Wont rev out and misfiring - carb issue?

[victor]

My Tv 175 with stock standard cylinder, race crank, gori sport exhaust and points ignition wont rev out and spits and misfires at sustained full throttle.

I dont normally notice it since I dont rev it out that much driving between the stop lights in London, but trying to hold it at max throttle the other day in second on holloway rd it first pulls fine but then when you hit the rev roof it first flattens out and doesnt increase revs any more and then after some second starts misfiring and spitting and scaring the s**t out of bypassers.

Tried repeatedly today and still does it.

Carb SH1/20 is setup close to standard (50/50/106) with only main increased to 112. Plug colour nice at a 3% oil mix.

Do you believe this is related to too rich main jet, timing (think I set it at 19-20°), original air box which is of the "restricting" early type or could it be the points system playing in...?

As mentioned the scoot pulls well through the revs with no hickups or strange behaviours what so ever besides this...

Anyone who has had similar problems or knows what this should be due to...?

[tea5ive]

points bouncing ?, you may have to do a bob dillan

[victor]

Could be, I think the rest is setup fine... How could that be proven and what can be done to resolve it?

[tea5ive]

if its the points bouncing at high revs ( higher now with the gori sport ?) and nothing else, may be borrow a clubman to tame the revs . and the sell your gori to me :anbrgin; . have a look in one of the old tuning books ken herlingshaw or dave webster there may be some info on how to beef up the spring tension on your points. cheers simon

Could be, I think the rest is setup fine... How could that be proven and what can be done to resolve it?

[victor]

Anything that can be done to rule it out...?

Wish the SIP Dyno app existed for the iPhone, then I could have measured the RPMs...

[coaster]

The points would be my first thought (after the plug), not necessarily bouncing though as unlkess your TV is running an original set (unlikely I would have thought) they were uprated when the GP was launched (double spring?) and were all that were available after that. More likely is that the gap has closed up or the surfaces have pitted and need filing/replacing.

[victor]

I believe the points gap should be correct (.4mm on top of my head) but it has passed half a year since I controlled them so might be time now... We are talking revs that feel very unsafe to sustain over any longer period I feel I must underline...

No one who suspects to rich main jet or air box?

Also to underline is the fact that loud bangs are heard and it feels as if you hit a plateau which it doesnt want to pass...

[coaster]

I think I know what you mean with the missfire, and it could be down to a number of things. As mentioned, the plug would be a prime suspect, it might be need to have a hotter running plug during the winter and is possibly fouling? The points we've mentioned but what about the fuel system? have you checked the fuel flow, is it a standard or fast flow tap?
Regarding the jetting, the cold weather will naturally make engines run leaner so I'd be wary of down jetting.

[wack 63]

Go up on the main jet, it's probably too lean or you are getting fuel starvation.

[victor]

Went up in steps from 112 to 118 today (106 is standard on a Tv that but that's with standard exhaust)j and I think it got better, feels stronger, especially from low revs...

I also richened the air mixture half a turn.

However it didn't cure the problem, I think it's less misfiring and revving a bit better but still not good enough.

Unfortunately I dont have a 120 jet but will continue tomorrow with 122 etc.

But doesnt it sound like a lot?

Or could it be that the Gori really requires so much more fuel?