current issues (throttle and high rpm hesitation)

So. I spent a couple quality hours on the bike. Removed the engine guards, rear pegs and left side peg bracket (right side is exhaust bracket, so it has to stay) cleaned the throttle cable and fixed my idle.


The bike idles smoothly around 1300rpm. I can't get it to idle any lower without sputtering and dying. But It's fine with me, doesn't sound like it's too high.

I took the throttle cable off, blew a bunch of WD40 down it, and hung it to dry for 40 minutes while removing the extra bits of metal. probably shaved 5-6 pounds of central body obesity from the bike. cable feels much nicer now.

But upon taking the bike out, I noticed that the same "throttle stick" is there. It's only when the bike is warm, so it can't be the cable anymore. The bike is cold, no issues, but it clings to rpm's and has trouble dropping down to idle when the bike is warmed up. it will eventually get there.

The carbs were thoroughly cleaned and the float bowls rebuilt when it was in the shop. what could be causing this?


Secondly, the bike still hesitates at high RPM. I'm pretty sure the bike makes plenty of power (back end steps out on me in third and fourth under heavy throttle in the rain) it feels like it's just cutting out and in. and only between about 8500-9000 and 9500.

What may be causing this? Bike's got an aftermarket exhaust, and I am unsure if it was rejetted. it burbles and pops on the overrun.

 

First off: PULL THAT CABLE AND FLUSH IT RIGHT NOW. Then lube with Tri-Flow or some other LUBRICANT. NOT WD40.

WD40 is NOT a good cable lube; it will "gum up" after not too much time because of the engine heat. I learned this the hard way years back when it nearly caused me to dump my Norton.

WD=Water Displacement. That's what it was originally invented as, and all it should be used for; as a "preservative" spray, cleaner, moisture displacer.

Do a forum search for "WD40 is evil" and read the discussion.

Your problem sounds like throttle shaft seals. You could have one that's breaking up into "rings" and rotating around, binding the shaft. It's also consistent with the high-speed hesitation symptom.

 

i had a similar issue.
also ran lean on 3 & 4, poor idle at start, and a little hunting
at 1250 rpm.kept it around 1300/1350. and my carbs had been cleaned not long before.

this time i made sure to polish the throttle bodies, carb bods, throttle
slide bar. just like rick-o-matic describes on his carb cleaning
thread.

what a DIFF. idles at 1050 with no hunting, throttle up/down without hesitation, no more stumble over 7000 rpm, plugs ( after pilot adj )
look perfect.

oh....at first i used a single sears vac guage to sync....

forget it! find the thread on how to build a home made "two bottle system"
these work fantastic and i put mine together for about $5.00 using thrift store bottles, ace hardware rubber caps (freeze over night before drilling )
and the vac hose from the old system.


accurate as HE(( !

bike has NEVER ran so good!

 

oh definitely. I know WD40 is not a long term thing, from my extensive car modding work. It was 2 AM however, and I was unable to purchase any real lubricant, haha. I'll absolutely get some real stuff this morning.

Where are the throttle shaft seals located in the carbeurators? this bike is my first personal multi carb setup, and these little buggers are complicated as f***.

Get some sleep you crazy guys!

 

my carbs were cleaned by one of the best shops on the west coast, so I 100% trust their work. if it were my cleaning job, I'd definitely do what you described. But these guys are some of the most knowledgable xj750 mechanics I've ever seen.

 

So nobody has any other ideas about why the bike isn't running as sweetly as it should?

It started running very badly (as in, two cylinders badly) on the ride home at idle, but under revving and moving, it cleaned up until I came to a stop again.

I think that part had something to do with the fact that it was pouring rain so hard my air cooled engine may as well have been liquid cooled.

 

On the throttle shafts? (OK Fitz quit being a smartass.) On the throttle shafts, on each side of each carb where the shaft goes through. You can SEE two of the eight if you pull the c-clip and washer off the end of the shafts on the outer carbs. Each carb has its own separate throttle shaft (they link together it only looks like one long shaft) and each has a seal on both sides.

