlyfkryzis]

Yeah, go ahead and hold your throttle wide open with no load on the engine. Let us know how long it takes for chunks of engine to come flying out through the cases.

Don't listen to ADC
His is such a Scare Monger....

The chunks usually stay right in the engine..... Most often the engine just seizes or gets holes in the piston...

High throttle without a load is only going to overheat the engine and cause it to fail catastrophically.


The right way is to dig out the floor in your garage and install a Dynamometer. Then install a large fan to keep cooling air over the engine. Using a wide band O2 sensor, you can check and adjust the jets to exactly the right size for your application. No guessing. The dyno allows you to see where the mixture is lean and rich and compensate. Remember the there are also air jets as well as fuel jets. Bike use something called emulsifiers. These are like the aerator on your kitchen faucet. they help disperse and mix the fuel. The air jets supply air to these emulsifiers. If they supply too much or too little air, the aeration effect or air/fuel mixture is affected.

Search for "Hole in Piston" and you can see what running lean can help do.

Otherwise, just play around, make guesses, and either foul the plugs, or hole the piston, or just make the bike un-ridable. Most of the bikes I see that have modifications don't really run well at all. The may start and idle well, or run WOT O.K., or run in the middle ok but won't idle. They never run as well as they did when they were bone stock and properly tuned.

No reason you can't be in that same boat, er, on that same bike....

 

[Nebr_Rex]

The right way is to dig out the floor in your garage and install a Dynamometer. Then install a large fan to keep cooling air over the engine. Using a wide band O2 sensor, you can check and adjust the jets to exactly the right size for your application. No guessing. The dyno allows you to see where the mixture is lean and rich and compensate. Remember the there are also air jets as well as fuel jets. Bike use something called emulsifiers. These are like the aerator on your kitchen faucet. they help disperse and mix the fuel. The air jets supply air to these emulsifiers. If they supply too much or too little air, the aeration effect or air/fuel mixture is affected.

Some of us use our butt, cheap and reliable if not accurate.

 

[teazer]

Butt dynos are accurate to about +/- 10% or so if correctly calibrated but are notoriously unreliable and do not produce repeatable data.

Just buy a dyno and do the job properly. Go one. You know you want one...

 

[kopcicle]

proof that there may be no reason for a [sarcasm]~ [/sarcasm] font ...

~kop

 

[mydlyfkryzis]

Butt dyno's are the reason piston replacement manufacturers stay in business.

All you need to do is read the posts " my engine won't idle " " my engine stumbles at high rpm" my engine stumbles at part throttle" etc...

I can't tune the cv carbs so I'll get some Mikuni VMs and be unable to tune them.

If you are a person with heavy duty tuning experience, a butt dyno will work o.k. If your tool box is filled with a hammer, 3 adjustable wrenches and 2 pairs of vice grips, maybe carburetor tuning isn't your forte.

So I was sarcastic on my previous response, because blunt truth trauma is painful.

Most people should not waste their time trying to rejet their carburetors. If you are putting Emgo pods on, that fact is they are more restrictive then the stock system. They have less surface area and no plenum. I can't understand why you would put on a more restrictive intake, a less restrictive exhaust and then wonder why the carburetor is so hard to tune.

So if your engine doesn't run well after putting in decorative, non-pergormance enhancing mods, park the bike, take picture, then admire the work of art.

There are many beautiful, non-functional bikes around. They are like beautiful sculptures. Polished intakes. Fat tires, stretched swingarms. They barely run, they handle terribly, and they should be called cafe statues. They are not really cafe "racers" as they can't really race.

There are a few real works of art here, there are a few real machines here too. There are quite a few people who know some things, and there are some who are clueless.

You know what the first thing you should do to a recently acquired bike? Get it running. I notice many people spend a lot of time painting and body work and tab removal, and don't even know if the engine has compression or what it should be. What is the point of a motorcycle? The first word:MOTOR.

Seems to get forgotten in the rush to stretch the swingarm.

oops, left out the sarcasm. Lol







Sent from planet Earth using mysterious electronic devices and Tapatalk

 

[Nebr_Rex]

Butt dyno's are the reason piston replacement manufacturers stay in business.

All you need to do is read the posts " my engine won't idle " " my engine stumbles at high rpm" my engine stumbles at part throttle" etc...

I can't tune the cv carbs so I'll get some Mikuni VMs and be unable to tune them.

If you are a person with heavy duty tuning experience, a butt dyno will work o.k. If your tool box is filled with a hammer, 3 adjustable wrenches and 2 pairs of vice grips, maybe carburetor tuning isn't your forte.

So I was sarcastic on my previous response, because blunt truth trauma is painful.

Most people should not waste their time trying to reject their carburetors. If you are putting Emgo pods on, that fact is they are more restrictive then the stock system. They have less surface area and no plenum. I can't understand why you would put on a more restrictive intake, a less restrictive exhaust and then wonder why the carburetor is so hard to tune.

So if your engine doesn't run well after putting in decorative, non-pergormance enhancing mods, park the bike, take picture, then admire the work of art.

There are many beautiful, non-functional bikes around. They are like beautiful sculptures. Polished intakes. Fat tires, stretched swingarms. They barely run, they handle terribly, and they should be called cafe statues. They are not really cafe "racers" as they can't really race.

There are a few real works of art here, there are a few real machines here too. There are quite a few people who know some things, and there are some who are clueless.

You know what the first thing you should do to a recently acquired bike? Get it running. I notice many people spend a lot of time painting and body work and tab removal, and don't even know if the engine has compression or what it should be. What is the point of a motorcycle? The first word:MOTOR.

Seems to get forgotten in the rush to stretch the swingarm.

oops, left out the sarcasm. Lol







Sent from planet Earth using mysterious electronic devices and Tapatalk

Totally agree.