acceleration issues

[matakky]

Hello all,
i have an 82 cb750sc( nitehawk) DOHC, imported from Arizona to the UK, been restoring it for the last 2 years and now almost complete, i have overhauled the carbs replacing jets, needles etc and checked diaphrams and cleaned fully, when riding the bike if i open the throttle there is a lag in the acceleration, if i get up to the 3rd gear the maximum the bike will go is 30mph even with throttle fully open and it will not increase in speed anymore, there also seems to be no immediate acceleration which you would expect from a motorcycle.
 i have checked the spark plugs and plugs 1 and 3 are white so running lean, there does not appear to be any air leaks from the air box or to the engine, and the spark plugs are all firing ok, timing seems to be good also.

some hints or tips would be most welcome or any others with simmilar problems.

many thanks
mat.

[TOOLS1]

First thing I would check, would be for an obstruction in the fuel line, or pet cock.
TOOLS

[matakky]

cheers tools, i had checked the fuel tank internaly for loose debris and have cleaned the filter on the pet cock, also checked all fuel lines into the carb after reading some posts on the forum,i forgot to mention on my previous post , but i still have accel issues.

[Re-run]

White plugs indicate a very lean mix. Try closing the choke and see if things get better. Most likely, something is gumming up the idle circuit or the jets are too small.

[vern401]

It does sound like a fuel problem to me. Check your exhaust pipe temps. Be careful when doing this since they will be hot. What I do is get a water damp rag and tap each pipe. I have not tried an oven thermometer for this yet but it may be allot more accurate. A cold pipe is a firing problem, and a hot pipe compared to the others indicates it is running lean, or firing harder than the others. Some carbs are Hard to really clean out. You may still have some blockage in one or more carbs

[matakky]

Cheers Vern,
 I checked the Exhausts this morning and found that one of the cylinders was not firing properly, spark plug changed and that seems to be firing better now, bike still runs a bit rough tho, do you think the fact that i have an American spec motorcycle and therefore carbs which are setup for you fuel mixtures ( 89 octane level?) and i am trying to run it in the UK where our octane levels in fuel are 95 makes any difference with the running? will i need to get  UK spec carbs fitted?
 

[sgtslag]

The octane rating means how susceptible it is to pre-detonation only.  In other words, you can run any octane in your engine, as long as it doesn't ping on it.  If it pings, then up the octane rating to prevent it from pinging.  You will not gain any performance improvements by using higher octane gasoline, other than the pinging issue.  In colder weather, higher octane will make starting an engine even more difficult, so if you are in sub-freezing temperatures, try lowering the octane rating to improve starting.  Cheers!

[matakky]

sweet! cheers sarg