T500 not running properly

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sbaugz
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Suzuki 2-Strokes: T500, S32-2, GT185

T500 not running properly

Post by sbaugz »

Well, Some of you have seen my build in the "custom" section. Finally completed the build and now I am trying to get it dialed in for running properly.

Some summary of the bike:

- 1975 T500
- top end and crank rebuilt by Bill Bune with 1 over Wiseco pistons
- Higgspeed chambers
- no porting or any other mods
- stock carbs with 120 mains (per titan's recommendations).
- swapped out my late model for the early model shortened carb intakes from cruzinimage. (my UNI filters didn't fit so I am using short intakes)
- UNI pod filters
- 1.5 turns out on the needles
- powerdynamo ignition with its modern own regulator/ rectifier unit.
- new plugs
- float bowl height was set properly.
- I didn't really sync carbs, per se, yet. I more or less just eyeballed to make sure the carb pistons went up and down together at the same time with the throttle.

Here's the problem. Simple answer- runs like crap.

more explanation: Got it all put together a few weeks ago. Turned fuel on and fuel leaked out of the right carb all over the place. Was also leaking from the float bowl gasket and the bowl overflow. I purchased all new float bowl gaskets for both sides.

Got it all put back together. Started bike up and it seemed to run decent. Idled OK. Didn't attempt to drive bike because it wasn't completely finished yet. No gas leakage.

Another week went by. Today I turned on the fuel petcocks and wouldn't you know it, but fuel started pouring out of both overflow lines. I tapped on both bowls with a screwdriver and it seemed to stop coming out of bowl overflow. Bike started up. Seemed to idle decent. Attempted to drive bike and it basically bogs down or dies with any attempt at giving it throttle past high idle. Looked at the UNI filters and they are wet with fuel, but no fuel was coming out of overflow after the tapping with a screwdriver.

So, question is. Where the heck do I start? seems like obviously both floats were stuck today when I turned fuel on but the tapping must have dislodged them because the fuel stopped coming out of float overflow. Either way, it doesn't run well at all.

Does anyone have any advice for where to start with setup, where to start with troubleshoot and where to go from here?

Thanks.
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Jimroid
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Re: T500 not running properly

Post by Jimroid »

I would remove the bowls without spilling the fuel out and check to see if they are filthy. Check the brass floats to make sure they aren' t leaking and full of fuel. I think you have brass floats? Unlikely that both are bad, but you are in there any way. Eyeball the needle and seat that they are in excellent condition. Make sure needle is attached to float correctly.
sbaugz
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Suzuki 2-Strokes: T500, S32-2, GT185

Re: T500 not running properly

Post by sbaugz »

Jimroid wrote:I would remove the bowls without spilling the fuel out and check to see if they are filthy. Check the brass floats to make sure they aren' t leaking and full of fuel. I think you have brass floats? Unlikely that both are bad, but you are in there any way. Eyeball the needle and seat that they are in excellent condition. Make sure needle is attached to float correctly.

allright, I will check out floats. When I had the problem a few weeks ago, I removed floats and didn't appreciate any gas inside them, but this time I will submerge them and look for bubbles. There isn't going to be any crub in there, that I am sure of.. The carbs were just rebuilt after vapor blasting. Tank is freshly sealed with new ethanol free gas so its not going to be a sediment /clogging issue.

Say the floats look good. How do I check to make sure the float inlet needles are functioning correctly? If all that checks out, then what's the next step?
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ConnerVT
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Re: T500 not running properly

Post by ConnerVT »

These are what I installed in my T500. Have worked perfectly. I had made the mistake of using a set from some aftermarket rebuild kit. Combined with my leaky petcock, I filled to motor full of gasoline. I'll *NEVER* buy anything other than genuine Mikuni again (everyone, repeat this 10 times each day).

Mikuni VM28/163- Needle and Seat Size 2.5 - VM28/163-2.5

https://www.denniskirk.com/170335.sku

Get the fuel flow issue resolved first, then we can help with the carb tuning.
sbaugz
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Re: T500 not running properly

Post by sbaugz »

ConnerVT wrote:These are what I installed in my T500. Have worked perfectly. I had made the mistake of using a set from some aftermarket rebuild kit. Combined with my leaky petcock, I filled to motor full of gasoline. I'll *NEVER* buy anything other than genuine Mikuni again (everyone, repeat this 10 times each day).

