Trouble with 1971 t500

noonblueapples · Jul 11, 2009

Hi, I tried asking about this bike on more restoration and stock oriented websites, but didn't get much response. You guys seem closer to understanding what I'm doing, anyways:

I have a 1971 t500 I was given for free a few years back. I have tinkered with it on and of for a while, and just now got it on the road. It is the first two stroke anything I have ever owned. Right now the bike has pod filters on it, it also had no muffler baffles in it when I got it, I have since been given a damaged pair that I salvaged about 9 inches of and installed. Try as I might I could not get new fiberglass packing to slide into the muffler; so I folded some and pushed it into the baffling: this greatly improved my mid throttle response.

Right now the bike will only idle cold and enriched, once it warms up it starts to die, close the choke and it dies instantly. I switched the pilot jet from a 30 to a 40 and get the same response (if I pull the mixture screw completely out it will almost idle on the 40 pilots)

I have a 150 main jet in it right now. I have absolutely no full throttle, it sputters and dies. However 3/4 throttle is a blast, it takes off and goes.

but never for long. Today was my longest trip ever, 3 miles a wonderful ride........then the throttle started feeling "soggy" so I pulled over. the bike revved right up in neutral (with more smoke than usual though) so I put it back in gear and headed for home.

I ran fine for about a mile and then had to start milking the throttle back and forth to keep it going all the while getting slower and slower sometimes cutting out completely and finally dieing for good about half a mile from home.

I sat beside the road for about five minutes contemplating and gave it another kick. The bike roared to life as if nothing had happened and took me home no problem.

Three miles was a new record but this is pretty much the pattern I have dealt with on every trip on this bike.

sorry for the long first post, hope the situation rings a bell with someone

anyone know any good starting points to use for jetting when running pods?

Thanks in advance for any help

Geeto67 · Jul 13, 2009

you need to clean your carbs. Full disassembly and soak. You can probably salvage most of the "hard parts" and may only need new gaskets. Pay close attention to the needle seat and float needle.

Additionally you will want to rebuild your petcock. suzukis use vacuum operated petcocks and sometimes the diaphram gets a old or a hole in it and does not deliver fuel consistently. You can get new petcocks from suzuki (alphasports) or you can rebuild yours (I recommend getting a new one). I would replace this first before tearing down the carbs just because it is easy, cheaper than a carb rebuild, and will probably need to be done sooner or later anyway. I would also do new vacuum lines to the petcock.

joe c · Jul 13, 2009

all good advice to start.

Geeto67 · Jul 13, 2009

BTW, try setting the petcock to PRI (prime). This bypasses the diaphram and will just constantly feed your motor fuel. don't switch it over until you are ready to start or already running, otherwise you will allow the carbs to overfill and dump fuel into the engine, which could cause you to hydrolock it when you try to start it. It is just an easy way to test whether the petcock is roached or not.

noonblueapples · Jul 13, 2009

That is good advice; the carbs have been cleaned extremely well, all passages cleaned, and a rebuild kit installed

The petcock was bad when I bought so I capped off the vacume fitting on the carb and installed a conventional petcock........havn't had any trouble with carbs overflowing, but could that lead to this behaviour?

KeninIowa · Jul 14, 2009

quote:Originally posted by noonblueapples

That is good advice; the carbs have been cleaned extremely well, all passages cleaned, and a rebuild kit installed

Put the OEM needle and jets back in it if you used Keyster or similar rebuild kits.

Bad news is; if that doesn't fix it I'm saying crank seals. Or perhaps you have a coil or condensor that gets funky as it warms up. Probably crank seals....

Or it's plumb wore out. Have you checked compression?

Geeto67 · Jul 14, 2009

crank seals would be easy to tell, it looks like you are fogging the neighborhood for bugs (lots of smoke). It would also be easy to check, take a look at your tranny fluid level and see if any is missing.

could be coils.

bench test the carbs. Your problem sounds like it is running out of fuel. This aftermarket petcock you got is it a researve petcock? if so try switching it to researve and see if the problem clears up.

Geeto67 · Jul 14, 2009

oh, I forgot, get the stock baffels as they are part of how the chamber works. Remember on a two stroke your pipe is not just a passage for exhaust, it is basically part of your fuel timing (I would have said valve timing but that is incorrect even though that is what it would be in a 4 stroke).

Geeto67 · Jul 14, 2009

and clean the carbs again. it usually takes 2 or 3 times to work all the junk out.

kenessex · Jul 14, 2009

sounds like jetting to me. If it won't run at full throttle but cleans up at 3/4, I suspect it is lean on the main. Especially considering it has pods and limited baffles. What do the plugs look like after a full throttle run and a plug chop? Getting slower and slower could mean hotter and hotter due to leaner and leaner. That usually leads to seized and seizeder.
Remember, 2 strokes are the work of the devil, but the T500 is one of the coolest.

Ken

noonblueapples · Jul 15, 2009

This is sort of what I have been thinking. Any ideas on how big a jet I should try with this set up? It has 150's now

won't get back to this till next week, but I'll try soaking the carbs again, and checking the tranny fluid level

-thanks

quote:Originally posted by kenessex

sounds like jetting to me. If it won't run at full throttle but cleans up at 3/4, I suspect it is lean on the main. Especially considering it has pods and limited baffles. What do the plugs look like after a full throttle run and a plug chop? Getting slower and slower could mean hotter and hotter due to leaner and leaner. That usually leads to seized and seizeder.
Remember, 2 strokes are the work of the devil, but the T500 is one of the coolest.

Ken

Diamondj · Jul 16, 2009

Bear in mind the tank cap is vented. If it's clogged, you'll get the symptoms you've described where the bike starves for gas after a few miles. Give it a few minutes off and enough gas flows to the carbs for it to run for a little while longer. Was the tank coated by any chance? If so and the coating got on the cap, this could be your issue.

I second Geeto's advice on replacing or rebuilding the stock petcock with the vacuum fitting intact.

The stock jets on your T500 are a #30 pilot and a number #150 main. You shouldn't need more for the bike to work correctly if everything else is okay.

The T500 never had any packing. Technically, there should be no room between the muffler and baffle for packing.

There's tech tips, a parts book, and other good tech stuff here:

http://www.ozebook.com/compendium/t500_files/tech.htm

There's a scan of a factory T500 service manual here:

http://www.3cyl.com/diamondj/SuzukiT500.pdf

And there is a T500 oriented board here:

http://www.motorcycleracer.net/phpBB2/index.php

kenessex · Jul 16, 2009

With the pod filters it may (not will) need larger main jets. I don't know how restrictive the stock air filter set up was on the T500.
Do those carbs have a fuel screw or an air screw?
Could also be that the pilot fuel passages are still clogged, too.
This could be one of those situations where it is a combination of issues that are causing all the problems.

Ken

UngaWunga · Jul 16, 2009

Check the easy stuff first. It sounds very lean to me, which generally means that you have an intake leak somewhere. Especially since your jets sound like they're in the ballpark. Look at your intake manifolds for cracks. How's the gasket between the engine and the manifolds? Did you use any sealant there?

Trouble with 1971 t500

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