Rae Posted February 7, 2022 Report Share Posted February 7, 2022 Hello all, ive got a new to me 2018 Montesa 4rt with a backfiring problem. it tends to only backfire (or after fire) when I’m holding revs at a higher rpm than idle. It tends to continuously foul plugs as well. I’ve gone through 3 plugs so far and after every warm up, it’ll foul a plug. The plug also slightly smells of gas. It starts 2nd kick when cold, but starts 1st kick when warm. things I’ve checked so far: 1. Cleaned air filter and removed excess oil 2. new spark plug (cr 6) 3. Valve clearances set per manual 4. resealed and tightened exhaust connections 5. new fuel (93 octane non ethanol) Other things I’ve thought but haven’t tried: new coil different gas with 10% ethanol hotter plug (it’s 30 degrees f recently) could anyone guide me in the right direction? Not sure if the idling sounds right either… Quote Link to comment Share on other sites More sharing options...
lineaway Posted February 7, 2022 Report Share Posted February 7, 2022 2 hours ago, Rae said: Hello all, ive got a new to me 2018 Montesa 4rt with a backfiring problem. it tends to only backfire (or after fire) when I’m holding revs at a higher rpm than idle. It tends to continuously foul plugs as well. I’ve gone through 3 plugs so far and after every warm up, it’ll foul a plug. The plug also slightly smells of gas. It starts 2nd kick when cold, but starts 1st kick when warm. things I’ve checked so far: 1. Cleaned air filter and removed excess oil 2. new spark plug (cr 6) 3. Valve clearances set per manual 4. resealed and tightened exhaust connections 5. new fuel (93 octane non ethanol) Other things I’ve thought but haven’t tried: new coil different gas with 10% ethanol hotter plug (it’s 30 degrees f recently) could anyone guide me in the right direction? Not sure if the idling sounds right either… T he starting point would be the idle needs to be set at 1800 rpm. It will not be happy at any lower setting. AND any 4 stroke will back fire if you rev it in nuetral and hit the rev limiter. 1 Quote Link to comment Share on other sites More sharing options...
Rae Posted February 7, 2022 Author Report Share Posted February 7, 2022 7 minutes ago, lineaway said: T he starting point would be the idle needs to be set at 1800 rpm. It will not be happy at any lower setting. AND any 4 stroke will back fire if you rev it in nuetral and hit the rev limiter. That’s good to know! My idle is set at 1850 when warm… bought a tach/hour meter just to check. It idles and sounds similarly to a 4rt owner on YouTube so I believe it’s idling fine. I didn’t know that all 4 strokes backfires when in neutral. I did notice that it backfires less when in gear and I rev it up but still backfires. I checked it when on the stand. Maybe it’s different if I’m riding and revving… I’ll check that later. ive also checked the throttle body to make sure that the restrictor is removed. maybe I’m chasing my own tail here. May not even be an issue. It’s just that the plug continues to foul and I can’t for the life me figure out why Quote Link to comment Share on other sites More sharing options...
jrsunt Posted February 7, 2022 Report Share Posted February 7, 2022 Could the engine have been apart? If so, perhaps the timing could be a tooth out. Check for spanner marks on cylinder and head bolts, also a sealant would have been used on the head cover giving indications of engine work Quote Link to comment Share on other sites More sharing options...
jonnyc21 Posted February 8, 2022 Report Share Posted February 8, 2022 Coil swap is my first thought when I see the list of everything you have done... on that note. Edge case here, however I had an issue with my 07 4RT not running correct when it had the fan motor die on me. Would run fine for a few but to rev it up in or out of gear it would have all kinds of running issues and get really bad once it warmed up and tried to use the fan. I would see about swapping the coil first though. Good luck! Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 8, 2022 Report Share Posted February 8, 2022 Presume you let it warm up on tick over for a short while before opening throttle. Are you doing a lot of stop start riding. Do you stop it with the kill button -don't stall it to stop. Try staring it and just let it tick over for 10 mins - they often sort themselves out -I have had it on cold days when doing a few section close to each other at the start of a trial, -just leave it ticking over when you walk the section Quote Link to comment Share on other sites More sharing options...
billyt Posted February 8, 2022 Report Share Posted February 8, 2022 Jimmy. Can you please help us understand why " Stalling the bike with the bike in gear vie the clutch" is a bad thing ? Thanks.... Quote Link to comment Share on other sites More sharing options...
Rae Posted February 8, 2022 Author Report Share Posted February 8, 2022 21 hours ago, jrsunt said: Could the engine have been apart? If so, perhaps the timing could be a tooth out. Check for spanner marks on cylinder and head bolts, also a sealant would have been used on the head cover giving indications of engine work just checked for any spanner marks but there are none on the head or around the cylinder. 16 hours ago, jonnyc21 said: Coil swap is my first thought when I see the list of everything you have done... on that note. Edge case here, however I had an issue with my 07 4RT not running correct when it had the fan motor die on me. Would run fine for a few but to rev it up in or out of gear it would have all kinds of running issues and get really bad once it warmed up and tried to use the fan. I would see about swapping the coil first though. Good luck! the fan seems to run fine when i'm warming it up. no issues with the fan but the coil may need to be swapped. i noticed while riding for a bit today that when it backfires, it almost feels like letting go of the clutch for a split second and back on. could be a fuel problem... although the fuel is new. maybe it just doesnt like non ethanol gas? 5 hours ago, jimmyl said: Presume you let it warm up on tick over for a short while before opening throttle. Are you doing a lot of stop start riding. Do you stop it with the kill button -don't stall it to stop. Try staring it and just let it tick over for 10 mins - they often sort themselves out -I have had it on cold days when doing a few section close to each other at the start of a trial, -just leave it ticking over when you walk the section i always let it warm up until the fan kicks on. i do not rev the bike when warming up. no start stop riding, i usually just keep it running whenever i walk away this is a rather interesting situation... maybe i need to check the valves again... Quote Link to comment Share on other sites More sharing options...
