hard to start

[tconroy]

Ditto here -- no difference between prime and on on my bike.

Since vacuum isn't actually pumping the gas, only actuating a valve to allow gas to flow, and since a properly working petcock/vacuum hose/vacuum port should always have enough vacuum to be actuated when the engine is on, there shouldn't be any difference that I can see when the bike is *running* between prime and on. When the bike is off, though, if gas is leaking past your float needles, you'll have a problem.

Perhaps for the people whose bikes run differently between prime and on there is an issue with float height *and* petcock? If the float height were too high and the petcock wasn't flowing as well (diaphragm not moving freely?) on "on", maybe the restricted gas flow would compensate or something? Ok maybe that's far-fetched but there has to be some explanation... ;-)

I know that my petcock is working fine ,but Im not a carb guru,I wish i was! The next time I go riding I will put it on prime and see if there is a difference and report back.I do get 58 to 60 mpg.and everthing seems to be in working order.I do run an inline filter.That might have something to do with it.

[steve-lloyd]

Thanks for your contributions, guys.
The simple fact remains that the engine should run exactly the some on "On" or "Prime"
If it doesn't, there is something wrong, it's as simple as that!
Just for the record, I have owned 5 Suzukis and they all ran identical regardless of which was used.

[Planecrazy]

Thanks for your contributions, guys.
The simple fact remains that the engine should run exactly the same on "On" or "Prime"
If it doesn't, there is something wrong, it's as simple as that!
Just for the record, I have owned 5 Suzukis and they all ran identical regardless of which was used.

In theory I would agree with you that there shouldn't be a difference between the two settings ... and yet there is.

I know the carb is clean and I know that it performs efficiently ... and since there are absolutely no adverse performance issues there is absolutely no reason to go searching for a problem that functionally doesn't exist.

By the way, many others have stated that if the petcock is left on "prime" when the bike isn't being ridden that excess fuel will contaminate the oil, so regardless of whether there is a difference during running I would be extremely wary of leaving a petcock on "prime" and risk destroying the motor through oil contamination. I'm not a carb guru either, so I don't know the "whys" relating to these issues. Only that for whatever reason there does seem to be a difference for a lot of people.

Regards,

[UncleMike]

In theory I would agree with you that there shouldn't be a difference between the two settings ... and yet there is.

I know the carb is clean and I know that it performs efficiently ... and since there are absolutely no adverse performance issues there is absolutely no reason to go searching for a problem that functionally doesn't exist.

By the way, many others have stated that if the petcock is left on "prime" when the bike isn't being ridden that excess fuel will contaminate the oil, so regardless of whether there is a difference during running I would be extremely wary of leaving a petcock on "prime" and risk destroying the motor through oil contamination. I'm not a carb guru either, so I don't know the "whys" relating to these issues. Only that for whatever reason there does seem to be a difference for a lot of people.

Regards,

Gas should only get into the oil if your floatneedle o-rings leak.

[Planecrazy]

Gas should only get into the oil if your floatneedle o-rings leak.

That may be, but is that a risk you want to take when it can be so easily avoided??

Oh, and incidentally, mine would appear to be just fine. How do I know? Because the bike sat on "prime" for a week before the Brown County Rally that year, and not only DIDN'T I see any leaking fuel outside the bike, but the oil never smelled of gas, nor did it appear contaminated when it was changed ... and I haven't suffered any catastrophic engine damage almost two years after this happened...

[tconroy]

Gas should only get into the oil if your floatneedle o-rings leak.

I just went for a ride and found no difference in on or prime while running.HOWEVER,i will not risk leaving my petcock on prime while sitting or not riding.I have never had gas in my oil and dont want to know what it's like if it does happen this way.Why do some people get gas in the airbox?I had that happen last week when I changed fuel lines.I wiped it out and cleaned my filter and everything is fine now,but what makes that happen?

[Nerobro]

Clean the pilot jets. Clean the pilot screws and their orafices. :-) That'll fix it.

[UncleMike]

I'm not advocating leaving your petcock on PRIME.

[tconroy]

I'm not advocating leaving your petcock on PRIME.

I know you wouldnt do that.Ive just heard so many horror stories of gas filled crancases that I always make sure that once the gas fills the line to the petcock I turn it back to "on".I have a urethane fuel line that I can see threw. I just wish i had a spare set of carbs to disect and learn more about then I wouldnt be so paranoid about taking my good ones apart.Mine seem fine but Im sure they could use a good cleaning.

[t3rmin]

When I first got my bike there was lots of gas in the oil because the float valve o-rings were shot. Since I replaced them, no amount of leaving it on prime will have any adverse affects. The vacuum petcock is an extra layer of protection against that, though, so leaving it on "on" is definitely what you want to do. You never know when you'll get a stuck float or an o-ring will go out again.

Incidentally gas in the oil does not mean certain death for your motor. It means the oil's capacity to lubricate has been diminished and you risk excessive wear. Over time that may mean engine failure, but not if you catch it within a reasonable amount of miles. Just keep an eye on oil level and smell.