The International CBX Owners Association

Hi all
6 Months ago I purchased my 1st CBX, it was it pretty poor shape, could not be ridden but the owner fired it up and it idled quietly and responded to throttle Ok. So started a frame up rebuild, on removing exhaust noticed exhaust valves looked a bit oily so decided to give it a set of rings, valve stem seals and lap valves, set cams as per the manual, long chain must have stretched as could not get punch marks to line up exactly (cams running retarded) - Bought and installed master overhaul kit for cabbies, set valve clearances had to adjust 3 that were too tight. Engine was hard to start but got it going, it would idle OK but any attempt to open the throttle it would stall, if choke was fully closed engine RPM would go up and you could open the throttle, was able to ride it, but no power, ran better with choke on, seemed to come OK at higher RPM, I am thinking big air leak, replaced carby clamps, not the problem. So I thought I will connect a vacuum gauge, the gauge went crazy back and forth, I noticed I was actually getting a positive pulse, air pushing out of the vacuum fitting. OK now I am thinking valve timing, can the chain be stretched enough to do this? If so why did it run when the original owner fired it up? At a loss at the moment, thinking I will put a degree wheel on it and see if I can determine what is going on. Did compression test on number 6 90psi hot with throttle open. 1981 Prolink
HELP!

Your compression is way too low. With new rings you should have 150 + . Are all 90? Did you do a wet test after you lapped valves? They should hold fluid for 3-4 minutes. You need to get compression up. Even after that you might have carb issues.

I'm with Terry - compression is too low. You did a lot of things - any one of them screwed up could be a problem. Assume you got the valves reseated fine - I think your cam timing is off. I would NOT run it again until you rechecked that. The carbs are likely another problem.

Dave

Stevo wrote: set cams as per the manual, HELP!

What manual are you using? Make sure you have a later one that includes the revised procedure. The early manuals had a wrong cam installation instruction.

Thanks for the replies, yes I know compression is way too low, either there is a problem with rings, valves or cam timing, as I mentioned vacuum is all wrong, I am getting air pulsing out of the vacuum port weird! I don't think there is a carb problem, need to get some vacuum there to get them to work properly, What is the part of the cam timing procedure that is wrong in the manual? Is it possible to swap the left exhaust inlet cams? I am so over it at the moment I don't want to look at it. I am also restoring a VFR750 so working on it at the moment. I have built hundreds of engines over the years mostly V8 car engine, this one has got me scratching my head.

Have not compression tested all cylinders yet, will do that and also a cylinder leak test, to see where compression is going.

Stevo wrote:What is the part of the cam timing procedure that is wrong in the manual? Is it possible to swap the left exhaust inlet cams?

Hi,

The very early manuals had the wrong procedure for installing the cams - resulting in one set of cams being 180 degrees out. When correctly installed, at TDC, #6 cylinder cam lobes should both point to the spark plug and #1 lobes should both point away (or vice versa):
For the left side cams, yes inlet and exhaust cams can be swapped inadvertently (they are both marked EX or IN).

Paul.

Thanks very much Paul
I have compression tested all cylinders, all at 90psi warm throttle open - I purchased the rings online they came in unmarked individual sealed bags, maybe they are crap! I Knew about the timing issue, that was definitely correct, I marked the cams when they cam out but suppose I could have mixed up somehow and got the left ex and in , will check that 1st, if all seems OK will open engine again and replace rings, what rings do you recommend and where to get them?
Thanks again, Steve

Have rechecked valve timing and left ex and in cams are in correct position, I guess I will have to remove engine and strip down and do a wet test on valves, think I will replace rings with a set from IMD, install a new cam chain and start again, funny how trying to save a buck ends up costing you more. Will repost if I find a problem.

Ok found the main problem, a bit embarrassing but have made mistakes before and will probably make some in the future. Carby No 2 had the piston stuck in the fully up position, how it got there I can't explain, why it was stuck was because the screw holding the piston bell or housing, which also holds a little flexible clamp for the vacuum pipe to the fuel cut-off was loose, this caused misalignment and piston jammed. This explains why the engine would idle OK but as throttle was opened a huge air leak was introduced through the balance tubes to all carburettors causing stalling rough running. If the balance tubes were not there then I would have had one cylinder not running. The air balance tubes can cause an air leak to effect all cylinders.
Does not explain low compression, maybe rings need to bed in before compression pressure will reach 150 psi. I noticed the problem after engine was out, so will put a branded set of rings in to be sure. At least I found an issue that explains the symptoms.