Motorcycle and Scooter appreciation

True to its heritage.

Think I might try tinker the carb on the DR. Haven’t touched the setup for a year or two and have just been riding around the issue. DR has a TM33 without the accelerator pump, so effectively a flat slide. Larger bore, aftermarket can with baffle. So, it has a bigger capacity than standard and could be lacking in back pressure compared to a heavy stock can.

Having tweaked the air/fuel and idle, it starts on the button and idles beautifully. No hunting, no risk of cutting out by dropping too low then rising again.

1. When riding, from anywhere from half to WO throttle then closed, there’s popping on the overrun.

2. When riding there’s a hesitation at mid rev range. You can turn the throttle super slowly and just about ride around it but it is there. Definitely there if hard crack open.

So:

1. Popping means lean on the idle circuit. I don’t want to increase idle jet at risk of upsetting starting or idling. However might be the only option here?

2. I tried a number of main jets before and it just moved what revs the hesitation happens.

Finally now, I might just try to drop the needle (raise the clip). If that is enough to adjust the fuelling, and smooth out the delivery, maybe it resolves the point where it hesitates from getting too much fuel?

Alternatives would be an even smaller main jet or a bigger idle. I guess at this point a bigger idle jet is the most sensible test, since the main jets didn’t help.

Need to do a plug chop as well.

….

Thing is under load, on the lanes, I’m sitting below 6k all the time and it drags me along fine. But it feels like it’s dragging me along. If I open the throttle quickly at 3-4k it putputputpuuuuts its way up to 6k. Above 5k so long as you’re above the point of hesitation, you crack the throttle and it revs up fast like you’d want.

Clearly I’m riding it at the lowest throttle getting that bit of low down torque, but the transition from the low down torque into the (limited) peak power at 7-8k is where I want to be able to lighten the front, and the hesitation is bang in that zone.

I’m strongly considering selling my s1000r as it’s not getting the use it should - where’s the best place to sell these days? 20 plate, low miles and very good condition so I think Facebook marketplace is out (even if it wasn’t full of scams).
Think it’s worth around £9k

Pics please 🙏

I kind of still feel like FB Matketplace is quite good these days although I suspect there would be a fair few time wasters alright...

Motorcycle News is the OG but actually seems to be a slight drop-off in volume which suggests people are advertising elsewhere?

Autotrader? I presume you want a private sale also and not a trade-in or dealer sale?

Dropping the needle will lean it out. If you think it’s lean, drop the clip and raise the needle. The little hesitation you describe when you crack the throttle, sounds like a temporary lean bog (that’s the condition the accelerator pumps can cure - they squirt extra gas at that point.)

You can play around with bigger idle jets too as they do have an effect. Going a bit bigger won’t hurt starting / idling.

Plug chops don’t tell you much aside from mixture at WOT. I’ve never tried doing one on a four stroke but if you do, you need a new plug, pop it in and load up the engine in 4/5th gear, flat out, uphill. Cut the engine when you’re flat out and coast to a stop clutch in. Take the plug out and ride home on a spare.

I find it very hard to read the mixture without cutting off the threads but you’re looking for a solid brown ring about 2mm up the base of the ceramic insulator. Black or much higher is rich, less or feint is lean.

Right:

It was bogging like this/worse when I had the accelerator pump still attached.

It is popping on sharp close of the throttle = leaner idle than main.
Hesitation like it is bogging from too much fuel when cracking the throttle too fast from low revs.

My thoughts to drop the needle was reading about whether it's getting too much fuel too quickly causing the bog, rather than too little fuel. I tried larger main jets and it got worse not better.

The plan was to drop the needle to smooth out the fuel delivery, rather than add more fuel to the problem. Dropping the needle is the only thing I haven't tried yet.

37.5 pilot, 127.5 main. So I put the smaller main back in way back whenever.

Looking at the needle, it has a spacer equivalent to one clip, and then it is the second from top (as in, leanest).

I tried putting it together with the spacer the other side, effectively leaning it further and the taper of the needle suggests it stays lean for a long time then the taper of the needle kicks in above half throttle and enrichens it like a step.

So maybe I raise the needle not drop it, see if it fuels more sooner… hmm.

Maybe after all it’s the needle taper that’s the issue.

Generally, if there's a hesitation when you crack the throttle, like the bike falls on it's face and then picks up, that's a lean condition - raise the needle first to see if that makes it better.

Rich bogs tend to be stuttery and more difficult to ride around. Ride along with the choke on to get an idea what they feel like. If it's rich, the plug will be sooty. If it's really rich, anyone riding behind will see a puff of black, every time you whack open the throttle.

