Dragstar 125 Power

[Markyboy27]

..following on from advice i read o this site i went in search of the Petrol Tank overflow valve which is supposed to restict airflow through the tank (creating a vacuum and possible flat-spots on the power curve).

Here's how it's done:

Remove pillion seat (one nut)

Remove seat (2 allen bolts)

Remove single Petrol tank securing bolt (or 2 separate bolts on underside of frame) and lift rear of tank slightly to loosen it.

Slide tank backwards about 2 inches (so forward mount slides off rubber seat mount)

Pull off rubber seat

Remove 8mm bolt securing black plastic cover protecting filter area

Remove left hand plastic cover by unclipping top joint (which joins both plastic panels from LHS & RHS together)

Follow tank breather pipe from where it hangs down to where it joins the black plastic valve itself.

Undo the bolt which secures the filter clip to the frame, thus releasing the valve.

Remove both hose clips and pull hoses off valve, allowing valve to be removed.

With valve removed you can now seek a junction that will re-join the 2 hoses together but without the one way valve.

What I noticed immediately was that the valve operates by way of a ball bearing that is free to move within the valve body, and naturally sits in the base of the valve thus blocking the pipe. This bears out the theory that it would indeed restrict air-flow and hinder air from entering the tank when the ball is engaged in either end of the valve (although you'd hope the free movement of the ball would allow free passage of air).

I presume the proof is in the pudding in that if there's an improvement in performance then it's probably worth-while, which is what i'm about to do.

I'm still suspicious that a valve is indeed needed, but agree that probability of the bike falling over are very low, and the benefit of decreasing rpm at cruising speed will indeed extend the life of your engine.

Hope this helps you Dragstar riders, i'll let you know if it runs better as soon as i get it back on the road.

Mark.

[Markyboy27]

Mod Update:

Bought a 6mm plastic right-angle elbow connector from the local automotic parts retailer (£1.99) and it fitted perfectly, although the clip that secured the original valve to the frame is too large in diameter, so a piece of tubing was needed to pad it out and secure the hose to the frame.

All in all it worked well with regard to the physical replacement, and for 2 quid it seems worth the effort especially asit only takes 15 minutes to reinstate the original with no damage to any parts.

[Airhead]

You seem to be going to an awful lot of trouble to overcome this supposed vacuum in the tank. After all this I hope it works for you but I have my doubts. But whatever you do, Dont be tempted to just run down your fuel level, open the filler cap and stick a rag in there to prove or disprove the theory!

[oldtimer]

for fear of upsetting any one again this is just advice,The elements of internal combustion engines are; correct fuel/air ratio, spark at right time, adequate cylinder compression.The main points about fuel tanks are these: they need a way of letting fuel out to the carbs, and they need a way to let air in as the fuel goes out, to avoid a vacuum buildup in the tank. We will call this "venting" or "breathing."

The tank should have a "reserve" function that will allow you to access an additional supply of fuel when you start to "run out of gas" and thus allow you a few more miles of driving to find the nearest gas station.

The fuel runs downhill from the tank through fuel lines to the carbs. Some models have one petcock and some two, but the method is the same. One petcock just requires a splitter and two pipes to feed the carbs.

The petcocks are vacuum operated petcocks. This means that they have a little diaphragm and valve set-up, which responds to engine vacuum and allows fuel to flow only when the engine is running and supplying vacuum. This is how things work when the petcock lever is set to the "on" or "run" setting. So we see that the "on" setting is actually the "off" setting when the engine is not running. So if the engine quits for any reason (as in a "down" situation), the petcock(s) will automatically close and prevent the fuel from flowing out. by removing the valve this wont work

These petcocks also have two other lever settings:

The "prime" setting bypasses the vacuum function and allows fuel to flow at all times, even when the engine is stopped. The purpose of this setting is to allow the carb float bowls to be filled when the engine is not running. Note that if you run your petcock(s) on the prime setting all the time, you lose the safety feature provided by the vacuum petcock. Note also that on this setting, fuel is prevented from flowing out through the carbs, into cylinders, etc.) only by the float valves in the carbs, which close when the carbs are full. Should one of these float valves stick open or leak, you then get flooding through that carb.