Mikuni VM28/163- Needle and Seat Size 2.5 - VM28/163-2.5

https://www.denniskirk.com/170335.sku

Get the fuel flow issue resolved first, then we can help with the carb tuning.
I took the carbs off and removed the bowls again. I took the brass floats out and submersed them in water and there were no bubbles- so no leaks. No fluid inside them either.

You mention you "filled the motor" with gasoline. My UNI's were pretty wet with gasoline. I wonder if some spilled into cylinders. Technically that should have burned off when I started it right? It wouldn't be like, say my Kawasaki ZRX that can fill the entire crankcase with gas and vaporlock right?

Should I go ahead and order the new float needles? I suppose it can't hurt, although I don't particularly like randomly throwing money at it if I don't have it.
While the carbs are apart, is there anything else I should check over again that I might have missed?
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jabcb
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Re: T500 not running properly

Post by jabcb »

If the floats are dented in rather than being the proper shape, then they will not give you the correct fuel level because they will sink into the fuel more than they are supposed to.

I’ve had sunken floats, floats dented in by a PO, and floats that were too heavy because a PO got some black crud on them.
When in doubt, I just replace them.

Suzuki used standard Mikuni needle valves.
You can figure out which ones you have at http://jetsrus.com
Then order them from JetsRUs or eBay.
I think they are ~ $20 each.

As with the floats, when in doubt I just replace them.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
sbaugz
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Suzuki 2-Strokes: T500, S32-2, GT185

Re: T500 not running properly

Post by sbaugz »

jabcb wrote:If the floats are dented in rather than being the proper shape, then they will not give you the correct fuel level because they will sink into the fuel more than they are supposed to.

I’ve had sunken floats, floats dented in by a PO, and floats that were too heavy because a PO got some black crud on them.
When in doubt, I just replace them.

Suzuki used standard Mikuni needle valves.
You can figure out which ones you have at http://jetsrus.com
Then order them from JetsRUs or eBay.
I think they are ~ $20 each.

As with the floats, when in doubt I just replace them.
I had already looked at jetsrus. Unfortunately it's not very helpful. The t500 chart they have doesn't list float or needle valve part numbers. The link that connervt provides above looks right for the needle valves, but I'm wondering if that's the correct rate? They list about five different flow rates for that particular size needle valve- from 1.0 - 2.5 GPH.

Where did you guys get your floats? Again, no specific link on jetsrus that shows which ones are correct
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ConnerVT
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Re: T500 not running properly

Post by ConnerVT »

sbaugz wrote:The link that connervt provides above looks right for the needle valves, but I'm wondering if that's the correct rate? They list about five different flow rates for that particular size needle valve- from 1.0 - 2.5 GPH.
The flow is stamped on the Float Needle Seat. 2.5 is the highest flow rates for that part model, which makes sense given the large displacement of the cylinder which the the carb is attached.
sbaugz
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Re: T500 not running properly

Post by sbaugz »

ConnerVT wrote:
sbaugz wrote:The link that connervt provides above looks right for the needle valves, but I'm wondering if that's the correct rate? They list about five different flow rates for that particular size needle valve- from 1.0 - 2.5 GPH.
The flow is stamped on the Float Needle Seat. 2.5 is the highest flow rates for that part model, which makes sense given the large displacement of the cylinder which the the carb is attached.
Gotcha

Here are some pics of the floats. They look perfect. No dents. Not bent.
No bubbles when I submerge under water. I don't think new floats are necessary

Image
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ConnerVT
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Re: T500 not running properly

Post by ConnerVT »

OK, let's get back to basics. Sorry if I tell you what you may already know, but it is always best to be sure we are all at the same starting point.

The float system in the carb is not unlike that of the fill valve in a toilet. 2 components - a fill valve and a float. The toilet tank (float bowl) fills, raising the float (float) to a set level, where the float closes the fill valve (Float Needle into the seat). When the tank (bowl) level drops, the float also drops, opening the valve and allowing the bowl to fill up again.

So why is fuel going past the valve?

