t3 hanging idle help oh please

[jabberwocky]

My T3 has been nothing but trouble this year! So here's what's up now….
If I'm sitting with the bike at rest, and blip the throttle, big or small, it always returns to an idle, no problem. But when riding, any time I pull in the clutch and release the throttle, the engine will stay at about 4K, which makes the transmission bang when I shift up. No amount of throttle blipping between gears will make the engine speed reduce. WHat is interesting is that if I slow down or stop with the bike in gear, thereby bringing engine speed down, when I pull in the clutch the idle is as it should. The other thing is that when the engine fails to drop revs, it is running smoothly on both cylinders, so if it is a carb problem, it is acting the same on both cylinders.

So I'm thinking that it might be one of two things; a messed up advance mechanism in the distributor, or carb slides that hang up under high vacuum situations.

They are old VHB30's which have always worked for me as they should, but I'm sure they do wear, and new this season is a set of lighter slide return springs from MG Cycle. I've not replaced the throttle cables on the time I've had the bike, but they feel free and smooth when I scrutinize them.

Any ideas? ANyone had this happen before? Thanks for your consideration

[fotoguzzi]

put the old heavy return springs in as a test?

[n3303j]

I vote for a hanging up advance.

The BMW /2 series behaved similarly when their mechanical advances would hang up.

Watch it with a timing light. It will tell you a lot.

[jabberwocky]

Two good suggestions, but I have a problem with each...... my timing light isn't working, and the original springs are 600 miles away in Maine! I guess I need to get another timing light, and springs are cheap

[Antietam Classic Cycle]

put the old heavy return springs in as a test?

^^^ This. I've had the same issue with the lighter springs.

[jabberwocky]

Perhaps when the factory put in those heavy springs, there was a reason why. Because I'm a man of means, Ima get me some new springs, and cables, and hope that does it, because I don't want to crab the frame to get the distributor out! Thanks guys!

[Antietam Classic Cycle]

Perhaps when the factory put in those heavy springs, there was a reason why. Because I'm a man of means, Ima get me some new springs, and cables, and hope that does it, because I don't want to crab the frame to get the distributor out! Thanks guys!

You don't need to crab the frame to remove the "distributor". Just loosen the bolts, swing the clamp up and away and pull the "distributor" out. After it comes out so far you can tilt it down to avoid the frame tube.

[wirespokes]

I've got lighter springs in the 40s and the 30mm Dells. They don't have that problem, so I wouldn't suspect that as your issue.

And since it's both cylinders, I'd find it highly unlikely it's a problem with the carbs, since what are the chances of BOTH carbs having the same symptoms at exactly the same time???

Checking with a timing light - I can't figure out what good that will do. Of course the ignition will be advanced if the engine is running at 4K.

I'd check the advance first. This can be a problem with the airhead BMWs as well and sounds very similar.

[jabberwocky]

So what are the common symptoms of worn out vhbs? I've heard that the slides wear out, and the grooves they ride in in the carb body. What kind of running issues does this usually cause? Wirespokes, it's nice to see that you're on here, I'm Jonnycash on ADV, and I'm glad you finally got a Guzzi and that you like it so much. I installed the lighter springs in the carbs last winter and hadn't had any trouble until a few weeks ago, but I'm really having a hard time understanding what would cause this problem I'm having. For every possible reason listed so far, we seem to be able to come up with a good reason why that isn't the issue. I'll get a chance to work on it later this week, but just thought I'd put it out here to get a discussion going and try to figure out where to start looking.

[n3303j]

Perhaps when the factory put in those heavy springs, there was a reason why. Because I'm a man of means, Ima get me some new springs, and cables, and hope that does it, because I don't want to crab the frame to get the distributor out! Thanks guys!

I don't remember having to pull the distributor to address the advance. Get the tank out of your way and it's all accessible from the top.

[jabberwocky]

Glad to hear that. I've definitely changed out my points without splitting the frame, and would certainly have tried pulling the dist before splitting the frame, but I thought I had read here that there wasn't clearance to get it out of there.

[jvb]

The symptoms sound familiar to me but I can't remember the cause. As I still have the original slide  and mechanical advance springs I can only presume the cables were tight either from incorrect specification, old age or contamination.

Bleeping the throttle only uses a small amount of cable travel while normal riding uses much more. The reason why it adjusts back to normal idle if left in gear is the cable may be restricting closure of the slides and you are allowing time for them to slowly close.

