Cylinders not firing at idle

Ok, if you have been following my long and arduous story of 1 cylinder not firing on my 82 Maxim 650, then welcome to the new version of the story. So far, I have completely disassembled (up to the point of seperating the rack, but not quite that far). Cleaned everything I could find to clean as spotless as possible, replaced a couple of jets with ones I happened to find at a salvage yard yesterday (but still need to replace a couple others because they are badly damaged but still flowing). Put it all back together, did a little dance (breathing in carb cleaner all day is NOT a good thing), fired it up and....wait for it...#1 & #2 are not firing at idle. If I rev it up, they start firing, but at idle, it's just dumping gas in the cylinder for grins, but I don't think it's enough fuel. I pulled the plugs and threw in the colortune to see if maybe I got the mixture all screwed up during cleaning, but notice NO fire. Lots of spark, but no fire.

Which portion of the carb provides the fuel while at idle? I'm pretty sure whatever it is, I must have clogged something inadvertenly while trying to clean things.

 

IDLE jet's do, Located right next to the main jet (Mikuni Carbs)

 

You need to turn the pilot mixture screws out to let more fuel in. They located beside the choke plungers. This is what the colortune is used to set.

 

BlueMaxim, turning the mixture screws didn't really help. I originally had them set at 3 turns out as a baseline for starting from and intended to go from there. But, at idle, I'm getting no fire in the cylinder no matter where the mixture screw is set. Looking at the colortune, I can tell that I'm getting all sorts of spark, but there just seems to be no fuel for it to light until I give it a good bit of throttle.

I bought some seafoam last night and I plan on soaking the jets and the little pickup tube in it tonight (if I get a chance). Hopefully that will help clear it up a little.

 

well at least you narrowed down the problem a bit. You are one step closer to figuring out what is going on. Good luck with it.

 

Then Maan gets the blue ribbon!, it has to be the idle jets. This does mean pulling the carbs again if the Seafoam doesn't work. The idle jets have such a small hole it is hard to see light coming through unless the light is bright. But once clear they do their job well. I would also install an inline fuel filter after verifying that they are clear. After the Seafoam treatment if it doesn't work, I would first blow the jets out with compressed air and see if that clears them before having to remove them.

 

BlueMaxim (or anyone for that matter), would I be better suited putting the seafoam in the tank and running around town for a few miles (knowing this won't use up a lot of the tank) or would it be better to pull the carbs and jets and just soak the parts in the seafoam.

 

soak the parts...then blow out with compressed air. If you don't have an air compressor, just use that air in a can stuff they use to clean computer keyboards and internals.

it works.

 

Cool, that's pretty much what I was thinking, especially since the problem is at idle, so the necessary jets/orifices wouldn't be getting used while riding around. And I'm set on the compressed air. Have a cheap air compressor that works real well at blowing air around, doesn't do a good job doing much else though.

 

If you are going to soak them then soak them in carb dip. Soaking in Seafoam alone doesn't do much good. Mix some gas in with it and that would be better. Seafoam is meant to work with gasoline that's why I suggested running some through the tank. One thing that would be better than a can of compressd air is a can of Berryman's B12. That would give you the compressed air can and a carb cleaner. If you get carb dip remember that only the brass bits go in there. Don't soak the carb bodies. There are orings in there that will not be there if you do.

 

I haven't gotten a chance to get back into the carbs, but there was one thing that I just remembered that I didn't include previously. When I was running the bike the other day and realized that I was getting no firing at idle, I noticed something quite odd to me. The intake portion of the carb (the portion going into the engine) was rather cold and sweating. Any ideas what would cause that? I've NEVER seen a carb get cold and sweat, car, bike, radio control plane, never.

 

IF it was the cylinder that was not firing then it is quite normal. Fuel plus expanding air makes things cold. The cool air inside the venturi will make the humid air condensate on the outside of the intake. Most of the time the heat from the firing cylinder keeps the intake jst warm enough to stop the condensation.
We have this problem so often on aircraft that part of the throttling down procedure is to pull the carb heat on. A valve that runs warm exhaust air to the carb to prevent icing. A condition where ice forms on the backside of the throttle plate or butterfly valve.

 

You know, if I would have thought back to my r/c plane flying days, that would have made sense. Not that r/c planes have THAT much in common with full size, but because I did all sort of various research about planes while I was flying them.

I took the 2 offending carbs apart and cleaned the living daylights out of them again and reassembled them and put them back on, same problem. So, I hooked up a funnel to my fuel line and poured seafoam into the carbs that way. Started it up and let it run until all sorts of smoke was coming out and shut it off. I'm going to let them soak that way. Sound good?

 

Sound good! In the morning fire it up and let it run for a few minutes and see how it goes.

 

just a thought, if it is too lean pull up on the "choke" plunger and it should get some fire in the hole, or if it's too rich pull off the vacuum plug a bit and see what happens
r/c gotta love a scatcat 500 with a fox 45 swinging a 8x8, no gear hand launch
land in the crown vetch

 

well, I've gone through the carbs about 40 times in the last couple of weeks. Had a friend from another forum come over and help me look at it. We concluded at the time that the issue was my float needles weren't allowing enough fuel in the bowl because when we tried to do the float level test, there was barely anything coming out of those 2 bowls. Bought all new float needle assemblies, installed them, and same freaking thing. So, I figured that somehow I had screwed up the float levels with all of the off and on over the past few weeks. Took them off tonight, adjusted all of the floats to be at the same level while upside down (as a baseline). While I had the float bowls off, I decided to clean out the drain screw holes and lo and behold the 2 that were producing next to nothing were partially clogged. So, I got them all back together after cleaning the bejesus out of them again. Bench tested the fuel level and everything was doing good. So, I put them back on the bike.

