Only running on two cylinders (1&2) - SOLVED (I guess)

Ok so I'm getting really excited. I know the weather this week was a bit of a fluke, but I'm so close, I've got all my gear and I'm just days from registering and inspecting it (after working on it for more than a year).

While trying to color tune, I got 1&2 looking good, but I noticed that on cylinders 3&4, I really couldn't "see" a flame. I thought the color tune plug might have gotten damaged, because I could see a spark, but the color wasn't bright enough to distinguish orange from blue. If I rev it, or "choke" it, I can see the orange. I tried it on cylinder 1 again, and it was working fine. 3 & 4 seems to ignite, but not on every combustion stroke. I have an aftermarket MAC 4into2, with no cross tube between 1/2 and 3/4, and I noticed that the exhaust pulse out of the left muffler is strong and even, but out the right it's weak with an occasional "strong" pulse.

What I've done: compression test last fall, all within 10 psi of each other and about 140, clean the carbs (breaking the rack, replacing all the rubber bits, except the diaphragms, which looked good and I used the parfin wax chacal sells), rtv and bike inner-tubed the intake boots and new gaskets), plumb-quicked air box boots, new air filter with replaced air box (ebay said it was from a 750 seca), balanced and was in the process of colortuning the carbs. I even checked the float height on 3&4 and it looked to be in spec (maybe 5 mm but I was measuring on the back of the carbs from the mounting surface, with the carbs on the bike, so they are tilted forward a bit).

Given that it shouldn't be the coils because they are on the same side, the only thing I can think to do is dive into the carbs again. I really tried to clean them right (HONEST! ), but of course I had to do it again because I measure float height (the first time) with wind shield washer fluid and it gummed everything up. Is there anything else that I should check before I pull 'em out again?

 

Re: Only running on two cylinders (1&2)

Ok I don't think it's the coils, but I measured the resistance in the coils and got 20k Ohms (my multimeter said 20 on the 200k Ohm scale, so I hope I'm reading this right) from cap to cap on both of them. Is this a problem? I read in the Haynes that you shouldn't have more than 13k Ohms, but then I read on some other posts that plug caps are 5k Ohms (I assume each cap), so then I would be fine? How to you measure "behind" the caps?

 

Re: Only running on two cylinders (1&2)

Unscrew the caps off of the end of the high tension lead and measure from the copper conductor you should find there. Be advised, the copper may appear blue (corrosion) so be ready to cut the ends off and start over.

 

Re: Only running on two cylinders (1&2)

Wait so is that too much resistance? How exactly do I screw off the cap? There was one rubber bit that I could pull back, but I didn't expose any screws or wires, and didn't feel like tugging on anything late last night.

 

Re: Only running on two cylinders (1&2)

The HT leads have stranded copper wires inside and the plug cap has a male thread which screws into the centre of the lead. Hold the lead and twist the cap anticlockwise for about 5 turns - it should come off.

 

Re: Only running on two cylinders (1&2)

Thanks markie...that was easy! So yeah, 11k for both coils, 5k NGK resistor caps at both coils (haynes says it should be 10k for cylinders 2 and 3), no corrosion. So I don't think it's the coils. So am I hitting the nail on the head with the pilot/carbs needing to be torn apart...or about to whack my thumb :roll: I guess I'll pull them off tomorrow and clean them again

 

Re: Only running on two cylinders (1&2)

I guess I'm going to pull the carbs again tonight if no one responds. I've cleaned them already, and tried to do everything right, but I'm starting to suspect that the snowblower tank that I've been using might be less than perfect.
I remember thinking, "Hey, it's plastic, that means no rust." I can't remember if that led me to not flushing it out. And of course I had plans to put the inline fuel filter from Chacal...when the real gas tank went on.

 

Re: Only running on two cylinders (1&2)

I was having similar issues.Found out my inline filter was clogged.Runnning good now.

 

Re: Only running on two cylinders (1&2)

don't know if you've already pulled the carbs - but, if you haven't, here's some things you can do before pulling the carbs:

-open the drain screws on the non-running cylinders and verify you are getting gas.

-try revving the bike up and see if the non-running cylinders start to become running cylinders - the thought here is that if it is carbs, i think it is unlikely that the enrichment, pilot, and main fuel circuits are ALL clogged. if you can rev it up and it fires, then you know it's probably the enrichment and/or pilot circuit.

-you could try swapping the plug wires around (everything ohmed out ok - so it shouldn't make a difference, but if it does- then you don't need to pull the carbs)

oops - i just re-read your post and you said "if i rev it or choke it i can see orange" - that leads me to believe something is blocked up in the pilot circuit, so - if you already pulled your carbs - it wasn't for nothing.

 

Re: Only running on two cylinders (1&2)

yeah I pulled them and I'm cleaning the main and pilot fuel jets, and the pilot mixture screw hole. I did 2 and 3 first, but didn't "see" anything wrong. I did notice that on 2 the pilot mixture screw was turned out 6 turns, and this was "good" according to colortune plug.

I'm wondering if I started the pilot screws in a bad place, and threw off my mixture/balance so far that I'm having trouble getting everything hashed out. Or if the plumb-quick airbox boots have anything to do with it.

