Just put a fairly tame performance kit on, with a Keihin carb and a Reed valve assembly. When I let out the clutch as expected it idles up real fast, but it won't stay running and the throttle has not noticeable effect when I twist it to try an warm up. Any ideas why this may be happening, I am also afraid I may have a air leak somewhere. I'm happy to take photos and make videos as needed. Fairly new to motorized bikes, only made one before complete China stock. Thanks in advance for the help.
Just put a performance kit on, can't get it to run. Any help?
- Thread starter James Watkins
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First of all welcome to the forum.
Several things come to mind, but I'll keep this short. If you didn't install a new "window" piston or alter your old one with a piston window, the reed valve and new carb won't actually help performance and I would uninstall and put the kit carb back on the motor.Trying to get the new carb working at this time is a waste of effort. New valve reeds are initially quite stiff & require some break in time to start to flex properly and this sometimes makes carb setup a moving target that's hard to hit. Idle speed included. You may actually have an air leak as well with the new kit setup, especially at the point of engine to reed valve sealing. If you did put in a piston window or alter the "jug" with a third port then carb setup will be time well spent.
Let us know what you have exactly in addition to the Keihin carb. Post a photo of the reed valve and carb mounted on the engine. There are a few different brands/designs of reed valves Zeta, Gas Bikes, RSE types & some sell a couple of different versions of reed valves. Photo is best.
The people that sell the reed valves are either not honest or are uneducated in their claims about bolt on performance gains with reed valve,never mentioning the futility of installing them without one or both of the motor alteration that are absolutely required to make them function properly and the final fine tuning once everything is in place.
Best of luck.
Rick C..
First of all welcome to the forum!
Several things come to mind, but I'll keep this short. If you didn't install a new "window" piston or alter your old one with a piston window, the reed valve and new carb won't actually help performance and I would uninstall and put the kit carb back on the motor.Trying to get the new carb working at this time is a waste of effort. New valve reeds are initially quite stiff & require some break in time to start to flex properly and this sometimes makes carb setup a moving target that's hard to hit. Idle speed included. You may actually have an air leak as well with the new kit setup, especially at the point of engine to reed valve sealing. If you did put in a piston window or alter the "jug" with a third port then carb setup will be time well spent.
Let us know what you have exactly in addition to the Keihin carb. Post a photo of the reed valve and carb mounted on the engine. There are a few different brands/designs of reed valves Zeta, Gas Bikes, RSE types & some sell a couple of different versions of reed valves. Photo is best.
The people that sell the reed valves are either not honest or are uneducated in their claims about bolt on performance gains with reed valve,never mentioning the futility of installing them without one or both of the motor alteration that are absolutely required to make them function properly and the final fine tuning once everything is in place.
Best of luck.
Rick C..
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Unfortunately I purchased this kit, https://www.gasbike.net/products/gt4-pro-racing-66cc-80cc-motorized-bicycle,and installed it on a entirely stock bicycle. So I don't actually have any other carbs I would be able to swap onto the assembly. The parts listed in that link are exactly what I am using currently. Would you suggest I scrap the "upgraded" carb and reed valve assembly and go with the basic kit carb? I have only previously built one other bike with the cheapest possible engine I could find. So I have basically no idea what I am doing. Ill post a picture soon, not home as it is fathers day at the moment. Thanks for the help so far, I greatly appreciate it.
"Scraping the reed setup" and using a kit carb and intake makes sense only if you can't get what you've got running and if you don't want to add the necessary components to make the reed setup work and produce more power.
One extra comment fuel mileage with a fully functional reed setup (piston window & third port will drop between 25% and 75%...no free lunch with performance. The setup I show gets about 75 miles to the gallon in town riding.
I'm not certain I understand what you mean the throttle "has no noticeable effect" ? Is the carb slide opening when you turn the throttle? Does the choke function correctly? Does the engine not rev up when operating the throttle?
James I looked at parts that Gas bike has available and they do offer both a 3rd. port cylinder and a "window" piston (they call it a ported piston I believe) for the engine setup yo have. One or the other will allow the reed valve to work...both even better. The piston is $25. I'm adding photos of my own setup that I machined so you will recognize when you look at Gas bikes performance cylinder parts. I use a much larger round window in my piston than they do (small square window) but I'd think both would make power with your reed setup, but first get what you've got at least running!
