VHB29 Throttle Hangs...Maybe Solved

[Tom H]

The issue is that my throttle hangs a little just above idle, but will come down in a few moments. You start up from a stop and go to shift to second and the revs stay up a bit. Not as high as just before you shifted, but higher than idle.

The carb slide screws are adjusted to give a nice idle when warm. I take it for a few minute ride and all seems well. But if I take it for a longer ride and especially on the freeway, once off the freeway the throttle seems to hang a bit. The only way so far that I have been able to minimize this is to back the stop screws out and then the bike won't idle very well. But sometimes even with the stops backed out, when I come to a stop, it will idle high and then idle down. It's like the slides are hanging up on something. Everything looks smooth.

EDIT: One thing I forgot to mention. When I come up to a stop and it hangs, if I give it a quick on/off twist, it still is high. But, If the idle has dropped to normal which it does after a moment or two, I can give it the same quick on/off and it goes right back to a normal idle as it should.

I thought it might be the cables, but you can hear with the bike tuned off the slides snap shut. And again, it seems to happen most with the engine on the hot side.

Before anyone says it IS the springs. I do have the lighter springs in the bike right now, but this also happens with the heavy stock springs. Also, my Ambo is most prone to this issue, while my Eldo very very rarely has had the issue. I seem to remember that the dist. springs if worn out could cause this, I installed new springs and it still does it.

Anyone else have and issue like this? How did you fix it?

Thank you,
Tom

[Chuck in Indiana]

Idle that is a little too lean will take it's sweet time going down.. but assuming it *is* a mechanical thing.. maybe the slides are worn? Just a shot in the dark. Stuff like this is really hard to diagnose from 2000 miles away. 

[bodine99]

Like Chuck mentioned lean pilot circuit and or vacuum leak. wiff around the intake with some brake cleaner and see if the idle changes

[Idontwantapickle]

Tom,

The list could be long!

Cables too tight? Check for slack.
Splitter full of old grease?
Idle adjustments out of whack? If the air and fuel screws are too far out of range it will act this way.
Slide hanging up? If it's one side it will run rough. Best to look in there and watch it, take the air cleaner off.
Slides too high? See #3
Slides in backwards? Don't laugh, it happens.
Float level too high? Too much gas bleeds into engine at high vacuum.
Bad gaskets or loose bolts at manifold?
Valves adjusted too tight?
Might as well check the ignition advance just to be sure!

That's a good start, if it isn't one of these then looking for these will probably reveal the culprit!


Good luck!
Hunter

[Tom H]

There are some interesting points, especially the lean idle. To answer the questions"

Cables too tight? Check for slack.

No

Splitter full of old grease?

No, two cables.


Idle adjustments out of whack? If the air and fuel screws are too far out of range it will act this way.

I WILL look at this as well as too lean.

Slide hanging up? If it's one side it will run rough. Best to look in there and watch it, take the air cleaner off.

I don't think so, it idles/runs smooth even at the high/stuck idle.

Slides too high? See #3

Slides in backwards? Don't laugh, it happens.

NO LMAO!


Float level too high? Too much gas bleeds into engine at high vacuum.

Now this is as interesting a question as well as the too lean at idle. I don't have a "float gauge" for a Delorto VHB29, so I kind of wing it with a caliper. I don't remember the exact number, but Benders site has it and that's what I tried my best to measure.
Bad gaskets or loose bolts at manifold?

Loose bolts...No
Gaskets "should" be fine. But as mentioned, I might hit them with carb cleaner and see what happens.

Valves adjusted too tight?

They are a tad tighter than spec.. Been running both bikes the same for 35 years. The issue is sonething that I have dealt with over the last maybe 10 years on and off. But I will look at this as well. But I will do the suggestions one at a time.

Might as well check the ignition advance just to be sure!

Per my timing light, all is well.

Thank you ALL so far. Any other thoughts??

Tom

[acogoff]

wiff around the intake with some brake cleaner and see if the idle changes

      This.

