Loss of power when hot

What would make a bike lose power when hot or after going slow for a long time? Running under 3k. It runs good idles perfect sounds ok but wont pull hard with a load.
I can rev it up to 5k in first but it just sucks wind. It does not pop or anything. It feels like it has the power of a 400 not a 1100. It sometimes kicks in and goes like hell for sec or two. I did put on prime to see is the vacuum diagram was working......it did not help.
Any takers?

 

You say it has problems when it's hot, how about when it's still cool or at least not completely warmed up?

 

It runs great lots of power. It almost seems like the tranny or drive is binding. But I just don't know what is happening. It only happens on hot days when I ride for hours. I have put about 600 miles on the bike and It only happed twice. Both times I was riding on a hot day for hours and at sea level.

 

It seems like you would be able to tell from the sound/feel if something were binding or trying to sieze up. Sounds more like a fuel starvation issue.
I have seen high performance cars get so hot that the fuel in the carburetor bowls actually starts to boil with similar symptoms which I suppose is possible. I don't know if applying some choke (enrichment) would help in this situation. Maybe. If it only takes a 10 minute or so break to get it running right again but then the problem returns after only a short distance this is a possibility.
Of course if this is the problem I don't know just how to address it other than moving to a cooler climate.

 

Are you sure its running on all 4 cyl when this happens? Could be your ignition is giving up when hot? Or coil for that matter

 

Clogged Emulsion Tubes.

You have good-enough Manifold Vacuum to "Suck-Up" the Main FUEL Jet Output.
But, the Emulsion Tubes are not completely Clean.

Instead of the Main AIR Jet Supply being able to Flow freely through the Ports on the Emulsion Tubes ... there is blockage.

Consequently, ... the VOLUME of Main FUEL Jet Output is Lessened AND what Main FUEL Jet Volume does join the Intake AIR Stream is NOT sufficiently atomized ... causing the Mixture to be less powerful.

Punch-out the Emulsion Tubes
Scrub them CLEAN with ScotchBrite Pad
Probe the Air Metering Ports to be Open and Clean -- (See light through them)
Twist 3 Pipe Cleaners together and "Scrub" the Center Passage.

Clogged Emulsion Tube:


Cleaned Emulsion Tubes:


Main Jet / Washer / Emulsion Tube with Cleaning Tool

 

I talked to a friend that is good with mechanical things and he thinks it is a bad coil that only acts up when real hot. That would explain why it has only happened on hot days and long rides. It did kick in and out real fast twice and it was like turning a switch on and off. I think I will replace them and see what happens. I let it sit for 2 hours and it ran great for 20 min trip to a friends house and back several hours later. He said that the heat can cause a weaker spark.

 

Why would this only be a problem when the bike is hot?

 

It's actually a problem all the time.
When the Bike is Cold, you get additional Fuel from the Enrichment Circuit.
When the Bike warms up and the Choke is closed; you're starving it some.

If its not the Emulsion Tubes and you are losing Power because the Engine is
Getting TOO HOT ... that would mean the Mixtures are TOO LEAN and the Cylinders are Losing Power by BLOW BY.

Since you didn't indicate that the AirBox was Oily and the Engine Smoking, I guesses Emulsion Tubes were the cause.

Emulsion Tubes Clogged
Wrong Main Jets
Misplaced AIR Jets
Diaphragm Pistons Sticking
Diaphragm Rubbers Cracked or Pin-holed
Float Heights
Wrong Main Jets
Bad Gas
Beenie Screens Clogged

Something Robbing you of Full Power that does not seem to be Ignition Related.

 

OK I got the carbs off and am ready to knock out the Emulsion Tubes.
How do you do that? What way do you want to hit them from the top of the carb so it comes out where the screw is?

Thanks

 

The BEST Tool to have is a Metric Cap Screw that is the SAME Thread Pitch as the bottom of the Emulsion Tube.
Thread the Cap Screw inn until finger tight.
Tap on the Allen Head of the Cap Screw
(Progressively harder until the force defeats the GRIME or the Press Fit)
Once the Emulsion Tube moves ... Pull-out the Cap Screw.


Use the Cap Screw in the Bottom of the Emulsion Tube for Cleaning.
Chuck the Cap Screw in your Drill
Rotate the Emulsion Tube at Medium Speed
Apply a ScotchBrite Pad to the rotating Tube and SHINE it CLEAN.

Probe the little holes with a wire,
Twist 3 Pipe Cleaners together and Scrub the Main Hole.

Use the Cap Screw again to "Pull-down & Seat" the E-Tube during reassembly.

 

Thanks I found one and got them out.......they look ok I can see through the holes. The carbs are dirty in other places like the main intake screens.
Thanks for the tip!