gasgasshetland Posted July 18, 2018 Report Share Posted July 18, 2018 Hi there just wondered if anyone has experienced a problem like I’m having. my 15 repsol starts fine and runs away fine, but after a bit it starts dropping the engine speed on shutting off the throttle and it goes below idle speed and stalls. It will immediately start again and idle away fine, but drive the bike again and it will drop the idle speed and stall. So it’s happy idling from start up, but drops off from shuttling the throttle off. Seems to be once it’s warm. While running it takes full throttle and seems fine, but once shutting off it will stall. I have cleaned the throttle body main venturi butterfly passage and the air passage that is in use when idling. There had been an alteration done to the bike prior to me buying it and the head breather oil catch tank had been moved to under the seat and wasn’t doing it’s job and oil was getting into the airbox then going through the throttle body. I have put a small breather filter up under the headstock. Its my first montesa 4rt so not really that well read on the injection setup. Quote Link to comment Share on other sites More sharing options...
jimmyl Posted July 18, 2018 Report Share Posted July 18, 2018 3 hours ago, gasgasshetland said: Hi there just wondered if anyone has experienced a problem like I’m having. my 15 repsol starts fine and runs away fine, but after a bit it starts dropping the engine speed on shutting off the throttle and it goes below idle speed and stalls. It will immediately start again and idle away fine, but drive the bike again and it will drop the idle speed and stall. So it’s happy idling from start up, but drops off from shuttling the throttle off. Seems to be once it’s warm. While running it takes full throttle and seems fine, but once shutting off it will stall. I have cleaned the throttle body main venturi butterfly passage and the air passage that is in use when idling. There had been an alteration done to the bike prior to me buying it and the head breather oil catch tank had been moved to under the seat and wasn’t doing it’s job and oil was getting into the airbox then going through the throttle body. I have put a small breather filter up under the headstock. Its my first montesa 4rt so not really that well read on the injection setup. What idle speed have you got it set at? Quote Link to comment Share on other sites More sharing options...
pauls320 Posted July 18, 2018 Report Share Posted July 18, 2018 Thats a very good question, factory specs it to be 1800rpm. Wondering how much oil your motor is blowing out the breather, possibly rings worn out ?? Hope you get her sorted soon. Quote Link to comment Share on other sites More sharing options...
ourian Posted July 18, 2018 Report Share Posted July 18, 2018 Another possibility is a dirty fuel pump filter Quote Link to comment Share on other sites More sharing options...
gasgasshetland Posted July 18, 2018 Author Report Share Posted July 18, 2018 Ok guys thanks for your reply’s. I will keep trying to see if I can find the fault. Might try another TB, but not keen to pay £300 Quote Link to comment Share on other sites More sharing options...
jonnyc21 Posted July 18, 2018 Report Share Posted July 18, 2018 I remember reading a post where there was a little play in the PTB and when shutting off the throttle it would go past 0 and stall out, a small drop of super glue under the stop was used to diagnose the issue. I don’t remember 100% what the final fix was , but there was some talk about a washer as a shim and a few other options talked about. not sure if that will help but good luck figuring the true root cause out. 2 1 Quote Link to comment Share on other sites More sharing options...
sportsawyer Posted July 19, 2018 Report Share Posted July 19, 2018 14 hours ago, gasgasshetland said: ... So it’s happy idling from start up, but drops off from shuttling the throttle off. Seems to be once it’s warm. While running it takes full throttle and seems fine, but once shutting off it will stall. ... Given the things you've already checked, and that you already corrected the previous owners breather modification, you may want to: 1) Check the throttle cable to make sure it has enough free play per the manual. 2) Adjust the idle up (CCW) a quarter turn. Start, let warm up until fan comes on, blip throttle a few times. The idle should be adjusted after this much warmup. If, when it drops, it then stalls, try again with another quarter turn. See if you can get it to the point where it idles and doesn't stall after the warmup & blipping. Then adjust to proper idle. 1 Quote Link to comment Share on other sites More sharing options...
jimmyl Posted July 19, 2018 Report Share Posted July 19, 2018 13 hours ago, jonnyc21 said: I remember reading a post where there was a little play in the PTB and when shutting off the throttle it would go past 0 and stall out, a small drop of super glue under the stop was used to diagnose the issue. I don’t remember 100% what the final fix was , but there was some talk about a washer as a shim and a few other options talked about. not sure if that will help but good luck figuring the true root cause out. Had that on full throttle but not at zero throttle - I think there maybe a screw for zero position ?? 1 1 Quote Link to comment Share on other sites More sharing options...
sportsawyer Posted July 19, 2018 Report Share Posted July 19, 2018 (edited) 2 hours ago, jimmyl said: Had that on full throttle but not at zero throttle - I think there maybe a screw for zero position ?? There is a stop setscrew, but it's set and painted from the factory. Don't know how to set it. Do you need to be measuring TPS resistance (How? Undocumented pin on the 32P connector? Access ECU board?) and setting based on some value? Or is it just a stop that's set so the butterfly valve doesn't rest hard against the TB bore? Or is the butterfly valve set for soft closure, and then the ECU is calibrated so the TPS is zeroed? I'd be reluctant to start screwing with that screw without more knowledge. With a used bike, also brings up the question of whether or not the previous owner tried to adjust idle with that screw rather than the air bypass screw. You may want to look and see if the factory paint was broken. Edited July 19, 2018 by sportsawyer 1 1 Quote Link to comment Share on other sites More sharing options...
section swept Posted July 22, 2018 Report Share Posted July 22, 2018 (edited) You really need to confirm these settings before goining any further: Valve clearances set to specification. Throttle body, air filter hose clamp not ovetightened causing distortion to TB housing. Honda put the various breathers into the design for a reason put these all back to standard, ditch any extra contrivances as unnecessary. Ensure all breathers and entry and exits are actually clear. Engine oil as specified and quantity correct. Fuel is fresh and fuel filters good. Fuel pressure to specification. Engine idle speed to Honda specification. No air leaks in inlet system or exhaust. No restrictions in air filter, system. Throttle cable adjusted as per Honda specs. Coolant temperature within Honda parameters. Cooling fan operates to Honda specs. Compression test to specifications, not guessed to be ok. Observations: too tight on the inlet and/or exhaust valve operating clearances will cause unsustainable idle speed. Coolant temperature above specification will cause erratic idle behaviour. Excess crankcase pressure will cause engine stalling and erratic idle behaviour. Poor compression will cause erratic behaviour at idle. Also poor performance in the mid range. In general it will probably come down to being something trivial being missed so be extra vigilant when making any investigations. Hope this is helpful and you get sorted.? Edited July 22, 2018 by section swept 1 1 Quote Link to comment Share on other sites More sharing options...
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