Everything fine then... wild rpms?

Went out riding today. Everything was going swimmingly... was about 5 miles away from my house and noticed the idle would spike when pulling in the clutch to change gears... Like 6k or more... honestly, I'd let the clutch back out in gear so I'm not sure how high it would go...

I limped home... stop signs were a problem... but I made it...

Here's the weird part... About a block away from my house, I stalled it while trying to coordinate the clutch with downshifting, while trying not to roll through the intersection all the while with that wild idle...

When I started it again... ALL BACK TO NORMAL! I'm talking idle just over 1k. Just like when I set out...

I don't believe I had a stuck throttle cable as there was response with it after I realized the idle problem. I even gave it a couple snaps to make sure, but the problem persisted. The choke cable likewise... Normal and in the OFF position.

What I've done in the last few months:

Petcock Rebuilt (Thanks Len!)
Carbs Rebuilt (with exception of separating them, New kits... thanks Len!) & Bench Synced (just got a set of gauges... vacuum sync this weekend!)
New Throttle Cable (Len... can you tell where YOU should get your stuff?)
Shims Swapped and now in spec - Thanks Hogfiddles!

What is freaking me out is how unpredictable and "out of no where" this problem is. It was a crappy feeling dealing with a seemingly run away throttle.

I've got just over 160 miles on it after I did the above work... I'm thinking a vacuum sync will help to smooth out things even more... more to come on that...

Thoughts on Mr. Toad's Wild Ride???

 

sounds like throttle shaft seals leaking air causing rpms to rise.
hope this helps

 

Sticky throttle shafts, slide pistons that didn't pass the "clunk test" leaking throttle shaft seals, float levels off, carbs out of sync.
It's all about the carbs being squeaky clean and adjusted properly and maintaining them to stay that way. You may end up pulling them off and giving them the once over again.

 

Wow... Awesome suggestions... Interesting you point out the slide Pistons... that sounds like something that could be suspect... Like maybe one or more got hung up... Then after stall and restart, they dropped and reset themselves... I'm thinking that is totally plausible... Some of the other suggestions may present a more consistent problem of the same kind... Syncing the carbs this weekend... And Just an FYI... Several additional starts this evening after the racing idle problem resolved itself... Purring like a kitten now no idle issues...

Just looked at my initial thread post... Comment about the throttle cable looks weird...

What I meant was that I got that from Len too... Awesome product knowledge, speedy shipping and parts SPOT ON!

 

I'm thinking sticky slide then.
Polish the slide bores to mirror finish and drop them in they should hit bottom and Clunk when they hit bottom.

 

Any suggestions on the "how to" of polishing? Materials/methods? I feel like I read something about VERY fine sand paper... But that just scares the heck out of me...

 

Early stages of vacuum leak can be intermittent too. Are your carb boots cracked? Perhaps the propane test is in order.

 

I use a die grinder with a cotton polishing wheel and jeweler rouge

 

Well, if you haven't done your running sync/balancing yet I wouldn't do anything else until THAT is done!! if it hasnt been synced yet, that in itself will create enough problems til it's done

 

a sticking slide can't cause a problem like this, it's on the wrong side of the throttle buterfly

 

Is

Is there any chance the clutch cable was interfering with the throttle ???

 

this would be a good place to start

 

check for proper routing of the cable and that it is not to tight up at the forks or loose and binding. start it up and move forks from full side to full side
also check if it is properly sitting in the cable holder on the carbs

 

Cable routing looks good... No side-to-side rpm fluctuation when turning forks... Cable end seating is good and throttle cable comes to rest with no tension when off throttle. Also did a propane test for leaks (even before I encountered this problem). Good here too!

I'm bummed that perhaps it Is NOT the sticking slide problem because of its position in relation to the butterfly... Pull and clean/polish... Easy fix... Maybe someone can elaborate here and help with better understanding on what exactly happens here. Twisting the throttle opens the butterfly's... Opening the butterfly's, increases the air going into the carbs which draws the slides up thereby raising the needles and increasing the fuel going in as well? If so, this is why sticking slides makes sense to me. After stall, the low pressure above the slide diaphragm dissapeared, therefore the sticking slides dropped and reset... I could be totally off on this though...

I don't have a block off tool, (I know we have a split house on it being absolutely necessary) but will attempt to do the sync today without it... Should be able to get it better than the bench sync I currently have...

Thank you all... To be continued.

 

Update...

Set up the test and attempted sync. Gauges bouncing like crazy at first, then tightened up on each of the white plastic gauge valves. Seems like such an inexact science with these borrowed carb gauges. Tightening or loosening the valves produced very different readings and getting them to be the same "openess (for lack of a better term)" proved challenging. I put a black dot with a marker on each valve knob at lightly seated (just where the gauge STOPPED indicating vacuum pressure), then rotated 1/4 turn counter clockwise (open). Seemed like a good "middle ground" between closed too much and open too far.

The needles on the gauges look close to being consistent at the top of the bounce. Can't upload a video here but I put it in my drop box at the below link if you want to take a look.

https://www.dropbox.com/s/3hnx78lgllm7cq7/sync_85_xj700.MOV?dl=0

Believe me, if I had the cash to buy a Morgan Carb tune, I would. Just trying to get it closer to where it should be with the means I have. Gunson Color tune plug is on my list too.

What do you think?

 

so far so good. now the slide sticks and it's letting in fuel to run at some higher throttle setting. the throttle closes but the slide is still up, the throttle is letting in less air/fuel mixture but the fuel in that mixture is still for a open throttle.
when you adjust the idle mixture, leaner mixes give higher idle, to a point. So with the slide stuck up, the mixture will be way rich. the idle on that cylinder would go way down
someone with pods could find out by reaching in and lifting a slide while it's running

 

But we all know... Pods is a dirty word... Ha ha...

I plan to remain totally stock. I love being able to open the service manual and get the info I need without variables... That and this forum! Thank You!

 

The needles are oscillating too fast. The set up needs restrictor tubing. The vac line that comes with it isn't very good. I modified my set. It works fine.



Gary H.