If the rack wasn't broken down completely for the cleaning, there was no way they were replaced. The rack has to be broken completely down AND each carb disassembled completely INCLUDING the dreaded butterfly screw removal, in order to access them.

If the rack was simply field-stripped and then DIPPED, chances are good they got screwed up if they weren't already worn out.

The throttle shaft seals themselves are unique little X-section "o-rings" that will eventually wear out if they don't dry out and disintegrate first; a lot of "knowledgeable" shops either ignore them or simply pretend they're not there.

But they are, and if they're failing or failed, they will produce the symptoms you're experiencing.

Crappy running in the wet only generally indicates an electrical problem, which can include micro-cracks in the coils themselves making them susceptible to moisture.

 

wouldn't the wet issue present itself in the pouring rain whilst moving, as well? the problem clears up on the move.

Also, I really trust this shop. They've been around a long time, and have absolutely nothing but a raving happy customer base. They were expensive because they're the best in seattle.

That said, Is there a way to look at them without disassembling the entire carb setup?

God it's embarassing asking these questions when I just finished building an ITB setup for a friend's SR20. :lol:

 

you can see two of them on the outside of 1 and 4 carb by popping off the e-clips on the throttle shafts, take off the washers and there they are

 

also- could carb synchronization be an issue?

 

Just a shot in the dark:
Is your sidestand cutout (if you have it) connected? Sometimes the sidestand flops around while you're riding and activates the switch.

 

You got to bring that "13-Hundred, ... seems a little high, but you can live with it" ... down to a grand or 10-50 ... before you can start tuning to get it right.

Lube the Throttle Shaft Hinges with Silicone sprayed into a glass and soaked-up by a Q-Tip and squeezed out on the Hinges.
Replace the Throttle Cable with new Cable and Sheath from a Bicycle Shop.

Bench Sync the Carbs so you can begin with the Throttles closed.

 

Lord, last thing I want to do is take off those carbs.

Maybe when I move into my new place I'll take the thing apart.

 

i too raved about a shop here in town.
they didn't do work on the bike but specialized in vintage
bikes and i could get lots of cool parts there.

but every time i ordered parts the wait ( 2,3 or more weeks) became
longer and they cared less.

so you can't go by other peoples satisfaction.

just learn to do it yourself-that way you can be sure BEYOND DOUBT
that nothing was missed............you will also learn the name of the various
parts and not feel embarassed anymore

 

So. I took it back to the shop, and the owner took the bike in.

He yanked the tank off, determined that my cables were routed wrong, and in a matter of seconds using what can only be described as witchcraft, found some slack in the clutch and throttle cables.

He also noticed that pilot screw #4 wasn't responding. He yanked the carbs with the intent of cleaning it. We were figuring the hesitation was caused by improper jetting for my 4 into 1.

Turns out, someone used the internals from a stock xj650 on my bike. Which has been starving it for fuel all over the place. causes the inability to idle at low RPM, the hesitation at high RPM...

And he did that all for free. including syncing the carbs another time right in front of me.

He's going to find me new internals without resorting to yamaha, and he's going to get my jetting right for my 4 into 1.

Yeah, I'm going to keep raving about a guy who does $200 in labor for free, just because he wants to keep my patronage. This man will put the work I do myself to utter shame.

 

how come when they did the carb clean the first time they didn't
notice that the carbs had parts belonging to a different bike nor establish from the begining whether you had a stock set up? .

i'v had work done in the same way when someone finally notices that they missed something and are more then happy to make up for it to save their customer base.

 

when he did the cleaning he had no reason to check the shims on the parts. It's not a visible difference unless you spend all your life working on 650's and 750's.

The carb housings are the same, the only difference is the size of the needles and pilots.

Not his fault. If I was cleaning the throttle bodies of an S54, I wouldn't have any reason to check and see if they were from a different engine. It would be silly. hell, it's silly that some moron put 650 carbs on the thing in the first place!