Inconsistent throttling/idle

Hey guys,

I changed my oil (think easily half of it was gas, as there appeared to be more than a gallon of fluid that came out, and it stunk like gas) and plugs (only three cylinders were firing before, and all four firing now), but it seems like the engine is getting fuel inconsistently. Unless the petcock is on prime, the engine seems to run out of gas, so I think I may have a vacuum issue (new vac hose just installed) - any ideas how I can test this? Also, the bike is tough to start unless I have the choke fully engaged, so there definitely seems to be an issue getting gas to the engine.

Also, when I rev the engine, the idle stays high until I drop the bike into gear - I was thinking this may be due to the carb pistons sticking, but I just polished them and had a successful clunk test, so wondering if it's an idle screw or mixture screw issue - any thoughts? I'm still reading through the threads to figure out how to adjust the idle, but figured I would see if any of the experts can help me diagnose. Appreciate the help!

Bill

 

sounds like you need to investigate the petcock, id also double check the carbs and make sure all the passages are pristine also check your floats and needle valves it sound like your sticking open (full crankcase). have you done a carb sync? how are you valve shims while your in everything?

 

I was having the same issue then Rick sent me some detailed stuff on carb cleaning and it helped out allot... with the high idle it was an issue with my flout being set two low due to a new needle... still having the same starting issues... I’m going to be replacing the vacuum house to the tank as well as checking the cracking in the carb boots for leeks

always remember to drain your carbs before you store your bike in winter... or this will happen...
well i had a photo of a Gummed up enrichment valve (it looked like a chain smokers teeth after 3 years of not brushing) but it will not load...
suffice it to say that when the gas sits in the carbs for that long you will need to spend at least a half hour cleaning each carb thoroughly

Also when I was cleaning my carbs I was lucky enough to be cleaning out the mixture screw threads and notice that one of then didn’t have anything in it… I did not take out the washer or O ring because I didn’t have a tool (bent paper clip or any other piece of wire handy to take them out) so I checked out the rest of them and sure enough others were missing or not there at all… so I ran up to the motorcycle shop and got there about 10 min before they closed…
So make sure all the fixings are there that can save you some time digging through the carbs time after time…

 

The petcock functions as follows when engine is running the petcock should flow in all positions: on, res and prime. With engine not running the petcock should only flow on prime. If your crankcase had fuel in it whether the petcock functions correctly or not then the floats are either stuck open, leaking or set to high. You should also check the vent in the top of the fuel tank. Looks like you need to go through the carbs. PS the carb (pistons) slides are not in use at idle

 

So, to summarize:

Gas in the oil requires both a petcock issue (or being left in PRI) PLUS one or more floats not shutting off correctly. This can be due to crud in the float valves, or improper float height adjustment.

Your idling issues and starting problems are generally symptomatic of floats not being correctly adjusted AND/or carbs needing to be sync'ed.

Just adjusting the idle won't help if they aren't synchronized. And it's hard to get a good sync if you need a valve adjustment.

Also: The new vacuum line: Is it vacuum line, or just a piece of tubing? Unless it's actual vacuum line, it could be collapsing in on itself once warmed up and with vacuum applied.

 

Really appreciate the advice and feedback. I haven't sync'd the carbs yet, as I'm still not sure how to do it, but that'll be next up, along we re-adjusting the float heights. I read through Fit'z valve shimming thread, and that looks a bit daunting, but I'll need to look at that as well. The piston sticking concern was because the engine wasn't returning to idle immediately when I let off the throttle, but it sounds like that's probably not the issue.

The vacuum hose is brand new, and it's definitely vac hose, not just tubing - Chacal hooked me up.

Can someone post a link to a good carb syncing thread on this topic for me? Do I need to get a colortune tool to sync the carbs?

 

Not sure of a thread here...so will leave that to others...

but here is a link on how to sync carbs....http://dave_jack.tripod.com/id38.htm

for the special tools, eg the all important YICS tool...see Forums › XJBikes Marketplace › XJ4Ever - Supporting Vendor › XJ MAXIM, SECA, AND TURBO PARTS CATALOG

 

i agree with fitz hi idle then slowly coming down is a sure sign of carbs being out of sync. You definitely need to get the float heights set properly first. After the plug not firing i would replace the plugs better safe then sorry. Also if you have to pull the tank to pull the carbs just rebuild the petcock its worth piece of mind

 

Does the bike only have 1500 miles on it, as in your sig? Or did a "0" get left off?

If it only has 1500 miles on it for real, you have 1500 more before you need to do the (initial) valve adjustment. You must have fixed your sig since I posted about valve clearances.

 

If you drain your bowls, your more likely to get varnish due to the gas drying up faster.

 

i'd get 4 carb rebuild kits, Petcock might be leaking gas into it. But i honestly leave my bike on PRI all the time and it doesn't give me no issues with anything like that. carbs might need to be cleaned, then synced up. Generally when they are out of sync, they have a screwed up idling that is EXTREMELY annoying and frustrating. you can buy a sync kit on ebay for less than 60 bucks. i'd just buy a rebuild kit with it as well, with all new gaskets. that might help.

 

Fitz,

The ODO says 1500, but the speedo is currently not working, so I'm not sure how many miles have been ridden that haven't been recorded on the ODO. I did adjust my sig recently to reflect the miles and current status. Appreciate the link to the external thread - will keep looking on this site, too, as I'm sure there has to be some good tutorials on syncing.

I did put two new float valve assemblies in the carbs, and used the needles that match the originals, but may just go ahead and replace the other two anyway, just to have a fresh start.

 

i've nver drained my bowls in the winter. specifically for that reason.

every other year though i'd take the carbs off and hose the insides down with carb spray.

 

You could try adding Seafoam in the last tank full of the season as I do. I put it in at the gas station and by the time I ride it home (2 miles) it is already running thru the carbs. Then I shut off the gas (manual shit off valve on mine) and let it sit like that all winter. Seafoam keeps everything clean and also is a fuel stabilizer, so it starts right up in the spring, no problem. I never need to clean the carbs anymore. I also have an inline fuel filter that takes care of trapping the dirt.
I have never drained any float bowls in any of my bikes, ever. I don't see why you would want to if there is clean gas and fuel stabilizer in the gas, you should be good to go.

 

Did you then check/set the float levels using fuel and the "clear tube method?" Very important. Correctly verified float levels are very important; if they're off it will throw off all other tuning efforts.

I wouldn't worry about the valves unless you've put 1500 more miles on it; if so, then by all means they need to be checked, that's the VERY IMPORTANT "initial" interval.

So, assuming valves in spec, then:

Float levels verified as above;

Bench sync;

Vacuum sync;

Fine (mixture) tuning (ColorTune, plug chops, etc) is last.