vac mod, gas in lines, thoughts...

[gamorg02]

ok so this past weekend, i put the vac mod on and it didn't seem to do much except for maybe helping the starting. Also raised my needles which made me run lean so i put them back where they are.

Then for a few days kept the mod on (and running vboost all the time). it was and had been running a bit rich (with open vboost), but nothing too too crazy, was getting like 32 mpg, when normally i got like 34-35.

so i always noticed a bit of gas in the vac mod lines with the air since i used clear lines, but didn't think anything of it.

So maybe half a dozen times since putting the vac mod on, at very low RPMs mostly when the engine is cold though (temps are staring to get in the 50's here), the bike stumbles and almost dies, esp if i'm in too low of a gear. never happened before. Once it happened starting from a stop, pulling out into traffic, and can't have that, but the bike was cold, shoulda had more choke on.

So in talking with danny, he said he wouldn't expect any gas to be coming in the lines, where i thought since it had mixture in there since its on the manifolds it would be normal.

so last night i took the vac mod off and had been running with stock vboost the whole day to try to clear any of this up. def stumbled with stock vboost once and didn't get enough testing to make a determination with the vac mod off.

question here i guess is, would people expect gas to be coming in those lines? also i guess if my sensor sucked some in, would that be bad and causing the low rpm stumbles? i really hope i don't need a new sensor, i just looked at the prices, like $300 - $400 new, but i'd probably tlak to Sean first.

anyways, tia guys.

EDIT: i should also say, the clear lines are stained an off tint brown from the fuel, but i could still see some fuel in them even running stock vboost which by all rights should be making the bike right on (dyno a/f tuned), if not a tad lean.

 

[zippo6]

Let the damn thing warm up before you ride! IMHO you should not need any choke to be able to ride! I know, this doesn't help one bit.... sorry.

 

[gamorg02]

i leave it minimal for early mornings. the needle is about 1/4 way up the temo o gauge.

it still did it once at low rpms, like 4th/5th gear at 15 mph, bike was warmed up

 

[gamorg02]

i guess another question would be, has anyone synched carbs or run vac mod with clear hoses? if so do u ever notice a tiny bit of gas in them?

 

[zippo6]

That's seems odd to me? This is what I do (right or wrong?):
Full choke, start bike. Within seconds bike is around 3K rpm, as soon as it begins to climb past that I back it down based on RPM to some where in the 2200 - 2500 rpm range. I adjust the choke to keep it there until the needle hits the lower most indicator on the 'normal range'. At that point I can shut the choke off completly and ride or idle. I don't crank on for about 5 more minutes until the motor is completly warmed up.

As for your second question about synching. I use a Morgan Carb Tune pro with the supplied black lines and have always been careful to let them hang (as suggested) when I'm done, but I've never seen any 'moisture' in any of them...... mind you I've only synch'd twice now

 

[gamorg02]

That's seems odd to me? This is what I do (right or wrong?):
Full choke, start bike. Within seconds bike is around 3K rpm, as soon as it begins to climb past that I back it down based on RPM to some where in the 2200 - 2500 rpm range. I adjust the choke to keep it there until the needle hits the lower most indicator on the 'normal range'. At that point I can shut the choke off completly and ride or idle. I don't crank on for about 5 more minutes until the motor is completly warmed up.

As for your second question about synching. I use a Morgan Carb Tune pro with the supplied black lines and have always been careful to let them hang (as suggested) when I'm done, but I've never seen any 'moisture' in any of them...... mind you I've only synch'd twice now

thats about what i do, but when the temp is lower, i sometimes ride for a few miles with the choke on so it would idle at like 1500. just so its getting a little extra gas. i don't crank on the engine until the temp is in the right range and my oil pressure is down under 15 PSI at idle or its following the 1k = 10psi rule. and even then i don't crank.

hmm. i've synched maybe half a dozen times. its apretty minimal amount of gas though. my hookup isn't any different (vac mod) than anyone elses and i can't imagine i'm running THAT rich to cause issues.

 

[zippo6]

Ok cool, I thought you meant that you needed the choke to keep it running.

 

[gamorg02]

not at all. i can usually take the choke off completely within a second or two, it runs rough but will run, but plus why not give it a little extra richness to start, no reason to TRY to put a hole in my piston.

another thought. this only seems to happen at low rpms when i give it throttle, maybe there is a slight amount of residual fuel in the line, blocking the air, so its not getting the right vac reading. hmmm. i'll unhook it tonight to let it dry out, see if it helps.

 

[zippo6]

not at all. i can usually take the choke off completely within a second or two, it runs rough but will run, but plus why not give it a little extra richness to start, no reason to TRY to put a hole in my piston.

LOL, no sense of adventure :rofl_200:

 

[zippo6]

another thought. this only seems to happen at low rpms when i give it throttle, maybe there is a slight amount of residual fuel in the line, blocking the air, so its not getting the right vac reading. hmmm. i'll unhook it tonight to let it dry out, see if it helps.

I'm curious how this works out because it's a mod I was thinking of doing too.

 

[gamorg02]

good stuff shane,

can anyone else chime in with experience/thoughts?

 

[maleko89]

I don't think fuel should be coming from the hoses. When I sync there is never any residual fuel in the sync hoses. Idle might be rich, plugged purge jet, etc.

 

[gamorg02]

hmm ok thanks for the info mark. let me ask u this, there isn't really any liquid in there when i'm done, but, do your hoses smell like fuel?

looked at my sycnh tool and i think some was even there with stock jetting and supertrapps...

this was being run after idle being set with a/f meter and since then th eonly thing thats changed is my mains have been dropped, so it might be a little leaner if anything.

however, i was running this with open vboost, so i may try again with running stock vboost.

 

[naughtyG]

I did the vac mod with clear tubing too. All of them turn into quite a shade of dirty yellow/light brown during the time they were on (just a few weeks). Never noticed any fuel in them, but I could see 'pulses' while the motor was running. Today I took them all off and went back to stock on the vac line.

I'm tryinna eliminate every possibility to get to the root of my problem. I swapped my fuel pump relay too - I think this guy may have had some thing to do with it as when I pumped all the fuel out of my tank (fuel hose from pump straight into fuel can), with my original fuel pump relay a couple of times the pump stayed on for almost a minute, whereas the rest of time it only worked for 4-5 seconds each time then I needed to turn ignition off then back on to restart it.

 

[GREEN light BLITZ]

I have a full time over-ridden Vboost as well and the same carb mod.I used clear hoses and see fuel creeping in the lines at times as well.I have had no problems at all though and noticed when you rap on the throttle or ride off the fuel sucks back down into the cylinder.I might not have had issues because i constantly blip the throttle at stops.Not sure though.Never had gas make it more than a couple inches up the hoses though.ALSO the clear line also turns brown a little bit from the engine heat but the fuel has the same effect.Hope I helped a bit.

 

[gamorg02]

ok well at least it isn't just me! interesting. that issue has cleared up for now too.