inconsistant plugs

been having problems with my plugs. fouling out my number 2. about every 30 miles. also number 4 is really black with carbon. 1 & 3 arent bad. lowered my main from 120 back to 117.5. pilot it 17.5 needle jet up one notch. i dont think it is my jets. because there are not all the same. could this be because i havent synced my carbs?

Yes.
It can also be a clogged air/pilot jet.
An air leak on the "better" cylinders.
Have you properly tuned your mixture screws?
Are your valve clearances ok?
Check engine compression as well.

Changing the mains wont have any affect unless your riding the bike consistantly in the 2/3rds to WOT position.

When do they foul? What rpm range, and most importantly the throttle position?

GL.

Grade,type of gas being used? Any Alcohol in the gasoline? Alky can make a plug had to read if the mix is E85(like sold in some states).

Tried changing brands of sparkplugs? For my bike I use either NGK B8ES or Denso W24-ESU gapped .028" to .032".

Bad choke plunger or warn seat. I had this problem on my 76 900. Mine also fowled out after about 25 miles and the cylinder would stop firing. When I cleaned the plug it would run again for another 25 miles. The "enrichening" plunger is just not seating all the way and is allowing gas to pass by. This is a very common problem.

Would agree it's not the main jet size, would put all jet needle clips in stock middle position, and before blaming sync, would check other possible causes such as:
Compression (and valve clearances);
Ignition (properly timed fat blue spark);
Fuel level (clear tube test);
Pilot air screw adjustments (default is 1.25 turns out from lightly seated; out more gets leaner);
Some pods obstruct entrance to pilot air passage;
Pods might be over-oiled;
Air box filter may be dirty or blocked by something stored under the seat.

Good Fortune!

i did change my plugs. had ngk went to denso. using regular low octane gas. just cleaned my carbs. very thoroughly. payed extra attention to pilot and air screws. blew air through all passages. took choke plungers out too. no air leaks. ive sprayed it before. but had carbs off since then. havent checked valves or compression. i think they foul at idle, because both times i have noticed it, it has been right when ive started it up. what do you mean by tune your air screws. you mean turn screws in or out till you get the highest idle? if yes. then yes i have they are 1 1/4 turns out. ill chech valve clearances and compression. and get back with you. thanx

yes i have pods Patton. cheep ones too. did check spark, though outside and hard to see but had spark. cut my wires back 1/4 inch. pods are giving me problems. want to get airbox. thanx.

I overhauled mine too and still had the problem. Try tapping the suspect plunger in with something and see what happens. I solved my problem by not just closing the choke lever, but by slamming it up and down two to three times in rapid succession to make sure it was seated. It works every time. If I don't do that than the cylinder will fowl out.

ok. checked my valve clearances. not good. moving to another thread. thanx.

asevans wrote:

been having problems with my plugs. fouling out my number 2. about every 30 miles. also number 4 is really black with carbon. 1 & 3 arent bad. lowered my main from 120 back to 117.5. pilot it 17.5 needle jet up one notch. i dont think it is my jets. because there are not all the same. could this be because i havent synced my carbs?

A bad coil will do this, don't remember if the same coil feeds 2-4?

Yes a bad coil can do this, but coils fire 1/4 and 2/3. Check the voltage coming to the coils and make sure that it is the same as at the battery.

Assuming other factoring in spec i.e. valve to shim clearances... I'm thinking with the others going for possible faulty electrical...

Possibly coils but I didn't catch where points/condenser or Dyna... Nor did I catch what is the coil voltage (Vdc) measuring in at.

Possibly oxidized engine ground....

OMR