more voltage, more power

[stilkus]

hey, I have noticed something really weird and I don't know if it's related to the engine being cool or if it's the battery charge.
I would leave the bike connected to an external charger overnight and start it in the morning and after some time when it's warmed up I would run it hard and it feels so powerful. I let it some time in traffic till it heats up normally and the radiator fan kicks in several times, then it will feel waay under-powered till I stop the engine for 20 minutes and run it again to find the beast breathing only for a couple of minutes. is it the engine heating up which reasons for the loss of power or is it the battery gaining some charge from letting it. ( I had some charging issues before and it's fixed now with the alternator giving 13.6v on the meter ) . I am also thinking it might be a carb problem ??

it's a 1992 vmax with 26k miles

has anybody experienced the same on his bike ?

 

[wildweasel_pt]

Check electrical section. This issues has been addressed several times recently...

 

[jfeagins]

Re-test your charging system at idle speed, but this time, make sure the motor is heated up AND your fan is running. If you are getting 13.6v with the fan running, I'd say your charging system is OK.

If the hot voltage, with fan running proves ok, I'd start looking at your fuel system with ventilation in mind. Perhaps it's not getting enough fuel after running a while? Does the pump sound like it's performing correctly? Are your vent tubes free from any obstructions? etc... Could be starving for fuel when hot. I've never had that happen, but have seen many people on this forum discussing their vent issues and frustrations.

 

[MaxMidnight]

Never heard of 'extra' voltage after a charge make it run better.

It will be fuel related to to the high temperatures that is transferred to the carbs when in traffic and (IMHO) nowt to worry about..
Mine doesn't like that scenario either and has some erratic running and poor tick-over when it gets very hot.
Once back on the open road and things start to cool down then all is back to normal.
Do you still have the heat shields in place?

 

[RaWarrior]

Mine would tend to idle poorly when if it got veryhot, as in sitting in traffic and letting the bike turn the fan on (not until 225 or so). After 10-15min of this the fuel was practically boiling in the carbs.

Turning the fan on manually at 190(so it never exceeds 200), solves this problem.


My Yamaha 4 stroke snowmobile had this problem. It piped coolant through the carbs for heating them. On warmer/low snow/slower riding condition it would start to idle poorly and not have much power until the temp dropped again. It was a well known issue, and the solution was to cut the coolant line to the carbs and put a cutoff valve on so flow could be stopped on warmer days when it wasn't needed. This also immediately solved the problem.

 

[stilkus]

this old bike sure has a good community. so many replies in no time

it all makes sense now, I believe it's carb/electricity related. man this is going to be a complicated fix. I will have to reactivate my battery voltage gauge as some local mechanic here cut the wires. I want to know if my bike is responding normally.

I have another question, is the vmax usually vibrating so much on high rpm's as I heard a rumor that v4's are butter smooth with no vibrations at all ?

another thing, if I let the bike idle while on 1st gear, then suddenly hit full throttle what do I expect ? because with my bike it will accelerate normally till 2.5-3kpm then the rear wheel would go crazy spinning till red mark on tacho. is that delay normal or is it indicating something ?

 

[MaxMidnight]

it all makes sense now, I believe it's carb/electricity related. man this is going to be a complicated fix.

I really don't think it is an electrical issue, nor do I think it is a fault but more of a characteristic of the motor when very hot.
I suggest that the best course of action would be to follow Mr Warriors advice and fix a fan switch if it bothers you.
Don't waste time fixing the unifiable.

I heard a rumour that v4's are butter smooth with no vibrations at all.

Not true, I don't think there are any engines (rotary & turbines excepted) that do not produce any vibrations.
All will produce some vibration due to the forces created by the internal components (differences in weight and alignment) and forces due to combustion (all cylinders not producing identical power) not cancelling each other out.
Primary balance forces can be reduced by counterweights on the crankshaft and secondary by the use of a balance shaft.
Vibrations can also be introduced by a rocking couple (for example, if you push down on one side of a see-saw the opposite end goes up.) due to the firing order.
All the above can be reduced and manufacturers also take further steps, such as rubber mounted engine mounts and handle bars to isolate any vibrations that remain.
Aftermarket also offers such things as the 'Bar Snake' and the wonderfully named Vibranator (both of which, in a parallel universe are probably sex toys!) to reduce vibration.

