MB100 development

[Grumph]

[QUOTE=Hilleye;1130230943

Do you think a length of fuel hose stuck over the main jet extending down to the bottom of the float bowl to act as a syphon might work?[/QUOTE]

NO - you need to increase fuel flow into the bowl - get Mike to drill out the passages as has been suggested - or just run more fuel in the bloody tank.....

[sidwyz]

Symptoms are after coming out of any sort of extended period lent over, particularly to the right hand side, about 100 - 200m further down the track the bikes power dies right off. By this I mean that the only thing keeping it running is the momentum of the bike, if I pulled the clutch in the motor would stall. It stays this way for what seems like 2 - 3 secs then clears and the bike is off again. At Ruapuna it's doing this after the long right hander out of the in field, which hits coming out of the right hander that follows it before the lefts that lead into the dipper. It's also doing it after the dipper and is hitting right as you go into the sweeper. It has only done this since the bike was dyno tuned and a bigger main jet was installed (no other changes were made).

I had problems with fuel supply but only at Taupo, my bike would do a lap or two then starve of fuel, miss fart and die.

I thought it may have been because I was lent over for a lot longer with minumum fuel in the tank and wide open throttle for so long down the straight and not enough time to fill the bowl, so put heaps in, still did it.

After looking at everything it was suggested to me maybe I was getting a fuel lock in the tank,
The next race I undid the fuel cap evertime I was going down the straight.

All of a sudden the problem was gone, I now have another fuel cap with a vent for taupo.
Worth a look.

[speedpro]

Leaning will have nothing to do with it. Force on a bike is always more or less through the centre ine of the bike to the contact patch of the tyres. If it isn't then you are about to or have just crashed.

I like the suggestion above, having suffered the exact same problem myself.

[Hilleye]

NO - you need to increase fuel flow into the bowl - get Mike to drill out the passages as has been suggested - or just run more fuel in the bloody tank.....

Grumph, I've brimmed the tank and it still happens.

I have now drilled out the passages. Fuel passage taken from approx 3.5mm to 4.0mm (30% increase in flow area if my maths are right). Float valve taken from 2.5mm to 3.0mm (44% increase in flow area), could possibly go bigger, because this is the limiting factor now, if someone could tell me what the max size it can be and still seal properly. Float valve was about 3.4mm - 3.5mm across so was reluctant to open it up anymore. Opted for the conservative approach to begin with will try it on the track and see how it goes before going crazy.

I had problems with fuel supply but only at Taupo, my bike would do a lap or two then starve of fuel, miss fart and die.

I thought it may have been because I was lent over for a lot longer with minumum fuel in the tank and wide open throttle for so long down the straight and not enough time to fill the bowl, so put heaps in, still did it. After looking at everything it was suggested to me maybe I was getting a fuel lock in the tank, the next race I undid the fuel cap evertime I was going down the straight. All of a sudden the problem was gone, I now have another fuel cap with a vent for taupo. Worth a look.

The tank is vented, but I had thought maybe I was getting a fuel lock in the tank so I did check it. Filled the tank to the brim and drained through the fuel line to see if there was any interuptions with supply. There wasn't any problems at rest, but that doesn't mean that it couldn't be happening whilst on the track, so I'll check it out. I might have to increase the size of the existing vent hole in the cap, it may be insufficient or getting covered as the bike is lent over and it may be enough to create the fuel lock. Unlikely though due to the nature of the force acting on the fuel in the tank during cornering which should be trying to push it towards the lowest point in the tank (i.e the outlet pipe).

You don't think it's weird that it always happens in the same places on the track though?

[husaberg]

Grump, I've brimmed the tank and it still happens.

I have now drilled out the passages. Fuel passage taken from approx 3.5mm to 4.0mm (30% increase in flow area if my maths are right). Float valve taken from 2.5mm to 3.0mm (44% increase in flow area), could possibly go bigger, because this is the limiting factor now, if someone could tell me what the max size it can be and still seal properly. Float valve was about 3.4mm - 3.5mm across so was reluctant to open it up anymore. Opted for the conservative approach to begin with will try it on the track and see how it goes before going crazy.



The tank is vented, but I had thought maybe I was getting a fuel lock in the tank so I did check it. Filled the tank to the brim and drained through the fuel line to see if there was any interuptions with supply. There wasn't any problems at rest, but that doesn't mean that it couldn't be happening whilst on the track, so I'll check it out.

You don't think it's weird that it always happens in the same places on the track though?

Some real simple maths here how many hp did a TZR250 have well i guess it is a lot more than 2x the the output of this bike.

Std the TZRs have quite a large inlet pipe on the carb.Thus the fuel pipe way larger than the normal VM Mikuni.

Your tank has a very low outlet so i would dummy up another tank a take a couple of laps and see what happens.