[SED]

Another vote to check lean idle mix.  Was idle mix set with engine warm or hot? 

Mechanical ideas: worn slides (LMIII experience seemed indicate that worn slides make it more susceptible to lean hang),  plastic twist grips distort and don't hold cable settings well ('80s Guzzis).


You guys are quick!  Edit to remove: not enough cable slack, 1 to 2 cable splitter hanging up,
 

[Cam3512]

That happened on my Eldo when I put the lightest springs in the carbs.  Switched to the medium weight, and all was well.  Only happened when riding and it was hot.  Also, remove the locknut from the cable insert on the carb to get enough slack.

[80CX100]

     My VHB30's on my CX100 developed a bad hanging idle, I think my problems were a couple of things.

     The traditional routing of the throttle cables along the centre of the frame and crossing under the tank,,, didn't operate smoothly on my bike, it created a tight bend down into the top of the carb, contributing to the problem, after discussions with a person in the know, I routed the cables very loosely along the right side of the frame under the tank and only the left cable crossed over to the carbs, I tried to make wider bends going into the carbs(I think some bikes actually came with curved fittings on top of the VHBs to smooth the curve)

      The main culprit were poorly sized/stretched throttle cables(probably jobber replacements?), I didn't have enough available room in the adjustment to tighten them up properly, and sometimes the outer casings of the cables was actually popping out of the ferrule on the top of the carb and getting hung up on top of the edge, instead of inside the ferrule. I shimmed outer casing at the throttle end, and that tightened the cable and forced the casing back down into the ferrule, solving my hanging idle, fwiw.

      Good luck

       Kelly

[Tom H]

Another vote to check lean idle mix.  Was idle mix set with engine warm or hot? 

Mechanical ideas: worn slides (LMIII experience seemed indicate that worn slides make it more susceptible to lean hang),  plastic twist grips distort and don't hold cable settings well ('80s Guzzis).


You guys are quick!  Edit to remove: not enough cable slack, 1 to 2 cable splitter hanging up,

Probably when cold/warm as in did some work and then started it and waited till it had enough heat to idle and rev properly.

Worn slides. That is a good question. These slides still have almost all of the oliveish coating on them. Yes there are silver areas. Wish I could still get brand new slides. On fleabay, a guy did a repro on the slides, but the cutout was the wrong size for a stock setup.

Cam,
Cables are fine slack wise. As far as the springs. The stock heavy springs had this problem as well as the light springs from MG Cycle.

I'm still listening before I work on it in the next day or two. I'm kinda leaning toward the too lean at idle, even with the stock jet. I need to screw in and count the mixture screw and see where I'm at. I think it's pretty close to the initial spec which my Eldo has always been fine with +/- 1/4 turn.

Kelly, My cables are loose, but not so loose they are hanging on the end of the ferrule. Routing should be fine. Again, they snap closed when the bike is off. Can't hear the click when running. But then again, it is something to look at.

Thank you all so far!!
Tom

[wirespokes]

It's been a long time since I've had that problem and know exactly what you're talking about. As I recall, it was a jetting issue both times. You could try giving it a little choke when it happens to see if it's a lean condition. Over the years I've had both - where the idle stayed high coming off a high speed run or dying. The rest of the time it was fine. In your case my guess is a fuel issue.

[80CX100]

     I'm just thinking out loud, have the carbs been rebuilt?

     If not, what would the typical symptom be, if on the choke/enricher plungers, the bottom rubber piece is brittle/worn and not dropping down and sealing properly?

     fwiw

     Kelly

[Tom H]

I would have to look it up, I think I did the choke slides about 2 years ago. I had the float bowls off recently when I played with the jets, it was very clean inside. I have the stock (per the specs) pilot jet in it. My Eldo runs the same pilot. My main is a size or two smaller to get rid of a rich issue at W/O.

Also just to be clear, the bike I'm working on is an Ambo. Though the Eldo has had the same symptom in the past.

