Vibration out of control

[crassius]

you can cut a bit off bottom of the front bracket for that chain guard to lower it a bit as it seems they left more than an inch of up/down clearance between chain & guard - while you're doing that, put longer screws to hold the guard front & rear and add a nut to those screws to prevent them loosening from vibration

look closely at the flat plate of front mount, if it seems that the sharp edge is digging into frame, you might want to bend or file a bit on that plate to get a smoother seat there, or add a piece of PVC to protect frame

 

[George Tirebiter]

OK, good ideas. The front mount is already bent slightly around the frame. Thanks,
George

 

[KCvale]

Thanks for the info. Very helpful.
BTW, is it Ok for the right side gear housing to rest on the chain guard?

Other than vibration rattles the engine hitting the pedal chain guard is OK.

As Crass mentioned you have a bunch of room between your pedal sprocket and chain guard.

Chain guards have a lot of clearance above the front sprocket to make it easy to put a chain back on in front.

I am a ' low center of gravity' kind of builder that builds a lot of fender and guard type beach cruiser bikes so a pretty easy task to lower the pedal guard 1/2" there, essential on 4-stroke builds like this uber tight fit I just finished.

Just put in the back mount screw loose, and from the left side so you can see whats going on.

Lower the chain guard to not hit the engine or sprocket, mark a spot on the guards mount piece through your frames mount hole, and then drill a hole there.

I have to do this often, especially with 4-stroke builds, but done right you can use a chain guard between a mount plate and sprocket in a 1/8" gap, just enough to hand push a chain on the sprocket like the 4-stroke above.

I did the grab and shake test. It's solid.
Let me know what y'all think. Thanks,
George

Good for you George, you caught on to what is important quickly.

You are darn close to ideal, but depending on your demands on it, how long it will stay good needs to be a 'grab and shove' checked often thing for loosening as I see 2 things just not 'ideal' as it were....

It may just be a pic shadow, but it don't look like your new back bridge mount is flush with the seat post.
This is the most crucial mating of the engine to the frame there is.

And then there is the front mount which is the 'improvement' over drilling your frame for those that don't have a drill and bit...

U-bolting a flat plate to a round tube directly.

Engine mounts are all about at least two tube attachments as near to 360 degree grip points to the frame as possible to make the engine one with the bike.

That small U-bolt/plate will do a great job of combating the front mounts major job which is keeping the engine from turning left, it just isn't a 'make it one' mount with a flat plate against a round tube with only ~180 degree grip for twist and vibration.

You have a flat plate mounted to your engine front mount to bolt to.

I suggest you replace that U bolt with a muffler clamp that fits your tube, heck they are $1.35 at the auto parts store and work the same, they just have piece that has one side to grip a tube and the other side be flat.

That will give you near a 360 great grip in front to 'make it one' as it were.

You should fine as is, just do the test often, when it's time to fix try that.

 

[George Tirebiter]

KC, thanks for all of the great info. Now that I've finished my first build it's almost like starting over to correct everything I did wrong. BUT, I am having a ball learning all this great stuff. This forum is a goldmine of information. Thanks to everyone here for your help.
George

 

[KCvale]

KC, thanks for all of the great info.
Now that I've finished my first build it's almost like starting over to correct everything I did wrong.
BUT, I am having a ball learning all this great stuff.
This forum is a goldmine of information. Thanks to everyone here for your help.
George

I don't mind helping in my spare time George and you are welcome.

It's all downhill easy one you make the engine one with the bike and the drive chain in alignment with the trued sprockets.

 

[George Tirebiter]

Well, I have everything tight and secured. It runs good at 3/4 to full throttle but the bucking and vibration is still terrible at slow speeds, but it seems to get a little better after it warms up. Moving the needle clip up or down had no noticeable effect.
George

 

[crassius]

slow cruising thru parking lot won't happen with these - 2-strokes just don't go slow well, but it could also be a heavy 4-stroking condition due to extreme richness

 

[2door]

George,
How slow is "slow speeds" ? When you get below about 10 MPH you need to disengage the clutch and pedal. You have to remember that you're not driving a vehicle with an automatic transmission. You have to allow for slow speeds and make adjustments accordingly. That means using the clutch when you get too slow and revert to pedal power.

Tom

 

[Chaz]

Tom is right, George, you may have to occasionally move your legs.

Crassius brings up a good point. You may be too rich. This could be cured easily by buying one of those Sportsman Flyers for me, that should lighten your wallet just enough to do the trick.

I can't remember if you've modified your muffler. It might be time to drill a few holes. There's a few good threads on the process, much better than I can explain.

see you on the funway honky

 

[George Tirebiter]

I do use the clutch when I slow down and pedal up to around 10mph. The severe bucking starts then and continues up to around 15 -20mph. I think it is 4 stroking in the low to mid range.?
George

 

[Agreen]

4-stroking is when it feels like a machine gun. Braa-aa-aa-aaap braap braap.

If it's too lean, it'll just cut out and feel like you just shut the throttle for a second.

My suspicion is that it's too lean and you may need to drop the clip on the needle a notch. The needle controls fuel from 3/4 throttle and below. The needle is tapered to fit inside the main jet, which helps control the fuel flow rate when the throttle is partially open. Above 3/4 throttle the needle has no (or little) effect on fuel flow. So if the needle is too high (clip too low), it'll 4 stroke and braap at low speeds. Too low (clip too high) it'll cut out and buck.

