Issue over 4k RPM

[lsflp]

Good afternoon, I am from Colombia, here it is a problem to get to a good mechanic, so I ask you for a little help or advice.

My old '91 V-Max has the following symptoms.

above 4k RPM the bike starts to vibrate too much, it feels like it loses strength, the accelerator is released and it accelerates again and the bike "takes off".

We just changed all the carburetor jets, the vacuum is picking it up just fine. We have adjusted the mixture screw at 2.5, 1.5 and 3 turns and it remains the same.

Spark plugs have been checked, they are fine. the motorcycle has COPs installed.

the Vboost, make sound when power on.

the fuel pump was changed, along with the fuel filter, it improved too much but it's still the same.

Thanks for yours help

 

[Fire-medic]

Try draining your float bowls into a clear container to see what each float bowl has in it. See if there is a bit of water in one or more, it should be easy to see, as gas and water do not mix-together. Empty the container between float bowl drainings. Also check for fine dirt-looking debris draining out of the float bowl.

 

[sdt354]

What happens if you give it some extra fuel from the "choke" at the time of the issue? I'd be looking at the slide diaphragms for tears or pin holes. Stock carb setup with OEM needles or?

 

[MaxMidnight]

above 4k RPM the bike starts to vibrate too much, it feels like it loses strength, the accelerator is released and it accelerates again and the bike "takes off".

That sounds like you have weak mixture. Other symptoms may be:

1. It is difficult to apply the throttle quickly or the engine picks up speed when the throttle is rolled off.
2. The engine knocks or Pings or overheats.
3. The engine surges or hunts for a stable RPM while cruising at part throttle.
4. Engine acceleration is flat or slow to pick up.
5. When the pilot circuit is too lean, there will be popping or spitting in the carburettor as the throttle is opened. Sometimes there will be popping or after fire in the exhaust on deceleration after the throttle has been closed.
6. Engine performance improves in warmer weather, or runs poorly in cold weather.
7. Engine performance worsens when intake is removed.
8. Baked white and flaky spark plugs.

As it occurs after 4K then I would double check you have the correct jets i.e. the correct ones are mains 152.5, PAJ1 - 90, PAJ2 - 170, pilot - 37.5 or that you have substituted Mikuni jets with Dynojet ones of the same number (equivalent Dynojet main is a 162)

 

[lsflp]

What happens if you give it some extra fuel from the "choke" at the time of the issue? I'd be looking at the slide diaphragms for tears or pin holes. Stock carb setup with OEM needles or?

Stock carburator, with stock needles, stock Jets

 

[Woody]

Try draining your float bowls into a clear container to see what each float bowl has in it. See if there is a bit of water in one or more, it should be easy to see, as gas and water do not mix-together. Empty the container between float bowl drainings. Also check for fine dirt-looking debris draining out of the float bowl.

First place to check.
And the easiest.
DRAIN THEM BOWLS.
like FM suggested.
Water and debris is your likely culprit.

 

[lsflp]

Well friends, I tell everyone.
We found that the engine had one tooth camshaft out of phase.

Now the bike runs fine over 4k RPM but when it gets to 7k RPM the bike feels like it's out of fuel. It has a new fuel pump. What can I keep checking?

 

[MaxMidnight]

Is V Boost operating the butterflies i.e. can you see movement of the linkage during the test cycle?

 

[lsflp]

Is V Boost operating the butterflies i.e. can you see movement of the linkage during the test cycle?

Yes sir, the movement its OK

 

[lsflp]

Guys, I checked the pump, resynchronized, and i haven't been able to get the bike to work well over 7k rpm, it still feels like it's out of fuel, i have to drop the throttle and throttle again for it to start throttle properly progressive. Do you have any idea what could be going on?

 

[02GF74]

Is V Boost operating the butterflies i.e. can you see movement of the linkage during the test cycle?

That checks the power cycle but if there was no tacho signal to the vboost, the vboost will not open when riding. I can't think of an easy way to test that when riding, maybe stick an endoscope camera and record, or rev engine to 7+k when stationary.

Re. New pump - worth disconnecting the outlet and check fuel delivery, ie run it for 1/2 minute and measure volume (note pump stops after 5 sec if engine is not running).

Is fuel filter new, correct size?

 

[Fire-medic]

I think a leak-down test is in-order. A compression test also.

 

[MaxMidnight]

That checks the power cycle but if there was no tacho signal to the vboost, the vboost will not open when riding. I can't think of an easy way to test that when riding, maybe stick an endoscope camera and record, or rev engine to 7+k when stationary.

The point of the question was to ensure that V Boost could work - if there was no movement it would suggest which way the diagnosis would go.

Check that you have continuity from the ICU to the V Boost controller (yellow wire). If you have then you will be getting the necessary signal to open the butterflies.
Another way to check if that is the problem would be to run open V Boost. If the bike performs as it should in the 7K + rev range then you need to dig deeper into the V Boost operation.
If you still have the problem then check to advance unit is working...not sure if this would cause the problem?
If that's OK then double (or treble) check that the cams are set up correctly.

 

[lsflp]

That checks the power cycle but if there was no tacho signal to the vboost, the vboost will not open when riding. I can't think of an easy way to test that when riding, maybe stick an endoscope camera and record, or rev engine to 7+k when stationary.

Re. New pump - worth disconnecting the outlet and check fuel delivery, ie run it for 1/2 minute and measure volume (note pump stops after 5 sec if engine is not running).

Is fuel filter new, correct size?

The fuel filter its new

 

[Fire-medic]

check that the cams are set up correctly.

For both timing and valve lift. That's what I was thinking about mentioning the compression test and the leak-down test.

 

[Rick52]

i yhink dyill camshaft is out of phade
Well friends, I tell everyone.
We found that the engine had one tooth camshaft out of phase.

Now the bike runs fine over 4k RPM but when it gets to 7k RPM the bike feels like it's out of fuel. It has a new fuel pump. What can I keep checking?

 

[tvmax]

Why was the cam off 1 tooth? Did you perform some maintenance and remove the cams? Was the engine initially running fine and then this was caused after work was done?

 

[lsflp]

Why was the cam off 1 tooth? Did you perform some maintenance and remove the cams? Was the engine initially running fine and then this was caused after work was done?

The problem was some smoke, was fixed

 

[lsflp]

Hello, everyone, a small update, an error was found in the internal plugs that go in the carburetors, the plugs were released and the gasoline recirculated.
After correcting the motorcycle it allowed to accelerate, after a time of driving, one of the cylinders was at a lower temperature, the spark plug was removed and it was found that it was producing less spark, it was verified with another and effectively wrong.
Now I have another problem, the fuel tank is sealing and it doesn't allow fuel to be pumped, so I decided to remove the hose from the overflow valve and it seems that it was solved temporarily..

I'm waiting for the spark plugs to arrive so I can change them all. the bike when you accelerate slowly, it responds at all RPM, but when you accelerate it very hard it does not respond very well.

For now that's my update, thanks everyone.

 

[Fire-medic]

Use a wire to ensure the tank vent is not plugged, it's a very small opening.

Did you have the jet block rubber plugs in the wrong places? I bought a used bike, and I didn't even try starting it before I tore-down the carburetors. I found one of the jets wasn't even screwed-in the jet block.