I also noticed that there appear to be two "air" jets in the back of the carb body, on either side of the inlet to the box. What are these and were they supposed to be cleaned (I never saw them mentioned anywhere)

 

Re: Only running on two cylinders (1&2)

those two jets are vents to the bowls - keeps the bowl from building up air pressure as it fills with gas if you catch my drift - it is very unlikely that they will clog up.

6 turns out is a bit much. you might need to think about air leaks or re-jetting. i see you have a MAC 4-into-2 exhaust - i had to increase pilot and main fuel jets (and shim up my needles) for my 4-into-1 exhaust. Hopefully someone else on here has experience with the MAC 4-into-2.

if you still have your carbs off, i'd also double check that you are getting flow to the pilot holes just behind the butterfly. they are very tiny and are right behind the hole that the pilot screw adjusts fuel flow to. (i hope my explanation was is clear enough)

 

Re: Only running on two cylinders (1&2)

I'm hoping I've got all the air leaks covered. To make matters worse on the exhaust I had to replace the baffle the PO broke off, but the only one I could find that had the right size end cap was a perforated packed baffle, not cross tube. But chacal says +2 for 4-2 and +4 for 4-1 exhaust, (then -2 at the end) so I'm hoping I'm ok.

 

Re: Only running on two cylinders (1&2)

Ok I went through the pilot circuits once more. Nothing "looked" out of place or clogged up. I removed the pilot mixture screw, pilot jet, and pilot air jet, fished around with a 9 guitar wire, and flushed with b12 chemtool. I got plent of carb cleaner coming out the other side when flushing.

I had "sucessfully" colortuned cylnders 1&2 (as in I could back out and see orange, turn in and see blue white, then fine tune within 8 degrees, like Rick says, to get bunsen blue). number 1 was 5 turns out and number 2 was 6 turns out. I've put them back on and I'm going to try to tune again tonight, starting 3 and 4 5 turns out, balancing and tuning from there. I'm guessing that there will be some rejetting in my future for my exhaust :roll:

 

Re: Only running on two cylinders (1&2)

Alright...WHAT AN ADVENTURE! So I got to start tuning. RMV here opens at 10am on Thursday, so at 8am I figured 2 hours of tuning and buttoning everything up, then I'll register the bike, and start riding it. How quickly plans change :roll:

I turn on the fuel valve on the snowblower tank that I'm using, and I start getting gas leaking. I finally figure out that it's coming from the airbox hose. I think "OH GREAT...what did I screw up this time?" I didn't touch the floats at all cleaning out the pilot circuit yesterday, so what's wrong now. I pull 'em off, and notice that there's only fuel in the intake and airbox boots for the #1 carb. I level 'em off, fill 'em with gas, and then see the fuel dribbling out, as well as verify that the fuel level is WAY too high in #1 only.

I take that one apart and what do I find? Somehow, the tip of the wire on the float needle that hooks around the float tang instead got caught on the tang, holding the valve open. REALLY obvious. So I correct this, then re-check my float levels (a lot of extra work since I've got one bad float bowl drain) and everything's dead on.

I slap the carbs back on, adjust the pilot screw for carbs 3 and 4 to 5 turns out, then get to tuning, going from 4-1. Sure enough, I'm able to find the sweet spot, and easily adjust from orange to blue-white then in between (I left it with a little orange). I think all of my pilot mixture screws ended up 4-5 turns out...I don't feel like counting, but 1&2 were way rich.

I think either the pilot circuit was clogged (but I didn't SEE anything) or I started with the pilot screws in the wrong spot. Subsequent investigation in this forum revealed, that 3-3.5 is what the factory set the pilots to, and that was lean. I last tuned my snow blower...B&S, and I think you start those 2 1/2 turns out. I think I started them all at 3...thinking that would be a little rich, and I think this made tuning impossible.

Anyway...I get the the RMV at 2:30 and after waiting 1 1/4 hours to get my registration, I put the headlight back on (it drains the battery while you are tuning), installed the gas tank, and changed the oil. Of course I found out that although I rebuilt the petcock, some gas still comes out on "ON" :evil: . But I said what the hey...I know the float needles are working now, I'm going for a ride...THE FIRST RIDE I'VE EVER HAD ON THE BIKE (non counting when it was running roughly and I rode it across the lawn and into the garage). The weather was getting bad, but held off long enough to enjoy the last of the daylight. Wow...it sure pulls. There's still plenty to go through and check, but I think I can pass inspection, and I'm just dying for another good day.

EDIT: I went ahead and finally added some before and after pics to the gallery...but there's lot's more cosmetic work to be done!

 

"Subsequent investigation in this forum revealed, that 3-3.5 is what the factory set the pilots to, and that was lean"
"I think I started them all at 3...thinking that would be a little rich, "

more turns out = more vacuum= more gas=richer
less turns out = less vacuum= less gas= leaner

 

Hey Polock, I understand how to adjust the pilots, I was just mentioning a starting point. My carbs were a mess, and the PO was using pod filters, exhaust was leaky, so I didn't bother keeping track of their settings when I was tearing them down and thought that 3 turns out was a good starting point. For me at least, I think 4 would have been better. After that is was synch and colortune.