Different type of carb problem.

Sykottikk

New Member
May 19, 2011
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Winter Springs
Hey all, I'm new here. I bought a used motorized bike from someone nearby off of Craigslist and I've had nothing but problems since then. Luckily the man also included a box of parts, among which was an entire new engine assembly, chain, tubes, etc.

My brother found a nice mountain bike and brought it home for me, and we put the engine on the frame. I've had a couple problems but nothing that I can't deal with. There are only two things currently stopping me from cruising down the road on it.

One of them is that the chain is a tad too loose and keeps popping off and getting stuck in the spokes. I'm going to remove one more link from it, and even though it's going to be a tight fit, it should work fine.

The other is a tad more confusing. The bike starts up fine, but for some reason the throttle is held in the on position! There's still a little wiggle room on the handle, meaning I can increase the throttle if I want to. As soon as I start pedaling and let the clutch out it takes off, rather fast. Also when I pull the clutch in, no matter how far in or out the idle screw is, it idles REALLY fast.

This leads me to believe that the engine is constantly getting gas, but I can't find out why!! I have opened the carb up, and can't see anything that the fuel thing (Sorry, don't know what it's called. It's the thing with the pin :p) could be getting stuck on.

If anyone understands what I'm talking about let me know if you can help please :)

If you would rather, you can PM me and we can talk on the phone and I can explain what I see a little better, or I can add pictures. Let me know.

Thanks in advance! It's great to be here!
 

Greg58

Well-Known Member
May 1, 2011
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Is the slide 180 out in the carb? Take the top off of the carb and pull the slide out, there is a notch or cutout that the idle screw lines up with on the other side is a slot that lines up with the pin in the carb barrel.
 

Sykottikk

New Member
May 19, 2011
13
0
0
Winter Springs
Yeah I just noticed that. What happened was that little angled area for the idle screw was on the nub, because I thought that's how it was supposed to go. Then it kinda clicked in my head that maybe the nub lines up with the big hole in the side lol.

Anyways I figured it out about 15 minutes after I posted in the thread. Now I need a new chain because mine keeps coming off of the back sprocket and getting caught up in the rims. Going to a motorcycle shop later to have it shortened and get a new master link.

Thanks!
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Proper chain alignment and tension is one of the most important aspects of a successful bike. As far as tension, you'll want 1/2 to 3/4" slack in the top run of the chain measued when you're pushing the bike forward against a compression stroke, clutch engaged.

Alignment: Should be a near perfect straight line between the engine drive sprocket and the rear wheel sprocket. If you're not using a chain tensioner alignment is more critical than if you're using one. The tensioner will help guide the chain onto the rear sprocket and allow for a little lateral misalignment. Also the wheel/pully of the tensioner must align with the chain path which sometimes requires the bracket be twisted a little.

The rear sprocket installation is also extremely important. It can not have any wobbles or be mounted anywhere but dead center of the rear hub. Any up/down or side to side wobble will cause you grief. (like the chain jumping off)
Tom
 

Sykottikk

New Member
May 19, 2011
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Winter Springs
Thanks 2Door. I believe that may be what's causing the chain to jump off. I looked and it turns out that when my brother put the sprocket on, he put it on improperly and it's completely uneven. There's not an even distance between the center hub and the center of the sprocket all the way around, it's further out on one side than it is on the other.

I just went and bought a master link yesterday and put it on the chain. I got really lucky because the chain is a 415 and the man just happened to have one and only one in stock. The dang thing cost me $5 though -.-

I'm going to realign the rear sprocket and make sure that everything is properly aligned and that should make everything better. I picked up some high temp grease from Autozone and covered the chain in it, as well as the inside of the piece of metal that you use for the clutch (Once again, no terminology here) and now everything is lubed up nicely.

I'll let you all know how it turns out. I actually got it to run for about 30 seconds yesterday before the chain hopped and locked up (I burnt rubber) and it was getting good speed. Thanks!
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Sky,
How's your chain tension? If the chain is binding in the engine that's an indication that it might be too loose. Use the measurement method I described above to get that 1/2 to 3/4" slack.
Here's an old thread that might help too > http://motorbicycling.com/f30/motorized-bicycle-chain-noise-6682.html
I'm not sure about your choice of chain lube. They need a lubricant that is a little more liquid than grease. Something more oily is better. I like chainsaw bar & chain lube. It's thick and sticky and doesn't get slung off easily.

Let us know how you're doing.
Tom
 
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Sykottikk

New Member
May 19, 2011
13
0
0
Winter Springs
I don't quite understand what you mean by that amount of tension but I think it may be too loose. I tried using a chain tensioner that came with the bike and since this is a mountain bike and the bars aren't as wide as a beach cruiser, I got to around 20 MPH and the tensioner slipped into the spokes and ripped about 4 of them out, leaving me with a bent tire to deal with.

I don't know if I have the space to remove another link, because on this type of chain it's really removing two links. Not sure if I can do that or not.

I removed the rear sprocket and put it back on, making sure that there was just about even tension from every bolt. I tried my best to make sure that there was even space between the sprocket and the inside hub, but there's still a little difference from one side to the other. Not a huge deal though.

It's locked up right now, so I'm gonna go ahead and take some pictures and show you what's up.
 

Sykottikk

New Member
May 19, 2011
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0
Winter Springs
Here is a pic of the locked up chain, before I fixed it. I would show you the chain tension too, but for some reason my camera doesn't want to charge up.

 

Sykottikk

New Member
May 19, 2011
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Winter Springs
Well I tried to post a pic but it looks like someone is going to have to approve my comment first. In there should be a picture of the locked up chain.
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Sorry for the delay. It's posted now.

Your photo indicates to me that the chain is way too loose. Let me try to explain how to get the right tension again.

