Topic: Inconsistent Idle - Over a year later - ALMOST THERE!!! 9/24/11

[KB02]

I'm going to open up the mixture screws one full turn each and test with new or cleaned plugs. I should have time to work on it today. Hopefully the rain that is forecast will hold off.

Well, that didn't work... 

If the slides are clean what about the hole they are sliding in? Also if they work so good with cables disconnected but hang up when reconnected it seemes like it has to be cable issue.

No, it s not a cable or slide issue.




Upon full inspection of the D7ea plugs, #4 was very lean compared to the other three. Now I'm thinking there is some blockage in the #4 idle circuit that may be intermittent somehow? Will ave the pull the carbs... again... and make sure they are clean... again... 

[rangelov]

It appears as though that I am running WAY lean. This would account for the idle trying to hang high. a far greater amount of air is entering the combustion chamber vs. the amount of gas that is going in. Essentially this mimics the effect of opening up the throttle at lower speeds as the jets are relatively unaffected and it is just the slow jet that is being utilized. The engine thinks that I have the right sized jet but the slide is further open thus increasing engine speed (greater Air to fuel mixture). When I get it to calm down, the engine is realizing that there is only so much fuel.

Do this make sense, or am I way off base?

Running 7's does make it APPEAR that you are running way too lean, when you aren't.  Running 9s will make it look as if you're running richer.  But 9s are correct range for your application.

Fix your off mixture carb.  Then do full throttle chops with the 9s.  This will allow you to select the correct main jet sizes.  You have to tune for WOT FIRST.  Then you can tune for part throttle and idle.

The biggest problem with running a big cam is the engine needs more air at idle.  The means the slides need to be raised.  Which raises the needles.  You may need slides with a different cutout.  No clue on where or what.  You might get by with raising the slides and dropping the needles.

On cars, the air bleeds are changed (or modified) or the throttle blades have an orifice added.  This allows more air while keeping the throttle closed and keeping the fuel circuit from transitioning into the part throttle mixture.

Getting it right is an interitive process and a huge pain in the arse.  I usually get it close enough to tolerable and then give up.

HTH

[KB02]

Well, the carbs came off. I cleaned them out again. No blockage was found in #4 as previously suspected. I even pulled out the slow jet and made sure it was quite clean. Float levels were off (too low) so I raised them up to 14mm. I could have sworn I had them right previously. I reset the screws to 1 1/2 turns out. It is my understanding that the mixture screws on the '78 carbs INCREASE fuel flow the further out they are turned. I have been getting no real significant change with them out further vs. in. Any suggestion?

Anyway, still not right, but at least a touch more ride-able. Idle still hangs, still running like it is super lean. Pulling the choke out a little bit seams to help. I taped off about 1/4 of the surface of the pods to try and richen it up a bit, but it didn't seem to help.

[KB02]

I just bought another set of carb sync gauges off of ebay. I had been using the Motion pro Mercury sticks. Never really been happen with them. Hopefully these will work better (and maybe solve the problem?)

[MRieck]

Well, the carbs came off. I cleaned them out again. No blockage was found in #4 as previously suspected. I even pulled out the slow jet and made sure it was quite clean. Float levels were off (too low) so I raised them up to 14mm. I could have sworn I had them right previously. I reset the screws to 1 1/2 turns out. It is my understanding that the mixture screws on the '78 carbs INCREASE fuel flow the further out they are turned. I have been getting no real significant change with them out further vs. in. Any suggestion?

Anyway, still not right, but at least a touch more ride-able. Idle still hangs, still running like it is super lean. Pulling the choke out a little bit seams to help. I taped off about 1/4 of the surface of the pods to try and richen it up a bit, but it didn't seem to help.

In general idle mixture screws that control fuel (rather than air) have an effective range of 4 turns out. That is for CV carbs. You could go up 1 size on the pilot jets.

[KB02]

Okay, I am pulling this back up from the basement. I was finally able to get back to work on the bike. I had become convinced over the winter that the problem was out of sync carbs. I bought a really nice carb sync set and finally got the chance to use it today. While the carbs WERE out of wack, and the sync really helped, the idle issue is still a problem.

I just ordered one of Tintops's Filter kits (the Anti-Pod) and will try again once that arrives to see of that helps the issue. I figure I'll try the easy options first before tearing the carbs part.

[KB02]

AND I'm back... Kind of. Been really absent from the boards lately. Sorry. Been a lot on my mind and not a lot of time to do anything about it.  My poor bike has mostly sat all summer as I haven't had the time to work on it. Anyway, I finally got back to it today and realized that I have been chasing this stupid hanging idle for over a year now. Kind of frustrating, really.

So I re-read my entire post to remember what I have done. I got the Antipod and got it installed. There was a slight mix up in the order and I got clamping rings that were too small. BUT, they were the perfect size for the exit side of the carbs. IDEA! Replace all of the old clamps on the carb insulators to completely rule out air leaks (from there anyway). It took me forever to find more locally, but the Kawasaki shop helped me out.  I have a nice, little, 6 mile test route and half way through the ride the problem seemed like it was gone. I was very happy, then it came back just as bad as before.


