78 cb400 bike runs on one cylinder only and sputters at the other one

[apreludem]

Ok so this is where I am now. I started the bike yesterday and noticed only one side would fire right away but the right side would not. Now my coil pack and wires look like crap cause when we put starter fluid in the spark plug hole it fired then died. Also I noticed fuel at the tip of the hose that drains out the bowl which tells me that side of the carb is getting fuel...but maybe no spark...spark plugs have been gaped to 0.028...when I remove them they look wet so I really don't think fuel is the issue.

Regardless I purchased a coil pack that has the wires attached...my problem is they didn't come without boots or anything like that...just the insulated wire and sheath and electrical cables attached to coil pack...i have no clue how to connect the rest? Do I just buy the boots and they should come with everything needed? If so from where should I buy them?

Thanks a billion.

 

[Redbird]

You should be able to get new boots at your local dealership, BikeBandit.com, etc.
However you can try reusing your old boots. They will basically unscrew off the ends of the old wires (twist them off counterclockwise), then reinstall them onto the new wires.

 

[ichabod]

none

Yeah, your old boots will come off and you can re use them. If you really want to buy some new boots, check this place out (they aren't expensive at all):

http://www.charlies-place.com/PAGES/Store/store_spark_plugs_and_caps.html

I had the same thing happen to me when I first started my bike up. Did you take the spark plug out on that side and try to start it to see if it's sparking at all?

I wasn't getting any spark and thought the coil had gone bad. Got a test light, went to the points and that side wasn't getting any power period. Turns out it was just a wiring issue, a wire had come undone. Plugged it back in and everything is fine.

Yours may be a different situation but thought I would share...me being told that the coils rarely go bad saved me some money and time.

 

[apreludem]

Do they twist off? Seems impossible to move...

 

[apreludem]

Ok that worked. But now I can't seem to get he idle right....I'll hold the choke in the close position...fires right up but a few seconds later the idle is irratic and it will shoot to 3-3.5k...so I'll open the choke a little and it will drop but sometimes will stall.

 

[apreludem]

I know I'm supposed to synchronize them but it says to do it with a warm engine...about ten minutes of driving...that's impossible at this time. The manual says there are two screws used for calibrating the idle. One has a black little wheel that you can grip and spin and the others are lOcated behind the bowls...I know turning those one way makes you run rich while turning it the other way is lean...when the bike first started they were all the way screwed in there...unscrewing them made it worse..the manual doesn't say which way increases the idle for the other screw with the black top...help?

 

[Redbird]

The screws behind the bowls are the idle air screws. Those should not be screwed all the way in. The manual should tell you exactly, but they should be roughly 2-2 1/2 turns out from all the way in. The idle adjustment screw (with the black plastic knob) will raise the idle if turned clockwise, and lower the idle if turned counterclockwise.

 

[crazypj]

Screws 'behind' bowls are fuel mixture screws.
Lightly seat them then back out about 3-1/2~4 turns
400t really needs 1 or 2 sizes bigger pilot-jet
Carb sync is done by adjusting butterflies, single screw and lock-nut between carbs
It's a double ended coil, if one cylinder is running, the coil is fine.

 

[midgtmn]

Sychnronization can wait until after you get the bike to idle, generally. Unless someone has completely screwed up the sync screw. If you haven't cleaned up the carbs thoroughly, I would guess that needs to happen first. Generally the mixture screws are preset from the factory and don't actually need changing, so grab a manual and see where they are "supposed to be" or follow the guide of these knowledgeable fellows above.

It sounds to me a bit like someone tried to "fix" a clogged idle circuit/jet by messing up the mixture screws and idle screw setting. Clean the carbs, reset to stock idle and mixture positions, and THEN worry about synch and precise Idle adjusting. It doesn't matter if your bike idle's high for a while, once you get it running nicely you can synch the carbs and pull the idle down to whatever RPM your manual defines.