Round 2

Alright, so I was about to rebuild my bottom half, but I don't think that's the problem with my bike. I did a wet compression test today and came back with these readings 155-135-150-150. I think that's pretty reasonable. I shot some marvel mystery oil into all the cylinders too so I can hopefully loosen up any sticky valves. My exhaust readings once the bike was warmed up were about 135+ on #1, 3 and 4. Number 2 was reading about 90 and I could grab ahold of it and hold right on with no problems. It is about that time when I start missing on that cylinder. I have spark for sure, I tested it with 3 different spark tools to make sure it was good. I have compression, or at least 135 psi worth. And I know I'm getting fuel to it, because the plug was soaked with gas when I pulled it. It runs great when the engine is cold. Valves are all perfectly in spec too.
Aside from the problem with #2, I'm still fouling plugs like there is no tomorrow. Within 2 miles they're completely black. I've adjusted the mixture screws the full length by degrees, and it fouls them at every point. I think this bike came from sea level, and I'm over a mile high. Any recommendations for jet sizing for high altitude? Most of the riding I do is well over 5000 feet. Or it would be if I could ride more than 3 miles at a time. I'm definitely going to rebuild the carbs, I know there is an air leak on the throttle shaft (which isn't helping to lean out my mixture, as I am fouling plugs even with that leak). Cleaning wasn't enough for them. My number 1 cylinder doesn't foul out, just 2,3 and 4. It also has the highest compression. So, the breakdown of my problem as far as I can see it is as follows:

- cold exhaust on #2, even with fuel, air, compression, and spark. With colortune in I can see the spark, but fuel does not ignite.
- fouling #2, 3, and 4 no matter what the mixture screw is set at
- runs good until it comes up to operating temperature, then runs poorly until I let it sit for a few days.

I'll take any and all advice. I don't mind working on it or spending many hours on something that may help fix it. If there is any other information you might want, I probably have tested it already and have a reading.

 

I think you answered your own question. If you're fouling plugs even with good spark, you're practically pouring fuel into those cylinders. It sounds like carb surgery time! :mrgreen:

the fouling on the plugs.... does it look oily or just sooty black?

the latter would mean your mixture is way too rich, which could be caused by a whole host of issues -- leaking float valves, float level too high, wrong jets, blocked air jets, sticky slides... someone might chime in with more. This would also be consistent with the fact that it runs worse when it's hot.

 

Just sooty black. The floats are set exactly where spec says, so I figured that would be the only way to flood out the cylinders like that. What could cause a condition that rich as far as gaskets and o-rings are concerned? The carb is clean as a whistle, but I'm going to rebuild it anyhow just to eliminate any other problems I'm not aware of. I can't find a thread on the forums that recommends jet sizing, but I'm sure there must be one somewhere on here. I figure I might as well do the jets if I'm tearing it all down anyhow. Or would it be better if I did the rebuild and see how it runs with what is in there now as far as jets, and swap them out if the problems persist?

 

Did you do a dry compression? Wet is going to show higher although at 135 wet there should still be enough compression to run OK.

Did you have the idle mixture screws out? There is a washer and o ring at the bottom that flip very easily. Washer should be on top. That can cause problems. Also saw a member that had damaged Idle screw that caused a lot of problems. you may want to inspect them carefully.

Check the enrichment circuit too.

Stereo also mentioned blocked air passages - that's a good thought. Most running issues are carb related. I cleaned mine twice and did it right but still had issues (not near the problems you are having). I finally rebuilt them and changed all the seals o rings and the needles and seats. May not have been required to do them all but it resolved all my issues.

 

I posted this graph in your other thread Shad:

http://justkdx.dirtrider.net/images/Davids_Jetting.jpg

So if your 5000 feet above sea level and ride in 20 degree C air temp, you would adjust the size of your jets by roughly 0.955 So if for example, you had to change a jet that was a #100 jet, for your altitude, you'd goto a #95.5 ( 100 * 0.955; round up to whatever the closest jet would be) prolly #98

I don't know what your stock (sea level) jets are, but maybe try the change in jets to lean out your carbs.

 

Cool. I remember looking at that chart before and not knowing what I was supposed to do with it lol, but I get it now. I put together a list for Chacal a minute ago, so once I clear it with the "boss" I'll hopefully be in the carb rebuilding trade by the middle of next week. My original size for Main Fuel Jets is #120, so I'm going to order some #116, as it's the closest match for me according to that chart. I don't know what to do about the cylinder not firing, hopefully it's something simple like a clogged starter jet. Wish me luck. Any other ideas in the meantime will be great too, I'll check out all of the things listed so far while I'm at work tomorrow.

