Carb Questions

So I've had my bike "running" if thats what you want to call it. Even took it for a little ride. It doesn't like to start but with enough patience and sunlight ( still pretty chilly up here) it will. When it does start, it either dies right away or runs terribly and will only run with choke on.

Mixture screws are set at 2.5 turns out. Valves are in spec, carbs have been cleaned numerous times, and have been benched synced. New plugs, compression results were 1: 130. 2: 130. 3:125. 4:130. a little low but this was cold so the numbers could change once warmed up right? I have spark on all 4 cylinders. My number 1 cylinder is firing sporadically. The plug is colored but the header doesn't get hot.

Id like to get it vac synced but shouldn't all the cylinders be running? I had it running today a little and when it stalled i saw a puff of smoke or something coming from the enrichment plunger and the circlip on the end of the carb of the number 1 cylinder. Clearly I need to rebuild the top end of the carbs but that wouldn't be the only thing causing these conditions would it?

 

When you cleaned the carbs did you
remove all jets and emulsion tubes -clean
remove mixture needles and clean
blow all carb passages with air to make sure they are not plugged
check slides and diaphrams
wet set float levels
?????
Your symptons tell me you need more detailed carb work

 

Yes I had most of the carbs apart. The only things I couldn't get out were the enrichment plungers and the butterflys because if i tried any harder I would have broken things, they were stuck good. I did wet set the floats, New needles and seats for the floats. Emulsion tubes came out all the jets and such were soaked in carb cleaner. I didn't sand the bore but everything went "clunk" nicley. The boots were cracked on the out side but no visible cracks on the inside. I patched them up with some air plane gasket maker stuff. REAL thick and goopy.

 

the little puff of smoke would indicate backfiring through the carbs.

The fact that it won't run unless the enriching circuit tells us that the carbs STILL aren't completely cleaned out. Did you (and this goes for ALL 4 carbs, no matter how clean other related parts may look):

pull the emulsion tube AND make sure that all tiny side holes are clear
pull the mixture screws, washers, o-rings a clean them
pull the jets under the diaphragm
you MUST pull the enrichers out. Use a 6pt deep socket.
make sure that all the air jets are put back in the CORRECT spots

Not saying you haven't done this, but you're gonna have to do it yet again. There's others on here that have had racks off a dozen times, we've tried diagnosing carb issues, it's been sworn up and down they're correct, blah, blah, blah,etc......... gone other routes, suggestions, etc.... and I remember one case, where after other people looked at parts, and so on, turned out the carb rack was not assembled quite squarely. Redid that, and problems were gone. So.......came back to carb issues anyway.

I know this whole reply is one you don't want to hear, but I said it anyway.

Good luck, keep us posted, stick with it.......it will eventually get there.....

dave fox

 

Just looking through some pictures to make sure I got all the jets in the right places, are larger numbers larger bore on the jets?

 

Yep.



-Kaya

 

Had the carbs apart today and discovered that in cylinder number one I had two 45 jets and in number 4 I had two 107's. Any ways I continued to clean them out (I even managed to get the enrichment plungers out) and got a whole bunch of grime out, put the jets in the proper placer and put them all back together. I replaced the o-rings in the gas tubes too. Fired up right away but I had the same problem as some one else who posted earlier today, racing engine. I played with the idol screw. It went from hi rpm (dont know exactly how high as tach isn't working atm) to not starting and just before I called it a day (had to pick up the girl friend from work) it was idling better but still not perfect, then it started to die down and wouldn't stay running unless I kept blipping the throttle. Im gonna try and get it to a point where I can do a running sync and see where I am at. MOST of the running it did was with the choke on. Any tips? PLEASE DONT TELL ME I NEED TO CLEAN THE CARBS AGAIN..... that would really suck

 

Trying not to state the obvious but it sounds like you're cutting over to the mains and there's still something up with the idle circuit.

I'm even tempted to think that maybe it's not giving it enough idle mixture screw... If you have a spare set of plugs i'd start at 3 turns out and see if that helps. Keep the extra plugs in case they get fouled.

 

Three turns for the idol or the mixture screw?

 

Mixture screw, sorry.

 

So I tried turning the mixture screws up half a turn and tried to start it. It wanted to start and fired a few times but wouldn't go. Upon feeling the headers 1 was cold 2 was warm 3 was cold and 4 was warm. I checked for spark on all cylinders and they are all about the same, light purple ish blue ish. Not a great spark but not bad either. I got no clue...

 

Just read through this and I didn't see a note on if you have your float levels set. Did you check each carb and wet set the floats? Also did you bench sync with a piece of photo paper, film, or index card? Your difference between exhaust pipe temperature (and therefore cylinder firing) may be due to lack of air. Low float bowl levels can also have a large impact on air to fuel mixture and lead to this problem.

I know you don't want to hear it but if you don't have everything listed exactly spot on you will need to pull the carbs and at a minimum tackle these items.

 

The carbs and valves have to be done right,,,or it will have you chasing your tail till dooms day cant say it enough,,,,i learned the hard way,,

 

Carbs and valves are done....^^^^^^^

 

Been thinking about it and really the only thing I can think of is carbs if I have spark on all 4. Is there anything else it might be?

 

No Plugs in the Airbox? fresh gas? we're all wanting it to run ... do you have all the vacuum holes covered on your intake manifolds (well minus the #3 hole, used for the petc0ck). Yics port bolt sealed?

 

Shouldn't be anything in the air box but a filter. Its brand new. Gas is from when I set my floats a few weeks ago with some fresher stuff mixed in. Vacume holes are covers and there is no yics on this one.... carbs then?

 

So I went to pull my carbs off again today and figured I'd give it another shot at starting it before I got too far, and what do ya know, it fired right up. I just got my colortune plug in the other day so it was a perfect time to start syncing and tuning.

It would only run with the choke on or if I kept on the throttle a little bit. I did get it synced which helped a bit but I couldn't keep it running long enough with out choke to do the color tuning.

I know it still sounds like carb problems but when I set the petcock to prime it idles perfectly (vacuum leak?) . I ran an unlit propane torch along the rack and boots and didn't notice any changes in idle speed. Or is this just another symptom of the carbs? Floats too low maybe?

 

Have you rebuilt your petcock? If it runs in prime but not in on then it sounds like the petcock vacuum valve is not functioning properly.

 

That makes sense I guess. I had considered the petcock but I was thinking that if it wasn't working right it would be leaking all the time. But if there is a vacuum valve in there, then thats a probable culprit.

Thanks, will check it out.

 

Watch also for watery fuel. Got watery fuel right after I got mine dialed in. Rode to work & it would not hit just off idle. Put in new fuel & problem went away. BTW It was from Shell. Still use it off & on but never had that problem.

 

Didn't have to rebuild the petcock, the valve passage was just plugged up. everything inside the petcock looked good.

It seems to be backfiring into the carbs. Lean???? Still gotta color tune and re sync, so hopefully that will help.

 

Since you played with the idle screw and it wouldn't keep an idle afterwards and now you have to use a little throttle to keep it going... it might be that your idle screw is too far out and not letting the butterfly valves open a little to keep the idle, therefore needing some throttle to keep it going