Carby kits common fault to be aware of..
Moderators: trixynut, Mincehead, dicky, phuk72, Jak, Kevtrx849
-
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Carby kits common fault to be aware of..
Have one of Marko's TRX's ( Black ) in the garage at present and the first thing that was obvious was the smell of fuel when idling. Plugs where black and sooty so I looked into the carbies and here is what I found.
A carby kit had been fitted before Marko purchased the bike and the needle was sitting at an angle.
I had only had this conversation with Rod the week before about the needles and tubes.
I remember when I placed a kit into Marko's blue TRX the needle sat oddly with the kit washers on the needle so I replaced them with the original washers and all sat well once located properly because there is a slight raised section effectively making a D shape on the base where the needle sits.
Because I didn't have the original washers as the kit was fitted before he purchased, I improvised things by filing a flat edge on the nylon and metal washers.
I tested the slide with a needle and the washers that where fitted and placed the spring on top of the needle to hold a little tension and it constantly sat at an angle.
Then I put in a needle with the modified D shaped washers and all sat nice and parallel to the slide and performed even better under pressure from the spring.
Once fitted back in the carby the needle will sit central to the tube not against the emulsion tube wall causing wear plus the needle will sit deeper into the tube just like if I had moved the clip from the 3rd to the 1st position.
So this throws into question why so many trx’s chew through needles and tubes every 20,000-30,000km. I rebuilt my FCR’s after 50,000km and had no real sign of wear. Still a down draught carby just like the std so the arguement about being D/D causing the wear of needles is thrown into the doubtful bin.
A carby kit had been fitted before Marko purchased the bike and the needle was sitting at an angle.
I had only had this conversation with Rod the week before about the needles and tubes.
I remember when I placed a kit into Marko's blue TRX the needle sat oddly with the kit washers on the needle so I replaced them with the original washers and all sat well once located properly because there is a slight raised section effectively making a D shape on the base where the needle sits.
Because I didn't have the original washers as the kit was fitted before he purchased, I improvised things by filing a flat edge on the nylon and metal washers.
I tested the slide with a needle and the washers that where fitted and placed the spring on top of the needle to hold a little tension and it constantly sat at an angle.
Then I put in a needle with the modified D shaped washers and all sat nice and parallel to the slide and performed even better under pressure from the spring.
Once fitted back in the carby the needle will sit central to the tube not against the emulsion tube wall causing wear plus the needle will sit deeper into the tube just like if I had moved the clip from the 3rd to the 1st position.
So this throws into question why so many trx’s chew through needles and tubes every 20,000-30,000km. I rebuilt my FCR’s after 50,000km and had no real sign of wear. Still a down draught carby just like the std so the arguement about being D/D causing the wear of needles is thrown into the doubtful bin.
laughter is the best medicine
- dandywarhol
- Site Sponsor
- Posts: 1639
- Joined: Fri Nov 24, 2006 12:56 pm
- Location: Edinburgh, Scotland
Re: Carby kits common fault to be aware of..
Interesting. SU and Stromberg car carbs, also CV, laterally came with a spring bias needle. The theory was that the needle rested lightly on the jet and stopped fuel "globbing" into the intake at idle speeds which caused misfires. By having a bias, the neat fuel "blob" would slide down the jet and not into the intake.
https://www.moss-europe.co.uk/su-carbur ... edles.html
https://www.moss-europe.co.uk/su-carbur ... edles.html
1996 TRX 850, blue, Ohlins 46HRCLS, Race Tech Gold Valves, 0.90 springs, Venom pipes, R6 brakes............
1974 Yamaha RD250A, Candy Blue
1998 Yamaha SZR660, blue of course
1967 Yamaha TD1C 250, Blue and white
1974 Yamaha RD250A, Candy Blue
1998 Yamaha SZR660, blue of course
1967 Yamaha TD1C 250, Blue and white
-
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Re: Carby kits common fault to be aware of..
Trx has I intake working on 1 carburettor and a multicylinder car motor would have multi cylinders impacting on 1 or 2 manifolds. Maybe why the difference????
laughter is the best medicine
-
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Re: Carby kits common fault to be aware of..
