Rough Running? Idea's please

[Shep]

Ideas please.

My '88 R100GS para

A real bitch to start from cold, cranks for ages then startes to fire on one cylinder then slowly catches to two cylinders and eventually starts, once started it restarts very very easily even if its still cold, so it feels a bit like fuel starvation, the carbs have been to bits many many times new kits cleaned as best as I can etc etc. Choke seems to have little effect starting from cold but will stop it dead once warm

Runs very well for 20 miles but then, when properly hot, it starts to hesitate and fek about on small throttle openings.

These two issues may be connected I suppose.

Shep

 

[DrFarkoff]

Are you sure your slow running mixture is set right?

Worn Needles?

Electric Monk's para had problems when it was cold starting cured temporarily by shutting fuel valves round corner and leaving them off till the bike was to be started again

 

[(RIP) Proff]

Make sure the white pipes are not dripping sludge crap into center hole bottom of carb..

 

[Shep]

Are you sure your slow running mixture is set right?

Worn Needles?

Electric Monk's para had problems when it was cold starting cured temporarily by shutting fuel valves round corner and leaving them off till the bike was to be started again

No, i'm not sure at all now and there could be the possibility of worn needles and jets, the whole bike was stripped and re-fettled, it had the problem before and still has the same little issues, from cold it feels like there is no fuel there rather than over rich, it's almost as if the slow running/choke jets are blocked but it's all been cleaned quite a few times.

Problem is, it needs to be totally cold before I have any signs of starting problems, so any little things changed are very difficult to prove to be the fault or not, until the next time it's stood for a day or two.

Proff, no goo from the pipe now, but that might have been the issue when I bought the bike perhaps.

Cheers

Shep

 

[cheap'n'cheerful]

I had a simular problem with my bike a few years ago and eventually found i had put the chokes on the wrong side carbs
Cheers C'n'C

 

[Shep]

I had a simular problem with my bike a few years ago and eventually found i had put the chokes on the wrong side carbs
Cheers C'n'C

Mmmm that's interesting, i've never taken both carbs apart at the same time but the previous owner might have

 

[bubbles]

Are the paper gaskets under the 4 screws that hold the choke carb on the side of the main carb in good condition, if they leak it becomes very difficult to start a cold bike.

 

[fayeslane]

If your gut feel is fuel starvation, start from the tank. Check fuel flow from the taps (remove and clean mesh strainers if you have time). Check the fuel lines for deterioration, kinks etc. Check fuel cap vent.
Good thing about these checks is they are cheap and easy to do before you delve into the tricky bits.
I have just done an XLV750 Honda that ran like a 250 -only getting about 25% flow from the tap. Easily fixed, with full fuel flow it ran like a 350

 

[Steptoe]

Check the little jet in the float bowl isn't blocked. The one down the bottom of the small tunnel in the corner of the float bowl.

It unscrews from the float bowl. If it's blocked you'll not get any fuel with the choke on.

 

[Beemerboff]

I like to set the fuel level by checking the level in the float bowl, as detailed on snowbums site. Take the bowl off one side , check depth 21/23 mm, replace bowl , flick tap off/ on then remove other side and check it is the same- done this way stops the hose draining into the second bowl.

There are also a lot of small passages in the carb that can block and be hard to clean, but I have found that a dose of fuel injection cleaner in the tank will clean them out eventually.

And I have come round to thinking that the best place for online filters is in the bin , so if you have them I would start there

 

[redsoul]

Check the little jet in the float bowl isn't blocked. The one down the bottom of the small tunnel in the corner of the float bowl.

It unscrews from the float bowl. If it's blocked you'll not get any fuel with the choke on.

I had same problem with bike having difficulties cold starting after been left for a few days.

Under advisement from Rob Farmer I took off the float bowl for a different problem(petrol pissing out over my right foot).Not only did it solve the leaking petrol problem but the bike now cold starts with no problem.

 

[Shep]

No surprises but it turns out there is more than one fault, new HT leads and plugs cured the rough running when warm and the hesitation on small throttle openings.

However the cold starting has not improved so i'll guess i need to do the carbs yet again, the chokes just do not work (it's is a very effective kill switch!!) I'll get around to checking the correct choke is on the correct carb first!!

Runs well once started though, a real pleasure to ride now

 

[(RIP) Bin Ridin]

Float bowl gasket has to be airtight to allow choke to pull vacuum and thereby get fuel from the ickle jet in the bottom corner of the floatbowl. If leaks, then choke pulls air not fuel.

 

[Shep]

Gaskets were faulty originally (a year back), but they appear fine now.

It feels very much like fuel is struggling to fill the carbs, but the taps and filters flow well enough, it starts well if left only for a day, but leave it a few days and it really tests the battery. The float bowls are pretty much similar levels with no crud/water evident.

Next time its sat for a while i'm going to switch the fuel on, a hour or so before trying to start it just to see if things improve.

There is one thing it appears to be a little slow when shutting off into a bend almost as if the throttle is being kept open slightly, ruining the engine braking. If i dip the clutch it's certainly not any more than tickover, perhaps the slow running jets/needles are worn?

Shep

 

[BROTOWNBOY]

Hey Shep I had exactly the same probems as you with my r100. Was for ever pulling the carbs apart and even put them thru the ultrasonic cleaner which did'nt make any difference. A new set of plugs and lead fixed the rough running problem. Also had the same starting problem where it would crank forever then slowly start on one cylinder, that problem turned out to be a worn leaking inlet valve. Starts on first crank when cold now

 

[Padmei]

I found one choke lever the wrong way round when I rebuilt my carbs. If you had told me to check them I would have sworn black & blue they were the same way