Airbox disconnected & poor low end performance

Hey guys,

I know that this is a heavily covered topic, and just so you know, I did search before posting. I bought a 94 Tomos Sprint last week, and I am having a blast on it. My boyfriend got a nearly identical one though, and it seems like it has a little more pick up. The only difference between the two is some miles (about 2500) and the fact that mine doesn't have the airbox connected. They both have biturbos and bigger jets, but are otherwise stock. We both weigh about the same (within 10 pounds), so that wouldn't be a factor either.

His seems like it takes off a little faster, and mine will almost bog until it gets to about 5mph, then after it shifts into 2nd (at 20mph) it doesn't pull that hard until 25mph. I know it is pretty much stock and is not going to be a speed demon, but his will jump out in front and take off considerably faster. Mine seems like it might go a hair faster on flat land when the throttle is buried (at about 42/43mph on the speedo, whether that is correct is another story), but I would really rather have some more low-end due to driving in traffic.

The only thing it looks like it is missing is the boot between the mesh material on the carb & the airbox itself that is in the frame. I am hoping that the air filter is behind that mesh, but I haven't had a chance to look for it. Should I try running with the choke on for a minute to see if it needs more gas to balance it out? If that works- should I just upjet and not worry about it, or what? I am new to small engine performance and repair, so you will have to bear with me.


Bethany :)

Re: Airbox disconnected & poor low end perform

Also, I understand that you can get K&N filters for these. I understand how they work, but where would it go? Does it go right there at the carb, or somewhere inside the airbox?

Re: Airbox disconnected & poor low end perform

Right on the carb.. If you had a picture of what you have, it would help, it's a little confusing to visualize your description of your setup. Is the box connected to the carb. airhorn, or just hanging there?

Re: Airbox disconnected & poor low end perform

Ben Van Zoest /

Why don't you switch 'airboxes' and see IF it really makes a diff! Not, than you have another problem

Re: Airbox disconnected & poor low end perform

Hooray for searching before you post!

Anyway, I'd do a plug chop on both bikes to see how their mixtures are running. Without the air filter, the tendency on your bike would be for it to run lean. If it's too lean, it can cause bogginess. But there's no way to tell until you do a plug chop.

Re: Airbox disconnected & poor low end perform

▣ß@ηℊℙℐṔ∃▣ ™ /

if you have no filter its probably lean. on my sprint i had no filter and it bogged until i got a HUGE jet. i would get the k&n the part number is rc0790 just go to autozone its i bit over $20 you still use the rubber connector that goes from carb to box. just heat up water put connector in untill rubber is warm then spread it over the rubber on the k&n. i would show picture but having trouble adding them i hoped that helped

Re: Airbox disconnected & poor low end perform

Yes, your fuel mixture is not right across the whole range. The main jet determines how it runs at near full throttle, the throttle piston needle fine-tunes the mid range, and the idle mixture screw fine-tunes the low range and has a small effect on how the transition occurs from low speed to the main jet. I've heard the idle mixture screw called an air screw, too. Looking at how it's made (on the Dellorto carb supplied with the A55), I think it regulates a small stream of air that bypasses the throttle piston. It seems to make the mixture richer when I turn it in, which is the opposite of how idle mixture needle screws work on many other carbs.

Put some sort of air filter on it, get it working right at full throttle and at idle, then adjust the clip position on the needle, re-adjust the idle mixture with each clip change, and then when you get most of the mid-range bogging cured, go back again and try small changes on the idle mixture screw. If it is bogging in the mid range, your throttle piston needle probably needs to be raised.

Re: Airbox disconnected & poor low end perform

you say there both stock, but did you check to see if your gearing is the same?

Re: Airbox disconnected & poor low end perform

running without an airbox will make you run much leaner. A lean mixture has these symptoms when extreme: really slow awful takeoff and then you can't reach top speed. If you can, put the airbox back on, or upjet. You can also make an air filter out of fabrics and such -just find a way to wrap it over where the air enters the carb.

bandits are riding this wed and meeting up at cafe 360- if you need any help with it bring it on by.

Re: Airbox disconnected & poor low end perform

I think you answered your own question. Get the piece that you need for your airbox. They are are there for a reason... Without your air box you are getting too much air in your mix which will cause shitty acceleration and possible seizures at top speed...

As far as replacing it with a high flow, you will need to upjet your carb. If you are happy with the speed of your BF, get a new airbox piece or whatever from a Tomos guy.

Re: Airbox disconnected & poor low end perform

do you have a smaller back sproket? that would explain the slower accel. and faster top end...

Re: Airbox disconnected & poor low end perform

Thank you for your help guys- I am looking at getting an airsal kit next month, and my buddy recommended a side intake for better flow. I will rock this (as the air filter is hooked up) until I get the kit and since I'll upjet at that time I think it will work itself out.

Thanks again!


Re: Airbox disconnected & poor low end perform

my first bike was a 1994 tomos targa...

the biggest problem i had to it running perfect was that in-frame airbox, the exact gasket you mentioned never sealed right and killed its reliability

the best thing i did for it (of course i got a lot of expensive stuff for it including exhaust) was to get that intake that moves the carb from the center to the side - it makes tuning so much easier, and makes it so that you can run any air filter (which for me at first was a piece of duct tape with a hole in it over cut up fabric from a shirt, and then an actual wire mesh filter that slides into the carb

but yeah, running while that gasket was fucked up killed my low end, and kept me from keeping up with my friends, who also had mid-90s mildly-if-at-all upgraded tomos step-throughs

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