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carb? Ignition? Basic engine? I need help!!

  • Thread starter Thread starter twiggy2cents
  • Start date Start date
T

twiggy2cents

Guest
okay so ive made a bunch of threads on this but i really need help!

Overview
The bike runs great on the needle and up, like on the interstate. The bike screws up at the 1/8 throttle mark and lower while cruising. It will start to stutter and upon giving it full throttle it will bog(read: not dip like lean) and stutter then out of nowhere its off rocketing down the road. Everytime you pull the plugs 1 and 2 are black and 3 and 4 are whatever color you have the screws at. These are the dual throat/Siamese/double barrel (whatever you wanna call them) carbs.

What Ive replaced:
Replaced the intake orings
Replaced the filter with an emgo oem replacement.
Replaced the carbs!
Set the valves
Compression check is (1)140 (2)140 (3)140 (4)125
Swapped diahphrams, the new carb came with diaphrams. They have been swapped side to side and with different ones (they were swapped as an assy.
Swapped choke plungers
Swapped choke cable and plungers
Swapped coils
Replaced Plug caps
Replaced Plugs
Put on spare set of coils
Rebuilt the petcock(trying to make it turn easier) flows fuel good

What ive done:
Cleaned both sets of carbs(dipping over night then carb cleaner and compressed air)
The first set i cleaned twice in a month.
The spark is blue on all four when its screwing up
I have set the pilot screws down to 2 or maybe lower, when i do this the bike looses all power and still screws up.
I have set the bike in the 4 to 4.5 turn area and the bike has amazing power all around and still screws up.
When it screws up if i take the air box cover off it does nothing
Vice versa if i take a rag and lay it over the top of the intake snorkels it will run worse after just a couple seconds.
If i rev it while its screwed up i have half the power as normal and its not smooth.
If i pull the clutch going down the road when its screwing up it will die instantly
If you engine brake down closer to idle it wont die unless you let it idle.
If you rev it the revs will settle at idle and the start to fall after that.
Coil relay mod

When you try to tune it in a garage it idles fine but seems lean after a while(it gets a bog when revving it and if i put a rag over the air box snorkel it goes away) When i drive it this goes away.

If the bike starts to get hot in the garage it will develop a hiccup at idle or a stumble(hiccup sounds closer but stumble might be easier to understand)

The fins feel as hot as the do during stop and go traffic but it doesnt do this out side while driving that i know of. Unless this is related.

The boots are on tight and the airbox is all sealed up.


What i am asking:
Will some one please either give me some advice on where to go with this, or.
Will some one in the area come troubleshoot with me and help me figure out what im overlooking ( i would pay for food milage and time spent helping me)

Thanks so much guys!

P.S. sorry about the super long post!
 
Last edited:
I know you changed the coils, but if you are dropping some voltage somewhere in the wiring harness (often the ignition switch), it'll stumble at idle and low revs. I would check the plug gaps also. All 3 bikes I've owned did this with a weak spark. (Pulling the spark plug boots and checking for spark doesn't mean there is spark in the head under compression.)

But you said you replaced the plugs and 1 & 2 are always dark, which makes me wonder. I am free this afternoon to take a look.

If you're in first gear at a steady speed at high revs (and at low throttle) does it do this?
 
yes it will do it at anything under 1/4 throttle, more around 1/8 or lower. And i cant this afternoon, what are you free during the week?


Added coil relay mod to list!
 
reddirtrider said:
Have you synced the carbs?
Click to expand...

It does this with a bench sync and also a dynamic sync

Yes i have i have tried to get it in the middle and i have tried to just make the readings opposite to see if it changes sides and it doesnt.

I am using a homemade manometer but with only needing two lines i would think that its basically fool proof
 
Did you actually pull the pilot jets and visually inspect them? You can see light straight through them? It still sounds like it could be pilots to me. I usually push a strand of copper wire through them, although some experts say you should not.
 
battery voltage is good

The pilot jets are all the same size and i am sure they are clean.

And paul i will look at my schedule this evening and see if we can work something out
 
i just double checked the sync and 1/2 was a little higher than 3/4 so i resynced at 1700 to 2000 rpms. at idle number 1/2 is a little lower than 3/4 and reving the range its about even.

It still has the problem!!!

Come on guys somebody has to know something i over looked
 
I didn't exactly see this on your list, but have you checked the fuel height of the carbs with black plugs? Sounds a lot to me like the needle/seat are worn and you are getting too much fuel to the intakes at low speeds. This goes away at freeway speeds because your fuel usage increases and flows thru the mains.
 
i have replaced the needle seats and swapped floats, sorry i forgot about that. If i hadnt done the sync i would think it was that being that it happens at low throttle openings and not at 1/4 to mid throttle. I may try it again but im not sure a bout it
 
Sounds like you've tried about everything.

I had a similar problem with my #4 carb. Turned out to be the air mixture screw (top front of carb) had allowed rainwater to sit in the recess in which the screw sits. The spring inside had corroded and bits of corrosion were in that passage. Even after cleaning many times, it took months before the problem finally went away for good. Don't know if this applies to your carb design or not.
 
they have seperate screws for 1 and 2 and the chances that two carbs have the same problem are slim
 
okay p_s came over last night and we resynced it. For the most part when it didnt screw up he said it sounded pretty much like his. SO people what am i missing on this?
 
I still can't come up with anything.

The choke cable thing makes some sense though, since you've swapped around everything else that is common to 1 & 2 but that.

This is the online parts fiche that gets the carb jets right for all the variations of this engine: http://alpha-sports.com/

We also tried my new OEM air filter. (I've had problems with the Emgo as has Griffin.)
 
well i have swapped the choke cables and also t he plunger seperately. and also the carbs so i have no clue
 
i have taken the plungers off and set them in the bore and pushed t hem, they dont move anyfurther down. Im sure the answer is staring me in the face but it must be incognito
 
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