Nearing my wit's end!

[steve zodiac]

Hello.
As I have mentioned previous threads. Some of my current problems regarding my TX650.
I am now in a state of despair with the thing.
The bike runs great above 3k rpm.
But below that, it spits & farts. Backfiring at idle & just off idle. Mainly on the left cylinder.
I can set the idle so it just ticks away happily, but When I try riding it. The revs hang at 3k. I have changed the pilot jet from #42.5 to #45 & back again it makes no difference. Tho I do think the #45,s were too rich. The points are set the timing checked with a timing light.
Pilot screw,s from anywhere between 1 5 turns out. That doesn't make much difference either. The pipes are almost standard. With Uni filters. The floats are set at 23mm, new pilot bungs, new float valve O rings. The Diaphragm, appear to be in good condition. The Battery is fully charged. There doesn't apper to be any air leaks. So I am absolutely stumped.
And just to add to the fun. The starter bendix has jammed.
I was hoping to go to the Classic TT on this thing this week. But that ain't happening.
Any advice offered will be greatly appreciated.
Regards.
Sean.

 

[steve zodiac]

Ps. The carbs are Bs34,s with plastic floats.

 

[Its been a long time]

Ps. The carbs are Bs34,s with plastic floats.

Sorry to hear your troubles. I had endless issues with my BS38 carbs. I swapped to a set of much more modern carbs off a Kawasaki ER5. They work astonishingly well. Only drawback I can see is that this mod has caught on to the extent that eBay sellers want increasingly large amounts of money for the carbs these days. If you're interested there's a very long thread about this subject. Good luck.

I have sourced enough good parts to rebuild my BS38 carbs but they remain in a box on the shelf. I have no cause to refit them.

 

[jetmechmarty]

It’s gotta be something you’re missing. Slides in backwards? I know, I’m grabbing at straws.

 

[steve zodiac]

Hello again.
Here is where I am at now with this F... Ing bike!
I found the cause of the backfiring. I changed the Condenser and that problem went away. All I was left with was a hiccup when opening the throttle coming out of corners. So I have tried to tune that out. However, where the bike appears to run just fine above 2.5k rpm. Below that It bangs & farts through the exhaust & spits back through the carbs. Mainly on the left cylinder. The pilot screws don't appear to have much effect. The timing has been checked with a strobe & shows to be spot on.
I can't decide whether the problem is carburettor or electrical related. So please any assistance would be greatly appreciated as always.
The carbs are Bs34,s with short uni filters.
Pilot jets#45. Main jets#135. There is a 1mm washer under the needle clip.
The choke plungers have been resealed.
And the diaphrams have passed the drop test.
The exhaust almost standard.
The advance rod flicks back freely & the strobe light indicates the a/r unit is working.
Again any assistance welcome.
Tia.
Sean.

 

[JOHNDADDY]

Could your springs on the spark advance be stretched?

 

[steve zodiac]

They possibly could be. But I would have thought it would show up with the timing light. I shall order a ATU rebuild kit.
Thank you for your response.
Sean.

 

[uksparky]

Coils

 

[steve zodiac]

I have considered the Coil's. But had sort of ignored them, thinking that any problems would mainly show up at higher revs. I can swap the coils with my Rd400 to see what happens.
Thank you.

 

[steve zodiac]

Update!
I think that I am now getting somewhere.
It appears that I have been chasing two separate problems, without realising.
After following all the advice given by my fellow forum members. Thanks to all who came to my assistance.
I concluded that I had done everything thing possible to my Bs34 carbs, so therefore the problem must be ignition related. So I threw everything at it.
New Advance unit, coils, condenser.
The bike now starts perfectly & idles like a clock at 1200rpm.
There is just one small thing left.
There is a small Phutt sound in the L/h exhaust. This happens when the butterflies are just opening. I will try balancing the carbs again to see if that
Cure's it.
Do you Guys have any ideas as to the cause of this hopefully final hurdle?
Your assistance is as always appreciated.

 

[Its been a long time]

Indeed, it is very difficult with multiple concurrent faults. I had both ignition and carburettor faults along with a blocked right side exhaust header. It was never going to run until I eventually discovered the blocked header.

Good luck finally sorting it out. It took me 18 months to finally sort out my 650D. But it runs great now.