manual control for vacuum petcock- no more WOT bog  By  kingkaymo (Read 10,916 times)

ihave no prolbem with full throttle on a vacuum petcock running out of fuel. i had one where the fuel line wasnt downhi8ll all the way after i added a fuel filter, so i cut th lines, shortened them up, and had fuel flow. probabaly your problem

then i thik your petcocks bad. does it always flow?
3/16 fuel line can flow 200cc motor. thats why im saying yoru got some other problem

petcock is not bad. i can suck on vac and it will flow strong and fast like i already said. it will also flow thru the lines no problem, until i hook the lines back to the carb. then it will flow... until it fills the bowl and the lower fuel line up to the bottom of the fuel filter and a little into it, then it basically stops flowing.

if i open the bowl drain, the needle opens and then if i apply vacuum it will flow all the way thru, and out onto the ground. once i close the bowl drain, it will again fill... till it gets to the bottom of the fuel filter again and then stops again.

i can suck and blow on the vac line and work the diaphram like a fuel pump, and it will force fuel into the filter and fill it up, but my 45mph riding will still drain it pretty quick

ive talked to a few old bike people, and they all agree im having physics issues.

my next move it to go to all clear fuel lines to watch exactly whats going on, try my vacuum T idea, and if i cant figure it out then im going to put a brass fitting on the tank, and put an in line cut off, and FABRICATE an extension arm for the cutoff valve. id rather not do it this way, but id rather not run my bike lean again....

If you are running at over 80% throttle then you really need a bigger bike for the roads that you travel on. At WOT intake manifold vaccuum drops below a few inches so that fuel does not get atomized effectively and fuel economy falls way down. On a 150cc bike the sweet for fuel ecnomoy is between 25 and 35 mph while a 250 will get better fuel economy at 35 to 55 than a 150 will. When the intake manifold vaccuum falls the engine can also start running lean and hot causeing valves to sink into the seats and piston tops to get damaged from the heat so that you increase the chances of the piston failing causing the connecting rod to get thrown through the side of the crankcase.

Sustained WOT is not good for an engine and will result in an early death.

This may be my issue...

My petcock has 2 fuel outs one on the botom and one out the top, both work off vacume. I could put a filter on the second line and run a Y off the carb side. Then have twce as much gas to the bowl. If that dont help then go manual.... any pros see. An issue with this?

tripper- i would have to see those dual fuel outs... ive never heard of that or seen that and im wondering if its more likely that its a single fuel out and a vacuum port...

sailracer- you can be insulted if you want, i simply dont have any tolerance for "rigged" stuff. Once i moved to the mountains of NC i discovered they do some shoddy rigging on anything and everything and most of the work i end up doing is UNdoing someones crappy rigging to fix something correctly. I am only interested in fixing things correctly. Im picky about that stuff.


rockynv- no, i really dont need a bigger bike. I am already 30cc over whats legal, and capable almost 30mph over speed limit (for peds) I am really only interested in being able to maintain 45, which i can do under 80% throttle, probably closer to 75. also, its not a china scoot, its a honda. Not indestructible, but dang close. i know constant WOT is bad for an engine, which is why im not running a 50 because of the massive hills around my house. I ran my old 9k mile motor lean accidently because of the fuel delivery issue, but it kept running and purring like a kitten till i shut it off... i actually think it only damaged the exhaust valve because i had an exhaust leak (at the crush gasket and small leak at first bend) and it was extremely cold out. i think when i turned it off, cold air seeped into the exhaust and hit the valve and damaged it.

ive got a 150 swap waiting for a good 50 frame, but i havent found a 50 frame that i wouldnt be embarrassed riding yet. i trust the 80cc honda more than i trust a china scoot, as far as reliability goes.

sailracer- i can read fine, i just dont care about your temporary fix. i knew how to do that already. i wasnt stuck on the side of the road with this problem. ive macguyvered plenty of things that are still in use today because my temporary fixes are other people semi-permanent fixes.

any experienced mechanic would tell you that rigging something is fine to get home, but if you need to use your scoot daily, that sort of thing isnt good enough. I can do a lot more than read a book and turn a wrench pal, im not just some redneck hillybilly with a toolkit im a college educated mechanic,machinist, fabricator,welder, body man, carpenter.. the list goes on and on. i do everything from custom sub boxes and fiberglass enclosures to rebuilding engines and race prepping cars. ive got folks that drive over 200 miles to bring me their classic hondas because they dont trust anyone else.

im fussy alright. thats why i have customers that trust me to cut their cars into pieces and put them back together in a weekend, without a single error.

and you have NO IDEA about my improv skills son, so really, you need to chill with that crap. you DONT know me. dont pretend to.