The "reserve" setting is used to access an additional amount of fuel when you start to run out. Here is how this works. These petcocks have inlet towers, which stick up into the tank. In the "on" position, fuel flows down to the petcock through an opening high on the tower. So when you "run out of fuel" you actually have some more fuel sitting in the bottom of the tank, which lies below this high inlet. When you turn the petcock lever to "reserve," a lower inlet near the bottom of the tower opens, so you can gain access to this last bit of fuel in your tank.if the valve is removed you may find you are unable to use your reserve petrol

All these older tanks breathe through venting passages in the gas cap. When the bike goes over, and a little ball bearing rolls along a little passage in there and blocks the flow of fuel through this vent.

by removing the what ever you wish to call it one way valve ,non return valve you may in the short term gain some advantages but in the long term suffer some dis advantages and as you say you can always put it back good luck with your experiments

[Markyboy27]

..i'm typing this from my hospital bed, a knitting needle gripped in my teeth stabbing the keys... the drugs are working now and the pain from my burns are getting easier. Unfortunately the doctors told me not lay off the masturabation until the skin has grown back on my cock, although the upside is at least I can cancel my internet subscription.

Good advice to all: Don't smoke whilst riding with a rag stuffed in your petrol filler cap, although it's cheaper than a crack & sack wax....

Seriously though, I wanted to try the mod more to disprove it than anything else... was always suspicious it was a fruitless effort and in truth it was. Just took a run down the A6 (downhill section near Barton, Bedfordshire) and not much difference (still capped at a mind-numbingly screaming 70mph) so will be reinstating the valve this afternoon.

Still looking for different sized sprockets in pursuit of the magic 70mph cruising speed that doesn't make your ears bleed.

Mark.

[Airhead]

..i'm typing this from my hospital bed, a knitting needle gripped in my teeth stabbing the keys... the drugs are working now and the pain from my burns are getting easier. Unfortunately the doctors told me not lay off the masturabation until the skin has grown back on my cock, although the upside is at least I can cancel my internet subscription.

Good advice to all: Don't smoke whilst riding with a rag stuffed in your petrol filler cap, although it's cheaper than a crack & sack wax....

Wasnt me your honour...Never said anything

Seriously though, I wanted to try the mod more to disprove it than anything else... was always suspicious it was a fruitless effort and in truth it was. Just took a run down the A6 (downhill section near Barton, Bedfordshire) and not much difference (still capped at a mind-numbingly screaming 70mph) so will be reinstating the valve this afternoon.

Still looking for different sized sprockets in pursuit of the magic 70mph cruising speed that doesn't make your ears bleed.

Mark.

Hmm well what a surprise...NOT

[Markyboy27]

Wasnt me your honour...Never said anything

Hmm well what a surprise...NOT

Too late my old friend, right at this moment there's a black Humma pulling up at your door with 2 heavy's ringing your bell. Claims Direct accepted my case and you're going down for a long stretch.. guilty as charged: Wilfull Misinformation resulting in ABH.

Although if you're prepared to settle out-of court then i'll accept a set of Highway Hawk slash-cut drag pipes & we'll say no more... you know it makes sense.

[Airhead]

You seem to be going to an awful lot of trouble to overcome this supposed vacuum in the tank. After all this I hope it works for you but I have my doubts. But whatever you do, Dont be tempted to just run down your fuel level, open the filler cap and stick a rag in there to prove or disprove the theory!

Edit button....................What edit button

..i'm typing this from my hospital bed, a knitting needle gripped in my teeth stabbing the keys... the drugs are working now and the pain from my burns are getting easier. Unfortunately the doctors told me not lay off the masturabation until the skin has grown back on my cock, although the upside is at least I can cancel my internet subscription.

Good advice to all: Don't smoke whilst riding with a rag stuffed in your petrol filler cap, although it's cheaper than a crack & sack wax....

Mark.