I must be missing something..........

[KB02]

okay:
   #1.) It's a crappy cell phone video, so please forgive me for the quality.
   #2.) I'm holding the cell phone in one hand and the clutch in the other. Please take your Sea Sickness pills now before watching the video.

http://s152.photobucket.com/albums/s182/actorextreme/?action=view&current=Video0005-1.mp4

It doesn't like starting without a bit of throttle twist, so it stated right up at the fast idle which it doesn't always do, but it was great for the video. You can hear the engine slow down as I eased out the clutch (with the rear brake held firm).

The thing that gets me is that the engine will stay at the nice, lower idle forever until the engine is sped up. Using the brakes with the clutch fully engaged will slow the engine down every time.

I have not yet unshimmed the needles. I have not yet gone with a smaller main jet. The bike is still showing signs of being lean when I ride it.

 

[MADCB400F]

Afternoon, I have a 850 kit in mine and ran into the same problem. I finally found splits in my carb to head rubbers. Check them really good for splits. Good luck

[Gearheadgreg]

Well, the carbs came off. I cleaned them out again. No blockage was found in #4 as previously suspected. I even pulled out the slow jet and made sure it was quite clean. Float levels were off (too low) so I raised them up to 14mm. I could have sworn I had them right previously. I reset the screws to 1 1/2 turns out. It is my understanding that the mixture screws on the '78 carbs INCREASE fuel flow the further out they are turned. I have been getting no real significant change with them out further vs. in. Any suggestion?

Anyway, still not right, but at least a touch more ride-able. Idle still hangs, still running like it is super lean. Pulling the choke out a little bit seams to help. I taped off about 1/4 of the surface of the pods to try and richen it up a bit, but it didn't seem to help.

In general idle mixture screws that control fuel (rather than air) have an effective range of 4 turns out. That is for CV carbs. You could go up 1 size on the pilot jets.

Well...? i guess this fella just want's to pull his hair out..your advise is of coarse spot on! Slow jet needs one step up!! he has aftermarket pipes from what i can see,....stock air box is missing......but i guess if he wont listen....i have no choice but to watch his video..............................................cool looking bike he has. 

[Zodo]

It's pretty weird how the bike seems to run with those two very distinct 'modes'...and relatively happily in both. It really seems like when it gets up into the fast idle state that the increased vacuum fuel pull must be overcoming a seal somewhere.

[Spanner 1]

I'm sticking with my theory of Sept 2010 !!... that the engine vacuum is helping itself to more fuel @ idle by pulling fuel from the 130 main jet, especially with the slide needle raised  ... it's a bored-out motor, aftermarket exhaust, pods... all the carb rules are out-the-window, esp. with the increased engine breathing ( vacuum/volume ). The carbs are designed around the 736cc motor and it's amount of vacuum created at whatever rpm.... completely critical to their operation.....the full operation of the carbs are driven by the engine vacuum, put in a big-bore kit and use the 'stock' carbs = a lot of experimentation to make the motor run right .
One more thing OP.... take the pods off and when the bike is in 'high idle ' state, have someone sit on the bike and do like you did in the vid.; i.e. hold the rear brake and ease out the clutch while in gear... now observe the slides dropping !!!!!!!! ( engine vacuum + fuel having lifted them ! ).

[KB02]

Well...? i guess this fella just want's to pull his hair out..your advise is of coarse spot on! Slow jet needs one step up!! he has aftermarket pipes from what i can see,....stock air box is missing......but i guess if he wont listen....i have no choice but to watch his video..............................................cool looking bike he has.

It's not that I'm not listening  it's that I haven't had time to work on the f**king thing. As you can read I have not YET made changes to the set up. I wanted to be sure that everyone understood what I was talking about first.

[KingCustomCycles.com]

Low rpm = more vacuum for those chasing their tails here. 11 in/hg is a good idle, 29 in/hg is a good full throttle reading in naturally aspirated engines.  You will notice that the "vacuum" approaches atmospheric pressure as the throttle is opened.  This is why induction leaks are most pronounced at low rpm.  The difference between manifold pressure and atmospheric pressure is greatest at that low rpm.   Air flows from areas of high pressure (outside the engine) to areas of low pressure (inside the manifold).  This air is not metered by the carb as it never senses it and therefore never adds fuel to compensate.  This results in a lean condition. 

[Gearheadgreg]

Re: (No subject)
« Sent to: Gearheadgreg on: August 04, 2011, 10:57:13 am »
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Greg, thanks a ton. (no pun intended)
I installed my #38 slow jets, did a little adjusting and wow. The 750F runs like a beast!
Thanks for your time and patience!

[MRieck]

While working on a late model set of carbs i noticed I'd synch the carbs, it would run great but after blipping the throttle a few times it would stutter at idle. The problem turned out to be loose screws holding the throttle slides on their common shaft (at the top of the slides where the synch nuts are). The one slide would shift secondary to not being firmly attached to the throttle shaft.

