72 replies to this topic

[Dannyboy]

Once again I have discovered a leak from the carbs. This time its from the overflow on the offside carb. Strip it down, clean it including the choke mechanism and put it back together. Turn the engine over and eventualy the 850 fires up, and up and up and then red lines. Turn it off and have a tinker. Fire her up again and the same thing. Bike fires up and tries to rev itself to death. Strip it all back down and put it all back topgether and still the bike tries to kill itself via revs. Throttle appears OK with no snags, Choke works fine but still red lines. On the bright side the leak has stopped Its a pity as when she runs she runs loveley but Im just about peed off with stripping the bloody carbs down every month or so. Gonna sell her and buy a Honda 90.

Edited by Dannyboy, 25 August 2013 - 10:03 am.

[doboy]

the rubbers inlet rubbers from the carb to the cylinder head are not split are they ?

[Studley Ramrod]

Now now Danny, she won't reward you for calling her names you know ! Sidestand neglected his mk2 for over 6 months and it rewarded him by filling the sump full o petrol and blowing the carbs off the engine.

There are two throttle cables, I wonder if one isn't in the groove and snagging somewhere on the carbs, but the other still has the spring being worked, if ya get me drift.

Can't think what else would cause the throttle butterflies to stay open, or what's causing it to rev high if it's not this.

Oh, I wonder if it could be the tickover screw adjuster doohickey ?

I'll have her if ya gonna torch her anyhoos

[Dannyboy]

I checked the throttle cables and made sure the butterflies were closing correctly. The rubbers appear OK and double checked the carbs were seated correctly. I did have to disconnect the tickover screw from the frame but that's normal when taking off the carbs. Trouble is I don't get that much free time and I need a reliable winter bike for work.

[DazzerB]

I need a reliable winter bike for work.

Get a 900

[leehenty]

if she red lines it's getting a lot of air from somewhere, have you run with air box off to see what's happening?

[Dannyboy]

Yep I tried with the air box off and got the same result. Too knackered and cold now so will try again tomorrow.

[tdm850rider]

Have you tried giving the choke plunger a good oiling? They stick at times.

[Dannyboy]

Thomas, I will try that in the morning. Would it be worth taking the choke assembly off completely and cleaning it up. I did oil the slide just before the revving problem started.

[leehenty]

at this point maybe a call to Mr Studley master of the carburettor, for a quick diagnostic visit might solve things easier.
You haven't got a perforated diaphragm on the slide bit ? That would let massive air in wouldn't it ? I stand to be corrected, just fishing, haven't dealt with carbs for years.

[Studley Ramrod]

In an ideal world I'd be more than happy to go and have a look, unfortunately, I don't have the time available at the mo'.

[tdm850rider]

Thomas, I will try that in the morning. Would it be worth taking the choke assembly off completely and cleaning it up. I did oil the slide just before the revving problem started.

That would be best as you will be sure you got to everything. Could be the end of the plunger rod is not pushing in whatever it pushes/pulls.(technical huh?)

[Dannyboy]

Right, Ive taken the carbs off the bike completely. Stripped it down and cleaned it all up. I could not see anything wrong. Carb floats and vacuum doohickys all appear to be in good fettle. Choke slides taken apart, Cleaned and put back together, no problems. Checked as best I could for a perforated diaphragm but all looks fine. I cant get to the one between the carbs as I dont want to split them. I dont know how to balance and Im not even sure if you can with the carbs off the bike but so far Im just scratching my head at the mo.

[Studley Ramrod]

I think Lee was referring to the big diaphragms inside the carb tops Danny.

Do the revs climb quickly, or gradually ?

Have you tried turning the idle/tickover screw down (anti-clockwise) ?

Deffo not got the 2 cables crossed into the wrong grooves ? As in, top cable goes to top wheel groove and bottom one to...... ?

[Dannyboy]

Studders, I checked the big diaphragms as well. The throttle wires were as when I bought the bike so that's not it. The idle/tick over has never been messed with so that's going to be fine as well. The carbs have had an intermittent leak since I had the bike but to be fair I was still getting around 140 to150 miles to a tank so it wasn't a real issue. This started on the way home. The bike just ground to a halt and I thought it was a case of turning the fuel cock to reserve. I did this and the bike started but ran very poorly, stuttering and very hesitant hence stripping down the carbs. I do enjoy tinkering with the carbs but so far all I have achieved is wasting time. I can honestly say I'm stumped. May have to send the carbs off for a service if this can be done as I can't see what else the problem could be.

[Studley Ramrod]

I can check 'em over and set the fuel levels etc if you want to post 'em to me Danny ? No charge, except the P&P, bein' as yer a decent sportin'

[Dannyboy]

Studders your a star. Could you pm me your address please.

[Studley Ramrod]

Got the slaggin' carbs

First thing I've noticed is that both the throttle cable and choke cable brackets are reeeeealy bent. It looks like the carbs have either been dropped, or something heavy has hit brackets. Here's a piccy

[attachment=2732:Dannys1.jpg]

Any idea if they were like this or not before you posted them Danny ?

The bent brackets would certainly give one possible reason why the throttles seemed to be stuck open if they were like this.

[Studley Ramrod]

Just priced up a small (10mm o/d) carb O ring at Suttons ! Fhaaaaaaa kiiiiiiin' 'elllll !

Ninepoundsandfiftyfivepence +P&P please, ta !

Soooooo, I've just reviewed the product on their site.

Anyhoos, I've got most of the parts stripped out and been chicken 'em over. Up to now it's looking like you need some new o rings and gaskets.

Needles & Jets fine.
Float valve needles fine.
Diaphragms, feel a bit floppy/thin but no holes.
Main jet o rings worn.
Main jet holder gasket flat/worn.
Slider o rings flat/worn.
Float valve housing o rings worn.
float bowl gaskets worn.
Choke plungers.............
Air cut off diaphragms............

Hey ho.

[leehenty]

Fairly comprehensively worn then. Those screws on float bowl and carb tops look pretty ropey.
They will be M4, M5 or M6 probably, send me a pm of how many, size and length are needed, I'll send a set of stainless cap screws up to you, to help the sporting' lad out, it being nearly Chrimbo an' all.
Looks like he's having enough trouble as it is.