Vboost issue

[troncd]

Hi all, having a new problem.
The Vboost kicks in at 6000 rpm as it always has, however at about 7-7200 it drops back down to around 5000. It’s been doing that pretty consistently.

Two other notes. 1 or 2 times it would rev up in vboost as it normal should, but the oil light would light up at the upper end of the rpm range. Additionally one time the tach dropped all the way to 0 even though that was obviously wrong cause it was still running.
Any ideas??

 

[Fire-medic]

Check connections and grounds. If you feel especially energenic, you could open the control box and see if there are any solder connections which need to-be re-sweated. There have been some posts on here about CDI boxes having this done to them, take a look at your opened box.

The red light is the confirmation of "you're riding this the way it was designed to-be ridden" light.

 

[troncd]

Check connections and grounds. If you feel especially energenic, you could open the control box and see if there are any solder connections which need to-be re-sweated. There have been some posts on here about CDI boxes having this done to them, take a look at your opened box.

The red light is the confirmation of "you're riding this the way it was designed to-be ridden" light.

LOL glad to know the red light is probably not an issue.

Concerning the connections, where exactly are they located? Is the control box for the VBOost located under the front left cover? The strange thing to me is that The boost starts at 6000 RPM and then suddenly cut off. And when it does so RPMs drop below the starting point of the vboost. Somewhere down to 5000 normally. If vboost suddenly stops working, would the rpms not just drop back to right at or below vboost kicks in?

 

[MaxMidnight]

If I understand you correctly the bike will spin up to around 7K r.p.m. and then drop back to around 5K?

Why do you suspect the V Boost as causing the issue?
The V Boost butterflies open at 6K but are not fully open until 8K. If they were closing then I would expect to notice a slight drop in power but not to drop them down to 5K.
You say that you noticed the Tacho dropped out and this is what I suggest you investigate.
The V Boost needs the tacho signal to know when to start to operate and if you loose this signal the butterflies will close.

Depending on the year of the bike it gets it gets a signal from either an ignition coil (grey wire, OSF coil (85 - 89) or yellow wire, OSR coil (90 on)).
I would start by tracing the continuity of these circuits.

 

[veebooster]

Oil sensor is at that front. Heavy acceleration causes oil to slosh to the rear = light comes on. Consider it an accelerometer ha

 

[02GF74]

I agree with mmidnight. It is more likely the rpm signal is causing the vboost to close down instead of the other way round.

The fact tach dropped to 0 yet engine was running seems to indicate problem with the ignition module or bad connection from ignition module.

 

[troncd]

If I understand you correctly the bike will spin up to around 7K r.p.m. and then drop back to around 5K?

Why do you suspect the V Boost as causing the issue?
The V Boost butterflies open at 6K but are not fully open until 8K. If they were closing then I would expect to notice a slight drop in power but not to drop them down to 5K.
You say that you noticed the Tacho dropped out and this is what I suggest you investigate.
The V Boost needs the tacho signal to know when to start to operate and if you loose this signal the butterflies will close.

Depending on the year of the bike it gets it gets a signal from either an ignition coil (grey wire, OSF coil (85 - 89) or yellow wire, OSR coil (90 on)).
I would start by tracing the continuity of these circuits.

Yes that is correct. The bike is an 85. I got it from my dad a few months ago. I started having issues with getting it to start once he gave it to me. eventually it started and its been fine from cold starts since. I was having issues with warm starts which I've understood to likely be a starter issue.

Electrical work is not something I am all that competent with but I can follow basic instruction. I will check the wires from the coil. I am beginning to think my CDI may be faulty and that was some of my original starting issue. Could the CDI being faulty be causing my tach/vboost issue as well? Since my original post, I cannot get the bike to start even with fully charged battery. It just turns and turn but never fires. When last rode it ran perfectly other than the issue with the tach so I don't not suspect carb issues.

Lastly, are the Ricks Motorsports 4 brush starters any good? Or is there another starter I need to consider? Id like to get that taken care of as well while I am working on the bike.

 

[troncd]

I agree with mmidnight. It is more likely the rpm signal is causing the vboost to close down instead of the other way round.

The fact tach dropped to 0 yet engine was running seems to indicate problem with the ignition module or bad connection from ignition module.

Is the igniton module the CDI?