 

[Chaz]

George, your issues are over my head. Is it possible for you to upload to youtube as this may require video analysis. I think it might help the experts diagnose the problem.

Also, I've noticed that any changes to the clip position take a while to be noticed. I used to move the clip and ride down the block thinking that any changes would be immediately apparent. Now I change the position and ride for a while until it's fully warmed up and continue for a twenty minute ride or more to see how she reacts.

 

[George Tirebiter]

Well, I've moved the clip down a notch and took it for two 4 mile rides 2hrs. between rides and I did notice a little improvement, especially after it had warmed up. So, I guess I'll ride it for a while and see what happens. I'm thinking this may be as good as it gets and that would be OK. Utopia is not an option. Thanks for the help.
George

 

[Chaz]

Tirebbiter, I mentioned the exhaust because if you've got the stock one it's not very free flowing. Opening up the flow a bit can help with the 4 stroking and give your bottom end a boost. I mean the engine.

 

[George Tirebiter]

Chaz, Mudhead wants to know what you mean by opening up the flow?

 

[Chaz]

George, I meant the air flow through the exhaust. The stock exhaust is a bit restrictive, especially so since the stock carb jet is a bit rich. You can improve that air flow by drilling a few holes in the muffler's end cap. Here's some homework that Porgy told me about. http://motorbicycling.com/showthread.php?t=31440

 

[George Tirebiter]

Chaz, thanks, I'll check it out.
George

 

[Davezilla]

There are ways to drastically reduce exhaust restriction without adding more noise if you use an expansion chamber. I've been riding on 2 wheels with an engine thrown n there somewhere for nearly 40 years and working on them for about 35 years, most of that was in the boosting of performance as well as reliability. I currently own 3 motorcycles and 3 motorized bicycles.
You can run an expansion chamber with a side bleed which means the end of the pipe is sealed off and the exhaust exits from a stinger pipe coming out of the belly section of the pipe. This keeps all the sound trapped inside the belly section until it disapates before exiting the pipe. The exhaust is able to exit the pipe unrestricted but with a lot less noise, some side bleeds without a muffler are actually quieter than a typical end bleed with a muffler, and with a muffler added, these are even quieter. The size and length of the stinger pipe can also contribute to how quiet the setup is as well as how far the stinger pipe goes into the chamber.
An expansion chamber with the stinger pipe welded directly to the belly section at a perfect 90 degree angle from the exhaust stream will be quieter since the exhaust gasses want to go to the back of the pipe instead of straight to the outlet, but if the stinger pipe can go inside the pipe closer to the center it can let some more noise out... not exactly, what happens is now the sound waves headed to the back of the pipe and reflected back to the exhaust port are blocked by the wall of the stinger pipe so the exhaust gases can still escape efficiently but the sound waves have been deadened considerably before escaping out the stinger pipe... this can be quieted even more by perforating the stinger pipe inside the chamber and welding a cap so the exhaust now has to escape out thru the perforations instead of the end of the pipe (this is an effective way to quiet an end bleed system without restrictive it as well).
With the side bleed setup and a muffler added the sound level can be as quiet or quieter than a stock 4 stroke motorcycle, even with a free flowing straight thru design muffler.
This doesn't come without a few drawbacks tho since there needs to be enough room for the expansion chamber as well as the pipe coming out the side of the pipe as well, and these type pipes can be pretty heavy compared to a more conventional system due to the extra bracket work. Most side bleeds have the muffler run in parallel to the expansion chamber to help save some space.
Here is an example of a very well built side bleed pipe... http://www.treatland.tv/MLM-cali-pipe-for-puch-maxi-flat-port-w-side-bleed-p/mlm-maxi-cali-353.htm
This one is a high dollar pipe and brand, but side bleeds typically cost about the same as or slightly more than their end bleed counterparts... One can also modify a pipe they already have by welding the end shut and cutting a hole in the side then welding a stinger pipe in place.
There are other types of mufflers that can be made or purchased that can significantly quiet these engines without adding restriction as well the supertrapp design is one that's very effective and can be made adjustable, these can sometimes be found used on ebay for small dirt bikes and these are quieter than stock

 

[KCvale]

George, I meant the air flow through the exhaust. The stock exhaust is a bit restrictive, especially so since the stock carb jet is a bit rich.
You can improve that air flow by drilling a few holes in the muffler's end cap.

Good advice if you want to cut performance and pump out a bunch of un-burned fuel out of your tailpipe that likes to stick around and drip wherever you park it.

4-stroke engines have valves and a distinct cycle for intake and exhaust.
They like a free flowing exhaust.

2-stroke engines don't have valves and do intake and exhaust at the same time, and a bunch of potential fuel flows right out with the exhaust.

This is why pipes are restrictive.

Expansion chamber exhaust is even more efficient by actually acting like a reverse turbo charger by forcing all the flow-through back into the cylinder just before detention.

This is crucial timing thing.

Here is how it works:
(Follow the green gas, that is air/fuel mix).

A well tuned X-pipe is THE most impressive power increase you can get from one thing.

There are ways to drastically reduce exhaust restriction without adding more noise if you use an expansion chamber.

You can run an expansion chamber with a side bleed which means the end of the pipe is sealed off and the exhaust exits from a stinger pipe coming out of the belly section of the pipe.

Interesting.
I suppose it doesn't matter where the burnt fuel exits so long as it does not disrupt the shock wave forcing all the fresh fuel back in.

 

[George Tirebiter]

Lots of info there to digest. Thank y'all.
George