Honda-SOHC

This is doing my swede. Those dammed carbs. I cant understand it, i've had them apart so many times now its stupid. There seems nothing wrong with them. The bike pulls and drives away absolutely perfectly when cold or warm but as soon as it gets hot the problem starts. The exact problem Dan and lots of others have.

What I cant fathom is that its all 4 carbs. Plug chopping the bike flat out and at all speeds the plugs are the most perfect light tan colour. Leave it  ticking over though and they go sooty black.

There is one thing of concern and that is when the bike is hot an awful lot of steam comes out the breather. Way too much. So I pulled the airbox breather pipe off and left it dangling, things improved, but the steam was still pouring out. It suggests that there is blow past on the pistons and maybe i have a stuck ring or something, but this thing runs so smooth and doesn't smoke at all. 

The air screws seem to have little effect past 2 turns out yet if if i screw them in to 1 turn the bike will stall. 3 turns or even 4 turns makes no difference. Normally twiddling an air screw makes the engine speed up or down.

I have to say its been getting better every day and it is now quite nice but its definately still there.

Floats are 24mm, airscrews are 3 turns. Number 2 carb does occasionally overflow. Its always number 2, the others are fine, so it looks like I'll have to re-examine no2.   

Oh well more head scratching....hahaha

Well I got that wrong....It was seriously rich on the primary circuit not lean. I still dont know why. 2 turns on the air screw as my manual suggests leaves it 'hunting' away with sooty black plugs. 3 turns and its settled down to a nice throttle response, even tickover, and much cleaner plugs.
   I noticed when running it on my plastic bottle that as the fuel runs out (less in float bowls) it switched from eratic and lumpy to running lovely. Float heights are set at 21mm as manual. Its a strange problem. When cold the bike ran great, no choke was ever neede though. It all suggests a blockage in the air feed to the mixture screws, but i cant find any problem.

Turn your fuel off and see if yours improves (cleans up) as the petrol runs out (after say a minute on tickover). Makes a huge difference to this one. Suddenly it will purr at 800-1000 rev perfectly. Turn the fuel back on and it starts the lumpy horibleness again after a short while. The weird thing is that its all 4 cylinders affected exactly the same. I could accept one carb having an issue but not all 4 with exactly the same problem. It like someone has put a pin hole in all the floats. haha

I've not bothered connecting any throttle cables or airbox rubbers while I sort this so I can get them on and off quick. They are off again this afternoon for a final inspection and to set float heights to 22mm. 

At one point last night an awful lot of 'steam' was comming from the engine breather, mind you I had had it on tickover in the garage on and off for about 4 hours - engine was very hot.

Final go later today...on 3 turns out its very good, so if I cant find anything else thats what I'll leave it at and give the bike a good whizz around - do hundred miles on it and see if things settle down.


Edit:-

oh another thing....that foam breather filter at the bottom of the airbox...blimey that was just wet oily dust...it was horible.

Hmmmmm.. Ive just had a search around and it seems this is a very common problem with these carbs. It has to be floats. It has to be. haha. Well fuel levels in bowl..arrgh...I'll check that with a tube later.

Dont go there...leave well alone..screwing up the carburation is a nightmare..  haha. Absolutely no point anyway, the carbs dont hold it back - as proven by 460 kits practically doubling the power of the bike but with the same carbs.

Tom,

     Sounds very similar. On this one the header pipes are mint, actually look brand new. The silencer though showed bulging on the outside where the baffling was spot welded in. The first thing that happened was a large hole appeared in the recessed back bit next to the exit hole. The insides had allready well rusted and collapsed - you could here them rattling about, and exhaust was noisy. I was giving the bike a bit of a gunning when the sound levels rose to unbearable and the whole lot disintegrated.

     Wheel rims are good, spokes are average, chainguard is mint, all handlebar controls, headlight etc mint, mudguards very good - not polished them up yet to see just how good. Paintwork could be new, not even a scratch. Engine paint not as good as I first thought. All ancillary components and brackets really good and everything comes undone no problem.

    I cant remember how fast these things go, speedo said 90mph upright against wind and it seemed about right. Took a while to get there though. Acceleration is tame and requires lots of revving. Tootling about upto 60/70mph is absolutely lovely (I must be getting old). I'm 5'11 but I still find it quite comfortable - especially compared to my Thunderace.

    I do have a soft spot for these SOHC bikes, I raced a 550 and won a club championship on it, my mates had them as road bikes and they were all thrashed to absolute near death racing RD's but unlike the RD's -  no blow ups that I can remember. They were 460'd,  yoshimura'd, piper'd and ace bar'd. fancy seats , crappy paint jobs, culminating in total abuse. I bet most of them would still go with a little tlc. lol

Looking forward to a quieter less eventful ride in a few days. No more 'carb tuning' required I hope, it should be back to how it should be. A smooth quiet pleasing little thing.

I wont want to give it back.....he wont use it...I bet its on Ebay in a few weeks.

I bought a secondhand stand from the US. Cost me $15 and looked like new. Came with greased up pin. Wasn't worth the effort of fixing my rusty old multi wintered seized solid thing.

Back on the case..... my O-rings arrived...4mm id 1mm section seem to do the trick perfect.

My mate turned up with the head...Firstly its a black painted mess...its been 'chiselled' off its previous engine, gas flowed by an idiot, and half the exhaust studs are snapped or stripped. Oh and a Broken fin at the front...valves and guides seem good though, and not a mark on cam bearings...strange. So a quick wash down and both heads in the oven tonight for valve and guide swap.. Should be riding this by the weekend. Will knock out the broken ones first just to see what happens and how dodgy they are to do.

Must remember to take my camera in the garage tonight.

Well after a ton of effort...carbs all done except main jet O rings...As I am always searching for tiny o rings I have bought a large selection of viton o rings between 3mm and 6mm ID of various sections from 1mm -  all less than £20. Wont be here until next week. Should have rest of bike ready by then.

Carbs came up surprisingly well, they look very good on the outside and as good as any other set I've seen on the inside.

held up camchain and kicked engine over last night until oil spewed from barrel feed holes. Didn't take long.

All looking good ....come on matey with the head (the Senior is today so he should be back tomorrow).