Rae Posted February 8, 2022 Author Report Share Posted February 8, 2022 (edited) i also just remembered that the previous owner used a heat range 8 plug when Honda recommends 6. far too cold with the 8 plug. i've put in the stock 6 plug, put some fuel injector/valve cleaner in the fuel and ran it for about 10 minutes. it was sputtering for a little bit but it seems to have eventually smoothed out. i will continue using the cleaner for the rest of this tank and the next few and see how it goes... 2 hours ago, billyt said: Jimmy. Can you please help us understand why " Stalling the bike with the bike in gear vie the clutch" is a bad thing ? Thanks.... I'm not Jimmy but it's my belief that the only thing that hurts when you stall a bike is your pride 😆 Edited February 8, 2022 by Rae 1 Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 8, 2022 Report Share Posted February 8, 2022 Always best to stop with kill button as this stops engine in correct sequence Quote Link to comment Share on other sites More sharing options...
billyt Posted February 8, 2022 Report Share Posted February 8, 2022 (edited) 3 hours ago, jimmyl said: Always best to stop with kill button as this stops engine in correct sequence Now I am even more confused. If you stop the engine vie the kill switch or lanyard how does that sequence the engine as it is totally random from a 4 cycle position of the engine? The engine will die and coast to a halt regardless of its rotational sequencing and its final position in the 4 cycle is totally random to the mass, gearing and rotational speed when stopped Are you saying when you stop the engine with the stop switch or lanyard the CDI box decides what position in its cycle to stop the engine at ??? To do that the CDI box would have to have a sensor telling the CDI box the pistons position or the cranks position. Even then how could it stop the rotating mass that preciously? Total agreement that from a mechanical stress on the engine perspective killing the bike with it in gear is not a good idea. I am more curious about Jimmyl's comment in how it stops the engine in the correct sequences. Please educate us in what that means? I will grab some popcorn 🥺 Edited February 9, 2022 by billyt Quote Link to comment Share on other sites More sharing options...
Rae Posted February 8, 2022 Author Report Share Posted February 8, 2022 2 minutes ago, billyt said: Now I am even more confused. If you stop the engine vie the kill switch or lanyard how does that sequence the engine as it is totally random from a 4 cycle position of the engine? The engine will die and coast to a halt regardless of its rotational sequencing and its final position in the 4 cycle is totally random to the mass, gearing and rotational speed when stopped Are you saying when you stop the engine with the stop switch or lanyard the CDI box decides what position in its cycle to stop the engine at ??? I will grab some popcorn 🥺 i can't say for sure since I wasn't the one who started that comment, but I do think that you're practically lugging the engine to a stop which isn't good either. also, i believe I fixed my issue by increasing the idle. thank you all for your help 1 Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 9, 2022 Report Share Posted February 9, 2022 22 hours ago, billyt said: Now I am even more confused. If you stop the engine vie the kill switch or lanyard how does that sequence the engine as it is totally random from a 4 cycle position of the engine? The engine will die and coast to a halt regardless of its rotational sequencing and its final position in the 4 cycle is totally random to the mass, gearing and rotational speed when stopped Are you saying when you stop the engine with the stop switch or lanyard the CDI box decides what position in its cycle to stop the engine at ??? To do that the CDI box would have to have a sensor telling the CDI box the pistons position or the cranks position. Even then how could it stop the rotating mass that preciously? Total agreement that from a mechanical stress on the engine perspective killing the bike with it in gear is not a good idea. I am more curious about Jimmyl's comment in how it stops the engine in the correct sequences. Please educate us in what that means? I will grab some popcorn 🥺 I would suggest it stops injecting fuel so engine stops clean if you stall potential for fully charged cylinder full of fuel this is the difference a carb and injected engine how’s the popcorn 😂😂👍 Quote Link to comment Share on other sites More sharing options...
billyt Posted February 10, 2022 Report Share Posted February 10, 2022 Just chocked on apiece of popcorn when I read your latest logic 😂 A stop is a stop regardless to the CDI box. If the lanyard is pulled the CDI box signal is taken to ground and stops the bike regardless of crank and piston position. If the bike is stopped via the clutch the lack of a magneto pulse signal from the pick up coil is missing so it stops the bike. In either scenario the full injection system I still under pressure and piston and crank will stop at a random part of its stroke. Your are entitled to your logic I am also entiltied to mine and I don't buy your logic No foul, no worries, just opinions. Quote Link to comment Share on other sites More sharing options...
jonnyc21 Posted February 10, 2022 Report Share Posted February 10, 2022 (edited) 43 minutes ago, billyt said: Just chocked on apiece of popcorn when I read your latest logic 😂 A stop is a stop regardless to the CDI box. If the lanyard is pulled the CDI box signal is taken to ground and stops the bike regardless of crank and piston position. If the bike is stopped via the clutch the lack of a magneto pulse signal from the pick up coil is missing so it stops the bike. In either scenario the full injection system I still under pressure and piston and crank will stop at a random part of its stroke. Your are entitled to your logic I am also entiltied to mine and I don't buy your logic No foul, no worries, just opinions. From what I understand the Montesa has an alternator not a standard magneto setup. And with the EFI it has the kill switch is connected to the ECU not to a CDI box. So what Jimmy is saying to my understanding is correct, it isn't grounding out anything but the ECU pin that tells it to cut the fuel. Hope that helps clear up what Jimmy was talking about on his last post. Edited February 10, 2022 by jonnyc21 1 Quote Link to comment Share on other sites More sharing options...
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