Wasnt me your honour...Never said anything

Too late my old friend, right at this moment there's a black Humma pulling up at your door with 2 heavy's ringing your bell. Claims Direct accepted my case and you're going down for a long stretch.. guilty as charged: Wilfull Misinformation resulting in ABH.

Although if you're prepared to settle out-of court then i'll accept a set of Highway Hawk slash-cut drag pipes & we'll say no more... you know it makes sense.

No its all been a BIG mistake, HEeeelp...Call them off or i'll sue

[Markyboy27]

No its all been a BIG mistake, HEeeelp...Call them off or i'll sue

..no, you can't sue, coz i am, and I said it first.

[Airhead]

..no, you can't sue, coz i am, and I said it first.

You must have mis-interpreted my advice, hope it mends soon, i'm sure the nurses will take care of your every need..

[Guest Exupnutta]

Too late my old friend, right at this moment there's a black Humma pulling up at your door with 2 heavy's ringing your bell.

They're only ringing the bell to ask to use the phone, coz the Hummer broke down

LMAO... funny thread

[Guest Exupnutta]

Still looking for different sized sprockets in pursuit of the magic 70mph cruising speed that doesn't make your ears bleed.

Mark.

Perhaps a faster bike would do the trick

If you're complaining about power now.. if you change the sprockets for top end speed, it will be even worse

[Markyboy27]

Perhaps a faster bike would do the trick

If you're complaining about power now.. if you change the sprockets for top end speed, it will be even worse

...not botherered about power (wouldn't have bought an XVS125 if I was), just hate thrashing it's nuts off at 65mph. I love the laid-back relaxed riding attitude of the Dragstar range, it keeps me out of trouble. I just need to lower the RPM at cruising speed.

[Guest Exupnutta]

...not botherered about power (wouldn't have bought an XVS125 if I was), just hate thrashing it's nuts off at 65mph. I love the laid-back relaxed riding attitude of the Dragstar range, it keeps me out of trouble. I just need to lower the RPM at cruising speed.

Sorry Mark, didn't mean it in an unkind way.

I have the same problem with THIS.

It runs at about 4,5K rpm at 70mph. The red line is 6.5k.

Nothing for me to do but sell it. Gutted, coz I absolutely love it.

Strongest car ever built... just look at it now after 20 years

[Markyboy27]

Sorry Mark, didn't mean it in an unkind way.

I have the same problem with THIS.

It runs at about 4,5K rpm at 70mph. The red line is 6.5k.

Nothing for me to do but sell it. Gutted, coz I absolutely love it.

Strongest car ever built... just look at it now after 20 years

..wow, just test-riden it with a 1-tooth larger front sprocket fitted... did the trick perfectly !

Now i get 30 out of Second gear, 45 out of 3rd, 60 out of 4th, and... not enough power to test 5th to the max !

So as I thought, a single additional tooth on the front gives you an extra 10mph on the top end of the range but only if you can get up there. This is fine for my purposes as it's mostly flat where i comute so cruising at 60 without ringing the nuts off the engine is fine.

I did buy 2 sprockets (the second beng 2 teeth bigger) but i'm reluctant to fit the bigger one as the cost will probably severely outweigh the benefit (unless i can find a continuous downhill route on a fine day with no wind !!).

[Markyboy27]

Wasnt me your honour...Never said anything

Hmm well what a surprise...NOT

..wow, just test-riden it with a 1-tooth larger front sprocket fitted... did the trick perfectly !

Now i get 30 out of Second gear, 45 out of 3rd, 60 out of 4th, and... not enough power to test 5th to the max !

So as I thought, a single additional tooth on the front gives you an extra 10mph on the top end of the range but only if you can get up there. This is fine for my purposes as it's mostly flat where i comute so cruising at 60 without ringing the nuts off the engine is fine.

I did buy 2 sprockets (the second beng 2 teeth bigger) but i'm reluctant to fit the bigger one as the cost will probably severely outweigh the benefit (unless i can find a continuous downhill route on a fine day with no wind !!).