All back together with the needle clip on the top with the needle set deep into the tube and runs like a dream. Doesn’t quite accelerate as fast but runs nice and linear through the rev range. Stopped all the fuel smell on idle.
Pilot screws where set to 3/4 of a turn previously so I went to 2 turns as a base and no hesitation of idle or throughout the rev range.
Idle set at 1200rpm and a quick twist of the throttle it will rev and drop back to 1000rpm for a split second then settle again at 1200rpm. Warm, muggy weather today at 32* so I’ll leave it as is with winter on the way.
It was really nice to ride a completely stock std TRX and 0 to 100 is about the same as on my bike just this one is kph and mine is mph
Pilot screws where set to 3/4 of a turn previously so I went to 2 turns as a base and no hesitation of idle or throughout the rev range.
Idle set at 1200rpm and a quick twist of the throttle it will rev and drop back to 1000rpm for a split second then settle again at 1200rpm. Warm, muggy weather today at 32* so I’ll leave it as is with winter on the way.
It was really nice to ride a completely stock std TRX and 0 to 100 is about the same as on my bike just this one is kph and mine is mph
laughter is the best medicine
- dandywarhol
- Site Sponsor
- Posts: 1639
- Joined: Fri Nov 24, 2006 12:56 pm
- Location: Edinburgh, Scotland
Re: Carby kits common fault to be aware of..
The reason for the needle dragging on the jet is to stop the fuel running down the needle and "drip" into the airstream causing misfire symptomscobbadiggabuddyblooo wrote:Trx has I intake working on 1 carburettor and a multicylinder car motor would have multi cylinders impacting on 1 or 2 manifolds. Maybe why the difference????
1996 TRX 850, blue, Ohlins 46HRCLS, Race Tech Gold Valves, 0.90 springs, Venom pipes, R6 brakes............
1974 Yamaha RD250A, Candy Blue
1998 Yamaha SZR660, blue of course
1967 Yamaha TD1C 250, Blue and white
1974 Yamaha RD250A, Candy Blue
1998 Yamaha SZR660, blue of course
1967 Yamaha TD1C 250, Blue and white
-
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Re: Carby kits common fault to be aware of..
Motorcycle carbies have their own idle curcuit being the tiny little hole infront of the slide and the pilot curcuit being the small hole on the air intake side of the slide impacts up to 1/4 throttle so the needle shouldn’t impact on the idle or just above due to vacuum nature of the mikuni’s.
Got a pesky blocked idle curcuit on No2 cylinder on my FCR’s at present when I went on reserve.
Used contact cleaner under pressure and compressed air and can feel and see it flowing but the curcuit is so small with a few bend there’s something stuck somewhere and with very little vacuum at idle it’s just enough to hinder the flow of fuel to the tiny idle feed in the Venturi. Time to try an old guitar fine wire string to see if that will get me a result.
Got a pesky blocked idle curcuit on No2 cylinder on my FCR’s at present when I went on reserve.
Used contact cleaner under pressure and compressed air and can feel and see it flowing but the curcuit is so small with a few bend there’s something stuck somewhere and with very little vacuum at idle it’s just enough to hinder the flow of fuel to the tiny idle feed in the Venturi. Time to try an old guitar fine wire string to see if that will get me a result.
laughter is the best medicine
- Ragnar
- TRX-Enthusiast
- Posts: 36
- Joined: Fri May 20, 2016 1:32 pm
Re: Carby kits common fault to be aware of..
This carb problem is commonly known in Germany. I attached a drawing with the exact measurements.
Stolen from the German forum‘s Download section.
Or take a look at your carb info Thread where i linked it some Time ago
http://www.trx850.com/phpBB_forum/viewt ... 37&t=11606
https://ibb.co/hjVnWT
Stolen from the German forum‘s Download section.
Or take a look at your carb info Thread where i linked it some Time ago
http://www.trx850.com/phpBB_forum/viewt ... 37&t=11606
https://ibb.co/hjVnWT