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Engine Failing In Low Rpms After Hot, Then Dies.


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#1 AlexSmink

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Posted 24 September 2018 - 11:54 pm

Hello to all... Don't know how the forum works so please let me know if i'm missing or skipping some club rules before posting this!

 

My name is Alex and i live in Argentina. Have been riding a bike since i was 15 (now 42) and had almost various motorcycle styles (dirt, chopper, crotch, enduro). Two years back i purchased a 1992 TDM 850 from a close friend who had it semi abandoned in a warehouse. He had it since brand new new but over the last decade used it less and less until the last 4 years which it was run about 2 times a year, at most. Man, what a bike... Loved it within the first 3 minutes of testing it! Of course after bringing it home the first thing i did was a complete oil & air filter change. Then had its carbs totally cleaned and changed all the fuel lines (they were all rotted). Remade the fuel petcock for it was a complete lock too. Front forks were leaking too and changed the seals and oil.

 

Started using the bike but it had a fuel issue because it would turn off like it was out of gas (when i had more than half a tank!) so i had to constantly refuel very often and avoid long trips. I re-checked all the lines (the breathe line from the tank was clear too) but everything seemed ok. Finally l travelled to the US last week and bought a new vacuum fuel pump because my reasoning led me to believe that was the problem. Last weekend with the help of my cousin we changed it and tried it with only half a liter of gas, and it worked! Finally, that issue resolved and the bike seemed great, but as i rode into the first 15 minutes it started to fail at low rpms (2000/3000) coughing and coughing like if it were out of gas. Once or twice i could work my way into the upper range of rpms and after the studders it regained torque and smoothness (only in high rpms) but when a streetlight came and it idled, it died. I had to wait about 45 mins to get it going again. I quickly rushed home and arrived with some coughing just starting. The thing is that this was not the first time it did this, it did this two times before i changed the fuel pump so it shouldn't be because of that, and it wasn't the air either in the tank cause the first thing i did was to lift the lid.

 

Could somebody help me with this?? Has anyone experienced something like this? I've been surfing webpages and conversations and read about how the starter coil when not working properly can do this when it gets hot. The other thing that i heard about that could maybe cause this are the needle jets / emulsion tubes.

 

I'm in Argentina and spare parts for this bike are not easy (and cheap) to find... Hope whatever this is it will not be too complicated to fix.

 

Thanks in advance for taking the time to read this! If anyone has any pointers i would truly appreciate them...

 

Best,

Alex.



#2 TKH

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Posted 25 September 2018 - 02:37 am

Welcome Alex! The TDM is a really nice bike to ride.

 

I don't have an 850, mine is a 900. I'm sure someone with way more knowledge than me will be along, but until they do, usually problems are either fuel or electric. Have you checked the plugs?, plug leads? (for arcing or that they are properly connected), coils, cold start mechanism? Are all the fuel lines connected correctly? Is the air filter clean? Is the fuel tank clean and not letting bits of dirt get into the fuel lines? Are you getting any error codes showing up?



#3 TDM4ever

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Posted 25 September 2018 - 06:29 am

I have had a lot of carb bikes and also with symptoms like yours.

 

It is almost certain that it is a carb- and/or ignition problem. I would try in the following order:

 

Change spark plugs, leads and caps.

Change the coils

Buy a refurb kit for your carbs and change all needles/jets. If your carbs has diaphragms, then check them for holes.


Edited by TDM4ever, 25 September 2018 - 06:31 am.


#4 dablik

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Posted 25 September 2018 - 07:37 am

Hi Alex and welcome, you replaced all of the fuel lines but what about the tank !! have you cleaned it at all, is it possible you have some contamination which is causing a partial block ? you may need to re-check the carbs again and the petcock, do you have a fuel filter in-situ, you should have a filter inside the fuel pipe where it fits onto the carb and i suppose the diaghragms could be an issue standing so long, everything air tight, carb rubbers and airbox.