To reduce any vibrations that you have it may be worthwhile inspecting the engine mounts or at the very least, undo and re-torque the removable frame piece bolts and engine mounting bolts (including the cross piece).
Support the motor on a jack and then tighten the bolts in the order specified in the Service manual.

it will accelerate normally till 2.5-3kpm then the rear wheel would go crazy spinning till red mark on tacho. is that delay normal or is it indicating something ?

Yep, it indicates that motors do not produce as much torque low down in the rev range as they do further up.
The torque produced by the motor is bug*er all at idle and rises rapidly as the revs rise and is pretty flat from around 4K up to 8K

 

[stilkus]

I really don't think it is an electrical issue, nor do I think it is a fault but more of a characteristic of the motor when very hot.
I suggest that the best course of action would be to follow Mr Warriors advice and fix a fan switch if it bothers you.
Don't waste time fixing the unifiable.



Not true, I don't think there are any engines (rotary & turbines excepted) that do not produce any vibrations.
All will produce some vibration due to the forces created by the internal components (differences in weight and alignment) and forces due to combustion (all cylinders not producing identical power) not cancelling each other out.
Primary balance forces can be reduced by counterweights on the crankshaft and secondary by the use of a balance shaft.
Vibrations can also be introduced by a rocking couple (for example, if you push down on one side of a see-saw the opposite end goes up.) due to the firing order.
All the above can be reduced and manufacturers also take further steps, such as rubber mounted engine mounts and handle bars to isolate any vibrations that remain.
Aftermarket also offers such things as the 'Bar Snake' and the wonderfully named Vibranator (both of which, in a parallel universe are probably sex toys!) to reduce vibration.

To reduce any vibrations that you have it may be worthwhile inspecting the engine mounts or at the very least, undo and re-torque the removable frame piece bolts and engine mounting bolts (including the cross piece).
Support the motor on a jack and then tighten the bolts in the order specified in the Service manual.



Yep, it indicates that motors do not produce as much torque low down in the rev range as they do further up.
The torque produced by the motor is bug*er all at idle and rises rapidly as the revs rise and is pretty flat from around 4K up to 8K

That was really informative, thanks a lot. My main problem is living in Egypt, people know everything about Hondas, any other motorcycle would be totally strange and that's why I have nobody to consult here. Even the carb float level is an unknown and impossible to set at a mechanic.

 

[DMAN999]

^ Here are some manuals for you:
Factory Service Manual, Owners Manual and Parts Fiche:
https://dl.dropbox.com/u/55030067/VMAX%20Manuals.rar

Haynes Service manual:
https://dl.dropbox.com/u/55030067/Haynes VMax Service Manual.rar


PS
Read through the Tech Section and you should find all the info you need.

 

[stilkus]

^ Here are some manuals for you:
Factory Service Manual, Owners Manual and Parts Fiche:
https://dl.dropbox.com/u/55030067/VMAX Manuals.rar

Haynes Service manual:
https://dl.dropbox.com/u/55030067/Haynes VMax Service Manual.rar


PS
Read through the Tech Section and you should find all the info you need.

thanks, I already had the service manual, but I got really shocked to know that the haynes is 177MB. I believe im downloading it later as I have internet with a quota.

 

[MaxMidnight]

Further to my post regarding the power delivery.

The Max has CV (constant vacuum) carburettors, another reason why you feel what you do.

The throttle slides are opened by the vacuum (pressure drop) caused by the air flowing through the venturi. The volume of air flow is governed by the throttle butterflies.
In the scenario where you suddenly open the throttle the air speed through the venturi will be (relatively) slow thus the vacuum will be low and the slides will rise slowly.
As the revs rise and the airflow increases the vacuum will start to rise quicker thus the slides will rise quicker causing the revs to rise quicker, more vacuum, the throttles rise.....you get the picture?

As there is no direct link between the throttle and carburettor slide (a non electrical fly by wire?) they will only rise as fast as the available vacuum allows.

This is good as ham fisted throttle control is less likely to give a sudden increase in power which, in the wrong circumstances, could dump you on your arse!