Rick C
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I have visually checked spark and it is good so you are correct that the engine is getting both components needed to start. When I say the throttle has no effect what I mean is on twist it impacts the engine in no way whatsoever. The twist is also very short compared to my other bicycle. As for the choke it appears to be working because when set correctly it does allow for the starting of the engine. However I have not been able to maintain a running engine so I'm not entirely sure. I will attempt to find air leaks as it is very possible I botched a gasket install or under tightened a component. I may go with kit carb just as I lack the expertise and honestly funding right now to pay for more components. I also am doubtful it makes 3.5 HP but a man can dream I guess. Thanks for the consideration thus far. I will attach a photo soon of the setup I am running. It was a tight fit on this bike so if you have any placement suggestions I am open. Thanks.
I figured I would start with broad photos, in the event I have done something obviously wrong. Such as Installed something backwards or just blatantly incorrectly. I can take more specific photos on request.
Attachments
James I just took a look at your second photo & see what looks like a super long carb cable drooped temporarily (I hope) between carb and throttle and that's not good, and may be the cause of at least the lack of any throttle response. Cable should run shortest path along the straddle tube and then across the handle bar with just enough room to prevent binding when turning the bars, More on that latter, first take the air cleaner off and look through the carb as you operate the throttle to see if the "slide opens and closes properly with the throttle. do this with the droopy cable as is. If the slide doesn't function, fix your cable problem first. Then you may consider the following as well you may have installed the throttle cable wrong either inside the carb or at the throttle end or the lead ball pulled out or off the cable end ( either end). Kit throttles nylon or plastic guts often break or the lead cable barrel pulls out of the plastic, maybe installed wrong, lots of possibilities here, and in the end you have no throttle. If you see that the cable is lifting the carb slide and the spring is closing the carb slide with the throttle then try running with air cleaner off the carb. If still no go the reed valves may not be opening past idle or be hanging at the cylinder intake port. That can be a problem with the RSE type reeds but I've never been inside the Gas bike /Zeta style that your motor came with. Right now the lack of any throttle response at all is definitely a problem in my mind and your not thinking it feels right (short twist) in operation compared to your other bike build is re-enforcing my doubts about throttle to carb operation is hincky. I'll mention that the outside sheath of any cable should not move at all NOT ANY movement of the plastic sheath only the wire cable inside the sheath moves. If the cable sheath moves the carb won't function correctly. You can use cable ties at a couple of places along it's length to stop any movement. This is true with clutch cables, shifter cables and brake cables as well.
Your bike looks really great with the motor mounted.
Let us know I hate to see a guy struggle to get going 'cause the idea is to enjoy this hobby.... ...
Rick C.
Your bike looks really great with the motor mounted.
Let us know I hate to see a guy struggle to get going 'cause the idea is to enjoy this hobby.... ...
Rick C.
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Will do, I'll get to work on those things tomorrow. And yes it's a temporary set up, just wanted it to be easy to remove so I could mess with it before I get it all cleaned up. Thanks so much for the help, I'll get back to you soon.
Just took the air filter off and this is what I saw when twisting the throttle.
No visible effect that I could see. I went ahead and tested it with the filter off and it operated as it has every time I have tested it so no surprises there. I'm gonna work on straightening out the cable, and then investigating if I installed it into the carb correctly and I will get back to you.
Yes James good camera work...that slide doesn't open at all so the problem lies somewhere betwixt the throttle and carb and perhaps two or three problems including your shortcut mega cable hookup!
Incorrect cable routing inside the carb is common with Mikuni carb and the Kehin may be similar in that regard. Spring and cable shouldn't bind inside.
I'd say progress is made.
Rick C.
Incorrect cable routing inside the carb is common with Mikuni carb and the Kehin may be similar in that regard. Spring and cable shouldn't bind inside.
I'd say progress is made.
Rick C.
The slide doesn't move for some reason so take the carb apart and find out why. The slide may be binding (maybe because it's assembled backwards or just poorly machined), cable may be routed incorrectly, lead ball on the cable end not catching on the slide etc. investigate if the slide doesn't move up when you open the throttle and close smoothly when it's released something is wrong with either the carb, the cable or the throttle itself. All three of these elements need to be checked as the possible reason for the problem. The throttle may turn a half inch but if the slide doesn't move at all then sufficient fuel/air flow won't occur to feed the engine past idle.
Rick C.
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Very true..I forgot to think about the slide being open a little...I saw that too in mine it was gapped and how the above pic was closed