Engine won't idle after clean and rebuild

In March I cleaned the carbs according to the church of clean, clunk test, bench sync'ed, wet set the floats @ 3mm, did the valve shims within spec, vacuumed sync'd the carbs and the bike ran great. Started @ the touch of a button...

Two weeks ago I noticed fuel dripping from the fuel rail. Since I did not break the carbs apart prior, I ordered the fuel rail O rings, throttle shaft seals, and the pilot mixture screws springs, washers and O rings.

Broke the rack down and removed all the bowls and floats. Everything looked clean, but since I was "in there" I proceeded to redo the church of clean. No drills or bits, just some carb cleaner and compressed air.

Replaced the shaft seals and fuel rail o rings, used silicone grease on all parts indicated. Reassembled the carbs on the racks, bench synced, clunk test and wet set the floats.

Reassembled bike, wouldn't start.

Items verified..
Fuel verified visually thru filter and bowl drains..
New spark plugs
Battery new 2 months ago.

Unassembled, reverified floats in correctly and pilot screws are assembled correctly, turned out to 3 turns.

re wet set....re bench sync...

reassemble on bike...wouldn't start
Bike would start with a small spurt of carb cleaner in #1 vacuum nipple, but would rev to 5000 rpm without choke on.

verified..
no air leaks per propane check
no binding of throttle cable..
enrichment circuit is closed per plungers on carbs.

removed carbs,

verified that butterflies are installed with good fit to carb housing,
verified springs and linkage is lubricated with marvel mystery oil.
re verified clunk test.

re bench sync to .015 bottom center clearance.

reinstalled carbs, boots all good, linkage all good, vacuum nipples new, vacuum hose from 3 to tank new, air filter 2 mos old, no ethanol gas,
linkage good and verified.

Engine wouldn't start until use of a small spurt of carb cleaner in #1 vacuum nipple.

overnight cold engine..Rpms started around 3000 with full choke, as rpms increased over the next 5 seconds I backed of the choke trying to idle the bike down, it went to 2000 rpm for about 15 seconds and then started to increase. As it increased I shut off the enrichment circuit completely and the rpms increased to 5000 rpms somewhat quickly.

Bike restarts without enrichment circuit with a touch of the starter button every time, but races to 5000 rpms....blipping the throttle to 6000 rpms has no effect on lowering rpms below 5000.

As I said, the bike was running great before I replaced the shaft seals, fuel rail o-rings and the pilot mixture springs,washers and o-rings.

I know I am missing something but hadn't been able to figure it out.

Any useful ideas? :?

 

Unscrew the big idle knob a bit. Sounds to me like it's just got the throttles "cracked" too far to begin with.

 

When doing the bench sync make sure the idle adjusting thumb screw is in the middle of the thread length, so after the bench sync you can back those butterflies right off, or as Fitz says, if one of the butterflies is just a crack open it will send it racing off.

 

ok..turned the idle adjust knob until it had no contact with throttle mechanism. Bike started with touch of the starter button with no choke. When it started it jumped to 2000 rpm for just about a second and then idled down to 1100 rpm. Over the next 60 seconds the rpms increased and maxed out at 4000 rpm on it's own.

I know the diaphragms are good and the clunk test is good.

I fiddled with the butterflies this am to make sure they were seated good. When I shine a super bright led from the back of the carbs I can see just a hint of light coming through on the very bottom, not even a thickness of a hair without the idle knob in contact with the throttle mechanism on the carb. Is that the problem and if so, how or what is the procedure to set the butterflies so no light shines through because I couldn't get any of them "light proof."

 

Removed carbs and worked on setting the butterflies in closed position with no light coming through. Fiddled with for a while until all butterflies when closed showed no light when backlite.
bench sync'ed and reinstalled carbs.

Started with a touch and idled low around 600-700 rpms. I had backed of the idle adjustment knob to hardly touching before starting so I adjusted it to get 1000 rpms...

Took the bike for a 10 minute ride around the neighborhood and then did a vacuum sync.

Bike idled fine at 1000 rpms..

Took the bike out on the highway and after a 6 or 7 miles, the bike is idling at 2200 rpm.

Finished a 15 mile drive and the bike is still idling @2200 rpm...

done with it for the day....need to do some other things...will get back at it tomorrow afternoon...

 

All you probably need to do is turn the idle knob down a tad more.