 

[troncd]

As for the starter, I know 4 brush seem to be the way to go. That said, are there any cheaper 2 brush variants that seem to work ok? I am trying to be as economical as possible lol.

Thanks!

 

[troncd]

So I got it started today, rode it around and am confident now the tach is my issue. I took a video of me sitting in neutral and revving it to show what the tach dies. Not sure how to post a video but essentially when revving it it starts jumping around 6000 rpm and will even drop to 0. There is some stumble in the way it runs but not much. I believe the “stumble” is just the fact the tach drops and kills the boost.

So I guess it’s time to research the wiring from the coil to the tach. Is that correct? Are there leads going from both coils that feed the tach?

 

[MaxMidnight]

As for the starter, I know 4 brush seem to be the way to go. That said, are there any cheaper 2 brush variants that seem to work ok?

For potential fix for the starter issue look here. An alternative would be an OE four brush jobbie. Don't know anything about the Rick's Sports motor.

Is the ignition module the CDI?

Yes.

So I guess it’s time to research the wiring from the coil to the tach. Is that correct? Are there leads going from both coils that feed the tach?

Yep, I assume you have a wiring diagram?
I suspect (but you will need to confirm this) that as both tacho and V Boost are affected the issue will be between the ignition control unit (ICU) and coil or (less likely as you also loose power?) from the grey wire to the where they spilt to the V Boost control unit and tacho.

Before you start tracing the wiring also make and break the connectors in the circuit a couple of times. This will clean up the contact area and ensure that you get true continuity and voltage readings.

Check that you have continuity from the ignition control unit to the coil and that it is getting a good + 12 V. feed
On the '85 it is the tacho gets the coil feed from the O/S/F coil grey wire.
There is also the brown +12 V. feed and black earth wires.

From what I have read (others may relate different experiences) when the ICU fails it will often start the bike OK but cuts out when things start to heat up.
I don't recall of one giving the issues you have.

 

[troncd]

For potential fix for the starter issue look here. An alternative would be an OE four brush jobbie. Don't know anything about the Rick's Sports motor.


Yes.



Yep, I assume you have a wiring diagram?
I suspect (but you will need to confirm this) that as both tacho and V Boost are affected the issue will be between the ignition control unit (ICU) and coil or (less likely as you also loose power?) from the grey wire to the where they spilt to the V Boost control unit and tacho.

Before you start tracing the wiring also make and break the connectors in the circuit a couple of times. This will clean up the contact area and ensure that you get true continuity and voltage readings.

Check that you have continuity from the ignition control unit to the coil and that it is getting a good + 12 V. feed
On the '85 it is the tacho gets the coil feed from the O/S/F coil grey wire.
There is also the brown +12 V. feed and black earth wires.

From what I have read (others may relate different experiences) when the ICU fails it will often start the bike OK but cuts out when things start to heat up.
I don't recall of one giving the issues you have.

Thanks! I tried to get out and check some of these things over last night but ran short on time and got frustrated with another no start issue. Which brings me to a new question.

Is it possible that I am have hard starts due to flooded carbs? The bike will often turn over like a charm but never fire and start. Sometimes I will get a loud backfire or some weird noises from the exhaust which leads me to believe there might be a rich or flooded condition. I have drained carb bowls and sometimes right after it will try to fire up or it eventually will. However there is not consistent fuel flow from the carb bowls. Front right drains fine but the other three slowly or barely flow any fuel, even if I fully remove the bowl drain screw. When the bike is running I have no issue with how it runs other than the dropping tach, so I know the cabs are getting fuel...

So in all I have three issues:

1. Hard starts with symptoms described above.

2. The original issue for the post, the dropping tach. I will research this today hopefully.

3. Hard starts when hot. Ill look into the starter things as well but this is last on my list.

 

[daniel.gomariz.hernandez]

LOL glad to know the red light is probably not an issue.

Concerning the connections, where exactly are they located? Is the control box for the VBOost located under the front left cover? The strange thing to me is that The boost starts at 6000 RPM and then suddenly cut off. And when it does so RPMs drop below the starting point of the vboost. Somewhere down to 5000 normally. If vboost suddenly stops working, would the rpms not just drop back to right at or below vboost kicks in?

Left scoop, square black box, closer to driver position.