Vintage and Classic Hondas

Re: cb750 popping/backfiring

Posted by samgrylls on May 14, 2013; 3:48pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/cb750-popping-backfiring-tp4040698p4040747.html

Thanks for the advice. The previous owner said he just replaced the battery, plugs, and oil, but I'll check them anyway. I just put in a new fuel filter, too. I'm planning on checking the valves and cam chain tension today, hopefully I'll down the rest of the list soon.

The bike pops when it's cold or warm. I've typically let it warm up for about 5 or 10 minutes, maybe it needs longer? Also, when I cleaned the carbs, I made sure all the jets were clean and put back in the right spot. I could check again, but I'd rather not take the carbs off if I don't have to.

On Tue, May 14, 2013 at 9:23 AM, seestheday [via Honda CB750'S] <[hidden email]> wrote:

Like Lucky said, you need to do a full tune-up.

Tires - are they older than 3 years? If so, plan to throw them out and get new ones, doesn't matter how much tread is left - you REALLY don't want a blow-out at speed.

Oil/filter change - Rotella T 15W-40 is decent and cheap

Valve lash - get them between .004" and 0.006" (very important!)

Compression - Ideally at 170 psi and all 4 within 10 psi of eachother, but 150 is considered to be quite good. Bike shouldn't run at all if they get below 100 (most engines won't).

Spark Plugs - NGK DE8A (stock) or DR8EIX (Iridium upgrade). Don't use anything else. Replace them if they're fouled.

Fuel filter - make sure you use one (paper is best) and put it between the petcock and where the fuel goes into your carbs

Fuses - check them to make sure they're all in good condition

Battery - get it load tested at an auto parts store (every one I've been too will do it for free), or just plan to use a brand new one.

After all of this is done, you should then start to look at your carbs and check your timing.

Regarding the carbs - you mention that you jump from 2700 to 3100. Are you sure that you put the jets back in the right spot? Here is a quick video I made showing the locations:

Also, has the bike fully warmed up when you are hearing the popping, or is it almost cold?

1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals

My wife's recipe website that I'm trying to help promote: BuffyAndGeorge.com. Yes, I am a lucky man.

If you reply to this email, your message will be added to the discussion below:

http://honda-cb750-s.456789.n3.nabble.com/cb750-popping-backfiring-tp4040698p4040741.html

To unsubscribe from cb750 popping/backfiring, click here.
NAML