Bonneville Tech Question

[CarlS]

I received the email below through the admin email address. I thought I would post it here in the Lounge for maximum exposure and then move it to the Bonneville section.

I have an 02 Bonneville with only 9,000 km on the clock and a problem has cropped up. Two months ago I rode to the classic bike club , no problem . but now it starts but will not rev up & make decent poweer above about 3,500 RPM. I installed a new battery & new plugs & this made no difference. There is gas in the tank , I checked the diaphragms on the slides , no problem , removed one float bowl & checked needle & seat , main jet ... all fine.

It feels like it is getting no gas or the ign. is not advancing ... it will not respond to a larger throttle opening. Air cleaner is clean. The new batt. can only go in one way & it is correctly installed , I have unplugged & replugged every electrical conn. in case but no change.

Any suggestions , apart from taking it to the dealership ??

 

[CarlS]

This was my reply to him. Please add any ideas you may have.

The first thing to check is to make sure your gas cap is venting. There is a roll over valve in the gas tank vent line. This valve is supposed to keep petrol from leaking out in the event the bike goes down (it works - from experience). The valve is designed to let air into the tank but not let gas out. These things sometimes stick. With the bike running and when you have the problem at 3000 rpm, loosen your gas cap and listen for a "whoosh" as of air. If you hear it and/or your bike starts running properly, you have identified the problem.

The next thing that can cause this is a plugged or partially plugged jet - trash in the carbs (or one of the carbs). The jests can be removed without removing the carbs.

The third thing is the throttle pickup sensor. It must have the proper air gap to work and the sensors can go bad.

Lastly, on my list, is the coil. It may be going bad.

I have personally worked with all four of these problems on my Bonnie, my wife's Bonnie and on friends' Bonnies. I had the roll over valve problem and my wife had a partially plugged jet from bad petrol.

When you get the problem sorted out, please post the solution so that we all can learn.

I hope this helps.

 

[Rocky]

Good advice Carl. I can't think of anything else.

 

[devo]

While checking the fuel system dont forget the screen on the petcock and the wee filter INSIDE the line where it divides into two between the carbs.
I'm thinking the easiest way to eliminate the fuel system as far as the carbs,is to disconnect the fuel line from each carb, drop them into a container and open the petcock. If fuel doesn't flow freely from each side you have a problem.
Also, check the throttle cable hasn't slipped and you are in fact activating full throttle range at the carbs.
:y18:

 

[CarlS]

Thanks, Rocky.

'Preciate it, Harry. I will make sure he sees this.

 

[The Seeker]

My first guess would be ignition pick-up sensor or a coil (leaning towards coil myself).

Not knowing the Bonneville that well...is there anywhere in the intake system where an air leak could occur? I'm thinking of a rubber connection venturi leak here. Spraying some brake cleaner in the area and listening for a change in revs would usually detect that.

 

[CarlS]

There are two couplings where the carbs fasten to the outlets from the airbox as well as vacuum port plugs if the air injections has been removed.. If there is a vacuum leak, it usually affects the bike more at lower rpm and popping on deceleration. I'm not sure of the effects of the rubber boots on the carb intakes. I have never experienced that. But from what I have read, it causes rough running and poor idling. I, too, lean toward the pickup sensor of the coil.

 

[The Seeker]

Stock Triumph coils seem to be a weak point on many models. Replacement = Nology coils and HotWire leads.

 

[avion]

I'm by no mean an expert, but if it hesitates to go over 3.5k, it would appear to be something common to both cylinders? ie electrical or bad fuel?

...

 

[CarlS]

From experience, one cylinder not firing can do that to you.

 

[devo]

[quote author=CarlS link=topic=5305.msg29861#msg29861 date=1240435863]
From experience, one cylinder not firing can do that to you.
[/quote]
Your right Carl, but it would be audibly obvious.
:y18:

 

[CarlS]

And indeed it is. You can tell one cylinder is not firing or firing fully simply by the sound. However, mine did not begin to break down until it approached 3K rpm. Around 25-28k, it sounded fine. It was a partially clogged jet in the left carb and general crud in both carbs.

 

[Chris J]

Hi Chaps , I am sure it is not a gas problem , gas is fresh & clean & quality is strictly regulated here.
Gas is getting to both carbs , it really feels as if the Ignition is not advancing.
I have removed one float bowl & all is clean , however those accursed Phillips screws are enough to drive one to drink !!
The screws holding the throttle sensor to the RH carb are something else as well !!

Apart from replacing every electronic component , one by one till the problem dissappears .... what can be done .. by a home mech. at home ???

Regards , Chris J

 

[Silli]

What about the air filter?

 

[Chris J]

The air filter is clean ..... I have checked ... 9,000 km on tarred roads.

My experience with coils is that they either work or die stone dead & these are working , both cylinders are firing , head gets equally warm left & right , both pipes get hot and pulses out the silencers feel equal & both hot.

I can pull each plug wire off while the motor is running & hear a definite change when I do this & the motor picks up as wire is replaced.

Old stuff has trace-able faults !!!

Chris J

 

[CarlS]

Chris, welcome to the forum. I am glad to see that you were finally able to get registered.

The coil can, indeed, cause the symptoms you have encountered. The engine can start up well, idle well, and then begin to run rough at higher rpms and/or as the coil heats up. The pick up sensor can cause the same symptoms. I was fortunate that when Mae Lyne's T100 had these same problems, I was able to swap the coil from my bike to hers and vice versa and eliminate the coil as the problem. I was also able to swap the pickup sensors and eliminate that.

Since you have no sediment in the bowls - you have checked both bowls? - I would lean toward an electrical problem. The stock allen head carb screws are a PITA. You can get carb screw replacement kits from several sources. These stock screws are very soft and you can easily bugger up the heads. The first time I rejetted, I replaced the stock screws. I recommend that you do likewise. You can order these from newbonneville.com or bellacorse.com. If you have problems with the vendor shipping to SA, contact me off line.

If you know anyone with a Bonnie, try that coil in your bike and see if you still have the problem. I agree; the older bikes are easier to diagnose and repair.

 

[Doug]

The little Phillips screws on those carbs are an abomination. Take one as a sample and go along to your local nut and bolt supply and get stainless steel socket head replacements.
Did you say throttle position sensor? It's not a good idea to move that!
Have you checked that the vacuum slides are moving up and down freely?
That and all the rest of the guys advice done,it sounds like dealer and credit card time.
Is your local dealer any good?

 

[Chris J]

More fiddling ..... I have unplugged the wires from the throttle sensor where they go into the wiring harness & started the bike :It runs exactly the same as before , in other words it suggests to me that this sensor is faulty as the problem persists with it unplugged .... does this make sense ?? This plug is wedged between the airbox , frame tubes & frame plates where the rear of the gas tank mounts, the most inaccessible place possible !!!!

Everything on this bike is extremely difficult ; never yet owned a bike that you have to take the tank & seat off to remove the spark plugs !!!

Frustrated , Chris J

 

[CarlS]

Chris, it is probably not the the throttle position sensor but rather the pickup sensor or the coil.

 

[Chris J]

OK , thanks Carl.

S/S allen screws are easily available here , no problem.
I have not yet removed the left float bowl as it is more inaccessible than the right , will do that when I have new screws to install.

Do you have e mail address for Nology in case I need them , and I presume they are made for the Bonnie & will fit straight in ??