New to the T500, having a little engine problem, need advice

RacerRuss

Hello All,

I bought a '73 T500 about a month ago. It had been sitting for more than 10 years, fortunately, the previous owner had run the carbs and tank dry prior to parking it, so it was not horribly corroded and gummed up. I was able to clean everything up and get it running and rode it around the neighborhood to make sure the motor was OK. It seemed fine, so I set about dismantling the bike for a refurbishment. I had the frame powdercoated, repainted the tank and side covers/oil tank, polished all of the bright bits and replaced a few other things like tires, chain and battery. Got it all back together, it fired right up and seemed good.

But what I noticed after riding it about 10 miles, is that it starts idling erratically (3000rpm and is slow to return to normal idle, about 1 minute) and it had a very loud ping when decelerating. So after lurking here and reading all of the previous articles that seem to be related, I built some tools to check the lower end seals. I found a leaky base gasket on the right cylinder where it had been sucked into the crankcase. I replaced it and retested both sides and it seemed to be sealed holding 5 psi for more than a minute, so I thought all would be well. Took it for a 50 mile ride and this did seem to make it better, but it still wants to idle up after getting hot.

I have been through the timing, points adjustment and the carbs several times (including checking the carb jet sizes against factory specs), but to no avail. I finally yanked the engine and checked the main bearings and seals directly and they seem fine. I will be going back together with the motor in the next couple of weeks once my seal and gasket set arrives, but I really don't think anything I did in this teardown will make a difference.

Does anyone have any ideas that I may have overlooked to fix this problem.

Bikegeezer · Posted: Fri Aug 20, 2010 8:10 pm Post subject:

My vote would be for a vacuum leak developing at full operating temp. Things expand when hot. Get the bike to exhibit the fast idle problem, then spray carb cleaner around the head/carb spigot joint. I've seen more than one example of the gaskets in those joints leaking when hot. If that's the problem, rub the spigots on a flat plate till they're perfect, then assemble with new gaskets.

Stu

RacerRuss · Posted: Sun Aug 22, 2010 8:29 am Post subject:

Bikegeezer · Posted: Sun Aug 22, 2010 8:29 pm Post subject:

Just for grins, check the vacuum port on the petcock with a MityVac. It should hold vacuum. If it leaks down, you'll have a vacuum leak on the left cylinder, and both cylinders will be running low fuel levels.

Stu

RacerRuss · Posted: Mon Aug 23, 2010 1:22 pm Post subject:

BenEberle · Posted: Fri Aug 27, 2010 9:37 pm Post subject:

Now, when you say that you plugged the vacuum port on the left hand carb, what exactly does that do? I've seen the vacuum line coming down from the petcock, but honestly, I don't know what it's purpose is. I've been running my T500 now for about 75 miles, up to speeds of 85mph, almost near 90. Seems to be happy, but there are a few small issues with the left cylinder for sure. The pipe smokes more than the right, and I can't say yet if there's a bit of a ping or not. Seems to run REAL STRONG, though, from 3500rpm and up. Simply loves 70mph as far as I can tell. I has an oil leak somewhere which I can't find. Driving me nuts. Otherwise, it seems good.

What's the deal with that vacuum line? I'm very interested.

RacerRuss · Posted: Sat Aug 28, 2010 7:36 am Post subject:

The vacuum line is used to open the fuel petcock on the stock bikes. When the bike is not running and there is no vacuum, the petcock closes, preventing the carbs from overflowing if one of the needles is not sealing well. Once the engine starts, the vacuum opens up the petcock and allows fuel to flow. There is usually enough fuel in the carbs already to allow it to start and open the petcock. If it has set for a long time or the carbs have been run dry, you may have to put the petcock to the prime position to fill up the float bowls. This allows fuel to flow to the carbs even without vacuum being present

RacerRuss · Posted: Sun Sep 19, 2010 8:25 pm Post subject: OK, it is fixed now

I went ahead pulled the engine and replaced all of the seals and gaskets. Only obvious thing I found was the o-rings around the main bearings were damaged where the case halves come together. I got it all back together, pressure checked both cylinders and found a small crack causing a very small leak in one of the carb boots. I repaired that with some black rtv and got it all sealed up and holding pressure, put it back in the bike and it ran the same as before. There's a month of my life and $100 I won't get back Evil or Very Mad

So, back to more trouble shooting, I disassembled the carbs for about the 10th time, everything looked great. Checked the timing with a test light and it was spot on. I then decided to check it with a timing light and I could not even see the marks on the flywheel. So upon back tracking, I discovered I am a dumbshit (I could have asked my wife and skipped all of the above work to reach this conclusion, but like I said, I am a dumbshit). I was using the timing light and setting the timing for the points closing,not opening, and using the wrong points for L and R. Embarassed

I set the timing for the points opening, fired it up and now it purrs like a kitten. Man, it has been 30 years since I messed with points, and then it was on a '70 Maverick, so this was a little different.

I will post some pics when I get a chance. Thanks for everyone's suggestions.

zjeppe · Posted: Sun Sep 19, 2010 10:33 pm Post subject:

You are only a dumbass if you don(t learn from your mistakes Idea

Freaky_1 · Posted: Sun Sep 19, 2010 11:56 pm Post subject:

OR if ya give up and lean it against a tree for a few years of decoration Wink

Glad you got it! Now with all the time and energy invested, you'll be even more apt to enjoy it!

Frank

CaptCatFish · Posted: Mon Sep 20, 2010 3:39 am Post subject:

I think we ought to have a "dumbshit" competition. I'd bet there are quite a few of us that have done things so stupid as to be unbelieveable (in retrospect of course).

I know I have. My best to date (that I'll admit to) is trying to learn the kickstarting drill on a 1990 Suzuki DR350. After kicking the thing hundreds of times and having it start (sometimes) with no apparent rhyme or reason, I found that I had been inadvertantly hitting the kill switch (which pushes in to kill the engine but must be pushed a second time to clear it). I was used to the temporary kill switches which require holding the push button in until the engine dies and never thought to push it a second time to clear it. What a dumbshit!

CaptCatFish

RacerRuss · Posted: Mon Sep 20, 2010 7:10 pm Post subject:

Some pics as promised:

And it runs and rides.

650SF · Posted: Mon Sep 20, 2010 10:21 pm Post subject:

Very nice bike, thanks for posting.

paul66 · Posted: Tue Sep 21, 2010 1:18 am Post subject:

Allright Catfish, start a thread for "Dumbshit of the Year" and I'll post mine,
Paul

CaptCatFish · Posted: Tue Sep 21, 2010 2:59 am Post subject:

Beautiful bike! I sure hope mine looks that good someday...............

CaptCatFish