[KB02]

I get the feeling that the last three posts were supposed to be on a different thread?

[trueblue]

I don't know if this is any help, but I had a very similar issue with my 650, I would pull up at a set of lights and it would stay revving at about 4k then gently ease the clutch out and it would settle down and idle, but I always had to keep my hand on the throttle because otherwise it would all of a sudden have a stumble and stall, I replace my cam chain today, I found my cam timing to be one tooth out, new cam chain and correct timing and I now have a stable idle almost straight from a cold start, it is almost like it is a different bike.

[Gearheadgreg]

Re: (No subject)
« Sent to: Gearheadgreg on: August 04, 2011, 10:57:13 am »
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Greg, thanks a ton. (no pun intended)
I installed my #38 slow jets, did a little adjusting and wow. The 750F runs like a beast!
Thanks for your time and patience!

1 reply and a PM and he did NOT need to sit in front of his computer and have a year long discussion and 68 replies! He got off his A$$ and in the time it took to read these 68 replies he could have had the Phucking carbs off and on at around 3 times....what a joke! 

[KB02]

So I was actually able to get out and work on the bike before it started to rain. I owe you all an apology. I had 135 mains and not 130's as I had earlier reported. So I swapped out the 135's for 130's and lowered the needles back down to the stock position (all the way to the top, no shims).

The problem was not affected at all, in fact the bike was a little less ride-able. There was a much harsher transition from idle to moving.

I took Spanner's suggestion and pulled off the air filter and looked into the mouth of the carbs hoping to see SOMETHING that would hint me in the right direction but... no. The tach ran up to about 6 - 7 grand while I watched the sliders and they did not seem to move at all.

The return spring is nice and heavy so I really don't see the vacuum pulling up the sliders anyway. I was worried that maybe the vacuum was pulling fuel from the accelerator pump but that wasn't happening either.

My theory is now that the fuel is just being pulled directly up through the main.
- Should I try a dramatic drop down to a 120 main?
- If this is the case, will dropping the main be the solution?
  - Why is the fuel getting sucked up like that to begin with?

[Trav-i]

I would say go with 120's and see what happens.  I think you're on the right trail, also are your slows stock?  That tight fresh motor might be pulling a bit more vac then we're accounting for.

[Spanner 1]

Thanks for looking into your carb throats KB.... if the slides are not raising then you must have a stronger than stock return spring !.... but that big 850cc bore-out is creating much more vacuum and pulling fuel from somewhere or it couldn't race to 6 or 7,000 rpm.... my guess is still the main jet, try a 120 like you suggest 

[KB02]

Well, Since it has been suggested here and on other forums as well, I have ordered the next size up slow jet (38's) and am waiting for them to arrive. In the mean time, I figures I would start on pulling out the old ones. As I was looking at the carbs, I noticed that the #4 carb was visibly, and significantly higher that the rest of the bank. Now I know that every carb will be slightly different, but it was up by a BIG amount.

Possibly the problem?

I just spent the morning calibrating my Gauge style carb sync tool. As soon as I get my new jets, I'll do a bench sync and start from scratch.

[KB02]

I got the new slow jets in. I did a quick bench sync. I left the 130's in for now because I have a feeling the sync may have been the problem after all. Previously I had calibrated my gauges by using them all on the same carb and making sure they had the same reading. This time I used a vacuum pump that I had and made sure they were all reading the same not only against the gauge but also against each other. I thought it was a nice set, but doing this calibration showed me just how cheap of a set it really is. I literally had to take two of the gauges apart and adjust the linkages in the back to make them read correctly. I am thinking, now that even through 4-5 different carb syncs and two different gauges, I was chasing an out of sync bank. 

We'll see. Test ride pending dry weather...

[KB02]

Alright, #38 slow jets in, the needles turned one full turn out. Still at 130 mains. Carbs bench synced.

The engine's refusal to come down from cruising speed appears gone!

YAY!!

The idle is also gone!

BOO!!

I figured the title change to "A New Hope" would hit with the Star Wars fans as that seems to be where I am within this saga. I have a hope, but there still a lot of fight lest to go. - After a longer than normal test ride I was able to successfully get the bike to not have that nasty hanging idle with the above set up, but I also lost my idle. The bike would idle so low that it would stall. If I turned in the idle setting screw to where it would idle decently the hanging idle issue would come back. If I turned the thumb screw to just the right spot where it would just barely not stall out at idle, the idle would hang for a little bit when revved (10 to 15 seconds) and then drop back down.

Here is where my brain is at now:
- If the problem happens with the idle thumb screw turned further in, that means the slides are slightly higher up and the engine could be pulling fuel up through the mains as previously suggested with the extra vacuum from the 850 kit. With the slides where they need to be to idle correctly, there is not enough fuel to hold a steady idle due to the slow jets being so restricted at only one turn out. SO - by opening up the mixture screws another full turn, that will increase the fuel at idle WITHOUT raising the slides and keeping the mains closed off to the engine vacuum thus preventing the idle from hanging high.

Does that make sense?
       Am I way off base?
              Is anyone still reading this thread?