Wrenching on the 'ped for lunch

david f martin /

My bike has been running like crap the last couple of days... This morning, towards the end of my 11 mile trip to work, I actually had to get off and help push it up a hill.

Yesterday, I took the aircleaner apart and cleaned the element, and checked the plug. The plug was a nice toasty brown, like it's supposed to be. So today on my lunch break, I decided to take the exhaust off, cut it apart (mine is welded shut), and see what I could do with it.

It had lots of carbon inside, but didn't really look restricted. On a whim, I cut the muffler off the exhaust pipe and migged a new VW tailpipe in place. It looks pretty cool, but holy shit it is loud. Bike still ran like shit, and after running it for a mile or so, the plug showed that it was running too lean. I drilled the jet out one size, and ran it some more. Plug looked good, but the bike was still running bad. And loud.

Changed plugs, covered up the holes I drilled in the aircleaner, put another jet back in to correct for less air, tried different gap settings on the plug... I spent about 4 hours experimenting with different things, trying to get the bike to run better, always checking the plug to get the mixture right (yeah, I took a long lunch break)...

It is running better than it did this morning, but not much, and definitely not as well as it should.

Called the Yamaha dealer to price a new muffler. Discontinued.

My next step is to pull the head and check for carbon build-up. I may modify the holes that hold the CDI pickup on the flywheel to play with the advance, too. I'm also looking for a used bi-turbo to try on it, which I will have to weld to the exhaust pipe, since I'm sure no one makes one for my bike...

I'm guessing that a straight pipe exhaust is not really a good idea, performance-wise. I don't like all the noise, either. I don't like to draw attention from The Man, and I enjoy listening to the radio on my way to and from work...


1) Mine has a centrifugal clutch, which is pretty common on 'peds. I've noticed that the clutch will engage sooner with a heavier gear oil, and later with a light oil. I changed from 90w to 5w30 to 20w50, and now at least the clutch is working better...

2) The bike seems to prefer a larger gap on the plug than the book specifies.

3) The windshield amplifies, reflects and directs the exhaust noise directly into my ears and brain. Eh, what's that you say?!?

Any ideas from the gurus?


Guessing bout the 'ped for dinner.

Three guesses.

Either some of the tiny orifices in the carb got clogged.

(do you use an inline fuel filter and a capfull of some gas treatment occasionally?)

I swear ...I have to clean my PA-50 carb every 150 miles !

Or.... you sustained a seizure which damaged the rings and bore and caused a loss of compression.

Or.. the pipe is clogged.. and your straight pipe ain't cutting it.

(but I would think the straight pipe would perform better than a badly clogged stock muffler)

Could it be the 200 pound dog house you forgot to unchain it from ??.. ;)

Re: Guessing bout the 'ped for dinner.

david f martin /

I cleaned out the carb the couple of times I changed the jets... There was some particulate matter in the bowl. I'll put on a filter tomorrow.

I've got a gallon of premix (for the weedeater) I'm thinking about running tomorrow. Maybe my oil pump is on the blink. The bike hasn't had a seizure since I've had it, but it could be running hot.

As far as the straight pipe goes, it has to be much less restrictive than a muffler, but maybe the engine needs a little back pressure to operate properly...?

Dog sleeps with me. His house weighs much more than 200 lbs...


Re: Guessing bout the 'ped for dinner.

When my bike is running slower than it should, 9 times out of 10 it

Re: Wrenching on the 'ped for lunch

Ron Brown /


How quickly did your ped loose power?

Have you checked the timing.

Have you checked that the carburetor slide raises all the way?

btw, you are the first person I've noticed on this forum who confessed to drilling a jet and did not get stomped (advised that it was a no no). I think we are awe struck by your macro aproach to ped mechanics. Personally, I keep waiting for you to graft a VW cylinder and piston on to your ped.


Re: Wrenching on the 'ped for lunch

david f martin /

The bike seemed to lose power gradually, over a few days. I checked to make sure the brakes weren't dragging. I didn't make adjustments to the throttle cable, but pulled on the housing to see what difference it made. The problem is not in the throttle cable... I haven't checked the timing, but it is non-adjustable anyway. I figured changing the spark plug gap would affect the timing a little.

I'd drilled a bunch of holes in my aircleaner previously (on the dirty side of the filter), and I had a spare jet, so I didn't really have any qualms about drilling the jet to compensate for the extra air. Besides, I check the plug every time I make an adjustment, and try to keep the mixture right...

I've been working on VWs for around 20 years now, and I'm pretty well equipped in the tool department. Two-strokes are new for me, but I'm starting to catch on...

This morning I stopped by the convenience store for gas, oil and coffee on my way to work. I thought I'd put a little oil in the gas (mine is oil injected, and I wondered if the pump was skimping out on me)... Got about 1/2 mile away before the bike died... Fooled around with the carb, discovered that I could get the bike to run with the choke half-closed. Took it back home (with a trail of smoke behind me), called work and got the day off (only work 4 hours on Saturday, anyway)...

Drained the tank, put fresh gas in, topped up the oil reservoir. I can't really test drive it right now, since it is raining...

I'll keep ya posted.


Wrenching on the 'ped for lunch

There is a difference between drilling a jet to get more gas flow on purpose to richen the mixture ... and sticking a hard drill bit in just to clean out some dirt that can be gotten out other ways without messing up what might have been a good air/fuel mixture.

I have drilled out 3 or 4 jets to do just that.

And the best way is with an "orifice drill" set sold to heating and cooling techs for altering the orifices in heating furnaces for different gas types.

They have very fine incremental increases in size and are imbedded in brass hex's with the size stamped on them and are to be operated with just finger "torque".

I have 2 running bikes right now with drilled mains...and one is a ped.

David... If your ped is the type with the exposed cyl head and cyl.... pop the head off and have a look.

Takes 10 minutes at most.

Re: Wrenching on the 'ped for lunch

Ron Brown /


I was not picking on you about the jet drilling, just pointing out that we defer to your obvious "try it and see if it works" attitude.

As for your current problem. There are only two simple reasons for needing choke on a warm engine. One is too much air, such as a manifold leak. The other is too little gas, as in water or crud in the carburetor. Assuming, of course that the mixture was ok to begin with.

There are more complex reasons such as crank seal leaks but they are less common.

You seem to have the exhaust off a lot, you can look in through the port and see if the piston is scuffed or the rings siezed.

Keep us posted,


Re: Guessing bout the 'ped for dinner.

Hey David, Just started working on my peds to get them ready for the spring, Ha! None wanted to start so I drained the gas (stored full) and blowed out the carbs, went and bought some racing gas 110 octane leaded, mixed with my synthetic oil, and they run and idle better than ever, i also use a little Sea Foam carb cleaner in each tank. Should give it a try....racing gas is about $2.60 a gallon and wont damage the motor, they sell it a lot of places here in VA. Keep on Pedden---Doug D

Re: Wrenching on the 'ped for lunch

Reeperette /

>>3) The windshield amplifies, reflects and directs the exhaust noise directly into my ears and brain. Eh, what's that you say?!?<<

It says you can always tell a hardcore 'pedder by the bugs in his teeth when he grins.

>>As far as the straight pipe goes, it has to be much less restrictive than a muffler, but maybe the engine needs a little back pressure to operate properly...?<<

For all that I have never really seen proof either way, I suspect this may be the case, as in adding a little compression, but don't take that as established fact.

>>I can't really test drive it right now, since it is raining...<<

What, you don't think the drowned-rat look is fashionable ? LOL !

All in all, seems general suspicion is the rings, and I agree, it's worth a look anyhow.

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