spitting and sputtering.....

nic81xs

nic81xs

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whats up fellas, i was wondering if its normal for my 81 to sputter around 4000-5000 rpms. if i let off the throttle a little bit i can ease threw it but it always happens. is this a float level or needle issue? im thinking carbs
 
No, it's not normal. Running the cheap pods by any chance?
 
What carbs? the stock BS34s? I am no carb tuning expert but a hesitation at that RPM sounds like you are lean on the mains. Are you still running the stock needle jets, have you shimmed them up to fatten the midrange a touch?
 
i am running cheap pods but i dont see how that could affect this particular problem. ive had the bike jetted but the needles were never shimmed. i am running bs34's. do the needles control mid-range fuel delivery? can you buy just a shim kit for the needles anywhere? i dont really wanna have to buy a whole other jet kit.
 
It's been a known fact for YEARS that the cheap pods can cause the exact problem you're having, break-up in the 4 to 5K range. Do a little research, you'll see. Replace them with UNI pods and the problem should go away.
 
some had a lip inside that messed with airflow. I run the one from mikes, recent ones (the old ones from mikes a few years back has the lip)and they work fine on my bike.
 
CV carbs depend on vacuum to raise the slide, the intake has to have a bit more vacuum than ambient or the slides won't lift all the way. Cheap (door screen filter media) pods don't provide quiiiittteee enough (vacuum) lift to get the slides all the way up. You get that 4-5K hang up. Better filtering, a bit more vacuum, up they go. I keep some thin stainless washers to shim the needles and lose that typical just off idle BS34 stumble. Radio schack used to sell some of the right washer but may have stopped, I got a package of them from Mc-master Carr.
After all that I can't promise either idea is the answer to YOUR problem.

This thread covers a lot of the issues.
 
Right around 4K is when the slides begin to lift on these CV carbs. Blocking or obstructing the air flow to the ports with cheap pods causes the slide to flutter, hence the stumble or stutter effect. CV carbs also don't perform at their very best with a K&N style pleated element or one that tapers. As I said, if you want the best working pod for these, get the UNI. It's straight (no taper) and solid foam (no pleating).
 
I was on Mike's checking other things and found that he sells a straight K&N filter. That may work better than the tapered sets.
Leo
 
hell yeah guys! thanks for the info. Im a lexus mechanic so love knowing the tech side of how all this old stuff works. ordering uni-pods tonight. does anybody recommend a particular brand?
 
Uni-Filters is the name. www.unifilter.com
I used the dual layer, black inner, red outer. I can't recall If the #4200 fits the BS38 or BS34 carbs. The #UP4229ST is a bit bigger ID. The BS38 carbs are not quite 2 1/8 inch. So the 2 inch ID filters should stretch a bit and fit well. I think the BS34 2 1/4 inch so the #UP4229ST fits those.
They make them in just the black, # UP4200 and #UP4229.
They also make them with an 15 degree angled mount. #UP4200AST and #UP4229AST.
Leo
 
Some that have been using them awhile suggest 50/50 oil and gas.
I think it is because the pores are smaller and tighter and easy to clog with straight oil.
Or you could try some of the covers made for pods. Snow Chargers or some such.
Grizld1 has reported very good performance in the rain with these covers. I don't remember if he mentioned oiling the filters.
 
The UNI Australia web site recommends the 50-50 mix for the black foam pods. MrRiggs discovered first hand that the normal foam filter oil doesn't work on these pods. It clogged his all up and the bike ran like crap.
 

Attachments

  • UNI Black Foam Road Bike Pods.pdf
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