'75 CB360 Will Not Rev Over 3000 RPM

Message

Anthony M · #1 Unread post by **Anthony M** » Mon May 14, 2007 8:42 am

First post here! Im getting a CB360 together that I purchased for 25 dollars. The thing idles fine, has good low end, but will NOT rev over 3000 rpm under load. It Neutral it will rev fine.

The carbs have been cleaned and diaphragms are fine, synced as closely as I can manage, points gap checked, new plugs, spark advancer is not stuck.

I've cleaned the petcock out several times, and have inline filters in the fuel lines to make sure the carbs are receiving fuel.

What else should I check?

Thanks!
Anthony

Mon May 14, 2007 8:46 am

Sorry to break it to you, but it sounds like carbs.

While you may have cleaned it well, you also may not have cleaned it well. Also, if you aren't using an inline fuel filter between the carbs and the tank, you may have cleaned it well, and then "messed" it all to hell when a piece of crap from the tank came down the fuel line into the carbs.

When you clean them, make sure you can see through the jet. Sometimes foreign particles or gas varnish clogs it off so much that you need to put a small piece of wire through it to clean it out.

BuzZz · #3 Unread post by **BuzZz** » Mon May 14, 2007 7:09 pm

I would still suspect carbs as well.... but it could be low compression or tight valve clearances. But that's could be.

I still smell carb..... it takes more fuel under load (in gear) that under no load (revving in neutral), so I would guess the main jets are restricted or just too small (did the bike come from a location with a higher elevation?)

Anthony M · #4 Unread post by **Anthony M** » Tue May 15, 2007 1:30 am

Thanks for the replies. I will tear into the carbs today and clean 'em as thoroughly as I can. I hope it is simply just a carb problem...

The compression is ~160 psi in each cylinder. I haven't check the valve clearances yet...

The bike has been sitting since the late eighties, but only has 6900 miles on it, hopefully I can still get to where it should be!

Thanks

Nibblet99 · #5 Unread post by **Nibblet99** » Tue May 15, 2007 1:58 am

storysunfolding wrote:When you clean them, make sure you can see through the jet. Sometimes foreign particles or gas varnish clogs it off so much that you need to put a small piece of wire through it to clean it out.

Probably nothing to worry about, but I was taught to use nylon fishing line, as it will not scratch the carb, unlike wire. I personally can't see a scratch doing much, but then I've always had some fishing line kicking around the place, so don't know from experience

Anthony M · #6 Unread post by **Anthony M** » Tue May 15, 2007 7:12 am

Problem Solved!

The first two times I went through the carbs, I didnt realize the needle valve seats in a jet (Main?). This jet on the left side carb was about half plugged.

Bike accelerates great now!

Only problem is, now I have a hanging idle....
When I rev it up, then let off the gas it sits at about 2500 rpm for 2-3 seconds before dropping to idle.

Vacuum leak maybe?

Thanks guys!!

CORSCO · #7 Unread post by **CORSCO** » Tue May 15, 2007 3:13 pm

With the throttle hanging, check your throttle cables and make sure the throttle pulley is returning all the way to the idle screw stop. Also it may be a lean condition. Try turning out your mixture screws to richen up the idle circuit.

Anthony M · #8 Unread post by **Anthony M** » Thu May 17, 2007 6:18 am

Just to follow up on this, the hanging idle was caused by an obscenely low float level in the right side carb, obviously creating a lean condition.

I put new intake manifold gaskets in and reset the float level in both carbs. She purrin' about as good as a 30 year old bike gets!

Thanks for the suggestions!

Johnj · #9 Unread post by **Johnj** » Thu May 17, 2007 8:26 am

Now you owe us pictures. Don't keep us waiting.