72 T500 Restoration, can't control revs

[jamesclifford]

New member here. This forum been the best resource thus far during my project. I'll break down everything I've done and what's going on.

72 T500 doing a full restore. Pulled apart carbs, cleaned with all new gaskets, cleaned gas tank (large amounts of rust build up), replace ignition switch, replace throttle cable, replace throttle handle assembly (whole thing was locked up), Found all correct covers and replaced. I have put everything back together and for the most part fired right up.

THE ISSUES:
- The petcock seems funny as open doesn't flow gas neither does the reservoir. Where off should be are the letters PR and the gas finally flows to carbs. Figure this was an incorrect re-build at some point but may help explain the next issue:

- Once running it REVS uncontrollably without touching the throttle. All on it's own, up to 8k rpm and over in seconds. I was having to turn the engine off as it would blow up the way it was running. I had ran the battery down kicking it over so much and just turning it off. So I went back to it with a full battery and figured out that if I turned the key off I could switch it back on to keep the engine running and make adjustments on the fly virtually revving it up by turning the engine on. Starting with carb cylinders completely closed and idle jets adjusters close there was no change in this open or closed.

I'm baffled. I had this bike running great last summer and now since I cleaned it all up and have almost finished the restore it does this. Now I can't kick it over no matter what I do.

Looking for some suggestions. Oil injection seems to be working but is the next on the list as I'm out of options of what could be making this happen.

[GT750Battleship]

Hi,the fuel tap has no off position! The tap is a vacuum design..you should have two connections coming from the fuel tap...one is the fuel hose..the other is a vacuum hose that is also connected to one of the carbruetors,when the machine is kicked over,a vacuum is created in the hose allowing fuel to flow to the carbys,& continues to do so whilst the engine is running.The position marked PR stands for prime,it bypasses the vacuum side of the tap & allows fuel to flow directly to the carbs,a position that normally you don't use unless the carb float bowls are empty,once the machine is running,the tap should be returned to the normal straight up & down position (north/south)..hope this makes sense ? I say the high revs are due to your replacing of the twist grip & throttle cables not being given an play at all,& the throttle slides are now wide open !!! Might be a good idea that you take the bike to a friendly bike shop & get it sorted ! All a big learning experience working on old motorcycles.. As to NOT BEING ABLE to kick her over at all,,,I'd say you have a crankcase full of fuel...this will have to drained,I'm not familiar with the T500,as to how to drain the crankcase,I think there are drain bolts under the crankcase,someone here will know...taking the spark plugs out & kicking her over is one way to pump her dry,BUT with the plugs in & trying to start her,you run the risk of an hydraulic lock situation...& you could bend connecting rods..not good & requires a motor rebuild to fix....

Regards,
GT750Battleship.

[Vintageman]

Did you put the carb slides in backwards? Some bikes it is very possible to do that and when you start it will rev up high

[jamesclifford]

Holy cow tons of info already.
- slides: very possible there's 2 slide guides. One for the adjustment screw and one guide makes sense. Wouldn't be the throttle only one way to put it together right. The cable bends funny the other way. The other throttle possition simply doesn't allow anything to work (already double checked)

- I'll have to look but drain the crank case check. (How do I know I haven't gone too far and created an hydraulic lock situation?) Once it wouldn't turn over anymore, a few kicks, I turned to the forum again so there wasn't much.

- pr: makes perfect sense. Question: if I open the "pr" and fill the floats I can turn right back to open or kick it over first? Seems turning the petcock "open" has to do with the vacuum? And correct no off position. Makes sense too with the vacuum hose. Would this cause high revs if I didn't turn it back?

Thanks for the help thus far. Ill report back on current findings.

[Coyote]

If you didn't connect the vacuum line, you will have a massive air leak and that would explain the high revs. If you did put the vacuum line on, inspect it carefully for cracks or holes.
You only need to use the prime position if the carbs are empty. Otherwise the lever should be in the 6 o'clock for normal running and the 9 o'clock is your reserve.
When you turn the throttle, do the slides rise and drop to the 'home' position? If the cable is binding, you need to re-route it to where everything operates smoothly. I am not a T500 man so I can't tell you where the crank case drain bolts are. In fact, there might not be any. For a fact, the T250 does not (another post in this section). Another T500 man can verify if there are drain bolts. And yes, if it is very hard or impossible to kick over, the crankcase is full of fuel. Forcing it will most likely bend a rod.

[jamesclifford]

Well gents & genttille, vintageman is right not only double & triple check, quadruple check. 2 guides for 2 different Functions. Left side slide was bass akwards, even tthough it slotted right in.

Thank you all for the info it trully was a tremendous help. Bike has an extra 60 miles on it today from your input. From vacuum lines, primer valve, to quadruple check the slides. We have an idle tweek to look at which likely seems to be the throttle glide I replaced that is NOT oem.but do have an oem glide from replacing the throttle cable that I'll swap out.

Will post findings on that new issue with a new thread.

CHEERS!