Sherlock Holmes and the adventure of the large mai

James Corbally /

Ok, let me explain my carb situation, my conclusions, and then you can all tell me if I'm sniffing blue mud.

Recently checked the size of my main jet. Turned out to be #70, but the workshop manual showed nothing over #60. I think the dealer did this, and this is why I figure they did it.

After I got the bike, I ran it till its' first service. At the first service, it was derestricted. Ran great for a week or so, then the air filter cover gets stolen. Bike is laid up for a few days, while I try to get a cover. Filters (sponge) are removed and put in a plastic shopping bag.

I get a new cover, and reinstall the filters. Notice a flat-spot from around 1/4 to mid-range throttle. I contact the dealer, and arrange to bring it in some time soon.

Now, I'm travelling to work on the week it's due to go back, and I begin to lose power. Machine just gets slower and slower... Happens twice on the way in, and I arrange to bring it in that afternoon. On the way into the shop, it does this once again.

Bring it to the shop, and they check the filter cover (which they suspected of being incorrect and causing the flat spot and power loss) and determine it is the correct part. They tell me they think the cold is affecting it (November at this stage, quite nippy out, with v. cold mornings). I go off, have some food with my wife, and return to the shop to be told they've fixed it, and that the problem was with the "carb freezing". They install a carb heater. Not knowing anything, I accept this explanation, and sure enough, the machine runs better.

Over time, I notice the flat spot isn't entirely gone, and it takes a little time and throttle fiddling to get it to full speed. Throttle usually does nothing from halfway point up to full, except drink fuel. Meanwhile, I'm being left behind by other 50cc machines from a standing start. It also seems heavier on fuel, giving around 70-78mpg when I'm told these machines give 90+. I'm suspicious.

After learning a few things (many from this forum, thanks!), I recently experimented with the jet needle. Tried raising it one notch from original middle position (richened). Bike bogged. Lowered the needle one notch from original position. Bike runs much better than it has since the problems started.

My deduction is this;

Original problem with the air filter led to dirt in the carb jet(s). This led to the flat-spot, and the eventual "power loss" problem. Given what I've read here, it appears as though my power loss problem was in fact an engine "soft seize", as it fits the symptoms. This would correlate with blocked jets of course (over-lean mixture). Plug also indicated rich running.

I bring it into the dealer. They see that the air filter cover is correct. Most likely, they realize the engine seized (they never mention it to me, they're pretty sick of me by now). So they clean the carb, and at this point fit a #70 main jet, perhaps just to make sure. I'd called on several occasions about what I know now are quite trivial things, but it's clear they dread me calling. Hardly my fault, as I don't even know where the carb is at this stage (first bike, complete novice). I'm quite sure they'd rather never hear from me again. Nice customer service, eh?

Anyway, they fit the larger jet and carb heater and blame the cold, giving me back a bike which runs ok enough that I don't notice the flat spot is still there, only lessened. I didn't have it in its pre-theft state for very long, and haven't gotten used to the machine, so I only have gut-feeling to go on.

As a result of my suspicions, and general reading and learning about these machines, I then proceed to check the carb and needle, which leads me to now.

Apologies for the length, but does this seem like a plausible deduction, or is there something glaringly obvious I'm missing? Which link in my chain of thought is the weak one?

I'm currently getting a few jet sizes, from 68 down to 60 (hopefully) so I'll be able to determine whether I can fix this or not pretty soon.

Any comments would be appreciated.

Thanks,

James...

Dr. Watson and James's 'fine kettle of fish'

Hmmm... the fact that the dealer has installed a 'carb heater' makes the guessing more difficult..

And there is no point now in a lot of guessing about all the ups and downs in the machines recent history.

I think you are over-thinking this by guessing at a 'soft-seize'.

(I doubt it had a seizure)

If I beleived it might have had a seizure of any sort I would simply pop off the head (not the cylinder) and push the piston to the bottom and take a good look at the cylinder walls with a good light.

On an air cooled 2 stroke that is soooo easy that you should just do it.

