no low rpm torque - power t500

[Rocket350]

I've waken my bike up after many years of sleeping. I've rebuilt the carbs from cheap kits off eBay but replaced the needle seats from mikuni. The carbs are super clean. Rebuilt petcock, tank flushed, new intake boots, new fuel lines, new plugs, timing set, points adjusted etc. Fires right up 1st or second kick. Idles nice at 1500 rpm and revs great. I took the wife for a ride around the block and I had a hard time getting out of the drive way at a little incline. Once she got going it kicks in after 2500 rpms. I took it for a ride tonight and after struggling half way up the driveway I put the choke back on and man what a difference! It had the low end power and I was easily able to just get going. So it seams its not getting enough fuel I guess at idle and low rpms... should I put in the old idle jets back in? Maybe further air/fuel screw adjustments? They are about 1 1/4 turn out. And by the way the wife is not heavy!

[ConnerVT]

I've rebuilt the carbs from cheap kits off eBay... should I put in the old idle jets back in?

That would be a good place to start. Put the original needles back in, too, if you used the ones from the kit, if the old ones aren't trashed.

Idle screw adjustment of 1/2 turn shouldn't make that drastic a difference.

[Coyote]

+1 The old needles are better than any 'kit' needles you ca buy. Main and pilot jets too. The main jet needle is critical, and all I've ever seen it kits are junk. From a little off to way off. Some choice. if you buy cheap, you get cheap. Just a bag full of 'similar' looking parts.

[GT750Battleship]

I would not describe Cruzin Image kits as junk,happy with mine for the 750,a little cutting of the float bowl gasket & all is fine...bike running great...I think I've made mention before....the gaskets are marked made in the US
Cheers,
Roger

[Rocket350]

Thanks for the input. I'll mess with it next weekend. The thought of disassembling the air cleaner boot from the carbs makes me want to say a bunch of 4 letter words! I reused the float brown gaskets but replaced everything else. I'll replace the idle jet and pins with the old and see if that does it. Damn... if I had a dime for every time I've had these carbs off I'd be well off. But I know it will be worth it when she runs like she should and not settle for good enough.

[ConnerVT]

You can try swapping back the old needles first - They have more of a chance of affecting your torque problem than the pilot jets, plus you don't need to pull the carbs to change them - just the carb tops.

Also, I have found it easier to pull the seat, battery box, air box + boots, then the carbs, rather than fighting the carbs between the intake and air box boots. I can pull both carbs, re-jet, and have all reassembled in about an hour now. Amazing what practice will accomplish.

I don't know what kit you bought - Keyster, Cruzing Image, or ???. There are two different models of T500 carbs - Pre and Post 1973 are very different jetting. I have both sets of stock needles, and I once measured them along with a new Keyster needle. The Keyster was nowhere near the same dimensions of either, and didn't even have the same taper.

[Rocket350]

Yeah the needles felt different. I checked the specs reassembling and everything was numbered correctly for the year and what I replaced. I have no clue what the brand of rebuild kits they were. They came in a plain white box. I'll try the needles first since its the easiest but I figured it wouldn't make much difference since it was low end under 1/4 throttle but I'll try that first.

Just to be clear... the carbs with the silver heavier slides are correct for the 72 model? I have a set of carbs I bought 15 years ago with the lighter gold color slides that came off a later model... if memory serves. I just want to ensure I've got the correct original carbs which I'm 99% sure I do.

I've had this bike for over 20 years and have never talked to anyone that had a t500 until 2 weeks ago when I found this website! What a blessing!

Thanks again for the help. She is running awesome but just need to fine tune the low rpms/torque issue to be perfect.

[ConnerVT]

You would be surprised how much throttle you are actually at when pulling away from a stop. Especially if the bike is lagging from a standstill. Bet you are much closer to 1/2 throttle in that case.

The needle is most responsible for the bike's demeanor.

[tz375]

You can quickly see if the needles are much different if you have a digital caliper. One way is to measure both needles every 5mm and compare the results, but a quick and dirty way is to lightly grasp a stock needle in the jaws of the caliper and insert a kit needle beside it.

If the kit needle is thicker, it will not slide through as far and if it's thinner it will also be obvious. It ain't scientific but it's obvious if the needles are much different.

[ConnerVT]

Exactly what I did to compare a SFP8 (early), SFP17 (late), and a Keyster kit needles.

I may have posted the data here somewhere, but if I remember correctly, the SFP17 was a hair richer (thinner) overall than the SFP8, with the tapers similar (maybe also taper beginning a slight bit earlier on the SFP17).

The Keyster was much leaner (thicker) overall, with the taper not matching the stock needles at all. With the three of them side by side by side, you could eyeball the difference.

[Rocket350]

I put the old needles back in. The tips on the new ones looked skinnier than my old ones but I did not measure them with my caliper. It's ready for a test run but I've been working late all week! I'll post the results so maybe this can help others in the future. I really appreciate everybody's help.

[ConnerVT]

The tips have little influence during slight open to 1/2 throttle. The diameter at the other end (at the top of the needle) controls the flow at the small throttle openings.

Think - "What is the volume of the needle inside the jet vs. the volume of the jet." As the slide rises, the top of the needle is the first removed (and the tip is still inside).

It really doesn't take much of a change in the diameter of the needle to have a significant effect. Raising/lower the clip on the needle one slot has a drastic effect. I have been playing with shims that allow you to change it by 1/4 of a slot, and can tell the difference.

[Rocket350]

I just took the bike for a ride. It seemed a little better if any. But not so much. On flat ground its easier to get going, but on a slight incline it just has a hard time. If I was on a real hill at a traffic light, it would have a really hard time. Like I said, it was tough going up the driveway with my wife and I even stalled it once. If I put the choke on - it pulls great at low rpms (not so much after of course).

The clip is positioned in the middle on the needles. They are in great shape and are the originals. They are sfp8. Should I try a different position on the needles? I am in eastern N. Carolina so I'm at sea level if that matters.

[Rocket350]

I moved the clips down one notch, not much difference. I had it idling and noticed the left side exhaust is popping and the right is humming nicley. I felt both exhausts and the right is warmer than the left side. I felt the pipes and the right side is a lot warmer. I shut it off and unplugged the left plug wire and started it. It idled but I could tell it was on one cylinder. I unplugged the right side and it had a hard time idling on the left cylinder unless I turned the idle up. So my conclusion is the left cylinder is the one giving me problems at low rpm and idle. She screams after about 2500 rpm.

I've cleaned/gapped the points .014, timed it with a multimeter, new plugs/gapped .022, new fuel, carbs rebuild with cheap kits, original needles, new mikuni seats, new intake boots and floats set at 27mm. Compression is 130lbs on both cylinders.

I guess I'll recheck points/timing. After that I guess I'll put original jets back in left carb???

[ConnerVT]

Or, if you are really trying to find root cause, swap all of the jets (pilot, main, needle jet, jet needle) from one carb to the other. If the problem moves, then one of those pieces of brass are your culprit. If the issue stays on the same side, then something else is your issue, and you can stop messing with the jets (for now).

I know you don't want to pull the carbs more than you need. take my word for it, it becomes easier (and faster) with practice.