For all of those that thought this would be a happy ending story, wrong. The bike is STILL not firing on #1 & #2. I'm just about to the point that I'm going to start parting the dang thing out. No one in this area works on these things (business) and I can't seem to find anyone local with a lot of experience with them, and honestly, I'm getting about tired of having to walk around the d*mn thing everytime I go mow the yard, it just reminds me how p*ssed off I am at the dang thing.

Just had to vent.

 

Why don't you check to see that the Top-End Siphon Tubes for 1 & 2 are CLEAR -- Using the appropriately sized tool from a Welder's Tip Cleaning Set ... probe the Siphon Tube followed by blowing-it-out good with Carb Cleaner.

Set the Fuel Bowl level. Fill it to near overflowing. Look at level in Siphon Tube Well.

Use Q-Tips to absorb fuel in the Siphon Tube Well.
Fuel level should slowly and gradually refill to the same level as in the Fuel Bowl.

If it's all good ... do 3.25 OUT on the Pilot Screws.
If the two cylinders still don't fire ...

OK, then ... part it out!

 

Does it pickup running on those cylinders when you crack open the throttle and just not idling on 1 & 2?

If they are totally dead, have you verified there is spark ?

 

I know you really dont want to hear this but it still sounds like the problem is with the idle circuit. I had to put a single copper wire from a 12 gauge wire into the suction tube to get mine clear. After that a shot of B12 cleared things righ up. Also check that the small ports on the top side of the inside of the mounting side are not clogged. Especially the one almost hiden by the butterfly. This should be the one farthest forward. This is the one for the pilot screw. If you remove the pilot screw and spray carb cleaner through that small hole is should come out the hole where thee pilot screw came out. Make sure when reinstalling the pilot screw that the tiny o-ring and washer are still there and in the correct order or it wont seal properly. spring,washer then o-ring.
Wish I could help more. Very frustrating, to say the least. Send them on up to colorado and i'll take a look.
How is the compression on those cylinders? valves adjusted?

 

Go to the drug store and get one of these Ear Syringes.

Get a can of Spray Carb Cleaner ... put on the Red Hose ... shoot a bunch of Cleaner into a glass and get a good amount to Clean-out the Pilot Mixture Screw canals.

Remove the Screws, springs, teenie-tiny flat washer, and the even teenier and tiny-ier, liddle-biddy O-ring.

Fill-up the Syringe and squeeze-out some Carb Cleaner in the Pilot Screw Hole. Squish-out some cleaner and suck it back in. Blow-out the hole in the Carb Body with a good flush ... then, hold your finger over the tiny hole in the carb body while you stick the syringe in the Pilot Screw hole ... and do pretty-much the same kind of unclogging you do when you flush the toilet at your neighbors and see that there's a problem. (Without the panic)

Work at it until you can force Carb Cleaner through the passages and out the lower-end siphon tube.

Blow-out the passages from the Bottom-end through the top ... too.

Use the syringe to power-flush the ports at the bottom of the fuel bowl.

When everything is flushed-out and flowing ... guaranteed ... set the Pilot Screws in at 3 Turns Out and Run it!

 

Here is an odd question, is it possible that one of the exhaust headers being held on with only 1 bolt at the collar could cause the 2 cylinders to not be firing? like maybe it's screwing up the compression (haven't checked the compression yet, haven't caught my neighbor at the right time to borrow his guage).

I was messing around with the bike more tonight trying to see if maybe it wasn't running right because the carbs were out of sync when I noticed that I was getting dripping coming from the #2 exhaust header. Got to looking and there is only one stud there. The other one has been sheared clean off.

 

If it was dripping fuel. then you may just need to change your plugs to get it to fire. Its worth a shot. Swap the two outside plugs for the two on the inside and start it up. If it missis on the outer cylinders then there you have it. It is pretty easy to foul plugs. Too much seafoam always fouls mine.

 

Samsr, you may have hit the nail on the head. I know I've been told a few times during this that I need to check the plugs, and I have, but I finally decided to switch out the 2 that weren't firing for the ones that were and it seems like all 4 were firing like they were supposed to be. Not sure because not long after I switched them and started it up, I just happened to notice that there was a clump of wires that were getting mighty toasty and shut the bike down. I'll start another thread with a picture to try to get some help one what this clump of wires is so I can know where to start looking.

 

I had this exact same problem a few weeks ago. I would check to see if the carburetors are synchronized and that there are no leaks in the engine side of the intake rubbers.

 

based on what youve already done with the carbs, id say with 95% certainty. You dont have a fuel delivery problem. First verify this by taking the plugs out cleaning them and drying them well, then choke the bike and turn it over leaving the plug wires dissconnected. pull the plugs, ill bet they are all soaked with gas. Fuel delivery is not youre problem, you have a valve problem in the cylinder in question. It could be as simple as inncorrect clearance or may be a stuck open valve.You need to compression check the cylinder to determine this. I know its not spark if youve verified you have good spark unless the spark is impropperly timed, which i doubt is the case, and after what youve put youre carbs through, I highly doubt its a delivery problem, but I can say with confidence and almost assure you, its a valve related problem, ive had these exact same symptoms with many of my rides, and have usually gone after my carbs first only to find out later it was a valve problem. I wasnt even a member of this forum before now but when I seen youre problem and what youve already done, I had to chime in.