As long as the cylinder is smooth and unscratched/scuffed... then it didn't seize.

If you see scuffs, then take the cylinder off and you can get a better look.

And Yes... I am sure you are making a Royal pain in the ass of yourself to the dealer

: )

... and your amateur questions are surely annoying them.

Consider that it is not the responsibility to teach you "engines 101".

Fixing machines and pleasing a customer is not an easy task.

If the airfilter/airbox/carb heater is the way you are going to leave it, and you are unsatisfied with the performance, and the spark plug is dark brown/black... Then you can go ahead and try one step smaller main jet at a time to see if it runs better... but examine the spark plug color each time.

Re: Sherlock Holmes and the adventure of the large

Wayne Broderick /

Do you think the "flat" spot could just be the slide between gears?

For Example, on an uphill, before I added the Bi-turbo exhaust my Tomos had a "flat spot" around 13-15 mph. when I increased throttle, it made noise, but no power. after I added the bi-turbo, it still hits the 'flat' but at 17-20 instead.

That, at least on my bike, is normal. Cant get enough speed for to shift gears, but is kind of fast for first.

My bike would shift fine on a slight downhill, smooth on level, and a little slow uphill. Like I said, it's normal.

Re: Dr. Watson and James's 'fine kettle of fish'

James Corbally /

Fred wrote:

>

>

> Hmmm... the fact that the dealer has installed a 'carb

> heater' makes the guessing more difficult..

>

> And there is no point now in a lot of guessing about all the

> ups and downs in the machines recent history.

>

I'd say there is. Having an accurate picture of it's history can help diagnosing future problems.

> I think you are over-thinking this by guessing at a

> 'soft-seize'.

> (I doubt it had a seizure)

>

> If I beleived it might have had a seizure of any sort I would

> simply pop off the head (not the cylinder) and push the

> piston to the bottom and take a good look at the cylinder

> walls with a good light.

> On an air cooled 2 stroke that is soooo easy that you should

> just do it.

I will, but I need to get a torque wrench first. Don't want to make it worse than it is! It's quite an involved procedure for my machine too.

> As long as the cylinder is smooth and unscratched/scuffed...

> then it didn't seize.

> If you see scuffs, then take the cylinder off and you can get

> a better look.

>

Thanks for the tips, I'll be sure to look out for what you've mentioned.

What other kinds of problems can cause these symptoms? Soft seizing certainly fits, does it not?

> And Yes... I am sure you are making a Royal pain in the ass

> of yourself to the dealer

> : )

> ... and your amateur questions are surely annoying them.

Aw, sorrow for them.

> Consider that it is not the responsibility to teach you

> "engines 101".

I never expected it of them. But I don't have inbuilt genetic-based knowledge of how a two stroke works, can find no books on it and must trawl the net for information. I wasn't asking them to walk me through rebuilding the cylinder, I'm sure I asked questions anyone who is new to these machines would.

They were aware it was my first machine, they were aware I knew little or nothing. Should it really surprise them if I call? Or is there something trivial in my calling, wondering why my starter kicks in when the brake levers are pulled?

> Fixing machines and pleasing a customer is not an easy task.

>

So what? I'd love to see my bosses face if I tried pulling that excuse. It's still their job to answer any questions I may have. That is part of customer service, I know as I'm involved in it as part of my own work. They claim to have great customer service, but does their performance honestly match up with that statement? If they don't provide it, they shouldn't claim it.

> If the airfilter/airbox/carb heater is the way you are going

> to leave it, and you are unsatisfied with the performance,

> and the spark plug is dark brown/black... Then you can go

> ahead and try one step smaller main jet at a time to see if

> it runs better... but examine the spark plug color each time.

Will do, just need to get me a size #60 next week.

Regards,

James...

Re: Sherlock Holmes and the adventure of the large

James Corbally /

Wayne Broderick wrote:

>

> Do you think the "flat" spot could just be the slide between

> gears?