(Ten minutes tooling around the 'hood is NOT fully warmed up.) Once it got warmed up, your idle is simply set too high (by a very little.) Just back the knob off so it idles at the recommended 1050rpm AFTER about a 20-MINUTE ride to get it fully warmed up.

 

ok..backed off the idle adjustment knob completely, also used the adjustment on the throttle cable at the handlebar to give some slack and after 1/2 hour of highway riding the bike is idling at 1800 rpms...

Also, cold engine start this am, only needed 1/2 choke and bike stayed at 2000 rpm, after a minute it started to rise and went to less choke and the bike idled around 1500 rpm. At no choke, 5 minutes running, the bike idled at 1100 rpm.

Any ideas?

 

Have you done a RUNNING (vacuum) synch with the YICS passage blocked?

 

did now...and after a 30 minute highway ride....have blisters to prove it...haha....

blocked YICS, turned idle knob in two turns after contact.

Got all cylinders in sync and backed down the idle knob, readjusted as needed.

Reassembled bike and removed YICS blocker..Ran bike for 15 minutes on the highway and backed down the idle adjustment knob until it has no contact with the throttle mechanism. Bike idles hot at 1300 rpm.

which is not spec, but I had never had the bike idle at spec prior. It always idled at 1300 from the first carb rebuild in March.

 

Bruce, did you synch the engine using synch gauges (and with the YICS tool installed)?

 

yup....sure did....

 

If you make it richer, the idle should drop.
Is there a possibility that an enrichment plunger is bleeding some air??
Did you check the head-to-intake seal??

 

Probably a dumb question, but have you checked the throttle linkage. I wouldn't take much to cause it to idle high.

 

linkage has been verified free and unobstructed..

Making it richer...is that turning the mixture pilot screws out or in?

head to intake seal and plungers are air tight per propane test.

 

You may have done this, but when it is idling high try pushing the throttle linkage down with a screwdriver, if the revs drop you have a butterfly catching on something.

 

Yup..tried that...made no difference....

 

Out = richer

 

I have them set @ 2 1/2 now, will turn to 3 and see how she behaves in the morning.

 

You know 1/2 turn is massive, you can go right past where you need to be.

 

noted...will try 1/4 of a turn and see what happens...thanks..

 

Try 1/8 at a time. Quarter turn is still huge too. When it comes down to FINE fine tuning, the width of a dime (or the width of the slot) is the increment you need to use.

 

make sure the cables arnt moving around or carbs pulling them. also its not a choke. its a fuel dumping switch which would confuse the tuners ideas while adjusting.. make sure the fuel hose is not taut or stretched. resync, use a tiny washer between a screw if you need that hair extra opening of butterfly. make sure ur boots are tight on both sides of carbs. uhhh...ya the cold start goes to the left to start, right when right n warm. ur either running out of fuel or sucking air and with the 4 carbs its gatta be right. readjust readjust readjust. i had the same problem, ull get it. probly need more fuel for whaver reason...ive been playin with an 82 650 yics. yesterday my petcock fell apart 10 seconds after a long day and out of instinct i turned the fuel to prime (Im a moto guy, sideways is off) andignited the bike on fire. i couldnt believe the timing i had my face there and arm in the carbs all day. nope it waited for me to sigh releif then trys to blow me up...crasy ass diablo :lol: no harm no foul rode it to work 1st time taday

 

I know it is a fuel enrichment circuit, "choke" is just less typing...fuel hose is new and not pinched or taught. I put a 90 degree filter on it so it fits rather well. None of the cables are moving around and no binding or tautness of linkage. No air leaks per propane test, and fuel does not seem a problem at all.

Fitz, I adjusted the carbs at 1/8 turn richer this am, rode for 20 minutes on the highway. I did this until the pilot mixture screws are now 3 full turns out. This had no effect on the idle of the bike. It is idling between 1300 and 1400 rpms hot.

The bike responds fine from full stop through full acceleration. No flat or hesitation at all. As a matter of fact, it feels and sounds better at 65mph @5000 rpms then it ever did.


The engine idles right down to 1300-1400 as soon as the throttle is off and I pull the clutch in..

When I vacuumed sync'ed the plant, I managed to get all 4 cylinders in sync, however on #4 it took backing the adjustment screw to where it is just touching the linkage on #3. I still wonder if the butterfly on #4, which I have had the hardest time setting so no light would come through, is still a problem preventing the idle from coming down to 1050 when hot....

