Petcock fuel flow, to little ?
 

An idea came up today to the lean condition with open airbox/open exhaust, (someone far smarter than me ) Is it possible the diaphragm is not providing enough fuel to the carbs ? Why can't I block the vaccum line that opens the fuel flow, toss out the rubber diaphragm, make a plate to close the bottom of the petcock and just have a fuel on/off ? If the floats are set properly, they shut off fuel flow .

anyone with a concept of what I am suggesting agree / or not ?

thanks
Rock
I know most results are best with stock air box, but this is a hobby, and I like the learning process .

Well... There is no "why not"...;) There is only do, or don't do...

Buuut... You will need to figure out a new fuelvalve that has a reasonable flow for the bike, and get everything mounted up tight and good...

And then I suspect you still might need to re-jet... So there might be benefits, but they are behind a ton of work... And while you are at it why not fit a fuel pump instead?

I know, I'm one to talk with my build history... I don't exactly pick easy options... Oh, and yes, I'm contemplating fitting a Supercharger (Yeah, I know I'm bonkers... )

ON the rvf400 website there is talk of a similar mod - bypassing the vacuum petcock. apparently with some airbox/engine/exhaust mods on that bike the pull is insufficient to ensure adequate flow to the carb bowls at higher rpm's. the cylinders are tiny (4 cylinder 400) and even balancing the carbs doesn't generate much pressure in the manometer. I can't imagine our bikes would suffer something similar, but you could test that by measuring the pressures pre-post mod using a balancer. If interested you could search there and see how comparable the vacuum petcock is if you're interested. I'm sure there are other sites as well.

http://www.400greybike.info/newforum/index.php

Yeah interesting, Thanks both for the input. It occured to me that I have seen reports of VTR motors, built ,with 120 hp or there abouts. If the stock petcock would fuel that much hp, why would it not feed my less demanding engine.? I live 20 minutes from the Factory Pro headquarters,
so thats is who I need to talk with, in "the day" they too thought the VTR was Hondas dream machine for the racing future. They should have some data available, and they are as good of customer service the world can offer.... I think they are open Monday, I still need to re-jet , and the next
step up could be the one .. I am off to find calipers/mc/


tweety,
a super charger ?, whew, what a ride :)

The reason behind... I was given the opportunity to take this bike for a spin...

http://www.youtube.com/watch?v=EDylS0RbriA

And yes, the bike is as bonkers as you might think... I did a powerwheelie in 4'th gear 70+ mph... Just twisted it a bit to hard on upshift and it lofted the front quite easily... ;)

According to the owner it's possible to loft the front in 5'th gear on pure grunt and 6'th takes only a bit of clutch to loft it... I didn't have the balls to try that though... :eek:

The Factory Pro Tech I spoke with on Monday tells me there expirience with VTR1000 does not include open airbox, but if this was a track bike there could be gains made. He said they stocked main jets to 250 :eek: for the Hawk carbs. The diaphrapm in the petcock is not a likely cause,in this case, and I can eventually find a main(s) that will work .He told me, simply put, once I find the correct main, I can start fiddling with the needles to get some mid range torque back if there off a setting or two. I think I have a plan :)

Thanks for the input

I have a fuel pump fitted and still encountered problems with running a modified intake. When I went back to stock the problems were fixed.

Factory Pro are right - if you want a track bike then you can do it. When part throttle is not so important you can open up the intake and use a bigger airfilter. I did this and ran 205 mains and 50 pilots (dyno tuned) in my bike. The bike was awesome at WOT but for street riding it surged a bit on the mid range. I could not dial it out. The stock airbox and a normal filter (K&N) fixes it. Now I run 170 mains and 45 pilots. Big difference.

My guess is that the changed airflow cause by a modified airbox upsets the carb slides. No jetting change I tried made any difference. I tried a few variations of slide holes, and was contemplating some spring changes, but in the end gave up on the idea.

[quote=mboe794;233520]I did something very much like this when my diaphragm developed a tear. I removed the diaphragm and cut the center out of it so that all I really had left was something that resembled an o-ring and put it back in. Then blocked the two nipples on the petcock with one hose connecting the two and plugged the vacuum line. Now all I have is manuel on or off.

This wasn't an effort to gain any kind of performance. Just a quick and cheap solution.

Shayne, just the info I was looking for, I am all but convinced the stock box works very well, but in the effort of more top end for little work, we surge onward, literally. I rarely spend much time at mid range. Sad thing is ,I really would love to own a street Hawk also. The Hawk is great. and I own a m900 monster,no comparison.

mboe 794, nice fix for sure. any issues with carb overflow ? I guess not . I was concerned for fuel shut off in a tip over, floats are now the "off switch" I think. thanks for sharing the fix,seems I forget to hook the vac line up at least once a year.

Ok, well if you are only interested in the track then you can do some intake mods.

This is what I suggest:

Leave the airbox lid on and the snorkel in place. As we all know, no-one has ever done any good removing them, so I tried something different. I added two extra intakes to the airbox lid, one on each side of the snorkel. Each one has an internal diameter of about 20mm or so from memory. They are proper items made by a filter company, and have nice rounded intake side and a course pre-filter which goes on the inside of the airbox. Kinda like the small snorkels you see on some registered dirt bikes.

The next thing I did was to fit a larger airfilter. The standard airfilter only takes up a small amount op the plate it is mounted in. I used a Unifilter which has a larger filter area. I estimate it would be 50% larger than other filters such as stock or K&N. It is an oiled foam filter.

Whilst the intakes most probably contribute to the increased airflow, the main factor was the filter. I have left the intakes in place, but changed back to a K&N to dial out the midrange flatspot I have. The larger filter needed much bigger jets as mentioned above, and gave good power. Good for a track set up if that is what you want.

Interesting Shayne,
I appreciate your efforts and advice. I am running the airbox w/o snorkel and have widened ? (made larger) the opening. I have a BMC air filter installed. The mains are 195 front and 190 rear, w a 50 pilot, needles 2 up, this is chasing plug readings. I have yet to try this set up, but it looks like I will on Monday. I am considering a trip to Factory Pro (20 minutes from home) for there dyno work,they have a flat rate until it is finished. I will probably give them my spare stock air box if it gets to hard to sort out. They told me they have never dyno tuned a cut up airbox on a vtr, but feel for track use only there are gains to be had. Sooo I will see how Monday goes, and then plan from there. I am also trying a slightly aggressive geometry with my CBR 900 forks raised 15 and add 5 in back. It is going to be an epic day (for me) for sure. more to come

Oh you are right man!
Now a days diaphragm is not providing enough fuel to exhust so i think that will be a great idea and i think its really a spectacular task and there are so many things which is related to the exhust so please make sure that all things working properly .
I hope you got it.
Thank you.