Topic: CB 350 Four power loss at 3500 rpm

[thomas evensen]

After rebuilding a CB 350 four, the engine starts very easy, and it idles fine.

When taking it to the road, I experience powerloss at about 3500 rpm,
and the bike makes a top speed of 35 mph / 55 km/h. The spark plugs are all black
and dry. When more throttle is applied, the engine gets sluggish, and it sounds
like it misfires.

Any ideas?

I have checked the ignition with a strobe, and it looks correct at both 1200 rpm
and 3500 rpm. I have done a rebuild of the carbs, using a rebuild set. The floats
are adjusted, but I do not know if I did it correct. I had the carbs upside down,
and the top of the floats were at 21 mm when the float touches the float pin,
not compressing it. Will this be the same as measuring the float height having
the carbs in normal position (not upside down)?

Thanks!

greetings,
Thomas Evensen

[MetalHead550]

Sounds like your plugs are carbon fouling...too rich.  Dont know the specs but your floats could be set to high, allowing too much gas in or it could be as simple as leaning with the mixture screw.  A synconization of the carbs is definitly in order after a rebuild.  Do a search on that.  As for reading your plugs...http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

[don_m]

You said the carbs were upside down when you checked the float level but the float pin was not compressed.  Those pins compress very easily & it's best to hold the carb body horizontily with the float dangling, just touching the pin.  Also check to see if nothing is obstructing the airbox inlet under the seat.
No more posts, now as it's time to RIDE!
Cheers, Don Psycle Madden.

[Gordon]

What was the size of the main jets that came in the rebuild kits? 

[thomas evensen]

You said the carbs were upside down when you checked the float level but the float pin was not compressed.  Those pins compress very easily & it's best to hold the carb body horizontily with the float dangling, just touching the pin.  Also check to see if nothing is obstructing the airbox inlet under the seat.
No more posts, now as it's time to RIDE!
Cheers, Don Psycle Madden.

Thanks.

I will recheck the float level tomorrow. Regarding the airbox inlet: I have put a self made plate on top of the filter box, because I do not have the original part (I suppose there shall be somethingn covering the air filter box?). The air filter element is new.

Thomas

[thomas evensen]

What was the size of the main jets that came in the rebuild kits? 

One strange thing is that there were no printing on the main jets. The pilot jet had size
printed on it, and it is correct according to specifications. I also double checked that the
rebuild set was for CB 350 F.

Thomas

[Harry]

Try taking the plate off the airbox - this could lead to rich running!!

[jesse]

since you say it starts very easily,i would say you need to check that the choke is opening all the way and make sure the needles are in the center notch to begin with.if all else fails put the old parts back in the carbs.some of the kits leave a lot to be desired as far as jets and needles go.

[thomas evensen]

Thanks to all of your tips, the bike now runs perfect! The spark plugs are just the right colour

There were 2 major problems:

1) My seat is obviously so disformed, that it blocks the air intake completely - solved this by taking
    off the upper rubber part of the air intake.

2) The float levels vere about 0.5 mm wrong.

Thanks a lot!!

greetings,
Thomas Evensen

[don_m]

Chalk another one up to the group & thanks for the de-briefing.  It is hard to trouble shoot long distance without feedback.
Cheers, Don Psycle Madden.