Wirespokes, My Eldo would do the high idle or die after a run on a freeway when you hit the traffic light a bit off the freeway. Never did figure out why it would do it. It didn't always do it, just sometimes.

Looks like I have some messing around to do on Monday. Won't have time tomorrow.

Thanks again!!
Tom

[Chuck in Indiana]

     I'm just thinking out loud, have the carbs been rebuilt?

     If not, what would the typical symptom be, if on the choke/enricher plungers, the bottom rubber piece is brittle/worn and not dropping down and sealing properly?

     fwiw

     Kelly

It will run rich everywhere.

[wirespokes]

Tom - give us some history on the bike. How long have you had this bike? When did the symptoms start?

It could be that one of the passages has grunge build up and not flowing as much fuel.

I sort of recall that the hanging throttle in my case was resolved cleaning a part of the carb where air mixes with fuel from the idle jet. This was on Bing carbs, and grunge would solidify inside on the body at that point. I don't know the VHBs that well so don't know if there's anything comparable.

Perhaps try using some Marvel Oil or Seafoam in the tank - something for cleaning fuel systems.

[pehayes]

Everybody talking carbs and fuel mixture.  Nobody mentioned a sticky spark advance system (oops, I see Hunter did).  A slight spark advance will keep the rpm up even when the slides are sitting on the stop screws.  As the advancer settles down, so does the idle speed.  When was the last time the spark advancer system was thoroughly cleaned and lubricated.  You could test this by hooking up a strobe light and watching what happens to the spark position as you return to idle.

Patrick  Hayes
Fremont CA

[wirespokes]

I've never figured that one out - how to tell if it's a sticky advance. It's a chicken or the egg conundrum - is the idle high because of a sticky advance or is the spark advanced because the idle is high?

Reason I didn't figure it was the advance was because it only does it when hot. I'd think it would either do it all the time or LESS when hot.

If you look at a trouble shooting tree - for some faults you'll see a bunch of possibilities. I generally start out with the most logical trying to cut to the chase. But there have been times I've gone through the whole list, finding a number of things wrong, with the main symptom untouched. Boy did it ever run good when it was finally fixed. What I'm saying is if the most logical item doesn't fix, then move on to the next possible and so on. Sometimes when it's been really frustrating I've gone back over already checked territory a couple of times before seeing something previously unnoticed.

A little more data on when these symptoms showed up and history of the bike might make a difference in pinpointing where to look.

[pehayes]

Reason I didn't figure it was the advance was because it only does it when hot. I'd think it would either do it all the time or LESS when hot.

There are a number of parts here that slide concentric around each other and also fling peripherally.  Heat makes parts expand.  Anything that was close to binding is more likely to bind once warmed.  It is not a complex system.  It is probably easier to just disassemble, clean, and relube than it is to diagnose.  Good for the bike in any regard.

Also, with age, the centrifugal weight springs get weak and stretched.  Their ability to return to base is somewhat limited.  If these are original springs then it is highly recommended to replace with new. 

Either or both of these repairs might solve your problem.  Or, you still have a mixture/cable issue.   

Patrick Hayes
Fremont CA

[Tom H]

Patrick,

I did recently disassemble, clean and inspect the dist. and install new springs. See the pic. The old springs were the ones with the oval end. I installed the 8 and 9 coil. Still have the problem.




Tomorrow I plan to work through the suggestions, starting with an air leak at the manifold and working my to to the idle mix screw. I think that is where my problem is. As mentioned as a symptom of lean idle, it takes forever for the idle to come down.

Thank you confirming that the dist. springs can cause this type of issue. If working with the carbs does not solve the problem, I will have to take a harder look at the advance, even though I'm sure it's working "right?" per my strobe light.

Thanks again to all!!!
Tom

[80CX100]

It will run rich everywhere.

Hey Chuck, Tks for jumping in with that info, I figured it would be something like that, but wasn't sure exactly how it would behave, I'll file that one away.

