Newly recommissioned CB500

I have agreed to help the bereaved family of a recently passed-away friend by recommission his CB500. It is a 2002 model with a good history, but has not been MoT tested (and therefore I suspect not used) since 2018.
I checked over the fluids, and had to fit a new battery, but to my surprise it starter quite easily once I’d worked out which was the fuel tap and manual choke worked.
Once started the motorcycle soon settled down to an even tick over, the clutch and gears work, as do all the electrics and the engine soon gets up to working temperature (I can hear the fan cutting in and out). 

When I first got it going (a week ago), it would only rev to 3,000 RPM, since then I’ve drained out the 5 year old fuel and replaced it with new. There has been some improvement in that the engine will now run to 6,000 RPM, but then just stutters and the revs fall back to 3,000. Everything else operates as expected.

Mechanically everything is running as I’d expect, so it would seem this is either a fuel system or ignition issue. I have not taken the plugs out for a look yet, but that may be a good thing to do next. Does this sound like something that might clear with the new petrol, or should I be looking deeper for a problem?

I’d like to get the motorcycle re-commissioned and through the MoT so Shaun’s step-son can ride it in the summer (after passing his direct-entry test).

Any ideas on the fault or advice would be appreciated.

Alan

Sad news and well done for your efforts.
First thing would be to take the petcock (fuel tap) off and there will be a mesh screen that should be part of the petcock which may or may not come out when you remove it, this needs removing and cleaned, then check to see if there is any rust etc in the bottom of the tank that requires removing. 
This may well solve the problem esp if you run some PEA based fuel system additive when you put the new fuel in to remove any gum in the carbs. 
If it still stutters then the carbs will prob require removing and cleaning.
You should also look to put new tyres on it as they will be past their best

Al1040

Sad news and well done for your efforts.
First thing would be to take the petcock (fuel tap) off and there will be a mesh screen that should be part of the petcock which may or may not come out when you remove it, this needs removing and cleaned, then check to see if there is any rust etc in the bottom of the tank that requires removing. 
This may well solve the problem esp if you run some PEA based fuel system additive when you put the new fuel in to remove any gum in the carbs. 
If it still stutters then the carbs will prob require removing and cleaning.
You should also look to put new tyres on it as they will be past their best

Wonderful, many thanks.

I’ll certainly give the petcock filter a clean. I’ve already checked the tank and can report it is remarkably clean. I drained the old fuel via the two float bowls into a transparent plastic bucket and was really surprised to find no solid contamination.

The PEA based fuel additive is a really good idea, thank you for that. I’ll certainly get some this week and run it through with the new petrol.

The tyres (and brakes) seem to be almost unused. Shaun only bought the Honda about 6 years ago, it may well be that it came with new rubber. I’ll check the date codes on the tyres.

Many thanks, I’ll report back with a nice photo once I finish the recommissioning and get the MoT. I’m so pleased the family want to keep the bike, it is what Shaun would have wanted.

Alan

This post is just to test the serving.com account that came free with the forum:

cleaned air filter ?

Remove the tops from the carbs to make sure that no debris is in there which prevents the slides from opening fully. Quite often the foam from the sub filter, the little black box disintegrates and ends up in there.

ANDYC wrote:Remove the tops from the carbs to make sure that no debris is in there which prevents the slides from opening fully. Quite often the foam from the sub filter, the little black box disintegrates and ends up in there.

Thank you.

I had been wary about dismantling the carburettors, but I have ordered a Honda workshop manual (on a CD) which should be here in a few days, so I'll certainly tackle that job. This does seem more likely to be a carburettor or fuel system than anything else.

Alan

Hi,
I've had rev-related annoyances getting a couple of cb5's back on the road. Have a look at the vacuum hose that is on the left of the bike and goes from the petrol tap to a small pipe see on the engine. If its got any splits/frayed ends it'll mess the fuelling up a lot. Also, the rubber carb intakes have got to line up just so, took me ages to work this one out, 1/4 inch difference = much head scratching.

all the best

muttley1

muttley1 wrote:Hi,
I've had rev-related annoyances getting a couple of cb5's back on the road. Have a look at the vacuum hose that is on the left of the bike and goes from the petrol tap to a small pipe see on the engine. If its got any splits/frayed ends it'll mess the fuelling up a lot. Also, the rubber carb intakes have got to line up just so, took me ages to work this one out, 1/4 inch difference = much head scratching.

all the best

muttley1

Many thanks,
At the moment the motorcycle is being stored in a garage about half an hours drive from my house, I think what I’ll do is bring it back here on my bike trailer at the weekend so I can go through it methodically to find the fault. As you suggest the problem could be with some little pipe not sitting quite right. Once I have the motorcycle here I’ll post some better pictures and words.
I’ve bought a Honda workshop manual (on a CD) that seems very good, between that and the good advice on this forum I’ll get to the bottle of the issue.
Alan

jets are blocked , partially blocked 
the main jet mainly

panagiotis wrote:jets are blocked , partially blocked 
the main jet mainly

I'll check that out, many thanks.
Alan

Good morn again,

After a bit of a bit of a delay I’ve collected the CB500 from my deceased mate’s family today and got it started. It will only run with almost full choke (the lever pulled almost all the way back), and then the tick over is at about 2,000RPM, even when warm. It sounds very much like a fuel issue, probably carburettor just needing cleaning.