Easiest way to check is to twist the throttle , with the engine off, and it should snap back. If it doesn't check the throttle and cables. I don't know if you have two cable from the throttle or a one into two. I have the one into 2 as there seems less drag on the cables. Also the grips could be fowling on the switch gear.

All easy to check.

If the cables and throttle are OK , then my suspicions would be turning to sticking carb slides, caused be reasons unknown.

[chuck peterson]

Throttle Cables completely slack under the tank? No pinching?

[redrider]

The Mille had that issue. Cable splitter thingy under the tank was the culprit. Normal wear and tear at 150K

[SeanF]

They are old VHB30's which have always worked for me as they should, but I'm sure they do wear, and new this season is a set of lighter slide return springs from MG Cycle. I've not replaced the throttle cables on the time I've had the bike, but they feel free and smooth when I scrutinize them.

Start here, as it is the most recent variable to be introduced to the system. Return springs need to overcome all of the friction in the throttle, cable & cable routing in addition to getting the slide  down. Swapping the originals back in is a pretty quick test, and make sure to test at speed and not just in the garage. Best of luck!

[Kiwi_Roy]

May be a long way off but my EV started doing that it was the throttle linkage catching on the seam in the airbox. the carbs moved back or the airbox moved forward. I loosened everything off and used a tire lever to create some space, no more problem.

[acogoff]

     Intake gasket leak at the head can cause similar. Easy enough to check, just shoot the area with a fluid of your choice with the engine idling. Increase in rpm= air leak.

[80CX100]

I had the same thing happening with the VHB30s on my CX100, I thought it was a problem with the enrichment circuit but after complete carb rebuild it was still hanging with a high idle.

A couple of things were actually going on,,, my throttle cable routing was crossing over the frame under the tank as recommended by most,,, for whatever reason my bike didn't like that,,, my throttle cables are now very loosely hanging down on the right side and going straight back along the frame and then the left one crossing over loosely,,, doesn't look as neat,,, but it definitely is smoother and doesn't pull on them when I move the bars side to side.

The big fix, was figuring out that the cable itself had stretched a little longer than the case/sheathing and at max adjustment, I still couldn't get the cable casing snugged down tight inside the ferrule at the carb,,, I made little shims out of plastic zip tie material and shimmed the cable casing, so I could fasten them inside the carb ferrule securely,,, the cable case had been hanging up on the carb ferrule putting tension on the cable itself causing the hanging high idle.

Hope that makes sense,,, it worked for me

Good luck

Kelly

[wirespokes]

Johnny AKA Jabberwocky - good to meet you - again.

I guess it makes sense there could be friction in the cables and throttle, that the weaker springs aren't overcoming. And when RPMs are up around 4K, the air flow works to keep the slide up as well.

What happens if you cut the ignition when it's running at 4K and coast to a stop? I'm curious if you'd find stuck slides or advanced timing? I'm coming back around to thinking it's the advance mechanism.

That's a good idea - replace the stiffer springs as a test. If it's still doing it, that would be another point for stuck advance.

[jacksonracingcomau]

If I'm sitting with the bike at rest, and blip the throttle, big or small, it always returns to an idle, no problem.

Versus

But when riding, any time I pull in the clutch and release the throttle, the engine will stay at about 4K, which makes the transmission bang when I shift up. No amount of throttle blipping between gears will make the engine speed reduce.

Trick is to replicate this stationary,  I can't see the difference in scenarios
In neutral or clutch in, engine shouldn't be able to tell if wheels moving or not,
Just for shits & giggles, find neutral at speed,  if idle drops, then you know it's a clutch problem.
Between this and wirespokes coast to stop plan, it's nailed.
Adv mech really can't tell if wheels are moving without an ECU or somesuch, is cables or clutch, gotta love basic bikes

[tris]

....They are old VHB30's which have always worked for me as they should, but I'm sure they do wear, and new this season is a set of lighter slide return springs from MG Cycle. I've not replaced the throttle cables on the time I've had the bike, but they feel free and smooth when I scrutinize them......

To expand on SeanFs thoughts - its possible that the new springs arent as "springy" as a standard light spring should be

I suggest this because we had a problem at work whereby spring washers were repeatedly opening up.
We finally tracked it down to the washers not being made from spring steel as surprisingly the correct grade of spring steel is much more difficult to obtain these days so the supplier had used "the nearest equivalent".
Finding a more readily available and suitable steel made the problem "go away"

NOTE:
No criticism of MG Cycle is implied or to be inferred by this comment