Fine tuning ?

[straycat]

I posted this on my rebuild thread, but realised it would be better here :

I've recently been trying to sort out the poor idle problems -

Replaced intake o rings .Rubbers are still flexible.
Checked carbs for dirt
sealed up airbox (rubbers onto carbs are still flexible and tight)
balanced carbs
experimented with pilot screws - I'm unsure if 3 1/2 turns is correct.

It certainly idles better, but I now have a bit of "stumbling" when I open her up after hard use.
It will pull without a hiccup from about 1500 rpm in top, but occationally it will hesitate at between 3 and 4 K after throttle has been closed then reopened. Example of this is riding at 70-80 in 5th and then pulling up at a junction.In the past it would almost definitely have stalled,but now idles at approx 1000 rpm. I'll pull away and give it a hand full of throttle and there will be a slight miss stumble somewhere between 2.5 and 4 K,then it's fine again.

Maybe I should check the plugs ?

I have set the carbs for standard :

Jets and needle clip are as standard
Checked float height and found 1&4 to be correct at 22.4 ,but 2&3 were about 2mm lower (higher fuel level). set them all to correct.

Motad 4-1 which I thought could run as standard with airbox ?

Annoying as it wasn't doing this before - have I highlighted another problem by sealing air leaks ?

[Nessism]

Sounds like some plug chops are in order. Stock jetting and an aftermarket exhaust often leads to a lean running condition, but with the stock airbox installed it may be okay. Only real way to know for sure is to do the chops. Also, you might want to check your spark plug caps and contact to the coil wires.

[spyug]

Checked carbs for dirt

If you are having carb related issues, this statement tells me you haven't properly cleaned the carbs. There is only one way to do this. The carbs need to be stripped down to components and everything metal dipped in carb cleaner (i.e soaked) for a minimum of 24 hours.. Passages then need to be blown out with air and jet holes poked with thin wire. Reassembly should always include new o-rings and new o-rings should be fitted to the carb intake boots on the head.

Once reassembled and installed, the airbox should be fitted with emphasis on a tight seal to the carbs and around any openings.

Don't bother diving in to anything else until you are sure you have done this thoroughly as you will just be wasting time.

Follow the carb cleaning tutorial on the main page.

As a final note, you may think you have done a through job only to find it still acting up. If this is the case then suspect your tank and petcock for letting some crap flow. It only takes the minutest particle to plug a jet.

Good luck with it.

cheers,
spyug

[straycat]

thanks for the replies

I'll try the plug chop 1st .

I didn't want to pull it down again and completely rebuild the carbs,as it was running ok before I sorted the idle /intake leak, but I may have to bite the bullet and get on with it.

To be honest,I've never completely dismantled carbs before and am worried about breaking them !

sc

P.S. Bike is a GS 550 ET 1980 UK

[refeicul]

just take your time and try not to get frustrated and it will be running in no time

[David_510]

To me it sounds like you could be running a little rich.

I ran into the same sort of thing when i first installed my custom pods (83 gs550esd) and had my fuel mix screws at about 4 - 3 3/4... It would idle ok but taking off i would have a flat spot at about 3400-5300 rpms... but once it passed that it would really kick and take off...

[straycat]

I took a quick look at the plugs - not chopped yet. they are sooty

[straycat]

Never managed to find anywhere to do a chop,but it's not right.........I've ordered the o ring set and have decided to do the full carb rebuild,like I should have the first time !

Always tried to avoid it as carbs have always seemed like some sort of black arts !
The links on Basecliffs excellent site make it look fairly straightforward,as long as you are carefull and methodical

thanks for the advice

[straycat]

I've now stripped,cleaned,dipped and blown out carbs and started reassembly with new o-rings ! (thank you Robert Barr !) Decided to do the vinegar method of tank cleaning as well. I'll drain it tomorrow (thank you hampshire hog !).

I have 2 questions for the experts :

Should I rinse tank out with water then put WD straight in or could I dry it 1st with a hairdryer in the filler hole. Will WD affect the petrol ?

I'm setting the carbs to stock as a starting point. Float heights should be 22.4 mm. I don't have gaskets on. Should I measure from gasket surface or the carb body and if without gasket ,do I measure from the small raised "line" or the main surface ?

I've also noticed there is as much as 0.5 mm difference between the two floats on each float assembly - is this normal ?

oh........I think that's more than 2 questions !
thanks

sc

[ddaniels]

Float height should be measured with the gaskets in. Can you bend the floats a little to get them even with each other? I'd try that.

[hampshirehog]

When you drain the vinegar you have to be really quick - the thing will flash rust in front of your eyes. The only way to prevent the rust coming in is to stick a hose pipe in there and let the thing run for maybe half an hour to 'dilute' the vinegar to nothing. You'll see loads of crap come out in the water flowing out of the filler hole. You must stop the air getting at it - that's what causes the rust. Next is to make sure that it's full to the brim with water and pull the plate that is blocking the tap holes off. As soon as you have got some room in the tank give it a squirt of WD40 through the filler hole - you want to try and get a WD40 'mist' spray rather than a jet spray. Your aim is to cover every square inch of the inside of the tank with WD40 as the water runs out.

[Steve]

Float height should be measured with the gaskets in.

On the contrary, every manual I have seen says "measure to the gasket surface with the gasket removed" (emphasis is mine).

Not sure if the exact measurement is from the main body or the little ridge, but I have always measured to the main body.

.5mm is probably close enough for the two sides, you will have a hard time getting it closer than that.

.

[straycat]

Thanks for the quick replies. I think I understand both procedures now !

I'll post some pics tomorrow.

thanks again

sc

[straycat]

My 1st attempt at de-rust has not gone to plan . I had shone a torch in the filler hole and looked in the tap hole. I could see the underside of the top of the tank was shiny metal with no rust. I thought as I only had rust in the bottom of tank I wouldn't have to fill it with vinegar.
Left approx 12 litres in overnight , removed vinegar with the water filling method,then sprayed WD in as I removed tap blank. When I looked in the tank,the top was thick rust ! I think the vinegar vapours have removed any protection that the petrol has given to the tank and let it rust overnight.

Not willing to risk my super clean carbs with this so I'm off back to Asda for 35 bottles this time!

No pictures - just a red face.
Got my float heights sorted and carbs reassembled and fitted,so that's something in the right direction.

sc

[hampshirehog]

Never mind. Plenty of flavouring for your chips!

The trick is to fill the thing to the brim and get all the air out.