Vibration keeps breaking carbs!

[Fletch]

Good deal, thanks. I'm going to try it without cutting for now and see how it goes. Did you have CNS carbs brake on you too, or do you just do this as a precaution? I just got the mikuni 18mm and it looks a lot stronger than the CNS. I had to sand down the white collet to fit the intake. It would have been too big without it. Do you think a dremel would cut it too wide? What is the clear tubing used for at ACE? Maybe I'll pick some up. It doesn't get too hot right there, so the silicone is probably not needed.

 

[Dave C]

The second good thing about silicone is that it's one of the best vibration dampeners there is

The clear tubing is on a roll in the back of the store, usually I had to use something because the frame barely fits the motor despite having 28" tires. The frame is contorted to shorten it up. When I build my second bike it won't be a Mongoose Paver again The tubing is so the carb actually sits right besides the seatpost on about a 4" clear tube. My heel just clears when I'm pedeling.

I don't really like the clear for this. It doesn't like to bend so I think I'm trying a pre bent auto heater or polution control hose. I need one with about a 45 degree bend then cut to length.

 

[MikeJ]

Hi Fletch -

I took some photos of my bike with the "noose" around the cylinder; they should be attached. I remembered I ran a 1/4 inch bolt, about 6 inches long around, slightly bent at the center to form to the cylinder, in the front of the cylinder so to avoid "pressure points" on the side of the cylinder. In reality, I don't have any proof it is needed nor if it does any good at all. The metal-looking muffin-shaped things bolted to the frame are lead (as in the heavy metal) "muffins". They were intended to prevent excessive vibration of the tubes. They did not work; I need to remove them. The photos should better explain my previous wordy description. I hope this helps.

MikeJ

 

[Dave C]

Mike, I'm going to use your idea with slight modification. I'll be using steel flat stock to tie it to the frame. I'll have to have 4 turnbuckles to do what I have in mind. What I envision is 2 pieces of flat stock with 2 long bolts with the bolts running like you have the on top. 4 holes in each bar. Bolt on the turn buckles to the cross bars then enought flat stock to reach the frame to be bolted on there. I just don't like the wire but if it works for you it's all good

Actually the lead dampers are a good idea but I think it might take a lot more than you have. So much it could serve as a boat anchor in a pinch

 

[MikeJ]

Hi DaveC -

I am betting your idea works. I will be looking forward to the photos. Stiffer supports almost always mean better control over engine vibrations getting into the frame. If you like the results, I may follow suit. I used wire as a quick "proof of concept". It was easy to work with and did not need any machining. It worked well enough for me that I was satisfied and moved onto test rides.

After this, my next move may be to upgrade to a better carb and arrangement.

 

[Dave C]

Time to update this a bit. When I replaced the stock headstuds with SBP studs I added a Puch Hi-Compression head. After torqueing the nuts down there was about 3/8-7/16 of an inch of stud exposed. I went looking for a coupler nut to bolt on all 4 stud ends. There is no M8 1.00 coupler nuts made in the world, M8 1.25 sure... I ended up welding two M8 1.00 nuts to a small diameter 1/2 pipe 1.25 inches long. Made 4 of them. I now have a place to bolt on attachment points for extra frame mounting using the 4 head studs.

Not only do I hope it helps to cut vibration but also prevent the motor from twisting in the frame breaking more back motormount studs. The 8.8 metric bolts will help with that. I had to pedal home after the last 2 broke

I got to learn the photo thing, I'll work on it tomorrow:helmet:

 

[Lazieboy]

Bolts

Too much to read, but I replaced frame mounting bolts with stronger ones at Fastenal. I also broke off a stud inside but got it out.

 

[Irish John]

Fletch, post a good close-up picture of your engine in the frame and I will probably be able to tell you why it is vibrating.

 

[adb140275]

The more solid the engine is mounted to the frame, the less it will vibrate. I got more vibration when i used rubber than i do now with NO rubber. I hardly have any vibration. Granted, i have a puch head installed which effectively lowered (yes, lowered) the compression. get it bolted on tight and solid, you will be surprised. this is the only picture i have where you can see both mounts, but you get the idea.