Blowback through Carb 3

[Guest]

Afternoon all

I have spent the last 2 weekends trying track this down but not had much luck. I have properly stripped and dipped the carbs new orings all as recommended. I have put in new plugs, done the oil/filter change and this morning did the coil relay mod. The intake and airbox rubber boots seem fairly new so I have not replaced them yet but I will in time just so I know their history but I have checked them all and they are supple and not cracked or split so I am discounting them as the issue for now. I have the stock airbox in place except for the airbox cover which I didnt get from the PO so I have duck taped over the opening. I checked the cam timing when I did the valve clearances.

So after all that I tried to sync the carbs and the tube keeps blowing off the vacuum nipple and I can see the intake boot bulging under pressure surges. All the pliugs are very sooty after just running on idle and the choke doesnt seem to have much effect. the bike will start without choke but pulling the choke out doesnt increase the revs at all.

Any ideas suggestions tests that anyone can recommend? It sounded exactly like poor voltage to the coils so I did the relay mod but if anything its a little worse.

I'm stumped for now the only thing i can think of is that I have an intake valve sticking open.

Thanks
Tom

[rapidray]

You MIGHT have a bent valve if it is only blowing back in one hole. It sounds like you also need to adjust the mixture screws CORRECTLY. Ray.

[haggisbasher]

Thanks Ray

I was thinking it might be something liike that. I got a hold of a compression tester and the pressure for each cylinder

1 140psi
2 130psi
3 140psi
4 140psi

This is on a warm engine with the throttle held wide open. Does this rule out a valve issue? I set the screws at 3 turns out from seated as per all the advice here. I know I need to dial them in but I am having trouble doing that with the issue at hand.

Thanks
Tom

[Big T]

Thanks Ray

I was thinking it might be something liike that. I got a hold of a compression tester and the pressure for each cylinder

1 140psi
2 130psi
3 140psi
4 140psi

This is on a warm engine with the throttle held wide open. Does this rule out a valve issue? I set the screws at 3 turns out from seated as per all the advice here. I know I need to dial them in but I am having trouble doing that with the issue at hand.

Thanks
Tom

No bent valve there, but an adjustment is always needed if you haven't done one as yet

The lack of response from the choke (enrichener) circuit and the backfiring indicate the carbs did no get completely clean

[haggisbasher]

Thanks Big T
I followed the procedure to the letter even left them in the dip for 2 days each. time to try again I guess. I was pretty impressed with myself that it started at all after doing it the first time but at least I know \I can do it just need to try and be a bit more thorough this time.

Thanks
Tom