I would also put an foam air filter on it.

The other thing is are any of the fuel lines hard?
Looking on the last page i am unsure why the routing of the fuel line is not directly from the tap to the inlet of the carb even if you have to do a hard bend or put in a brass bend i think it would be better than the two you have tried.

Last one can you try the inlet manifold of mine from the box . The the modded rd250 one. Although it does look a bit like your engine may be on more of an angle than it would be on in the std chassis.

[Hilleye]

Some real simple maths here how many hp did a TZR250 have well i guess it is a lot more than 2x the the output of this bike.

Agreed, but they only run a 210 main jet. This bike is running a 350 (lets not get into whether it should or not, dyno says it should so it does, otherwise it runs so lean it'll seize). Remember the bike fueled fine before the increase in jet size and it was running a 260 main jet then.

Std the TZRs have quite a large inlet pipe on the carb. Thus the fuel pipe way larger than the normal VM Mikuni.

Yup, roughly something in the vicinity of 3.5mm in diameter.

Your tank has a very low outlet so i would dummy up another tank a take a couple of laps and see what happens. .

Low outlet is true, but tank still sits high enough to generate good fuel pressure. If the problem persists this will be my next option to try and sort it.

The other thing is are any of the fuel lines hard?

Fuel lines are all brand new. As is fuel filter.

Looking on the last page i am unsure why the routing of the fuel line is not directly from the tap to the inlet of the carb even if you have to do a hard bend or put in a brass bend i think it would be better than the two you have tried.

Although I haven't shown it I've also previously routed the fuel line as you have described (and with just the tap and no fuel filter). Problem is still there, weirdly if anything the more direct the routing the worse the problem seems to be on the track (could be my imagination though).

A right angle bend coming off the fuel outlet from the tank and one to get a better angle into the carb inlet might be beneficial so I'll look at these as well to try and keep the entire fuel line above the level of the carb inlet.

[husaberg]

Agreed, but they only run a 210 main jet. This bike is running a 350 (lets not get into whether it should or not, dyno says it should so it does, otherwise it runs so lean it'll seize). Remember the bike fueled fine before the increase in jet size and it was running a 260 main jet then.




Low outlet is true, but tank still sits high enough to generate good fuel pressure. If the problem persists this will be my next option to try and sort it.


Although I haven't shown it I've also previously routed the fuel line as you have described (and with just the tap and no fuel filter). Problem is still there, weirdly if anything the more direct the routing the worse the problem seems to be on the track (could be my imagination though).

A right angle bend coming off the fuel outlet from the tank and one to get a better angle into the carb inlet might be beneficial so I'll look at these as well to try and keep the entire fuel line above the level of the carb inlet.

Wait a min

Are you saying there was no problem until you upped the main jet?
PS you will get away with a smaller main with an air filter
next yes one fuel pressure varies according to height the variance is about 1.42 psi/meter fuel in tanks slosh around though.

[F5 Dave]

I think with the passages increased as you have should nail it. Float will need to be reset so it doesn't flood as it will sit further in of course.

btw TZR250 1KT =45hp, or 22.5 per cyl. This only takes a airfilter-less less efficient engine to make this borderline.


So it was a TZR carb with power jet? Think so. Same body carb w/o pj is what my H ran. Off KR250. Ran the button type jets rather than the longer hex jets. They didn't extend down into the float very far, hence the extn. Fuel line on the jet won't seal enough to be used as a straw & could slip causing a starvation. I'd try it as is & also make an extension jet to jam in if you still have issues.

btw mine always used to run out a bit before the right hander after the hairpin at 'puna, sometimes exiting the hairpin.

[Hilleye]

Wait a min, are you saying there was no problem until you upped the main jet?

Yup, that's exactly what I'm saying.

So it was a TZR carb with power jet? Think so. Same body carb w/o pj is what my H ran, off a KR250. Ran the button type jets rather than the longer hex jets. They didn't extend down into the float very far, hence the extn.

It's the TZR carb with the power jet. Running the longer hex type jet.

[speedpro]

Take the float bowl off, connect the fuel line, hold an ice cream container under the carb, turn on the fuel tap. I'd be very surprised if it flows less than the motor could possibly use in your wildest dreams. I've got a 430 main in my bike which has been fitted on the dyno. No other mods have been made to the carb.

[husaberg]

I think with the passages increased as you have should nail it. Float will need to be reset so it doesn't flood as it will sit further in of course.

btw TZR250 1KT =45hp, or 22.5 per cyl. This only takes a airfilter-less less efficient engine to make this borderline.