Also the idle adjustment knob is screwed back to where there is no contact with the throttle linkage.

 

Loosen the screws on the butterflys, push them into the bores & re-tighten, one of them is catching on the carb body, if that doesn't do it you have air getting in, somewhere. Did you renew the rubber caps on the manifold spigots? if these are old & hard they can be a biotch to seal, remember a tiny air leak is all it takes.

 

Have new rubber caps on vacuum ports 1,2, & 4, also new vacuum line from # 3 to gas petcoqk. I have reset the butterflies before and adjusted so no back light can be seen around them when closed. I also lubricated the shaft seals and shafts with silicone grease. Also sprayed Marvel Mystery on the springs and other throttle linkage. Open and closing the butterflies slowly as well as quickly they all seem to react, look and sound the same.

 

When you re-assembled the rack, did you place all the carb throats against a FLAT piece of something-or-other and make SURE that carb bodies didn't twist out of alignment as the rack screws were being tightened? Because of the very tight fit of the new fuel tube O-rings, getting the alignment of the upper/lower rack brackets/screw to the holes in the carbs is difficult, and thus as you tighten the screws it's also trying to force the fuel tubes into their holes, and thus twists the carb bodies and the rack gets out of alignment.........

 

leveled and squared as per write-up.

 

Have you checked your idle mixture oring? I checked mine 2 weeks ago and they were fine. A week later pull them to clean the carbs I found one broken. I think I might have tightened it to much. Just a thought. Good luck!!!

 

Just replaced them with this rebuild with new ones from xj4ever...verified twice that they all are installed correctly.

Overnight cold bike starts with 1/4 fuel enrichment circuit opened and starts around 1000 rpms, then creeps up to around 2200 after 30-45 seconds. I ride the bike to the street (long driveway) and then turn the F.E.C. off and away I go. Bike runs fine and accelerates nicely. At the first stop, which is 4 miles, the bike idles at between 1300 and 1400 rpms, and the idle adjustment knob is not in contact with the throttle linkage. Performance wise, I can feel nothing wrong with the bike and everything else is in spec. Not sure if taking the carbs off and starting over from fully disassembled carbs off the rack with throttle shafts removed is going to help anything as I basically did this already to verify and double check the reassembly. Maybe in Dec or Jan I will feel like it, but right now I do not.

Thanks for everyones help and input. It has eliminated many variables of cause, but none has corrected the cause of the bike not idling down to 1050 hot. Like I said, total disassembly may be the correction. Some air must be getting in somewhere, but not enough to make the engine change while doing a propane test. Oh well, at least it is running nicely for the nice fall weather

 

Don't you see the problem ? the idle screw should always be in contact with the lever, like I said at the start, the idle screw should be in the middle of the thread, THEN bench sync using the adjusting screws,

 

That's what it sounds like to me too, just ran yourself out of adjustment range. If you had a bind, pushing on the linkage should make the idle drop.

 

Does the gear rating indicate level of experience? BruceB does your bike have YICS on all the covers?

 

The running sync "supercedes" the bench sync.
I agree - air IS getting in there - somehow.
A ColorTune plug would tell which CYL and intake track has the air leak.

What's the plug color VS Pilot screw settings??
Got one a bit "white" or too far out??

 

Do not have a colortune, but what a great suggestion to pull all the plugs and see if one is burning leaner. My instinct tells me it is #4 as that carburetor was the most difficult to set the butterfly and when I did the running vacuum sync, the adjustment screw had to be backed off all the way to get the #3 and #4 vacuum reading in sync.

Also, yes the YICS bolts are in and tight.

I did the bench sync a number of times, and even used Fitz's procedure by adjusting the butterfly to the little port hole on the top of the inlet. I assumed that a running sync would supersede the bench sync.

When I do push down on the linkage or individual adjustment screws, the rpms stay static and do not decrease.

Anyway, not going to be able to do anything more to the bike for a couple of days...has spent to much time in the shed....or so what I have been told..lol..actually just need a break from it.

betting money on #4 being the demon culprit as resetting the butterfly on that one got me from 5000 rpm to 2000 rpm, then running sync and a slightly richer air/fuel mix got me to 1300-1400 rpms...

so we shall see when I pull the plugs...