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Old 04-10-2012, 12:51 PM   #1
elioporky OP
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Joined: Oct 2011
Location: Pittsburgh, PA
Oddometer: 31
1971 Suzuki T500 Titan Fuel Delivery Issues - Vacuum Petcock Valve

**MOVED FROM AIRHEADS (MEANT TO STICK IT HERE IN THE FIRST PLACE )**

Thanks for you all help, guys! You all are geniuses and I can't believe how quickly the 2nd gear trick worked to free the stuck clutch.

Now I seem to have a small fuel delivery issue. It runs and got me around the block no problem but I have a few questions:

1. When I got the bike, the vacuum hose from the intake to the petcock was removed at the petcock end and plugged. Do people commonly operate this bike with this sort of setup to compensate for a failing vacuum system in the petcock? If this is common, how perfect should the seal be? I'm pretty sure the vacuum hose has a hole in it so I'm prepared to replace it anyway. I read in the T500 shop manual that you're not supposed to attempt to fix the vacuum valve system in the petcock. What is your experience with this aspect of the delivery system?
2. The fuel lines on the bike as I got it were clear and of a larger diameter than the nipples on the carbs and petcock. To compensate for the discrepancy, little bits of rubber were placed on the nipples to make the clear hose fit. The seals seemed sketchy so I swapped out the clear hose for black hose of the proper diameter. Will this effect the flow of fuel into the carbs? If this is the case, what sort of adjustments do I need to make to make everything work as it should?

Thank again for all your help. I'll send more pics soon.
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Old 04-10-2012, 05:15 PM   #2
Scrivens
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The vacuum seal may have failed in the tap or the owner may simply have not liked petrol taps that couldn't be manually turned off. If the vacuum seals fail and your float needles aren't sealing properly you can end up with a crankcase fuel of fuel. You can pull the plug, re-attach the hose and see if it still works, or unscrew the tap unit from the tank and have a look at the innards. The old 3 position vacuum taps had 'On', 'Prime' and 'Reserve' - how is the fuel being turned off now - is it flowing only when the tap is on 'Prime' or when on 'On' or 'Prime'? If there is no shut-off (ie, it flows in the 'On' position) then the tap needs to be replaced ASAP as it is faulty.

Using normal fuel lines will not have any effect on the bike at all as it is the original spec.

If you have a look at the pic of mine in your other post you will see that it has clear fuel lines; some of us like to see there is fuel going into the carbs.
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Old 04-11-2012, 09:00 PM   #3
elioporky OP
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Quote:
Originally Posted by Scrivens View Post
The vacuum seal may have failed in the tap or the owner may simply have not liked petrol taps that couldn't be manually turned off. If the vacuum seals fail and your float needles aren't sealing properly you can end up with a crankcase fuel of fuel. You can pull the plug, re-attach the hose and see if it still works, or unscrew the tap unit from the tank and have a look at the innards. The old 3 position vacuum taps had 'On', 'Prime' and 'Reserve' - how is the fuel being turned off now - is it flowing only when the tap is on 'Prime' or when on 'On' or 'Prime'? If there is no shut-off (ie, it flows in the 'On' position) then the tap needs to be replaced ASAP as it is faulty.

Using normal fuel lines will not have any effect on the bike at all as it is the original spec.

If you have a look at the pic of mine in your other post you will see that it has clear fuel lines; some of us like to see there is fuel going into the carbs.
So it turns out that the vacuum hose was plugged when the previous bought the bike and has remained that way ever since. How common is it for the vacuum petcock diaphragm to go bad on these bikes? Is it repairable, or would I need to just find another one? My father in law recommended looking into getting another petcock for it, one with the traditional On, Off, Reserve settings and I think that sounds like a totally reasonable idea to me. I'm going to replace the hose and see if the whole system still works. Maybe I can suck on the tube and get the diaphragm moving if it is stuck.

I'll let you guys know how it turns out. Compared to my 350, this thing was a rocketship when I took it around the block. I can't wait to get it dialed in!
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Old 07-05-2012, 09:15 PM   #4
elioporky OP
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Wrong diagnosis... Oh, the injustices of previous owners!

So when I last wrote I blamed my titan's intermittent starting issues with a questionable fuel delivery system. Turns out that was only a small part of the problem. When I finally built up the courage to ignore the "never dissemble" warnings regarding the automatic petcock in the manual, I discovered the the entire inner workings of the vacuum system had been taken apart and reassembled backwards. The spring was on the wrong side basically rendering the whole thing garbage and guaranteeing a constant stream of gas straight into the crankcase (no wonder I had to drain the cylinders weekly!). Once I reversed the spring -- using nothing but common sense, I might add -- and added a new vacuum line, the entire system worked like a charm...one problem down.

The next problem was that the bike was no starting with any sort of regularity. I assumed it was fuel related at first, but then ruled that diagnosis out and moved on to the electrical system. I found that the bike would start more consistently whe the battery was fully charged. I ended up tracing the problem to an aftermarket killswitch that a previous owner had installed. First I bypassed the switch, at which time the bike started beautifully. Then, just for shits and giggles, I broke apart the switch to reveal contact plates badly gunked and soiled. Damn you, aftermarket parts!!!

Anyway, just though I'd share. Anyone have any similar stories of having to undo the "improvents" of previous owners?
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