Tom, From reading the info, it wasn't clear to me if the hanging idle was a problem before you replaced the distributor springs, or only started after you changed the springs.

I know you said you'll be looking hard at the ignition set up as well, wondering if the new springs are made with crappier steel, and just don't have enough "umph" to snap the advance back and bring the idle down like you're used to,,, if nothing seems to work and you're running out of options, maybe the old springs might solve the problem, fwiw.

Good luck

Kelly

[Tom H]

I worked on the bike yesterday and may have fixed the hang. Time will tell.

The Ambo for as long as I can remember has suffered from this issue. Many years ago,(like 30??), I asked my local shop for help on this. He said the dist. weights could be hanging and to spray some WD-40 on them and see if it helps.  He also mentioned the springs. The WD seemed to help, but it would start to hang again after time. I replaced the springs and all seemed well. Then the issue would come back and I would spray again.

A few months ago the issue came back. I sprayed again but didn't really help. While I was looking at the weights and springs and how gunky it was in there I decided to clean and lube the dist.. I also noticed that with the oval end spring set (see above pic) the oval spring did not do anything until right at full advance. Since I had the dist. apart I figured I might as well change to the 8 and 9 coil springs. Installed the dist. and all seemed well.

With the dist. cleaned and working what I believe to be properly, I then decided to try the light set of carb slide springs to make the grip easier to twist. I did read that this could allow the slides to hang open, but it sounded to me that if they did, it would be at high throttle openings. I installed the springs and again all seemed well, no hang. That is until a few weeks after installing the carb springs.

Part of the problem with this issue is that it can be intermittent. I do one thing and it goes away. When it comes back I do the same thing and it doesn't help. That's why I decided to ask and see if someone had the same problem (as it tuns out, I'm not the only one) and when he did THIS, the problem went away forever.

For what I did yesterday.

Checked for air leaks with a propane torch. Couldn't find a leak.
Checked the points and the timing. I did find that the timing was off about 5deg instead of being at 10deg at idle. Fixed that and it still hung.

Turned in the mixture screws and counted how many turns it took and wrote it down. I also looked up what the book says for an Ambo. LH S/B 1 1/2-2, RH S/B 2-2 1/2 turns out. Well even after my random twist while on the road and not knowing how far I had turned the screws, I was at LH 2 and RH 1 3/4. the were close. I set them to be on the rich side since from replies that could be the issue. LH 2 and RH 2 1/2. Started bike and it still would hang, but seemed like not as bad. So I played with them for a bit in and out to see if it made any difference. No. Made sure they were still where I wanted them and moved on to the next thing

BTW,  the testing was in the garage, but when I thought I might have made a change for the better I would ride it around the block and do a few stop and goes.

I also played with the cables to make sure they were moving freely and they do.

Now I running out of ideas. Also remember that this issue would come and go. But this times it seems like it's happy to stay around.

While riding the bike and the hang would happen, one time I tried playing with the cables to see if both had the same amount of slack. They did seem to. I did try just pulling on one cable to rev the bike but the hang remained. Tried the other cable and the hang went away. Look it must be something with THAT carb or cable. Uh, sadly no. Most likely it came down on it's own like it will do. Just random timing.

Again, running out of ideas, I thought about the dist. springs. thought about the results with the timing light and decided that was not likely to be the problem.

As a last resort I changed the carb slide springs back to the stock heavy ones. Damn, I forgot how heavy they were. Well lets see what happens. The hang "seems" to have gone away. But this still makes me wonder. Why didn't they hang when I installed them?? I don't think my riding habits changed or the type of roads I was on. Maybe it's heat related and the hotter the engine, the hotter and maybe weaker the springs???

Maybe it just came down to the carb springs THIS TIME. I need to ride it some more to see how it goes. IF it comes back, I will have to take a harder look at the dist, advance and see if it hangs. I don't this it is, it does move smoothly/freely.

So for the time being it may be fixed. I would like to thank everyone that helped!!!!

Tom