-- Float level incorrectly set;
-- Float is sinking (holes, damage, excessive weight);
-- Float is binding;
-- Valve is damaged (dirty, worn);
-- Incorrect parts installed.

To troubleshoot, first thing to do is take things apart, and perform a visual inspection.

-- Is everything clean?
-- Is there crud on the needle, or in the mating seat?
-- Does the float have any holes/dents/repairs/bent?
-- Does the float move freely on the pin, and needle move freely?
-- Is the float height set correctly?

With the carb on the bench you can make up a temporary "fuel" supply (container and section of fuel line) to attach to the assembled carb (without the fuel bowl). Doesn't need to be gasoline - water is fine. With something to catch what is coming out of the carb, you can see if the valve completely stops the "fuel" flow when the float is held in the up position. Don't press it tightly, as it should stop flow with the lightest pressure when at the proper float height. Hopefully, the "Now I see it!" moment will come to you.

As for my earlier comment about "filling the engine full of gas", your 1975 carbs have externally vented carbs (overflow lines). My earlier 1971 carbs are internally vented (Homopressure), where the venting is in the intake of the carb, so the overflow of gas ended up in the bottom of my crankcase (and angered my wife with the smell of gasoline in the garage!). This is the major reason between the Main jetting for early/late T500.
sbaugz
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Re: T500 not running properly

Post by sbaugz »

Thank you very much for the detailed response. I'll try that this afternoon.
sbaugz
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Re: T500 not running properly

Post by sbaugz »

So, got home and did what you suggested.

Hooked it up to water. Both Needle valves work fine. The float height are both within spec.

Got the carbs back together, connected fuel, turned on petcock and NO leakage this time. I suspect the float was stuck or something.

Re-adjusted the slides so that they are barely open and symmetric between sides at rest. Started bike up. Runs but idles super low, so I turned in each idle screw until I was nearly at max. Still wants to die somewhat. Needs a little throttle to keep going. With UNI filters off, it appears like both slides are at exact same spot and they both start to go upward at the exact same time- so basically a rough sync has been done. I could shorten the throttle cables and bring the slides up so it keeps running at idle, but I have to bring them up past idle stop screw, making them basically useless. So, that's my first problem. Doesn't seem to idle properly, ie wants to die unless I raise slides up by shortening cable or give it some throttle.

Now, Second problem. Got the bike driving down the street. Seems to run very well at low to mid low throttle. As soon as I give about 1/2 throttle, it bogs down and the bike does like a "shuttering". Not sure that is the correct term, but it seems to describe what is happening. After about mid throttle, it seems to accelerate from there but rather slowly.

Any thoughts on where I should start from here?

120 mains. Uni filters. short (early model) intake boots. Higgy chambers. 1.5 turns backed out.
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Jimroid
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Re: T500 not running properly

Post by Jimroid »

You have stock pilots and needle clip position right now? If so you might want to go 2.5 or 5 richer on pilots.Raise the needle one position for starters.
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ConnerVT
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Re: T500 not running properly

Post by ConnerVT »

If you have the slides open that much, the pilot circuit is not working. I think you said you had carb bodies vapor blasted? You really need to make sure that the internal passages in the carb body are clean (no blast media stuck in there). Only way to be sure is to fully strip the carbs (down to just body), and you can blast water from a garden hose sprayer through each passage (amazing how the water comes out the other end of the passage!).

If you are certain (after checking 3 times :P ) that the passages are clear, you will likely need to go up 1 or 2 sizes in Idle Jet. One size up is notable. Two sizes is huge, but if all else is correct at the carb's current state, that would probably be what you are looking at.

Also, (been said here many times before), be sure that you have the correct slide in the proper body. The cutout on the slide faces the air box (pods in your case). The two slides are mirror image of each other, and spun 180 degrees, will fit in the wrong body.
sbaugz
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Re: T500 not running properly

Post by sbaugz »

Once again, thank you for the helpful information. I am confident that the idol passageway is clear. Vapor blasting does not use any media whatsoever. It uses high-pressure water.

I am embarrassed to say however, that I put the slides in backWards. The cut out is facing towards the engine. I will flip those around properly and try once again. If anything, this project has proved to be very humbling
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