Can't get bike over 23MPH

[Emcee]

Got my tach today and here is what I'm reading. I pulled my spark plug out and it was very rich and fouled. Moved the needle to the 1st notch and my engine is responding well to that and to the 90 Octane ethanol free I put in. Top speed is still 23 mph

When I spray the carb where it meets the intake manifold it stalls out. Sprayed it on the intake manifold where it meets the engine and it's fine.

1690 idle

2190-3100 RPM 10mph

4100 RPM 15mph

5100 RPM 20mph

 

[noah9988]

Got my tach today and here is what I'm reading. I pulled my spark plug out and it was very rich and fouled. Moved the needle to the 1st notch and my engine is responding well to that and to the 90 Octane ethanol free I put in. Top speed is still 23 mph

When I spray the carb where it meets the intake manifold it stalls out. Sprayed it on the intake manifold where it meets the engine and it's fine.

1690 idle

2190-3100 RPM 10mph

4100 RPM 15mph

5100 RPM 20mph

You have an air leak. Fix the air leak (and any others) before tuning the carb, otherwise you're just chasing your tail. The rpm checks out near where it should be, so it seems it's an air/fuel problem. Does your engine 4 stroke? This is what it sounds like:

 

[mony0_3]

Check the crankshaft seals for air leaks.

 

[Risk Man]

Got my tach today and here is what I'm reading. I pulled my spark plug out and it was very rich and fouled. Moved the needle to the 1st notch and my engine is responding well to that and to the 90 Octane ethanol free I put in. Top speed is still 23 mph

When I spray the carb where it meets the intake manifold it stalls out. Sprayed it on the intake manifold where it meets the engine and it's fine.

1690 idle

2190-3100 RPM 10mph

4100 RPM 15mph

5100 RPM 20mph

Curious as to what you use to spray the carb?

 

[Emcee]

You have an air leak. Fix the air leak (and any others) before tuning the carb, otherwise you're just chasing your tail. The rpm checks out near where it should be, so it seems it's an air/fuel problem. Does your engine 4 stroke? This is what it sounds like:

So I sealed off the air leak, it preforms better. It would make that sound but not anymore. Instead of stalling the RPMs would drop from 1650 to 1630 slowly so I'm not sure if some of it is going into the air filter.

Still can only top at 23 MPH. It just sounds horrible, unless the engine sounds that way at higher RPMs. Tomorrow I'm going to put my old exhaust on to see if that is creating some sort back pressure problem. I have the viper flex exhaust on it. In addition, I am going to follow what someone else did when this same issue happened to them and I'm going to see what happens.

 

[Emcee]

How do you know you're only doing 23 mph? Are you using a bicycle computer? How do you know you're revving high? Are you using a tachometer?

With your setup, it takes 5365 rpm to do 23 mph. If you're going over 5365 rpm and are only doing 23 mph it means either something is in a bind somewhere. Or you simply don't have enough power for the weight being propelled.

Is there a formula to figure out what my RPMs would look like based on sprocket size and wheel size? I have a tachometer and you were right. Without that thing I dont know if I'm revving high. I am at 5100 RPM at 20mph.

 

[Greg58]

It's times like this that's frustrating, if you lived close to one of the members here I'm sure it could be figured out. Just for info I have two 48cc powered bikes that are on 26" tires with the 44t sprocket, both will do 23 with no effort. One is modified and will do 32 mph on flat ground, the newest engine I've only cleaned up the ports and corrected the squish and it will do 29. The new engine only has about 25 miles on it. I run a expansion chamber on both of mine and have them jetted correctly, these are not complicated but can be hard to dial in.

 

[Greg58]

My best running engine I removed to rebuild, it has turned 8400 rpm. From my guess was probably close to 34-35 mph.

 

[weefek]

I'll also do around 35mph on a good day w/ 44t sprocket (somewhere around 7500 rpm ish I think) or 55~ish km/h. I don't think the motor likes it all that much but it will do it. You fixed your carb to intake mani leak but i'd also check the main seals. Pull off the clutch cover and magneto cover and spray water and/or starter fluid (what i use) on the seals and see what happens.

If that's not it then i'd guess there's something up with your carb, or you have a hot spot somewhere in the combustion chamber causing predetonation possibly (hence why it sounds like it's gonna explode even at 5300ish rpm). Pre-det is hard to hear a lot of the time because it sounds like a million orther things.

 

[Emcee]

I'll also do around 35mph on a good day w/ 44t sprocket (somewhere around 7500 rpm ish I think) or 55~ish km/h. I don't think the motor likes it all that much but it will do it. You fixed your carb to intake mani leak but i'd also check the main seals. Pull off the clutch cover and magneto cover and spray water and/or starter fluid (what i use) on the seals and see what happens.

If that's not it then i'd guess there's something up with your carb, or you have a hot spot somewhere in the combustion chamber causing predetonation possibly (hence why it sounds like it's gonna explode even at 5300ish rpm). Pre-det is hard to hear a lot of the time because it sounds like a million orther things.

I'm just thinking in my head, where are there seals under the clutch cover. I am not in front of my bike right now so I'm just trying to understand before doing this.

I am watching a video on this as we speak. Can I use carb cleaner? Is it even safe to spray next to the magnet that looks like a spool of sewing thread? So just for clarification. Idle the bike and then aim and spray behind the magnet?