Author Topic: cb750 bogs and backfires  (Read 2052 times)

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shooty

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cb750 bogs and backfires
« on: June 17, 2005, 08:20:39 PM »
The bike idles fine but bogs when given full throttle and backfires whenever i let off the gas. I have velocity stacks with a 4-1 exhaust. I'm guessing i have to adjust the needle jet..plese help. I know this is a newbie question but i have searched and really havent found the right answer.

Offline TwoTired

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Re: cb750 bogs and backfires
« Reply #1 on: June 17, 2005, 10:16:11 PM »
Pull your plugs a compare them to the pics at:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

This should give you an indication if you are running rich or lean.

It also helps if we know what year model you are working on.  There are different carbs across the years, for example.

Temporarily mark your throttle grip so you can tell when you are at 1/8, 1/4, 1/2, and 3/4 throttle.  At these throttle positions different parts of your carb are dominating of the mixture.  To do a complete carb adjustment you'll have to read your plugs after operating at each of these settings.

Finally, do all the other tuneup items before matching the carb tune to those settings.  Plugs, points, timing, cam chain, tappets, and clean air filters need to be at ideal conditions.  Carb sync verification is wise, too.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline dpen

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Re: cb750 bogs and backfires
« Reply #2 on: June 18, 2005, 08:32:26 AM »
re-jetting is what is required. Fitting stacks & not upping the mains gives you heaps of noise & no power (sucking all air, bugger-all fuel).
As for backfiring, there are several posts on this.
Causes range from needing a good tune to a sloppy muffler on your 4 into 1.
Dave