missing on 1&3 at idle.

[tarzan]

I'm working on the 78E I picked up a week or so ago.
The tank had bad gas and varnish and rust in it.I cleaned it out .Put it back on
and the bike runs.I have filters on it too.
It was supposed to have a bad alternator.The tach and headlight both work though.It still may have a charging problem.I have about 12 volts before starting and it drops after starting to 11.3 and only rises up to about 12.4 12.6 with rpm increase.
It misses at idle.I pulled each plug wire and 1&3 arent firing at idle.If I idle it up to about 2000 rpm it starts running intermitently on them.When I disconnect the wires on the two bad ones at 2000rpm it misses completely ,so I know they are firing at least somewhat.
I believe this points to the idle circuits as the most likely culprit.IIRC, if it were coils it would be bad on 1&4 or 2&3 right?
I have another set of SG carbs I can throw on it to see how they work.
I just thought I would poll the audience.Maybe save a little legwork if I am overlooking the obvious.
thanks.Rick

[bikerphil]

Coils fire cylinders 1+4 & 2+3. Try clipping off 1/4" of plug wires at the caps on the faulty cylinders. Could be gunked up pilot circuit. As for the charging system, check the connector behind the fuse panel with the 3 wht. wires for corrosion/melting. HTH

[tarzan]

I did cut 1/4" off the plug wires yesterday when I installed new plugs.
I also pulled the fuse panel mount and checked the connectors too.They seem ok.However I should have written down the values I got.I dont remember them, but they were lower than .4ohms on the white wires.
I havent heard yet of anyone having had a bad stator.That makes me reluctant to change it just yet.
I will go ahead and install the carbs I have off an SG and see if my running i problems improve.
Thanks Rick

[TopCatGr58]

Hey Tarzan,

With your possibly poor or low charging system, it can cause problems with the TCI if the voltage drops too much. Also, it's RARE, but has been posted before about your combo of problematic cylinders not matching either the normally paired ones electrically, as well as fuel!!

IF the ignition coils don't get enough juice/volts either, then they can fire poorly, low power. The coils are a wasted spark system, but what folks don't realize is that both ends of the coil wires need to contact the engine for proper firing of the plugs. The spark current flows from the coil, thru 1 wire, then thru the engine, then back UP thru the plug and to the other wire of the coil, and back to the coil! When you pull one wire, then the other plug can't fire as strongly because it can't flow up thru the one you pulled and disconnected from the engine/spark circuit. Also, with low voltage going into the primary side of the coil, you will get low voltage out, possibly enough to jump the 1st side/plug, but not necessarily enough to jump the 2nd plug effectively...hence the funky pairing of the 1-3 cyilnders not firing right!

Check the white connectors behind the fuseblock for corrosion, melting, etc., also clean the volt/reg/rect connectors, ground connections, etc.!! There are other charging circuit tests, but the common weak link is the reg/rect, along with corroded connectors!
T.C.

[tarzan]

Now the rec/reg is a go/ no go as far as it either works or it dont right?
Or can it cause a low charge.
The PO said he changed the rec/reg, however if he did he just put a used one on it.So maybe I should get hold of geezer.
Wow thanks for explaining the path of electricity through the coils TC.I didnt realize that is how it works.That makes sense about possibly not having enough voltage to fire both.
I'll go ahead and switch the carbs and check that and then start reading about further tests on elctrical.

[skids]

Plug caps are nortorius for going bad.

[bikerphil]

You could try tapping into the dk. green field coil wire and grounding it. If this jumps up your charging voltage, your regulator is NG.

[DGXSER]

Hey Tarzan,

I don't recall seeing if you still have the original fuse block, but that can help as well.

I was having the same problem on my bike not to terribly long ago and I found that it was carb related. I suspect your carb change will at least help your situation.

[tarzan]

Well on my SG I did the TC fuseblock mod.But I am working on the 78E i picked up a couple weeks ago and someone has replaced the old fuse block with a unit that is similar to the original.It seems to be pretty solid ,but your right I better check it out with the multimeter.
I wont get to this bike till late tomorrow however because I'm le4aving in a few minutes to ride down to Grangeville Idaho with my buddy and his wife.It will be About 200 miles each way.We'll ride down today and back tomorrow.
Thanks for the help guys.I'll be back later.
Rick

[tarzan]

Update,here are pics of the pilot screws.1&3 are the two that are broke.


So now the fun begins.I tried to push the tips out with a push pin but the pin bent.So I need to find a dental pick.I had one somewhere but you know how that goes.
I hope I dont have to take these to work and put them in a mill and drill them out.
Well, back at it. Rick

[tarzan]

Well it looks like I have to take the 78 carbs to work and attemp to drill the tips out.
Meanwhile I put the extra 80 carbs I have on it.It ran worse.
So I dismanteled one of the 80 carbs and whoever worked on those carbs put 137.5 mains in it.So that explains the problem with those.I just got off mikesxs
and bought new 115 mains and 42.5 pilots for that set of carbs.Hopefully that will get the bike running ok.

I also took apart the two 78 carbs with the stuck pilot screw tips in them and the yahoo that worked on those put 130 mains in them and 42 pilots.wtf
So I will use the 137.5 from the 80 carbs and use them and I,ll buy some 45 pilots and new pilots screws.Then I will put these carbs back on the 78E.
The sad thing about the 78 carbs is,the PO gave me a reciept from a Honda shop here in town from 2 years ago.They charged the PO $945 to fix the carbs two years ago.
Rick

[tarzan]

I got the carbs sorted out.
Now the #1 plug keeps fouling out.It fouls out within 5 minutes.
Also I found that #1 carb gets air coming backwards through it.Like the intake valve isnt closing all the way.

If the valves are too tight ,can this happen?I pulled the valve cover and that intake valve is .14mm and exhaust is 1.8.
So i am wondering if the valves are just too tight or maybe I have a bad valve.

BTW,the thing runs great briefly before the plug fouls again.