Troubleshooting acceleration issue help needed

[garncarz]

I have a 1972 Suzuki T500J and could use some help troubleshooting a problem. She starts well, usually on the first or second kick. When accelerating from a stop, especially on a slight incline, I need to increase the RPM's to 4000 to 5000 and slip the clutch to get rolling, otherwise it bogs and stalls. Otherwise, performance is as it should be.

I have ultrasonically cleaned the carburetors and all the jets are stock sizes and OEM. The carburetors have been synchronized. Idle is set to 1200 rpm. Confirmed good fuel flow from petcock. Float height set to 27.25mm. Fuel filter is clean. I have set the ignition timing to 3.25 mm and the points gap at 0.35 mm. Spark plugs are NGK B7HS gapped to 0.5 mm but are black in color (not fouled though). Pilot air screw is at 1 ¼ turns out. Jet needle is in stock clip position 3 (middle). Recently, the cylinders have been honed and new rings have been installed. The mufflers and baffles have been cleaned. Battery is fully charged. Fresh Mobil 1 v-twin 20w-40 in the crankcase. The air filter is stock and clean. Ignition coils, HT wires and spark plug caps are new. New cylinder and head gaskets.

Kind of at a loss at this point. Any insights would be greatly appreciated. Cheers.

[Madbuffalo]

It sounds like you've really checked everything!

My suggestion was going to be clogged baffles until I read you already cleaned those. You could still try removing them temporarily to verify not packed too tightly, or incorrect material..?

It sounds like you've done a lot of work on the top end. Have you checked compression through the spark plug holes? Engine warmed up, wide open throttle, I believe you should be getting somewhere around 120psi, and should have similar results between the two cylinders.

Both cylinders warming up evenly? I don't have a temperature reader but when troubleshooting I usually touch each header. Just a quick tap to avoid a burn

Plug gap: My GT750 manual gives 0.6-0.7mm gap (I don't have a T500 manual). That's maybe not enough difference to cause the symptom you're describing but you might double check your own manual just to see.

Good luck! Must feel frustrating to have checked so much and still be experiencing the problem.

[garncarz]

The plug gap called out in T500 manual is 0.4-0.5 mm. I did notice that the timing should be 3.40 mm. I will reset and see if that helps. Also, the baffles in the T500 are just perforate tubes, no packing. That said, I'll remove them and go for a short test ride to see if it makes a difference. I almost think its a dragging clutch issue. Very frustrating on such a simple engine. Thanks for your help though!

[Madbuffalo]

Good feedback.

With no packing in the baffles that does seem much less likely to be the problem.

Hopefully another member can offer more ideas.

[72T350J]

It might be too rich on the idle/low speed circuit. Try winding the air screw out 1/2 turn

[kawonda750]

I would agree with opening up the air screw a half turn and then adjust from there. Much more than that would point towards a smaller pilot jet.

Also, is the air cleaner an oiled type ? If so, maybe you have a bit too much oil on it which restricts the flow of air causing your richness on the plugs. Just guessing though.

[karl pa]

Do you have the old style carbs or are they the newer style carbs? The 72 and older carbs are quite a bit different than 73 and newer, sometimes over the years things get changed.

[garncarz]

I have the new style externally vented VM32s. One of the float bowls was wrong and was of the old unvented types. Fixed that. I am on to getting/new needles/needle jets as the current OE P-4/P-5 tubes are somewhat mangled from PO removal. Fingers crossed. Thanks for the help.

[karl pa]

I am not very good on carburation, they say the tube is to be shiny and smooth or it won't work correctly. What jets are you using?

[badgereng]

https://www.suzuki2strokes.com/forum/vi ... =5&t=15227

[garncarz]

I am not very good on carburation, they say the tube is to be shiny and smooth or it won't work correctly. What jets are you using?

main - 150
needle jet - R: P-5, L: P-4
jet needle - 5FP8
slide - 2.5
pilot - 30

[karl pa]

If you are using the newer style externally vented carbs, you need to go off the later models specs.
Main 97.5
pilot 30, (I went 32.5 to eliminate surging)

[garncarz]

If you are using the newer style externally vented carbs, you need to go off the later models specs.
Main 97.5
pilot 30, (I went 32.5 to eliminate surging)

150 to 97.5 on the main jet? That's a huge change.

[garncarz]

If you are using the newer style externally vented carbs, you need to go off the later models specs.
Main 97.5
pilot 30, (I went 32.5 to eliminate surging)

150 to 97.5 on the main jet? That's a huge change. I just looked up the 1973 T500K specs (service bulletin spec 6) and it calls for 97.5 for the main and 2 P-4 needle jets. Who knew?

[karl pa]

150 to 97.5 on the main jet? That's a huge change.

I can't tell you why the big change, but it has to do with the fuel flowing through the carb internals, difference between externally vented and non vented.