Tuning Problems

[kev64]

One of the jobs ive done this winter was to remove the carbs, check and clean jets etc
I received a set of fuel mixture thumb screws and fitted those,
So all in all, I think the carbs have been on and off about 3 times this winter !!
So the bikes rebuilt and a test run carried out.
When I started the bike I got a oud backfire on full choke, in fact the bike wouldn't start at all
on full choke, it would only fire up with no choke then would run ok on half choke
My mixture screw setting are roughly 1 !/2 front and 1 3/4 rear as was set last year.
Also after about 15mins on the test run, I stopped to have a tinker with my new thumb screws
no matter which way I turned either of them the engine doesn't cut out, even when fully screwed in !
The engine runs well and returns to idle off the blip test

so I know a forth carb removal is imminant, just wanna know what you guys suspect (I think maybe choke cable ?)

[Kurt999]

Are the hoses on the fuel tap in the correct places? Choke cable and choke plungers themselves is where I'd look first. However, I had the same sort of problem and it ended up being one of the carb float bowl vent hoses being crushed...one hose from each carb usually pushed through the side plates and banded togeether. They should be open to atmosphere. If one or both are blocked it causes a negative pressure differential in the float bowls, which draws extra fuel into the carbs causing rich running and associated problems.

[kev64]

All vac hoses are on, as I made that mistake previously, I ll take the carbs off in a bit, hopefully its just a choke cable,
as I think the back cable is rooted slightly wrong

[kev64]

Also ill check those vent hoses

[lloydie]

Did you fit the springs and washer and rubber O rings to the new fuel screws ?

Your cabs will need a balance too btw .

[kev64]

Yes swapped them over, one by one, bit by bit !
Had the carbs balnced last year but will recheck when I get the chance

[VTRDark]

So all in all, I think the carbs have been on and off about 3 times this winter !!

Only 3

no matter which way I turned either of them the engine doesn't cut out, even when fully screwed in !

A sign of being too rich that. Either the pilot jet is too big or you have a choke issue. Make sure you have the cable run correctly for the choke too. It should run over the top and around the back of the carb at the rear.

(:-})

[kev64]

Right, removed the carbs, remove and refit both choke connections, the back cable was routed wrong, so it is now free and the choke operation feels a little better, also removed both thumb screw pilot s and they both came out with washers and o ring, so happy with that.
Roughly set for now. TPS had to be reset, it was 473 ohms, now 497

You know , removing/refitting the carbs is ok, its just that tank that takes the biggest time for me, a right pain !

Fired up on full choke for a few seconds only as its getting a bit late and the vee twin sounds twice as loud in my side entry
Full run up tommorow

[VTRDark]

Nice simple fix then.

It's all the screws in the airbox lid that are the biggest pain Why they couldn't design a quick release airbox I don't know.

(:-})

[kev64]

or a quick release tank ! with quick release pipes !

[kev64]

Well, me and steve off the forum have been discussing this problem, the bike must be running rich as I get a back fire on full choke still !
Just presuming ive not F**cked anything up the only thing it might be is the fuel mixture thumb screws I fitted.
Will swap original screws over tomorrow night (im gonna modify a stubby screwdriver) and retry, hope its not the thumb screws as
they are a great idea and work well

[kev64]

So modified my stubby screwdriver and now have standard pilot mixture screws in , set at 1/14 turns front, 1 1/2 rear
The only thing that sounds wrong is my choke cable runs round the front, down through the middle of the two carbs, so the rear choke valve
potentially is the wrong way round (carl you said it should go over the back and above) would this make a difference ?
My choke action feels good though

[VTRDark]

On the rear carb the choke goes into the carb on the same side as the knob, so left side of bike. The cable for that carb runs up and over and around the the back. The front which is on the opposite side, along with the other cable as they link together, and the knob gets pushed through and under the small cooling hose that runs into the front cylinder from the thermostat alongside the coolant bottle. It's a tight fit but the knob and cable do push through with a bit of a wiggle and then obviously the knob attaches on the frame. I think the idea is that the plastic part where it goes from two into one sits between the coolant hoses but it never does.

You can see the rear cable in these pics




and the small hose by the coolant bottle in this one




And yes it does make a difference

(:-})

[kev64]

Thanks Carl, super detailed reply as ever, much appreciated thanks, ill re-route the cable again

[kev64]

Ok so today was hopefully final carb removal day !
Im getting quite quick at this now !
Carbs removed , jets removed , blew out and refit, ive done nothing else to the carbs exept I
forgot to mention (well I actually forgot I did it that long ago, before xmas) I removed the washer
on the needle slide and I think this may be the cause of the problems, from what ive read you
add a washer to the back carb not remove from the front !!
Anyway this is not for me so ive put the washer back and faffed around getting the rubber thingy
to stay in its groove for 30 mins, but I got there in the end,
Refit carbs , Re-routed the cables correctly and the bike fired up with full choke !!!

So I m hoping this problem is sorted.

Went for a small test run which ended up being a 70 miler as it was quite warm out today
Stopped for a little tweak of my mixture thumb screws and I think ive got them somewhere near, goes like a rocket !

Happy days