If you want a more interesting ride then invest in a set of flat-slides.
In this case, the throttle is directly linked to the slides.
Whap open the twist-grip and the slides will be fully open. To make matters even more interesting they have accelerator pumps which squirt some extra fuel to counter the initial weakness caused by rapid throttle opening.
This makes the acceleration almost instantaneous.
Huge grin factor potential but easy to loose control.

If you want to launch your Max quicker, have a read of this.

 

[stilkus]

Further to my post regarding the power delivery.

The Max has CV (constant vacuum) carburettors, another reason why you feel what you do.

The throttle slides are opened by the vacuum (pressure drop) caused by the air flowing through the venturi. The volume of air flow is governed by the throttle butterflies.
In the scenario where you suddenly open the throttle the air speed through the venturi will be (relatively) slow thus the vacuum will be low and the slides will rise slowly.
As the revs rise and the airflow increases the vacuum will start to rise quicker thus the slides will rise quicker causing the revs to rise quicker, more vacuum, the throttles rise.....you get the picture?

As there is no direct link between the throttle and carburettor slide (a non electrical fly by wire?) they will only rise as fast as the available vacuum allows.

This is good as ham fisted throttle control is less likely to give a sudden increase in power which, in the wrong circumstances, could dump you on your arse!

If you want a more interesting ride then invest in a set of flat-slides.
In this case, the throttle is directly linked to the slides.
Whap open the twist-grip and the slides will be fully open. To make matters even more interesting they have accelerator pumps which squirt some extra fuel to counter the initial weakness caused by rapid throttle opening.
This makes the acceleration almost instantaneous.
Huge grin factor potential but easy to loose control.

If you want to launch your Max quicker, have a read of this.

very informative, I got the whole idea and I think that's why there's this annoying bobbing low pitched sound when I open the throttle at a low speed/high gear. It's basically the vaccum caused by the piston which creates a -ve pressure causing the diaphragms to squeeze in more fuel.
I checked the link you posted but it says nothing about flat diaphragms, it's all about launching your max professionally and getting the most of it in runs. I would like you to explain more about the flat diaphragms and if I remove the diaphragm spring and stop it from moving will this give the same result ?

 

[MaxMidnight]

Not quite right.
The purpose of the diphragum is to provide a flexible seal between the throttle slide and the carburetor body thus creating a sealed chamber.

As the chamber is sealed any vacuum within it will lift the throttle slide.
When the slide rises it pulls the needle up, which passes through the main jet.

Also note that the drop in pressure within the venturi that creates the vacuum above the throttle slide and which causes it to rise will also pull fuel from the float chamber and up through the main jet.
Because the needle is tapered the higher it rises the more fuel will be able to flow through the main jet.

If you compare a standard needle with that of a Stage 1 or Stage 7 you will note that ther is a difference in the degree of taper.

Thus for the same lift of throttle slide a differnt volume of fuel will be able to flow through the main jet.

Removing the spring that sits in the diapragm vacuum chamber is a VERY bad idea!
The spring has two purposes:
1) It controlls the rate at which the throttle slide rises - without tyhe spring as soon as you introduces any vacuum above the throttle slide it would fully lift so it would effectively be eithr on or off.
2) When you close the hrottle and the vaccum dissipates it ensures that the sides will return to rest (for a closed throttle) or to wherever the vaccum dictates for a given throttle opening.

Not sure what you mean by flat diapragms - I referred to flat slides.
Wheras the the throttle sides in OE Max carbs are round the flat slides are, er, flat.
The point I was trying to make here was the difference in how the slides are lifted.
CV carburettors use a vacuum wheras flat slides use a cable.

Hope that makes things a little clearer?

 

[davidon]

Further to my post regarding the power delivery.

The Max has CV (constant vacuum) carburettors, another reason why you feel what you do.

The throttle slides are opened by the vacuum (pressure drop) caused by the air flowing through the venturi. The volume of air flow is governed by the throttle butterflies.
In the scenario where you suddenly open the throttle the air speed through the venturi will be (relatively) slow thus the vacuum will be low and the slides will rise slowly.
As the revs rise and the airflow increases the vacuum will start to rise quicker thus the slides will rise quicker causing the revs to rise quicker, more vacuum, the throttles rise.....you get the picture?

As there is no direct link between the throttle and carburettor slide (a non electrical fly by wire?) they will only rise as fast as the available vacuum allows.