>

> For Example, on an uphill, before I added the Bi-turbo

> exhaust my Tomos had a "flat spot" around 13-15 mph. when I

> increased throttle, it made noise, but no power. after I

> added the bi-turbo, it still hits the 'flat' but at 17-20

> instead.

>

> That, at least on my bike, is normal. Cant get enough speed

> for to shift gears, but is kind of fast for first.

>

> My bike would shift fine on a slight downhill, smooth on

> level, and a little slow uphill. Like I said, it's normal.

It's an automatic, so it has variable transmission.

It does go up steep hills slowly, but I think that's more a case of belt slip.

Regards,

James...

Re: Dr. Watson and James's 'fine kettle of fish'

No... there really isn't any point in guessing about its recent history.

You say "having an accurate picture of its history" can help....

The problem is you do not have an "accurate history".

You didn't do the work... are not sure what they did... you suspect they aren't telling the truth... and you think this or that might have happened.

(don't be offended!)

Which means nobody hearing all that can make a diagnosis based on those statements.

They will have to mostly go on the symptoms.

Some of the info is good... some is not very helpful (and can even be misleading).

A good mechanic pretty much listens to what the machine tells him.

............ On to the machine...........

Why is pulling the head such an involved process?

Is it watercooled (does it have radiators) ?

If it is not... and the cylinder head is exposed.. then you can pull the head off and look into the cylinder and put the head back on in 5 or 10 minutes.

And very few of us use torque wrenches for ped heads.. I don't.. (but those of us that have done it a hundred times have a pretty good feel for the correct torque.. if you are the type who breaks things all the time ... then DO use a torque wrench...since this bike is your transportation).

Keep in mind one other thing... as the weather cools off here now in the Northern hemisphere... if the ped is actually too rich... it will start running better and better.

Because the colder the temp... the leaner it gets.

For racing bikes... people generally use one size main for 'normal' temps (say a 100)... and then one size leaner for the hottest days (like a 95)... and one size larger for the coldest (like a 105).

That is a generalization to illustrate a point.

Trying to help. : )

Re: Dr. Watson and James's 'fine kettle of fish'

James Corbally /

It's OK Fred/Wayne, I'm not offended.

It may not be possible to build up an accurate picture of events, but I'm confident I'm near the mark, give or take small details. At the end of the day, I have to try. If we didn't, we'd have no Archaeology!

I wasn't expecting that I'd get a response back saying "you're exactly right!". I was more hoping that if I'd gotten some part completely off the wall, someone would point it out. Kind of a "plausibility check", if you will.

I think, as Wayne has said, only the cylinder can tell me now if it's seized in the past. It's air cooled, but the problem with removing it is that even with all the fairings off, the frame is still in the way. The workshop manual has it removed from the bike altogether, the whole thing supported by the centre stand which is mounted to it. I can't see any easy way to get at it or examine it without this step.

Haven't noticed any change in performance, but it is getting colder here so I'll keep a watch out for that.

Thanks again to both of you.

Regards,

James...

Re: Dr. Watson and James's 'fine kettle of fish'

Ron Brown /

James,

I have mentioned before in the forum that a "partial" or "soft" seize is highly unlikely if you are able to continue riding and especially if you can shut down to idle and it does not immediately stop.

The nature of an engine seizure is that the piston gets too large for the cylinder bore due to exessive heat (it could be out of spec if new). When this begins to happen, resistance to the engine turning is applied where it can have the most effect, at the piston. This makes idling out of the question as there is not enough power at idle to overcome the friction. As soon as the piston begins to seize, the friction in the cylinder increases the piston temperature so rapidly that under normal circumstances the engine locks up almost instantly causing pucker marks on the seat as the rider attempts to keep the ped under control with the rear wheel locked.

Typically, the only way a partial seize happens, is when going fast with a closed throttle, as in down hill or slowing for a corner. The problem here is caused by lack of lubrication and can sumetimes be avoided by opening the throttle when you feel the engine tighten up, but you don't have much time.

Ron

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