gimgim Posted February 12, 2022 Report Share Posted February 12, 2022 (edited) Hello everybody, new to the forum and to the sport 😀 I bought a 2001 Cota 315R a couple of weeks ago. The bike is in great conditions, but it has been sitting unused for the last 5/6 years. I bled brakes and clutch, lubed the chain, cleaned the carb (standard jetting I think, 110/33, there was a lot of dirt/crud inside) The bike starts without any problems but once I close the choke it idles very rough, like if I am blipping on the throttle rhythmically (not sure how to better explain this, I have a mp3 file with the audio, but I can't attach it here). I sprayed some starting fluid around the intake boot, but I don't see any difference. 1) What do I try next? I am using premium gas (100, I think) with Honda HP2 two stroke oil premixed 80:1. I haven't pulled the spark plug yet because the bike started without issues. 2) The previous owner was running a T on the fuel line and a transparent tube parallel to the fuel tank all the way to the top of the bike (open end). Any idea why? I have never seen anything like this Thanks!  P.S. I have owned quite a few motorcycles in my life and I do all maintenance myself. I haven't owned a 2 stroke recently (last 40 years 🙂 ) or a trials bike though. Last one was a Beta 125 Six Days, and Vespas, and Piaggio mopeds. My other bike is a XR650L. EDIT: Link to the audio https://drive.google.com/file/d/13fJei5yG5w911ezUR34FP690EsdXBWu4/view?usp=sharing   Edited February 12, 2022 by gimgim Quote Link to comment Share on other sites More sharing options...
stpauls Posted February 13, 2022 Report Share Posted February 13, 2022 Rough idling? According to some Conservative MPs, including Truss, Raab and Pritie Patel, the English are the worst idlers in the world. Is this Spanish bike worse? Asking for a friend.  British workers 'among worst idlers', suggest Tory MPs - BBC News Quote Link to comment Share on other sites More sharing options...
mcman56 Posted February 13, 2022 Report Share Posted February 13, 2022 It sounds lean. Have you tried adjusting the idle mixture screw to make it richer? I believe turning the screw clockwise makes the mixture richer on that bike. Clean the carb again. Check float height and take a good look at the idle circuit and pilot jet again.   1 Quote Link to comment Share on other sites More sharing options...
Gorsko Posted February 17, 2022 Report Share Posted February 17, 2022 I'd say - definitely look at the Pilot jet again, I recently restored a 315 for a friend, and I was plagued by slow-running lean issues. There are two jets - one on the tube, and another inside where the tube goes - the one inside is easy to block, hard to see. On advice of other posts on the forum, I binned that inner jet & it's been great since! 1 Quote Link to comment Share on other sites More sharing options...
gimgim Posted February 18, 2022 Author Report Share Posted February 18, 2022 Thank you mcman56 and Gorsko. I pulled the plug and it was dry and like new, so the bike does run lean. I cleaned up the carb again (carb cleaner + compressor) the manual shows two slow jets (outer is a 33 in my carb) and I can't see the one inside. I wonder if the previous owner removed it? I tried reaching in with a small screwdriver, I can feel the thread but there doesn't seem to be anything. Compressed air sprayed in the hole of the slow jet was exiting in the main body, but I can't see light through it. Am I supposed to? One last thing... The previous owner left me three slides, the one in the carb is labeled "50", I wonder whether it's the stock one or not. I will repack the silencer and try again tomorrow  Quote Link to comment Share on other sites More sharing options...
gimgim Posted February 20, 2022 Author Report Share Posted February 20, 2022 (edited) No luck. Cleaned the carburetor for the fourth time today. I used a guitar string to make sure the slow circuit was fully clean. There is not inner slow jet. The air filter is old, frayed and not oiled well and I ordered a replacement. I wonder it this could be the problem. Can anybody confirm the number on the stock slide? The bike came with 40, 50 (installed), and 60. Thanks Edited February 20, 2022 by gimgim Quote Link to comment Share on other sites More sharing options...
