Popping from exhausts on overrun - NOW SORTED!

[pbear62]

Hi guys,

As the subject says, my TRX has started to develop a popping/banging from the exhausts on the over-run or when
slowing down & changing down through the gears.

Also when the motor is turned off after a run, the heat radiating from the exhaust tips (behind the mufflers) is a
fair bit hotter from the RHS pipe. Don't know if this is related? (Header pipes show no discolouration)

Everything else seems fine - starts & idles ok, revs out cleanly, no fuelly smell when running etc.

The bike is only a Sunday ride toy & has only developed this issue on the last couple of rides.

Has anyone else had this problem? Any suggestions?

A couple of guys I know have suggested it could be sucking air somewhere on the exhaust: where the exhaust fits
into the front of the cyl head maybe? It had new flange gaskets fitted about 25,000kms ago & the bolts are all tight.
I've already checked & sealed where the cans slip-on to the pipes. Other suggestions are that it could be carb related?
Idle screw or mixture screw moved somehow maybe? Vacuum leak somewhere?

I replaced the emulsion tubes & needles 16,000kms ago so wouldn't think it could be related to this.

Any suggestions on where to look first?

Cheers, Andy

[Silver]

Carb diaphragms?

[pbear62]

Hi Silver,

What should I be looking for re: the diaphragms?

Cheers, Andy

[Silver]

Air leak somewhere, i had spare carbs and just swapped diaphragms. Cured my popping. I still fart though!

[pbear62]

Hi guys,

The problem I was having when I started this thread now seems to be fixed - on the right hand side of both carbs there is a round
cream coloured plastic 'plate' (about 25mm diam) with 2 screws holding it on. This is the cover for what Yamaha calls a 'cut-off
diaphragm' (in the carb section of the parts manual the diaphragm & its spring is shown as #29)

On close inspection, I found that this cover on my RHS carb had a series of small cracks around the centre boss - the plastic appears
to have deteriorated with age (& exposure to the Australian sun) & because the circuit wasn't sealed, it wasn't allowing the diaphragm
to be drawn open properly in a closed throttle situation.

This hasn't happened to the plate on the LHS carb as that one is hidden in under the tank & between the carbs & is therefore very well
protected from the elements. (I borrowed a spare set of carbs from a mate & his were exactly the same - RHS perished/LHS perfect.)

From the looks of the parts diagram, it appears that Mr Yamaha hasn't given this cover a part number so I don't like our chances of
being able to buy a new replacement! Luckily my local bike wrecker had a set of carbs which were 'suitable for parts only' & I managed
to get both covers off this set.

I went for a 240km test ride yesterday & all was good - no popping at all. Hope this helps anyone else who may come across this problem
at some time.

Cheers, Andy

[Rich]

http://www.kedo.com/products/28211.html

one of those?

[dicky]

This bit here...

Carb cut-off diapragm cover.jpg

Looks like the Kedo part should be the same.

[Con Rod]

had the same issue with mine. Glue fixed it but I eventually replaced it.

A metal part would be better but good to know new replacements can be had from Kedo

[pbear62]

Yep - that's the culprit!

I have a good used spare now off the wreckers carbs but good to know that they're available.

Cheers, Andy

[Trixed]

I used glue as well to fill the leaks then had to replace with fcrs long term

[deathtoll]

Unless I can find one somewhere other than Kedo I will have to attempt to make my own up. Kedo will cost me $25au + $60au for shipping. $60 for shipping of a part that small & light is just criminal.

[Con Rod]

contact these guys to see if they can help

http://www.kedopartsaustralia.com/

[deathtoll]

Cheers.
have emailed them with a link to the u.k part.

Failing that I will have to get one 3d printed, which will still be a lot cheaper than buying one in from the uk

[Con Rod]

let us know how you go, postage with Kedo is a killer so be good if we can get their stuff locally.

I dare say there are probably a few members in Oz who would look at replacing them for the right price

[deathtoll]

Will do.
Even if I have to go down to road of 3d printing one up I will let you know