78E Runs rough 1000-4000rpm

[PJSALERNO]

Here's what I've done.....

Sent carbs away to motorcyclecarbs.com for professional cleaning/diagnosis/repair

intstalled carbs, runs real rough from "idle" to 4000 rpm

rpms will sometimes hang at 2500 or 3000 then slowly drift down to 1200 idling really rough. won't idle at 1000, will stall

sprayed wd40 in to carb boots while idling high to check for leaks, no sign of leaks.

checked valve clearances. all in spec.

checked all fuel/vacuum plumbing, looks good

only thing i havent done which i will when guages come in is carb sync, but i dont think that will solve the problem since they were bench synced pretty close.

any help?..thanks..Phil

[Ken Talbot]

Bench sync is no substitute for syncing in place with vacuum gauges. Similarly, you can't adjust the pilot screws without the carbs installed and the engine running. I'm pretty sure you will be amazed at the difference you're going to see once you get it right.

[PJSALERNO]

Thanks Ken, I was going to email you directly if the carb sync doesn't help...Phil

[tab1324]

pilot screws?

Ken,

What are the pilot screws and does my 82 XJ have them?

Tom B.

[TopCatGr58]

Hey Tab,

Yes, you do have them on the XJ, but they are probably still hidden under factory sealed brass caps on the top of the carbs, that little round spot just next to the mounting lip on the forward side. Do a search, it's been talked and posted about many times, about how to remove the brass caps, etc.!

Hey Phil,
Sounds like the pilot screws may be set too rich, too many turns out, while you're waiting for the synch tools, see how many turns it takes to turn them in to a gentle seat, and then try backing them out to ~1&1/2 turns and see how it behaves? Rob Reil knows his stuff, but you still have to tune them to the specific bike they're on!

T.C.

[PJSALERNO]

Thanks, TopCat, I thought it might be too rich. Rob said he sets to 1.5 turn out, but i'll re-set, GENTLY. If once I'm 1.5 turns out and I'm still too rich (black carbon deposits on plugs, right?) do I turn in (clockwise) or out (counterclockwise) for lean. Also what's the procedure, bike running, what's the incremental turns, etc.

Also what's the possibility of the vacuum advance being bad?


Thanks! Phil

[randy]

PJ,

The screws control the amount of fuel let into the air stream, so in closes the orifice for leaner, out opens the orifice for richer.

If you've never synched before and want help, let me know. I'm on LI most evenings during the week. How far out are you from Queens?

[PJSALERNO]

Hey Randy, I'm in Glen Cove about 25 min from Bayside. Thanks for the offer - I think I'll be cool with the carb syncing, but I have a funny feeling I'm not going to be done there. I may need your help later if you're willing.

Because of the hanging idle symptom Rob Reil is sure I'm getting air in from somewhere........he says:

"Hanging idle is a lean condition symptom. Too much air/not enough fuel. Check your vac petcock hose, the nipples covering the vac ports for each cylinder etc. Air is getting in there from somewhere.
Maybe even by some strange circumstance from the butterfly shaft seals. Maybe from the vac petcock diaphragms it self. We saw nothing of relevance (in the carbs) that would show itself to be a lean condition in the 1-4k range."

I rebuilt the petcocks a while back, but maybe that's where my problem is. Question: If I wanted to run off an auxillary fuel source to see if the symptom goes away, how would I rig this up with the vacuum petcock hose?

Thanks...Phil

[randy]

Runaway idle can also be caused by poor synch, not just air leaks. So synch first.

To set up your alternate fuel source, you'll have to block off the vacuum lines. ( golf tees work well ) and connect an alternate fuel tank. I use a coolant recovery bottle. They're available at Auto Barn for like $8. You'll need a fuel tee and some fuel hose, too.

Hang the bottle from a rafter, put an electric fan in front of the engine, and away you go.

Auto barn bottle:

[randy]

PJ,

Strike that part about blocking off the vacuum lines. Of course, you'll have all four vacuum ports connected to the synchronizer. Don't know what I was thinking!

If you want to use the stock tank to provide fuel, turn the taps to PRIME and fuel will flow without vacuum.

I also use a handy tool made by S&K, It's a long carb adjuster tool with a 60 degree bend in the end and a 1/4" drive. Comes with a variety of sockets, a few slotted and a couple of ovals. Add a 1/4" universal and it can reach all of the screws. Perfect for adjusting synch and pilots without removing anything or even raising the tank. IIRC, it cost about $25.

I found you can spend more time just setting up to do a synch (seat, tank, aux fuel, etc. ) than the time spent actually turning the screws. And no burnt hands. That tool has definitely paid for itself many times over.

[PJSALERNO]

That's true, nice. But the reason I wanted to use the aux tank was not for syncing. I want to see if my possible air leak is from the petcock diaphram(s).

So how would I rig that? Aux tank t-eed to both fuel intake on carbs and block off the 2 vacuum lines with golf t's?

If the run away idle stops I'll know it's my fuel supply, right?

Thanks..Phil

P.S. Where did you buy the S&K carb tool?

[randy]

OOPS.

The carb tool is made by Snap-On part # 2006IT. My memory is not as good as it used to be, I've owned this tool for a dozen years. I checked the price and it's not what it used to be - -$75!



You know, if it saved me an hour each time I did an adjustment over the past years it's probably worth more than $75

[randy]

PJ,

You can find air leaks by spraying WD-40 at the suspect areas. I don't think runaway idle would be a fuel delivery problem. On the contrary, fuel delivery problems would more than likely lead to NO idle!

[PJSALERNO]

My carb guy gave me 1 possibility being the petcock diaphram vacuum is leaking air. Believe me, I don't want to chase ghosts, but I do want to elliminate possible problem areas. Maybe I'll narrow it down by winter. J/K. Any input is fully appreciated...PJ

[randy]

You can plug them both and run it on PRIME. That would determine if they were your problem.