Lost top speed

[Rudz]

My bike was hitting 30mph, now it does 21-22 continues to rev but doesn't go faster.

I have plenty of torque and she climbs just normal but top speed is shot. Every so often it will go back to normal, fly to 25-30 then lose power until 21-22.

I checked the exhuast and manifold, they're tight, replaced exhaust gasket as it was questionable. I went through the carburetor and it was clear, I am use an inline filter. Nothing blocking jet.

The float looked fine, I'm running an ngkbh6 spark plug.

I tightened the head bolts as well.

Running opti 2 at recommended ratio, hasn't been a problem in weeks.

I'm thinking maybe my rocket racing cdi might be acting up? I'm going to switch both the cdi to stock and the plug.

Anything you guys think of?

 

[nelsonk1969]

I agree your problem sounds like electrical however keep it simple and check for the obvious which it sounds like you have.
Bad fuel or a poor mix could be the issue also.,the flow of fuel mix could be restricted from coming out of your tank if it has debris stuck in it
Did you get a compression test of your motor when it was fairly new to compare your current reading to?

 

[Greg58]

Here in Ga. As the weather cools I have had one of my bikes do similarly, adjust the plug gap at different settings to see what your engine runs best on. I know some of the after market cdi makers recommend a gap but I would try it anyway. On my engines with the stock cdi 26-28 is where I get the best results.

 

[Rudz]

No compression test, the weather hasn't changed enough to affect anything, I live in southern California, we only have one season.

I'll post up after I switch cdi's

 

[nelsonk1969]

one simple thing I thought of if the fuel line if it is not compatible with the fuel-oil mixture you could have a restriction from a shrunken line.
much of the fuel we buy is blended with Ethanol which is harmful to many of the standard off the shelf fuel lines. Just thought for a possible easy fix.

 

[Rudz]

I use thick tygon fuel line. And a good inline filter. I already checked all that.

 

[nelsonk1969]

if your using Tygon fuel lines you must have a well thought out install, so your probably right about it being electrical.
good luck I am out of options that may help.

 

[2door]

How many miles on the engine?

Tom

 

[Rudz]

Probably over 200

 

[a.graham52]

how does the engine sound when it does this? is it four stroking? if you might have over 200 miles, then its possible its finally getting broke in and may need some adjustment of the main jet. what do you have for an engine, carb, exhaust, etc?

 

[crassius]

don't forget obvious checks - motor loose - chain, tire, brakes, wheel bearings dragging - loosen muffler a bit to check for clog - try lifting choke lever just a bit to see if better or worse

 

[KCvale]

One tip is it runs normal sometimes, then slower, then normal again.
You can rule out a lot of things if that is the case like actual bike caused drag, clogged exhaust, etc.

 

[Rudz]

Switched cdi's, it's still not right, maybe I need to clean my spark plug.

I am using the stock exhuast, all I did was cut the tube out from inside. It's louder but tons of more torque. I live in the middle of nowhere, so I don't care how loud it is. In town I never ride over 15-18 anyways, so it's not like I'm gunning it there.

But there's a lot of long stretches of road that I open her up.

 

[Rudz]

I'm going to buy a micro drill set to jet the carb

 

[Rudz]

I switched cdi's and it's the same. I switched spark plugs and the ngkbh6 works better than stock so it's not than.

I did have some tweaked spokes, I got those fixed today. I also took the air filter off and it worked better.

I tried adjusting the needle but it didn't seem to do much. I ordered the drill set so I'll re jet the carburetor.

I have a voodoo expansion chamber but I need to take it to the muffler shop because I have neither a vise or MAP torch.

I'm hoping my exhuast modification plus the fact after putting 40 miles on today I need to tune the carburetor.

 

[Rudz]

Should I open the jet or go smaller? I'm running opti 2 at the recommended ratio on the bottle. I think it's 70-1?

 

[nelsonk1969]

I think if your motor is operating erratically like you say you shouldn't mess with drilling the jet. you need to find the source of the erratic operation before you possibly make it worse.
we have been trying to help you but I feel we are not getting the whole story so its very hard to help without knowing for sure that you have good compression, good quality fuel, spark and all the basics right. drilling out a jet will most likely make it run too rich unless it is starving for fuel because a lack of supply to the carb. either way a jet modification at this point is pointless.
even low air pressure on your tires could cause your bike to slow way down and make it feel like it runs better if you have a tail wind that you didn't notice.

 

[Rudz]

I'm using 91 octane and opti 2 oil, been running that fuel and oil for a few weeks now with no problem. Just hit 300 miles today so maybe it's broken in?

If not getting any oil leak from they head, and I keep it snug. Should I replace the head gasket?

Spark is fine, ngk b6hs spark plug, rocket racing cdi.

Nt carburetor.

Fuel looks to be flowing fine, no bubbles.

It just started acting up, only thing I did was cut the tube out from the inside of the exhuast.

 

[nelsonk1969]

modifying the exhaust to allow less restriction may effect the overall performance to decline however it shouldn't be an erratic situation where it runs fine for a few minutes then bogs down then picks up again unless the piece you removed was holding packing or some sort of baffle in place. you shouldn't need to just hang parts on this engine to get it to run properly. if your head gasket is bad this would show up with a compression test and it wouldn't be erratic if your getting blow by from a leaking head gasket your performance would be down all the time. also you would see black staining from the head gasket area and possibly noise.
if your just tightening up fasteners randomly without doing it at the right temperature and without using a torque wrench you need to stop and find a manual on your motor
and get the specs and put everything back to factory specs.
while over tightening fasteners doesn't sound like your problem unless you over compressed your head gasket and caused it to leak and just haven't noticed any signs of it
however all this and more will be covered if you simply check the basics
1st you need compression the right amount of compression for your engine to perform properly. if you don't have a gauge you can purchase one for cheap at most auto parts stores.
Stores like Auto Zone and Napa have a tool loaner program where you pay for their used tool you use it and return it when your done and they refund your money once the tool is returned.

Contact your motor supplier to see what service manual is available for it as you will need the specs to compare your readings to.
if no specs are available you will need to find someone on this forum that has the same motor and a compression gauge and is willing to pull a test on their motor.
pretty much any engine needs a minimum of 90 Psi to simply run if yours is at 80 you know you will need to look into it further.
if the compression is low add some oil about one table spoon directly into the engine through the spark plug hole spin the motor over and if the compression goes up you most likely have damaged piston rings.
I can go on and on about covering the basics but this is the first place you need to start. As I think this bike is not operating erratically I think it is just running poorly and has a problem or several small problems that is causing your problem to seem that it comes and goes.
you need compression ,fuel oil mixture, air, and spark to make this motor run properly
one or more of those key components is your problem. unless like the others on this forum have tried to mention your bike its self can be causing the problem from worn wheel bearings to simply having tires that are low on air pressure.
if you have any thought that the exhaust modification may be the culprit
double check your work as the piece you removed could have a effect that you did not intend which could inadvertently cause the exhaust to get restricted if something came loose inside there.
Since you haven't posted any pictures it very hard to diagnose
I will say anytime I have ever come across a hard to find problem it was normally caused by the last person that worked on it. so eliminate the muffler from the equation by removing it to test the motor. if it runs better without it buy a new one and continue with your diagnostics if you still need to.

 

[Rudz]

Broke a darn bolt on the rear mount, no wonder.

Here I was chasing problems and it was right there.

I get to use that set of left handed drill bits. Broke off inside the case, I have to finnaggle it enough to grab it with pliers and turn it out.

I spent forever trying to screw a new bolt in before I realized the old one was still in there.

Darn rookies.