Honda Spree and Elite 50 Forums

Nope, just need tuning skills.

Look, here's the thing.. You can go out and spend $100 on one of Taz's BBK kits for the Spree, and you can make it work with just the main jet upgrade provided with the kit.

What you need to consider, is how that stock engine runs, and how Honda designed it to run. It was never designed for high end bigger pistons. It is tuned via the intake and reeds to run on a specified carb and pump system using a tuned air box.

When Honda beefed up the AF05 for the Aero (SB50), they knew to increase that intake size and reed size to handle it. Oil delivery makes a huge impact when playing around with it because of how that stock pump runs on a linear plane.

Something to consider: I had a guy ask me what ratio of oil to use for his bike (no BBK). He said he tried 70:1 and it ran great, but 50:1 in ran terrible. So what gives? He thought.. well, if I just use 70:1, I'll be just fine, and he of course, would be WRONG. Why is that? Why did it run so well when it was lean, have great pick up even, but run shoddy when he added a different ratio?

Well, the short simple answer, is these Honda engines are weird. They like lean at idle and take off (there is your good pickup), but they hate it if you try giving it more oil then what it needs at idle and takeoff.

This phenomena only noticeably occurs on a stock intake. With a BBK, you'll notice things like runs great at top speed, but slips down into lean condition going back to idle. This is not a problem that can readily be corrected by a jet change in the carb, or by changing to a different air filter/method because the issue is caused by the intake after the venturi. You have to think of how much more air mix volume the BBK wants to take in, and when you try making the carb take on the task of supplying oil instead of the pump, you weaken the gas flow on an already weak carb. You also weaken the suction created to take in that gas when you open it up to more air (pod filter). It's no wonder at all that someone might have some trouble tuning in everything right given the traditional tactics people try to get the engine to perform well. I submit to you, and contend, that the VERY BEST WAY to run a BBK if you only have $100 bucks to spend, and don't have resources for any other improvements, is DO NOT get rid of your pump, and DO NOT get rid of that air box.

You want that carb to do what it was intended to do as much as possible... supply fuel.

Now I touched on a bit about the stock pump running on a linear plane. You still need to add more oil to the tank to make the BBK run well. But it's not as much oil as you think. You only want the additional oil to supplement what the pump is capable of to handle the bigger piston and no more. Otherwise you will get the same conditions as running no pump with strait oil/gas mix at 32:1 or lower.. This is why I stress 96:1 in the tank, keep the oil pump. Let that carb worry about giving you gas, not giving you gas and oil. The linear plane effect on that stock pump will keep you in that (semi)-lean condition at idle that the AF05 likes for a good take off, and will increase output the higher you rev and enrichen it where it needs to be for 6500+RPM. When you decelerate, that linear plane will help keep the enriched oil ratio up because the engine is still spinning the pump pretty fast while decelerating. So yeah, set that pump up and tank up right for success, drill a couple holes in the air box... you're golden!!

Just for an FYI. It is my understanding that the biggest carb you really want to use on your Spree, is no more then a 17.5mm. So I ordered a 17mm Polini to replace my 21mm. Got it today and tore it apart. Wanted to see what jets it came set at stock. The Polini 17mm comes stock with a #80 Main, and a #38 Pilot. First thing I did, was replace that pilot with a #32. I'm running it as small as possible on the pilot, and will see what results a stock #80 gives me on the BBK.

Think about that... an 80 in the Polini. Is the #90 jet supplied with the BBK kits actually too much?? I don't know, buy some smaller jets, try it out, see what happens, let everybody know. Don't need to worry about the stock carb's pilot, should be just fine. But now I'm questioning the main jet being handed out for the kits. Don't know how a #80 Polini performance translates to standard issue Spree carb performance, but it is an avenue to consider.

Do they know what motor it's going on? I wouldn't trust whatever random jet it came with. The jets that come with the bbk are at least somewhat paired to the cylinder.

Very interesting. What do you think about up sizing the main with the stock air box and drilling no holes. I wonder what the biggest jet you can use with stock air box with no holes. I have heard of people up jetting just slightly on the SA50 with a BBK and still using the negative pressure of the stock air box with no holes and had good results. Just a thought. I have never tested this theory myself but have always wondered what the result would be on the spree with a BBK.

I just added that info to my instructions. Thank You.

taz

I was kind of wondering that myself after tearing apart the Polini.. It actually surprised me, I had heard there was a #100 in it stock, but when I saw it was actually a #80, I was like "WHOA".

I do have that ported BBK from 1man8scoots I'll be putting in my boy's later this year, which means I'll have the one in there now as a spare to play around with. Since it's already broken in. Might just slap it on the other Spree collecting dust in my garage, order some smaller jets (#70-#80) for that stock carb, and see what happens.

So, I guess if I had to choose, and was using an SB50 intake/reeds on a Spree, what to use that one lone nipple on the intake for, vacuum or oil, I'd choose oil and switch to a manual petcock. Other's might have a different opinion, but I'd want to still take advantage of the pump even with a better intake.

I agree. I like oil pumps. They make it a lot easier to fill up at the pump imo. I used premix on my aero and it ran fine but was a pain to fill up.

Ya know, when you think about it, smaller jets on the BBK makes more sense.

They are easier to find, and, as long as you play by the by law rules of a Spree BBK upgrade, a worthy investment at minimal cost.

I guess what leads me to believe this is the typical jet change one does on a Chinese 139QMB engine, when upgrading to an 80cc (72cc) BBK.

I have had best success with an #85 main on a 72cc setup. The Spree BBK gives you only 68cc, so somewhere in the lower 80's range makes sense. Just USE THAT PUMP AND AIRBOX!! You'll get close to 4HP+ through the powerband. Typically, 30-35mph.

12T (84-85 & Iowa) are sweet little rockets with a potential for wheelies kids, but it'll cost ya a Dio clutch swap.

Does this mean with my 48mm bbk and 90jet I believe it was (just purchased a few weeks ago from Taz) I should consider trying to block off some of the holes I drilled, double side of electrical tape maybe, or look for a new air box lid?

Can you take a photo of the holes you drilled? Also, how else is it configured? Still using pump I assume? 80-ish range main is just a theory, has not been tested yet. If you'd like to try, you're more then welcome to, just report back results.

Sure I'll snap a pic and post this evening when I get home, aside from 48bbk everything is stock 85 except larger "86-87" drive pulley that I swapped from the kickstart conversion I did, the larger one works so much better than the smaller 84-85. Smaller pulley closest to the engine, not sure of actual name. Still using pump and currently premixed heavy for break in so carb tune is on hold.

Next question.... Anyone have an extra air box lid laying around they want to volunteer? Lol

After thinking about it, I'm not sure the main jet replacement was ever specified. I don't know where I got 90 from. Only Taz would know the real number then. Everything seems to work great, rather amazing at the moment but I'm still 50miles away from break in mark.