mcman56 Posted February 20, 2022 Report Share Posted February 20, 2022 I happen to have one of those carbs that came off a good running 315, maybe a 2000. It has a 45 slide, 46 pilot and 114 main. I don't think that second slow jet is there. The manual says float height is 18.5 mm. A quick look on line suggests that 315s came with a 46 pilot so a 33 would make it quite lean. I would try a a 46 pilot or at least something bigger than what you have. I don't know how sensitive the bike would be to slide changes but that should just affect the transition off of idle as the slide lifts.  Stock Jetting A manual is here.   http://montesatrials.com.au/store/wp-content/uploads/bsk-pdf-manager/Montesa_315R_02_2002_2.pdf 3 Quote Link to comment Share on other sites More sharing options...
gimgim Posted February 21, 2022 Author Report Share Posted February 21, 2022 I looked at the parts the previous owner left me. There are quite a few jets (some even from other carburetors) but I couldn't find a larger slow jet. I will have to order a few and try. One thing I noticed though. I found a spare float valve and it's quite different than the one installed (I am attaching a picture of the spare one). The one installed has a rubber tip and a "mushroom" end, for push/pull float arms (similar to this one https://www.partzilla.com/product/yamaha/3L5-14190-01-00), while the spare one (in picture) has a metal tip and a push-only end. I haven't compared the two side by side, but I suspect that the previous owner may have installed the rubber tip valve to prevent flooding and that the installed valve is a bit taller. If so, the stock 18.5 mm adjustment of the float arm would be wrong and the float valve may close too early. Â Quote Link to comment Share on other sites More sharing options...
mcman56 Posted February 22, 2022 Report Share Posted February 22, 2022 This is the float valve in the carb I have. It is marked 270 on the brass part.   1 Quote Link to comment Share on other sites More sharing options...
gimgim Posted February 22, 2022 Author Report Share Posted February 22, 2022 (edited) > This is the float valve in the carb I have. It is marked 270 on the brass part. Thanks. I haven't checked the brass part, but the valve looks identical to the one in my carb. Do you have the dimensions of the three O-rings? (choke jet, in your pic - mine is damaged, idle screw, mix screw)    Edited February 22, 2022 by gimgim Quote Link to comment Share on other sites More sharing options...
Cube Posted February 23, 2022 Report Share Posted February 23, 2022 (edited) 270 is the right one. It sounds to me that you may have still some dirt in one of the jets. What I would do in any case: Check all the jets match stock sizes. How many turn is the air screw out? (Count from current position by turning in, and then bring it back into its original position. Compare to what it should be in the manual. I would have a 97/98 & 02 manual if needed. Maybe worth getting a rep kit for the carb. This will replace all the o rings and what have you. If you already have some damaged ones.....and the kit isn't too expensive. Edited February 23, 2022 by Cube Quote Link to comment Share on other sites More sharing options...
gimgim Posted March 24, 2022 Author Report Share Posted March 24, 2022 Me again, problem still there... What I did 1) Brand new air filter (AirTwin), oiled 2) All carb jets back to stock (110 main, 35 low. Bike had the 33 installed; I tried 38 as well, no difference), float level 18.5mm, air screw 1 turn out (problem doesn't go away with the screw all in or two turns out) 3) Bough a 6 liter ultrasonic cleaner and cleaned the carb again 4) O-rings replaced The only thing I haven't checked yet, as I need to remove the tailpipe header, is the reed valve. Can the issue be caused by a bad valve? From what I can see, there are two parts that are not stock: a) The sub-air cleaner housing is missing, what is this thing doing anyway? Where is it connected? (manual is not clear) b) The silencer is a FMF with a spark arrestor (tried the stock as well, no changes) I see on eBay the carburetor being sold for $80. I am tempted to get one, but it doesn't make sense as the one on the bike looks perfect.. Thanks   Quote Link to comment Share on other sites More sharing options...
Cube Posted March 24, 2022 Report Share Posted March 24, 2022 The reed valve can cause things like this, yes. I have had exactly this problem with my vespa. Kicked in, started and sounded like it is on full throttle but every few seconds someone is pushing and holding the engine off for a few seconds. Rev up and down. Reed valves Quote Link to comment Share on other sites More sharing options...
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