With the clutch engaged gently roll the bike forward until the engine is coming into a compresion stroke, or until you feel resistance from the engine. At that point stop and hold things where they are. Look at the top run of the chain and check to see how much slack is in it. You should only be able to lift or lower the chain no more than 1/2" to 3/4". If the chain has lots more slack than that it can cause a condition like your photo shows. The chain, especially on deceleration will try to wrap up at the front of the engine sprocket. If the tension is correct there will be enough pull on the chain to keep it seated into the sprocket teeth.

As for the tensioner; does your bike have horizontal drop outs? That means where the rear axle is attached to the bike frame. The slots where the axle sets are called drop outs. If yours are horizontal to the ground then you might have enough adjustment to make up for excess chain length but it is unlikely. Does your chain contact the frame at any point? If so you probably will need to use the chain tensioner which can serve as a guide to keep the chain away from the frame and to assist it engaging the rear sprocket. There has been countless discussions on the pros and cons of the tensioner so I won't try to repeat what has been written time and again. Use the search feature at the top of the page, key word, 'tensioner' and you'll see hours of reading available about this controversial subject.
Get back to us, we'll be here when you need more help.
Tom
 

Sykottikk

New Member
May 19, 2011
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Winter Springs
Will do. Thanks for the help :) Sorry if I get frustrated at times, I'm not a mechanical person :p

I may just try to drill a hole straight through the center of the tensioner/frame and put a bolt right through it at the correct spot, just to get this issue out of the way. It seems this is the last thing I need to do.

If it's making contact with the frame, I'll use the tensioner, if not, I'll just shorten it most likely. Either way I'll get back to you once I do some inspection and see what my possibilities are.

It's around 92 degrees here in FL so I'm gonna wait a bit before I go outside :p
 

GearNut

Active Member
Aug 19, 2009
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San Diego, Kaliforgnia
Do not, I repeat do not drill a hole through your bike's frame!!!!!!! An engine puts sooo much more stress and strain on a bicycle frame than it will ever see by pedal power alone. They were not designed for engine power, but if adapted with care and proper maintenance, they can take the extra punishment.
Drilling a hole through the frame will weaken it considerably, putting it at risk to break in half.
That said, some folks will drill a very small hole through the tensioner and only one side of the frame tube and use a small screw to hold it in place. I still cannot recommend this as any extra holes anywhere will ultimately create a weak spot.
I recommend a strap style mounting which spans the seat stay tube (upper tube) and the chain stay tube (lower tube). They are commonly help in place with a P style clamp. No extra holes in the frame are needed.
Here, read up on the subject for alot more info. (Thank you Dave31 for creating this list!)
http://motorbicycling.com/f30/tensioner-links-look-here-1st-your-27077.html#post254178
 
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2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Gear,
I'll have to disagree and I'll continue to unless and until someone can show me evidence to the contrary. I've seen the warnings not to secure the tensioner bracket here time and time again but not once has anyone ever posted a photo or documented a frame failure due to that method. I have a bike, my first motorized effort that has accrued a little over 1800 miles and to this day there is no sign of metal fatigue or failure at the point on the chain stay where I drilled and used a 10/32 bolt to keep the tensioner from moving. You know I respect your advice and opinions greatly nevertheless this is an area where I'll agree to disagree with you.
That said, I will always strongly advise against drilling a hole in the down tube for mounting an engine. That looks like an accident waiting to happen. I've seen photos of cracked down tubes, but a small hole in the chain stay is just not the same situation. IMHO :)
Tom

EDIT: I do not, nor will I ever advocate drilling into an aluminum framed bike. My advice is only for those with a steel frame. Even so there is a member here, well known, who has an aluminum Schwinn with over 5000 miles on it and his tensioner is secured with a bolt through the bracket and chain stay. He's never had a problem.
 
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Sykottikk

New Member
May 19, 2011
13
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0
Winter Springs
I attached the tensioner and everything got better :) I love you guys!

I believe the problem last time was that I *thought* I had tightened it enough, when in reality it wasn't all that tight. Last time I used two locking pliers, and this time I locked one set of pliers on the back and used my long ratchet to tighten them down insanely tight. It's going to take a heck of a lot more than some chain tension to get that thing to move.

Everything works fine now. One minor annoyance is that when I start it up, I can't give it full throttle, or it won't start. It's like I have to have the throttle RIGHT in the middle to get it to go, but once it's going it's fine. I've seen threads about that on here before so I'll go ahead and see how to fix it.

I didn't really mind the old beach cruiser frame too much, but this frame has so much more shock absorption. The seat is on its own shock, and so are the front forks. I took it through some dirt/bumps at top speed and didn't have a problem. Plus, this frame is light enough to lift with one hand, so it goes much faster. In fact I have to be careful how I start off from a stop sign or stop light because if I'm not I'll do a wheelie!

Thanks so much for the help. Hopefully I can learn more about MBs and pass it on :)
 
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onanysunday

New Member
Apr 21, 2011
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St. Paul
Is your engine still running too high at idle? If so, your throttle cable could be adjusted too tight. Reduce tension to the cable at either end to lower idle rpm. You should have two different areas to screw/unscrew throttle cable tension. One area is the throttle assembly by the front brake lever. The other is where the cable goes into the top of the carburetor. If you fine tune throttle cable tension in these two areas by screwing in (or loosening) your throttle cable, you should be able to lower engine idle rpm. With the engine at operating temperature, try loosening your cable just enough until the engine almost dies out at idle but keeps firing and doesn't stall. Then you'll know you've hit a good sweet spot and will have a whole range of throttle response available to you with just the flick of a wrist.

Remember - you'll need to screw the throttle cable IN more to loosen it (not the other way around)
 
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