cb350 not receving enough fuel when throttle fully opened

[Oldstuff315]

Hello any help is appreciated I have my mechanic working on final adjustments on my 69 Honda CB350 converted to a brat style he is very skilled with Hondas but very stumped by this issue. Have Mikuni vm30 carbs with cone filters that came with it from speedmoto along with new stator, rectifier, ignition coils, points upgraded the jets to the following
P-6 176 Needle Jet
6L1 Jet Needle
1.0 Air Jet
25 Pilot Jet
130 Main Jet

Mechanic has everything dialed in compression, timing etc
Kicks over around the third kick but in order to do that he has to remove the air filters from the carbs kind put his hands over the carbs air intake bike will sit there all day and idle terrific untill you start to open up the throttle it is bogging down and just seems to be loosing fuel intake

 

[redwillissuperman]

Re: 69 CB350 Idling

Yup.

While it can be done right, the VM30/32 etc swap is not bolt on. This "upgrade" migrated over from road racing where you are full throttle on higly cammed and increased compression machines.

 

[barnett468]

.
do you have a butterfly choke?

you have a problem because even without the filters, he should not have tp put his hand over the carb to start it so your butterflies dont work or the pilot is too small or the gas level in the carb is too low.

post a photo of the inside of the filter end of your carb.

some cone filters cover a port that is in the top of some carbs . . the filter needs to be modified to allow clearance there.

also, some cone filters have an edge that the air rams into when the throttle is open which can cause perf probs . . basically, most cone filters suck.

if it burbles when you open the throttle, it is rich . . if it just hesitates then revs up, it is too lean . . remove the f'n filters and raise the needle all the way and if there is no improvement, lower it all the way.
.

;

 

[carnivorous chicken]

Something else to check: if you've recently put a new seal on your gas cap (or I guess even if you haven't), check and make sure that the vent on your cap isn't clogged. Just unscrew it and see if that solves your problem. Shit can get caught in there and partially or fully block it, and that'll lead to fuel starvation.

 

[crazypj]

.
do you have a butterfly choke?

For someone who 'knows so much' about carbs you really do seem to know very little.
VM carbs don't have a 'choke, they have an 'enrichener' which is basically a tiny carburettor built into side of main carb body with around a 1.25mm hole as a jet on a ~8mm 'slide'
If OP is using carbs 'straight out of the box' they will never work right as they come 'pre-jetted' for a mid 70's two stroke dirt bike :
SUDCO may be great to work with but their 'proprietary' jetting totally sucks and I'm not at all impressed
The VM's are going to need a LOT if work to run right, time involved is going to be pretty high
OP, I hope your mechanic is giving you a great deal for the 'learning experience he's getting

 

[barnett468]

For someone who 'knows so much' about carbs you really do seem to know very little.

SUDCO may be great to work with but their 'proprietary' jetting totally sucks and I'm not at all impressed

Hy Barn,,,he's "not at all impressed.".

. .