This is good as ham fisted throttle control is less likely to give a sudden increase in power which, in the wrong circumstances, could dump you on your arse!

If you want a more interesting ride then invest in a set of flat-slides.
In this case, the throttle is directly linked to the slides.
Whap open the twist-grip and the slides will be fully open. To make matters even more interesting they have accelerator pumps which squirt some extra fuel to counter the initial weakness caused by rapid throttle opening.
This makes the acceleration almost instantaneous.
Huge grin factor potential but easy to loose control.

If you want to launch your Max quicker, have a read of this.

MM

I have the same carbs as you and when I go WOT it bogs down a little before it takes off..did you change your accelerator pumps?

 

[stilkus]

MM

I have the same carbs as you and when I go WOT it bogs down a little before it takes off..did you change your accelerator pumps?

I only checked one accelerator pump and I found so much difficulty in putting it back again as the rubber diaphragm was a little bit expanded for the rim, but with a little bit heat the rubber shrunk again and it was all fine.

I am a little bit curious if there's another way I can check for those pumps without the need of taking them apart ?

 

[stilkus]

Not quite right.
The purpose of the diphragum is to provide a flexible seal between the throttle slide and the carburetor body thus creating a sealed chamber.

As the chamber is sealed any vacuum within it will lift the throttle slide.
When the slide rises it pulls the needle up, which passes through the main jet.

Also note that the drop in pressure within the venturi that creates the vacuum above the throttle slide and which causes it to rise will also pull fuel from the float chamber and up through the main jet.
Because the needle is tapered the higher it rises the more fuel will be able to flow through the main jet.

If you compare a standard needle with that of a Stage 1 or Stage 7 you will note that ther is a difference in the degree of taper.

Thus for the same lift of throttle slide a differnt volume of fuel will be able to flow through the main jet.

Removing the spring that sits in the diapragm vacuum chamber is a VERY bad idea!
The spring has two purposes:
1) It controlls the rate at which the throttle slide rises - without tyhe spring as soon as you introduces any vacuum above the throttle slide it would fully lift so it would effectively be eithr on or off.
2) When you close the hrottle and the vaccum dissipates it ensures that the sides will return to rest (for a closed throttle) or to wherever the vaccum dictates for a given throttle opening.

Not sure what you mean by flat diapragms - I referred to flat slides.
Wheras the the throttle sides in OE Max carbs are round the flat slides are, er, flat.
The point I was trying to make here was the difference in how the slides are lifted.
CV carburettors use a vacuum wheras flat slides use a cable.

Hope that makes things a little clearer?

okay, its my bad, I read a little bit fast and as the topic was the diaphragms that's why I thought flat slides would have something to do with the diaphragms. Another thing which you helped a lot with is the needle at the end of the diaphragm cup, I always thought the fuel pic behind the diaphragm had something to do with the fuel emerging at the tip of the needle and the diaphragm compressing it :bang head:

since you know so much about carbs I have something wrong with one of the A/F screws but I've tried many different settings without the feel of a change, is this screw responsible for the idle mixture or would it also affect the mid/high rpm range ?

 

[MaxMidnight]

MM

I have the same carbs as you and when I go WOT it bogs down a little before it takes off..did you change your accelerator pumps?

MIkuni TDMR's?
I've-never had to touch the accelerator pumps, mine takes off like a scalded cat. Have to be a bit careful when pulling away as it's easy to over gas it.
I would have thought that there is an adjustment to alter the volume of fuel delivered by the pumps? May be worthwhile investigating.
Have found something on the HSR flat slides - not sure how similar they are to the TDMR's but I guess the principals are similar?

since you know so much about carbs I have something wrong with one of the A/F screws but I've tried many different settings without the feel of a change, is this screw responsible for the idle mixture or would it also affect the mid/high rpm range ?

The idle mixture is present all trough the rev range but the effect on the air/ fuel ratio reduces as the main jet flows more fuel with increase throttle openings.

It is quite common for the idle circuit to get blocked - doesn't seen to be a big issue in Europe, more in the States.
It may be worthwhile running some carb cleaner through first to see if that clears it/ them.

If that fails then you are into doing either the 'Peashooter' or 'Shotgun'.