So it was a TZR carb with power jet? Think so. Same body carb w/o pj is what my H ran. Off KR250. Ran the button type jets rather than the longer hex jets. They didn't extend down into the float very far, hence the extn. Fuel line on the jet won't seal enough to be used as a straw & could slip causing a starvation. I'd try it as is & also make an extension jet to jam in if you still have issues.

btw mine always used to run out a bit before the right hander after the hairpin at 'puna, sometimes exiting the hairpin.

Dave Hillies engine made 14hp yes 14 hp

The stock tzr carbs can flow more than enough petrol to handle considerably more power than 22.5 they are not even close to borderline.
this engine seems to a have a list of problems.
Was it raced sucessfully and did it seize before it was put on the dyno to sort out the fueling.
A while back i posted some mods for the tzr the race kit mods.
what does the plug look like as well.

[Hilleye]

Hillies engine made 14hp yes 14 hp. The stock tzr carbs can flow more than enough petrol to handle considerably more power than 22.5 they are not even close to borderline. What does the plug look like as well.

I agree the MB isn't making anywhere near what a TZR makes, but the MJ size it's running is a lot bigger, which indicates it's a lot less efficient than a TZR. Maybe we should consider what the carb is trying to flow, which seems to be a bit more than a standard or even race TZR (which runs a 250 MJ) not just how much power it's making.

This engine seems to a have a list of problems. Was it raced sucessfully and did it seize before it was put on the dyno to sort out the fueling.

It would appear the reason it seized was because it was probably running a critically lean fuel mix, so it wasn't having any of the fuelling issues because the MJ was smaller. The problems are being resolved slowly, I believe I'm down to the fueling issue and the bike should be on song (albeit a rather peaky gutless song at present).

A while back i posted some mods for the tzr the race kit mods. What does the plug look like as well?

I'd show you the plug, but the bike wasn't running properly for long enough last weekend for it to mean anything. I'm working through the proddie racer mods on the other carb and will chuck it on next time I'm at the dyno to see if it makes a difference. You'll also be pleased to hear a pod filter is on order and should arrive by the end of the week.



Here's a picture of the petrol cap. The positioning of the venting holes (red circles) is just stupid, they're outside the the tank seal, so the tank is venting atmosphere to atmosphere, which obviously achieves very little. I assumed there was one in the centre as well, but compressed air comfirmed there wasn't (there is now though and the other ones will be sealed up to prevent the fuel just washing out on to the top of the tank). However even without the new vent there was still seepage of fuel mix from under the tank cap to top of the tank, so I doubt it's airtight which is why I don't see any fuel locking when draining the tank from full at rest. It seals better than when I first got it though, the top of the tank was slick with fuel mix after a race, ridiculous.

[gav]

Is a Keihen carb off an NSR250 worth trying? They are angled so the float bowl sits in more level.

[husaberg]

I agree the MB isn't making anywhere near what a TZR makes, but the MJ size it's running is a lot bigger, which indicates it's a lot less efficient than a TZR. Maybe we should consider what the carb is trying to flow, which seems to be a bit more than a standard or even race TZR (which runs a 250 MJ) not just how much power it's making.

The mainjet will need to be bigger than a std TZR not because of power but because as it is it runs without a filter.

It would appear the reason it seized was because it was probably running a critically lean fuel mix, so it wasn't having any of the fuelling issues because the MJ was smaller. The problems are being resolved slowly, I believe I'm down to the fueling issue and the bike should be on song (albeit a rather peaky gutless song at present).

Some of the other reason i think it runs not right are as a result of an odd pipe overly long inlet manifold and err... unknown porting no offense to its creator intended.
here is the link to a race kit jetting mods not that i think it needs them.
http://edj.net/2stroke/tzr/racingmanual/
http://www.classicyams.com/technolog...g-2ma-1kt.html

are you able to put in the other reed valve and manifold.
I just reread your last post is the powerjet std ie not blocked have you tried running the bike without a mainjet to see where the fueling issue is?

[Hilleye]

However even without the new vent there was still seepage of fuel mix from under the tank cap to top of the tank, so I doubt it's airtight which is why I don't see any fuel locking when draining the tank from full at rest. It seals better than when I first got it though, the top of the tank was slick with fuel mix after a race, ridiculous.

I stand corrected. There is actually quite a good seal with the cap and the tank can be negatively pressurised to well over a complete atmosphere (positively pressurised not anywhere near as much, barely 0.2 bar, which is possibly why a little seepage occurs when it sloshes against the cap under braking or the like, but no air can get in). Unsure why this possible fuel locking didn't present itself at rest when allowing the tank to just drain out. Opening the cap didn't increase flow speed during these tests either. Fixed now anyway, tank is now properly vented and another possible cause is eliminated.

Fuel will flow from the tank like the water over Niagara Falls. The carb can now flow Niagara Falls type volume with the enlarged fuel passages. Things are looking up.