 

As above it could be an electric issue but sounds more fuel related to me, my initial thought was fuel pump but you've changed that already, did you replace the vaccum hose, no leaks..


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#5 madmopedracer

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Posted 25 September 2018 - 08:03 am

there is another very small filter inside the fixing at the T where the fuel splits between both carbs



#6 dablik

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Posted 25 September 2018 - 08:14 am

there is another very small filter inside the fixing at the T where the fuel splits between both carbs

 

Same one i mentioned mmp, he might end up looking for 2  :huh:  also check the tank vent is clear, access is under the rubber under the fuel tank cap.


Bigred mk1 R1 Calipers- Braided lines- Givi wing rack-Crash bungs- Hi vis bullets-PR2's- and a hoot to ride.

Quad 900 Silver Laser duo tech pipes-Scott oiler-Engine crash bars- Radiator mounted see me ring LED's-Datatool system 3 alarm -Centre stand- Extender fender-Renthal bars-Handle bar risers-Mirror extenders-BMW GS Handgaurds-Acumen uprated horn & Nautilus-Stainless steel Radiator guard-Givi wing rack-OEM screen-Yammy touring screen-MRA Vario-MRA Double bubble cut down for fast as fk riding-Tiger screen-Tank protector-Stomp grip panels-Optimate lead   Gone to Heaven  :sorry: 

 

1991 MK1 in need of some TLC watch this space   :) Sorted and on the Road Mick  :P  :P it's the bike that Jack built  ;) Gone to Heaven  :wub: 

 


#7 Studley Ramrod

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Posted 25 September 2018 - 09:37 am

Hi and welcome. :)

 

One thing that can/does happen is...... when bike gets up to temp the thermostat housing starts leaking onto the rocker cover and then finds its way onto the HT leads causing them to misfire.  Doesn't happen when the engine is cold.


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#8 dapleb

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Posted 25 September 2018 - 11:15 am

Hi and welcome. :)
 
One thing that can/does happen is...... when bike gets up to temp the thermostat housing starts leaking onto the rocker cover and then finds its way onto the HT leads causing them to misfire.  Doesn't happen when the engine is cold.


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#9 dablik

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Posted 25 September 2018 - 11:36 am

Hi and welcome. :)

 

One thing that can/does happen is...... when bike gets up to temp the thermostat housing starts leaking onto the rocker cover and then finds its way onto the HT leads causing them to misfire.  Doesn't happen when the engine is cold.

 

Forgot about that...could well be eh, silicone fixed mine in the past.


Bigred mk1 R1 Calipers- Braided lines- Givi wing rack-Crash bungs- Hi vis bullets-PR2's- and a hoot to ride.

Quad 900 Silver Laser duo tech pipes-Scott oiler-Engine crash bars- Radiator mounted see me ring LED's-Datatool system 3 alarm -Centre stand- Extender fender-Renthal bars-Handle bar risers-Mirror extenders-BMW GS Handgaurds-Acumen uprated horn & Nautilus-Stainless steel Radiator guard-Givi wing rack-OEM screen-Yammy touring screen-MRA Vario-MRA Double bubble cut down for fast as fk riding-Tiger screen-Tank protector-Stomp grip panels-Optimate lead   Gone to Heaven  :sorry: 

 

1991 MK1 in need of some TLC watch this space   :) Sorted and on the Road Mick  :P  :P it's the bike that Jack built  ;) Gone to Heaven  :wub: 

 


#10 Apache

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Posted 27 September 2018 - 05:08 pm

Just a different angle. Check valve clearances. If already tight at cold then hot will hold a valve open. Cools and runs again....worth a check..

#11 Bjørge

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Posted 29 September 2018 - 08:21 am

Does it help to open fuel cap and close it again ? Could be vacuum building up in tank if vent tube is blocked.


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#12 AlexSmink

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Posted 03 October 2018 - 07:34 pm

Thank you all for your feedback!!! Will start if I can this weekend to unassemble the bike... back to basics!




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