CB500 Four 1976- some issues!

[exelbyt]

Hello all i need your advice.

I have a 1976 Honda CB500 Four. I bought it three or so years ago from a fellow member of this forum called steve. I have got the bike through a mot after being sorn and been sculpting it into what i want it to be. (See photos). The main change is that the tank, seat and handlebar set are new and i have fitted yamaha xj550 maxim wheels and sprocket (which is noticeable larger than the original 34t Honda one)

Here are some issues i am now encountering;

1. The worst bit- the engine revs uncontrollably. At first it would only do this in neutral but recently these revs are actually driving the bike.  This makes cornering difficult.  I have checked the carbs and the idle screw.  I think air must be getting in somewhere between the carb exit and the valve. Thoughts?

2.  The large sprocket from the xj550 is too big for the engine and gearing. It accelerates but has not top end.  Does anyone know of a sprocket which would fit the wheels (xj550 maxim) 5 bolts but be closer to 34t?

3. In braking the front forks are compressing (as usual) however the front wheel is turning to the right (sligt feeling) . (Disc and caliper are on the left) what does this mean?

All any any advice are very welcome!

Regards


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[Chris400F]

2.  The large sprocket from the xj550 is too big for the engine and gearing. It accelerates but has not top end.  Does anyone know of a sprocket which would fit the wheels (xj550 maxim) 5 bolts but be closer to 34t?

Increasing the front sprocket size would have the same effect as reducing the rear and may be easier to achieve, assuming no problems with clearance in the casing.

[K2-K6]

For the front wheel turning right under breaking I'd first look at the pinch bolts of the top and bottom fork yokes to make sure they are tightened properly, then also how the spindle is clamped to the forks. Many spindle clamps go on one way only to make them secure when tightened.

[Aly-b]

1.Could the throttle cables be fouling under the tank?

[florence]

With regard, to the front forks flexing I notice you do not have a mudguard so there's no fork brace.  I don't know how much difference it makes because I haven't ridden one without a mudguard.

Also, if you are using that wheel, is it possible that the disk is out of alignment with the caliper?

[SteveD CB500K0]

Hi Tom.

I was thinking of you the other day as I was cleaning "Goldie".

You've made good job of that - only the custom-built sidepanels gave it away for me.

I'd make sure that the throttle cables aren't jamming too. Is the throttle stiff?
Runaway revs usually means that the slides aren't returning in the throttle bodies (ie sticking).

Is the bike still in Berkshire?

Steve

[Bryanj]

500 forks badly need the steel mudguard as a fork brace, or an aftermarket equivalent

[exelbyt]

Hi Tom.

I was thinking of you the other day as I was cleaning "Goldie".

You've made good job of that - only the custom-built sidepanels gave it away for me.

I'd make sure that the throttle cables aren't jamming too. Is the throttle stiff?
Runaway revs usually means that the slides aren't returning in the throttle bodies (ie sticking).

Is the bike still in Berkshire?

Steve

Hi Steve,

I am not far away in Hampshire nr basingstoke.  Throttle cables are new and lubed up.  Carbs have been fully stripped and cleaned.  I think now it may be time to take the head off and investigate further.  I asked nick robinson (@nickrobinsons motorcycles) and he suggested the head gasket.

Also i am looking for classic ride out in the area if your know any?

[exelbyt]

500 forks badly need the steel mudguard as a fork brace, or an aftermarket equivalent

Seems to be a common theme here - i will try adding a mud guard

Thanks for all the replies!

[matthewmosse]

I had a weeping head gaskett for years, in my case I had no issues with tickover being high. I read somewhere that Honda cables are tefalon lined and may swell if oiled, but a remote fuel supply rigged up should give a clear view of if the carbs and cables are free to move their full range, and give access to try spraying something like wd40 onto the inlet tract to see if it highlights and inlet leaks, I personally suspect it is how the cables are routed from carb to twist grip or someting jamming against part of the carbs. I take it the choke is working normally.

[exelbyt]

I had a weeping head gaskett for years, in my case I had no issues with tickover being high. I read somewhere that Honda cables are tefalon lined and may swell if oiled, but a remote fuel supply rigged up should give a clear view of if the carbs and cables are free to move their full range, and give access to try spraying something like wd40 onto the inlet tract to see if it highlights and inlet leaks, I personally suspect it is how the cables are routed from carb to twist grip or someting jamming against part of the carbs. I take it the choke is working normally.

I will try the WD40 trick.  The throttle cable is brand new, is routed freely to the carbs and the carb has full range of movement and rests on the stop when the throttle released.

[florence]

I notice that like me you have an adventurous exhaust pipe.  Have you increased the main jet size?

[Bryanj]

Plastic mudguard only works if you use the original bracket to fit the blade to, rubbers between carbs and head can leak as can the O rings between the alloy manifolds and the head. In a lot of years i have NEVER known a head gasket leak give high revs. NB clamps on the manifold rubbers need to be the narrow honda ones NOT jubilee clips

[exelbyt]

PROGRESS REPORT;
I have now sorted all the issues by replacing the sprocket to one closer to stock (35t) and rebuilt the carbs.

The latest issue is to do with tuning the carbs.  I have scoured all the threads on sohc and found a wealth of information about carbs etc.

I am currently running
100 main, 40 idle jets
1 and half air screw
Clip position 4/5
With the same exhaust and air filter from the picture about.

It still isnt running right.  There is a flat spot which occurs at 1/2 throttle and since i change to 100 main jet (from 130) it has been stalling intermittently at idle after a short run. Up until 1/2 throttle it seems to purr fine, but after 1/2 and about 5000revs it doesnt seem to be firing on all cylinders.

Any thoughts? Or any good ideas on where to look for advice?

Thanks!



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[JamesH]

Are you running the stock factory Airbox and intake stubs?