Taken your advice and raised the needle. TM33’s are a right pain to do, and impossible in-situ on the DR. I’m loathe to do this very often!

Anting advice. TRF subscription is surprisingly cheap for the year!
I’ve joined. I’m still in London so Herts and Essex are closest access. Only thing I hate about this is the Facebook aspect of it.
Guess needs must as it’s been a pain finding people to ride with. Seems like communities are, surprisingly, still like this, forum based.

Haha, at least there's only one of them! Good luck, carb tuning is a bit of a pain, satisfying when you get it right though. Do have a look at the plug, too.

My experience is it's definitely a Faceache thing. Was a TRF (Cambridgeshire) member last year and didn't hear of, or go on any rides as it's all communicated there and wasn't a member of the group 🤦‍♂️

I will get some pics sorted this weekend hopefully - need to put some bits back to stock first.

I wouldn't mind a dealer sale but the offers I've had from big traders have been lowballs at least 20% too little.

Autotrader might work, it's £20 for a couple of weeks.

@Chak yea unfortunately you'll find more riding buddies through groups on FB than elsewhere.

@Jung one is more than enough trouble! Bike's reassembled, which is the worst part of that damn carb on that bike.

To get the carb off, you must remove side panels, seat, fuel tank, open throttle body, undo cables, remove cables from carb, remove airbox mounting bolts, remove rear master reservoir mount, force the airbox boot back against frame, and maybe just maybe you'll have 2mm to rotate the carb out.

To put it back on is even worse, there's a particular angle it might just go back but the manifolds don't like it. I need to find another way, which might be removing mudguard mounts to let the airbox drop out the way completely.

Not a fun job if you want to keep adjusting the carb setup. I'd like to do it in situ but it's not quite possible because of the flat slide upper.

Yeah some bikes suck. My CR250 you have to yoink off the whole rear subframe. Getting the air box boot back on is skinned knuckles and swearing every time. Hope it’s a move in the right direction!

Probably I still need to up the pilot jet a size or two, but I hope it’s not unrideable now the needle’s raised. I don’t want to disassemble it again!

This looks amazing.

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Get access to TW2 which is the map you need. You can get it through Glass or the TRF. I have glass but I should have done TRF really as the community is better.

Minor update on the DR. I had a lot of issues with the TM33 when trying to fix the flat spot, and the main jet needle got damaged (don't ask), so now I've put the original BST33 cv carb back on and can't remember if it always felt this shit or if I need to make some adjustments there too. Hesitations everywhere, I think it's running rich and needs the needle moved there too. Dammit, bloody carbs.

Well. I currently have a running DR350 again...!

Having re-re-re-built the original BST carb, I just couldn't get it revving properly. In the end I put the needle all the way at the leanest, and it wouldn't even rev up on the driveway. So then I put the needle at the richest, and it would rev fine.

So, I went out and managed a couple easy lanes and some road riding and it felt as good as it will get I guess.

Now the question is whether to up the main jet size by one or two sizes.

As we know and as illustrated on this page from a Mikuni carb manual posted online, the needle height is doing something different to the main jet.

Question is, if the needle has been lifted so much and it could still run a little richer, I can either try going up a main jet, or shim the needle even higher. Hmm.

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Don't shim the needle, go up on the main. You might want to go up on the pilot too, if there is still a hesitation off idle, but go with the main first.

What size jets are you running and what are the stock sizes? You're running an open pipe and higher flow air filter, right?

Open pipe with a baffle in it, so not straight-through but limited backpressure.
Bigger bore cylinder from the King Quad/Arctic Cat - 82mm piston I think, instead of standard 79mm...
HiFlo foam air filter.

CV carb is still stock jets, should be about 37.5 pilot. 127.5 main.
Idles okay, starts okay. No big flat spots in rev range.

When I had the flatslide TM33 (minus accelerator pump) on the bike it was running fine with same size jets, but had the hesitation exactly where the needle changed taper. (Double taper needle). Going up in jet size made no difference to the flat spot.

Still waiting to see if Allens Performance come through with new needles, ideally one of the single taper needles will resolve the flat spot and I can go back to the TM.

TL/DR: Yes, I was thinking to go up the main, but looking at the page from the Mikuni book, seems like I need a huge jump in main jet to see the improvement I got from raising the needle.

If you've got stock jets, an open pipe(ish) and a hi flow filter, you're going to be pretty lean. I would try 40 pilot and a 145 main. If that's a bit too rich, maybe a 140.

What jets did you have in the pumper?

How much would a Dyno run be?

If you had the same size jets in the Pumper, they would be too lean too. If it's a bigger bore carb, they're likely even leaner.