Cylinder doesn't fire @ low speeds...

[Anonymous]

Hi,
I have a GS300L 1985. The curious problem I have is that one of the cylinders "ususally" only fires after getting over a certain speed, somewhere between 20-40 depending on the gear I am in. I took the bike in and the guy cleaned the carb but didn't really find anything else. The bike starts easy and runs smooth on the hwy. but it is pretty much useless in the city. Idle circuit,
coil, bad plug gap?

Good day,
intercessor

[Detman101]

Sounds like bad ignition components.
I kinda have that same problem on my #1 cylinder.
But I know that I need new sparkplug wires...cause the ones I put on my bike to get it running were crap to begin with.

I'm upgrading to Accel wires this friday. They will work great with my DYNA coils. Better than these crappy sub-stock Autozone car-wires did.
:roll:

[DMPLATT]

You can check the spark easy enough by laying the plug on the engine and crank. I don't see how a spark can change just by the RPM's alone.

My bet would be the idle circuit in your carbs.

[Detman101]

Yep, prolly that too as my tank is rustier than a crashed car at the bottom of the east river.

[robinjo]

You can check the spark easy enough by laying the plug on the engine and crank. I don't see how a spark can change just by the RPM's alone.

My bet would be the idle circuit in your carbs.

I agree with DMPLATT.

[Anonymous]

Are idle circuits hard to work on? I had the repair guy clean the carbs once... Also if the idle circuit is dirty I would think the problem would exsist 100% of the time?

Thank you for your input.
intercessor

P.S. I checked the ignition and it appears I have an electronic system. Magnet at the end of the shaft with two coils at 180 degrees apart.

[Detman101]

That's the same thing that I don't get.

I can find the main jet, I can find the needle-jet and jet-needle...
I have yet to find this elusive "Pilot Circuit" in the 2 years that I've owned this bike even after building the carbs from the bottom up.

Guess that's why it runs so crappy on the low end but roars half throttle to WOT.

:roll:

[DMPLATT]

Well, this topic is starting to get over my head. :roll:
However, go the the Carb cleanup series on the main GSR page. On Page 4 of the series, it shows the Main Jet and the Pilot Jet. I'm going to show my inexperience here, but I'm guessing the Pilot Jet is for the idle? Anyway, if you get to pages 5-7 it shows removal of both jets.

Good Luck.

[Detman101]

I know abuot the pilot jet. What is this "Pilot Circuit" I've always heard about. It always is described as a sort of tunnel in the carb body that you can't access without a pipe cleaner or something to blow it out with.

(If cleaning the pilot circuit is as simple as recleaning the pilot jet then I'm going to be one happy man this weekend.)

:P

[IanFrancisco]

On some carbs the pilot or slow circuit screws were sealed to keep people from altering the EPA-induced lean settings set at the factory. The seals had to be drilled out (carefully!) to expose the screws. I think they are not mixture screws per se, but could be wrong. I think they are screws to adjust the overall amount of fuel/air mix passing thru. Backing mine out to 2 1/2 turns out from 1 1/2 and backing off the throttle stop screw which controls the butterflies restored correct idle and made the motor run great at small throttle openings. On my bike they were exposed with no evidence of drilling. Stock '80 GS450 Mikuni CV carbs. The pilot screws are on the sides of the carbs near the top, toward the front of the bike and face out sideways making them easy to see and adjust.

[Detman101]

Ah ha!!! So that's where the infamous "Pilot Circuit" is!!!!
I was led to believe those were the "Mixture Screws" only!

Okay, it's all becoming clearer now...Thank you!