Try resetting the float height to the original settings I have just fitted new emulsifier tubes but not had the chance to try out yet been working away for the last three weeks, but have a similar problem and I had reset mine to 14mm but as previously stated I have lost the backfire from changing the pickups but it was still running rough on around 1/8 throttle hopefully the new tubes will resolve that if not I will be looking at resetting the float height. I still have the feeling it is running rich low end so may open up to 15mm.
When my problem first suddenly appeared, I went straight to the carbs thinking dirty petrol............and as the overflows had been occassionally dripping and appeared to be a little bit worse than normal, it was obviously a good time to have the carbs off. Spitting back through the airbox (mainly on one carb only) is supposed to be a sign of weak mixture etc etc.... No real signs of dirt and no cr*p in the tiny inline filter at the carbs, plus the float heights were all over the place (9mm, 12mm) but having set them to 14mm it is still did it (stiil waiting for the defective float assembly to be replaced)...... I am now wondering if I should keep them at 14mm becasue if the bike had been set up when one (or both) the inlet manifold rubbers might have been drawing air, then it would have run weak hence the float heights being off 'normal' to correct it.... So when it is all back together, I expect I shall have several adjustments to make, but.....if the problem is still there, well......where do I start.... AL.
Al I suppose one test for potentially faulty inlet rubbers drawing in air would be to spray 'easy start' around them whilst it's running, working on the theory that the revs would increase if they were faulty! Only other thing I can offer in an attempt to help is Ultra sonic cleaning of the carb's. Might be there is a little gremlin lodged in one of the fine galleys somewhere?
If there is something in the carbs he's a mighty tough little gremlin......the orifices have had loads of carb cleaner down them followed by 200psi...... There is one place on these OEM Mikunis that something could get stuck (although there was b*gger all in the float bowls) and that's a little chamber in the pilot circuit immediately below the three holes in the throat at the bottom edge of the butterfly......There is a plug to that gallery which can be seen from underneath when the bowl is off, but they are press fit at a particular rotation.....I took a broken carb body apart.....and I wouldn't like to say it could be got out without messing it up or back in again without creating small particles of the alloy inside the chamber.....specialist tools I reckon. Having really studied the rubbers, the manifold side sealing rings are very compressed on one side and there is corrosion from the manifold in there, so I guess they could have been drawing air.......Pics follow AL
Worst manifold connector.....Top pic = Manifold side, Bottom = Carb side PS....Don't criticise me for not seeing it earlier......I haven't ever had a problem with maifold rubbers before, so I didn't pull them off this time.......the nick out of the carb side couldn't be seen when looking straight down....... ....so when I took them off I put them to one side after a cursory glance at the outside of them........Probably not thinking straight at the time becasue of other things on my mind..... ....paul563 spotted the nick in the 'top' lip, so a closer look was taken and a decision to replace or get the silicone out was taken.....maybe it was them causing the problem....I won't know until I get the new replacement float assembly. AL
Who'd of thought that smaller amount of deformation would cause such an issue. Hm... this suggests I need to check out my intake rubbers.
Well......It might be that that caused it....won't know until I get the blasted carbs back on again.... AL.
Had to replace my 400/4 rubbers after they, uh... Fell apart. Classic bond failure, rubber had gone hard after getting cooked for so long. Here's hoping the rubbers are the problem - stupid niggles like this are usually something simple & cheap to fix that takes a LOT of time, money & stress to sort out.
:smile: mine is working great now had a blast on it last night, new emulsifiers have cured the problem on low throttle. Look on the bright side Arquebus things can only get better!
(Mild hijack) Sam - the emulsion tubes, I'm looking at the parts catalogue and the exploded diagram shows these as being removable through the top of the carbs, where the diaphragm & slide is? Is this correct or do you have the remove the bowls & jet holder etc?
You have to remove the bowls as well there is a 7mm head brass bolt with sleve this is removed first then the emulsifier is removed along with the light grey slide housing you can then remove the tube from there,take note on which way the cutout on top points (inward) as the emulsifier has a slot machined on the opposite end which locates in the carb, the jet holder which has the locating pin will come away along with the float holder when this is pushed in place.
You will also find that when you tighten the jet block retainer bolt thingy, the emulsion tubes turn slightly within the space allowed by the locating pin so that the cut away in the top of the emulsion tube is rotated / on the p*ss by quite a bit.......I had a very hard nylon tube which I compressed on one side to be able to keep the cut away in exactly the right position......you can't hold it with a spanner because the brass is a bit on the thin side. Also.....change the seal to the jet block and the one at the base of the grey throttle slide guide if they look a bit on the iffy side. When checking the float heights reverse the float bowl (without gasket) with two bolts to hold down the float assembly. AL.
Well.......I have just walked away from it in case I pick up a hammer...... All back together, nothing forgotten..............switched on ignition, let the pump prime the carbs for 30 seconds, checking for leaks. Choke on, press starter button, turned and fired up more or less immediately. Let it warm up a bit on half choke...... Turned choke off..............idle turned down a bit...... But it runs like a dog......revs won't die when throttle is blipped........cables aren't binding etc (you can hear the carbs snap shut when the engine isn't running)........ Balance gauge suggests they are about right at idle and at 3000rpm (tiny bit out), no air leaks. Un-f-in-believable!! AL.
Waste of money on a 750.........A 900, yes, dead right...... But........I have now got it just about rideable........Got fed up waiting for the replacement float assembly and stuck the defective one back in, but used different float heights** It still drips a bit when hot, but it might bed in. Even though the pilot screws were originally out 2.5 turns (roughly) and I set them to 3.5 as per Dynojet as a starting point, I have had to take them out to 4.5 approx.......That could be because the original float heights were 9mm and 12mm....Now 13.5mm so it would run weaker at idle than it was, I guess. ......still a bit sluggish picking up from idle, but having played with balance a bit (Yep, I can get on the bl**dy screw at last.......15" philips screwdriver, under the oil cooler once it is unbolted and wedged up...........Lie on the floor with a mini-maglite looking under the cooler, push the screwdriver up following the red sleeve on the patented trip meter cable/thottle stop, move the point left and shove that breather pipe between the carbs out of the way and I can just see the synch screw head........locate screwdriver in head and then struggle back into a crouching position still holding the driver.....fire it up hoping the driver doesn't jump out........) I think I can improve on it...... What caused it in the first place is unknown, but either the synch screw went walkabout in a large way or a manifold rubber was leaking....... Still......I'm getting somewhere.........like slowly round the bend. AL.
Hi Al, You have more patience than me!! If the rubbers i sold you made no difference i'll settle up the difference ?
Waste of money or not, I would have lost patience by now of over a months worth of stress & shite with the standard carbs, taken them and a shotgun to the woods - and returned alone...
No problem. mate............I think they are a bit better than mine....the only dubious bits were the carb side seal lips, but cranking the clips up tight seemed to have deal with that (plus the silicone bead I added to the ripped bits....it seemed to hold, just).... .......but perseverance and patience got me a Guzzi running better than the factory could and they acknowledged that.... .........I somehow doubt I will have the same success with the Ducati, though...... .......at least I am confirming why I never wanted one in the past....all my initial thoughts are proving to be correct. Thanks, AL.
