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1990 VFR750 Carb Settings

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I have a 1990 VFR750 that I have returned to the road after many years of sitting around ( 15,000km ) ( 9000 miles )

To give you an idea as to the current condition of the bike the following may help

Carbs totally torn down, cleaned and redone with new gaskets and fuel lines

Thin washers under the needle jets to raise them a hair to help with the filter and exhaust

Carbs balanced

I have a K&N Air Filter as well as a full Yosh. Exhaust system

New plugs

New Honda thermostat and hoses

Upgraded Voltage Regulator

The problem I am having is that the bike is just not running right

The following is an overview

In warm weather it will start from cold without choke

Once warmed up it will idle just fine but if you hold it at say 3000rpm she sounds like she is fluttering

When you take it for a run you want to keep the revs at around 5000rpm due to her feeling like she is not stumbling, if you creak the throttle past 5 grand she pulls like a freight train to red line

During the ride, at stop lights you may have to feather the clutch when you take off or she may stumble

I have noticed that based on the temp gauge it is hard to get the needle past the start ( bottom ) of the normal range during the ride

Once I have it back home if I sit there and blurp the throttle the revs will sometimes hang around 3 grand and after say 5-10 seconds it will settle  back down to a nice 1000-1200rpm  idle

During this Blurping you can see black exhaust blow out of the exhaust

So Guys what do you think

Too much pilot jet ( set at 2.5 turns out )

I screwed up installing the washer under the needle jet

Something else I am not thinking of




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Sounds a bit rich for lower throttle openings. You’ve changed a fair number of things that have some influence on air fuel ratio, washers under jet needles could be too thick, 2.5 turns out on idle mix screws is enough if not a bit much(they’re fuel, not air). If the filter requires oiling it might have too much applied. Richness can be caused two associated ways or a combination of both, too much fuel &/or not enough air. If you changed the foam in the sub-air filter it must breathe as freely as the OEM material, found out about this the hard way, thinking a denser (improvised) version would last longer... Can cause symptoms similar to what you describe. 

Should be interesting to hear your eventual solution(s)

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check the charging system output. consider cleaning and gapping or replacing plugs. signs suggest you may need  use a bit of cardboard to block about 1/4 of the radiator.  have you checked float levels ? blow out/clean air filter, and check tightness of carb boot clamps. even one leaky float needle or improper float level setting could be causing your symptoms.

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