 

The dry compression tests I've done on it have shown results pretty consistent with the wet test, only about 80% of the psi all around. My "clunk test" goes off without a hitch, but I repolished the pistons with fine grit finishing paper anyhow a few weeks ago. I can't find any leaks in the intake boots, and no clogged air passages that I have found.

 

have you checked your coils to spec (see repair manual) i checked spark with a spark tool (showed good) but later found that the coil was the problem, replaced it and fixed, the problem coil was weak in the secondary winding and still sparked but not enough.

 

Well, got my carbs rebuilt. The orings I ordered for the pilot mixture screws were slightly smaller than the original ones, but I think they'll work. I spent all day today trying to get it running. After spending 4 hours trying to get the floats right (which I may be a little bit low on 2 bowls) I put them back on the bike. I started it up, it barely ran. I couldn't get it to idle at all. It was either full throttle, or it would die right away. I adjusted the pilot air mixture screws out with a colortune plug in to see what was going on in the cylinders. At 2.5 turns out #2 and #3 cylinders were not even fining. I had to turn the screws all the way out to get either cylinder to fire. (I'm hoping this will turn out to be from float levels set to low, any thoughts on that?). I finally was able to get it to idle, but it would backfire in #1 and #4 even when the burn was tinted orange through the colortune. I had replaced the #120 main jets due to an impossible to tune out rich condition I had prior to the rebuild. I put in #116 main jets. I am now considering putting the #120's back in if I can't get the lean condition fixed. I'm at 5600 feet, so #116 was about the right size according to a chart listed above in the thread. I cannot get much more than a slight orange tint in #1 and #3. #2 and #4 are blue right up to the point where the pilot mixture screws are out of the hole. I made sure the orings and washers were in properly, although I am concerned a bit about the smaller size oring, even though it was a very small difference in size. My questions are: Anyone had issues with not firing in a cylinder from float levels too low? Has anyone tried smaller jets and had similar problems? Any other ideas I might look into? I have it to a point now that it will idle, but the #2 and #3 pilot mixture screws are only in about 1 full turn from falling out. This is the only setting for them that would keep the bike running. Thanks again guys, I really appreciate all your feedback and help.

 

The Pilot Mixture Screws don't enrich the mixture any more when you go past it "Fully Opened" area.
The Metering capability is Fully Opened not far beyond 3-Turns Out.
All you do when you continue to turn the Screw beyond 3.5 Turns Out is make it easy for the Screw to vibrate loose and fall out.

What you need to do if you need more Pilot Mixture Richness ... is Bump-up the Pilot Jet size by and increment or two.
The sizes of the Jets are stamped on them.
I can't read them any more, but I know they are there!

Increase the Pilot Jet Flow and you'll have more Fuel getting pulled-up to be regulated by the Pilot Mixture Screw.
Remember ... the Pilot Mixture Screw only regulates how much AIR is being drawn-in.
When you allow more AIR to enter ... the AIR passes-over the Pilot FUEL Jet Passage and BRINGS what FUEL is present above the Pilot FUEL Jet along with it.

If there is more FUEL above a larger Pilot FUEL Jet ... the quantity of FUEL getting drawn-up by the passing AIR will increase richening the Mixture.

 

Shad, you need to set the mixture screws at about 3 turns out each and then synch the engine before you start messing with anything else (also, have you checked your valve clearances?). An out-of-synch condition can lead to all sorts of next-to-impossible to diagnose and/or solve situation.

 

valve clearances are all in spec. I could not get the bike to run with any of the pilot jets out only 3 turns. Initially I had them all out 2 1/2 turns, but the bike wouldn't fire in 2 of the cylinders at that setting. I bench synced them before putting them back on. I tried to sync them a bit more with gauges, but it would not run anywhere near 1050 rpm. I could get it to run without stalling, but only with the choke on full and the RPMs at around 3500. I'm going to take the carbs off again today and see if there is anything I can do. I might try putting the #120 main jets back in after I clean them up a bit.

 

I'm not 100% sure (somebody will correct me if I'm wrong), but I think that your main jets should not affect the idle at all unless the pilot jets are seriously clogged/undersized. It seems that you are trying to idle the bike on the main circuit (which will never work right).

Are you certain the pilot jets are clean?

Good luck.