My plan is to remove the spark plugs and have a look first, this probably won’t tell me much as it has been running with the choke on. After that I’ll take the tank off and remove the carburettors for inspection and cleaning.



I’ll report back over the next few days on what I discover.

I had only about an hour of tinkering time today, but have done some reconnaissance.

The petcock seems to operate fine, the vacuum device works in both on positions. The plugs didn’t look too bad for a motor that has been operating exclusively with the choke (fuel enrichment device). I cleaned and gapped them, then replaced them.

The motor seems to run only with the choke operated, even when warm. It seems most likely that the engine is receiving fuel only from the fuel enrichment device, so the most likely explanation is the jets are blocked. I doubt that the motorcycle has been used in at least 5 years (the last MoT expired on 5 June 2018), so the residual fuel has probably turned into wax.

I should have more time tomorrow, so I’ll remove the carburettors and start cleaning then.

The rest of the bike seems to be okay (only 14,000 miles).

I agree with that suspicion

That was a good morning’s work. The CB500 is typical Honda: really well made with very nice engineering. The Honda workshop manual is very clear, so it didn’t take all that long to get all those pipes and stuff out of the way. Getting the carburettors out of the frame is a bit of a mission, there is about 2mm of clearance, but they came out in the end.

Rather as I’d expected the float chambers were horrible - full of crap as you may see here:



All 4 jets were encrusted, so I gave them all a soak in acetone then blew them through with cleaner. I had to replace a few JIS screws, and have reassembled all the seals with a WRAS grease and everything that moves (cables and so on) has been lubricated with copper grease.

The motorcycle was a bit easier to put back together than it had been to take apart, and I fixed a few little issues (like the battery box, why can’t folk just put the correct parts together in the right order?) on the way.

I decided to leave the top of the carburettors along for today as I didn’t have any replacement diaphragms to hand. I’ll see how it runs and if necessary re-visit that (without having to take the carburettors out again).

The motorcycle started up easily with the choke, and once warm would run without it. After the slow running screw was adjusted a bit it would tick over reliably at 1,200 RPM. It will rev all the way round to the red line now, but has a misfire at about 6,000 RPM. I have no idea about the gas inthe tank, it might even be 5 years old, so I’m thinking I’ll put some fresh gas in this afternoon and try it out before I start trying to fix something that might go away of its own accord with a bit of running. I’ll change the oil, check and adjust the fluids, chain and tyres then get it booked in for a MoT one day next week.

If anyone has an idea about the misfire at 6,000 RPM I’d appreciate any thoughts.

I’m pleased to report that a few ‘Italian tune-ups’ seem to be sorting out the misfire issue, after a few bursts of 9,000RPM (fortunately my neighbours are out) the 6,000RPM hump has almost gone. My theory is that there was probably a little contamination on the needles where they contact the mouth of the main jet. This part probably hasn’t had any gas flow past it for at least 5 years, and remember I’d left the top of the carburettors alone this morn.

Everything else seems okay on the motorcycle: I’ve pumped up the tyres (previously about 7PSI), waxed the chain and got all the lights and the horn working (the indicators were a bit tired but responded well to a bit of WD40). The brakes seem fine (I just tried it up and down our quiet cul de sac because it doesn’t have a MoT yet). A new oil filter arrived from that nice Mr Bezos so I think I’ll change the oil and clean it up with some snow foam and the pressure washer.

If all is well after all that I’ll get it in for a MoT test 

do not trade with bezos. They will know why when only he and someone like him remain

… actually I quite like the Bezos service: I can order stuff whilst working on a motor car or motorcycle, or sitting in the pub, and it shows up the next day. Sometimes pretty obscure items as well. I also get half a dozen live rugby internationals included in the price every year - which is rather more than the crooks at the BBC that charge me rather more .

Anyway, today has been a good day: Ed’s Honda is fixed. It still has a bit of a stutter around 6,000RPM, but I think what it really needs is to be ridden a bit.

What a ridiculous place to put the rear brake reservoir - not one of Mr Honda’s finest moments!

I suspect everyone undoes the reservoir, zip ties it to the outside of the frame and changes the brake fluid in that position?

I rather suspect the brake fluid was put there in Japan in 2002 - it was quite badly contaminated. Now both ends have been flushed with new DOT4 - much better.

The CB500 is finished. I’m pleased to report it passed the MoT test with no advisories (its first MoT in 5 years) yesterday, and I delivered it back to Ed today. I’ve donated a spare helmet and leather jacket to the cause, Ed has registered for a CBT and theory test, then intends to take a direct entry course. Everyone is happy.

The CB500 still has a small stutter at about 6,000RPM, but that is getting less pronounced with use. I think a couple of tanks of fresh fuel with some system cleaner additive should have it sorted out.

Many thanks for the help and advice chaps 

Fantastic, well done and great Job. They certainly don't build them like that anymore