When I took the spark plugs out the front was a good colour, but the rear was very black. Additionally on removing the air filter (that is supposed to have done 500miles) it has a dark stain over most of the inside above the rear throttle body. When I blip the throttle I can see fuel ejected back out of the rear throttle body. The front throttle body doesn't do this. Also I get the impression that fuel consumption and throttle response at low revs has been detiororating.... Seeing a similar thread I have checked the cam timing. The timing marks on the pulleys all line up as they should. I have pulled the rear injector, suspecting maybe a seal had gone allowing fuel to seep into the throttle body. The o-rings look sound. Is there anyway I can check the injector, or might I be looking in the wrong place?
Good chance the injector needs cleaning. It is a simple job to build a home cleaning kit. There are videos on YouTube. If you want an injector connector to build one then drop me your details on a PM, I have loads off old looms.
I can certainly try that. 2 questions though: 1) If they werent spraying properly, wouldn't that make the rear cylinder run lean rather than rich? 2) All the you tube videos show injectors where the fuel goes in through the top. Not sure how I could rig up a pipe to get the fluid in here.
Chris, Thanks for the offer. I think I have sent you a message about an injector connector. I was wondering is it possible to remove the filter from the injector and replace it without damage? Anyone done this? Reason being that the casing would then make a nice cup for holding cleaning fluid while cleaning the injector. I'm nervous just to prise it off without knowing how it is constructed. I may just end up breaking what may be a perfectly functioning injector!
they can be a total pain to remove the whole injector but if you manage to do it with relative ease you could swap front for rear unit as a lazy but easy check on function.
I have a similar problem on my old 851 and swapped over the injectors as a test - this made no real difference but at least indicated that the injectors were not the problem. Have not yet found the answer but will let you know if I do.
It is really puzzling me, and my mate who has a 749 and knows a fair bit about engines. I'll try cleaning the injectors out, then I might try swapping the injectors over. My other thought was fuel leaking past the o-ring seals into the throttle body, but they look ok (although looks might be deceiving). I spoke to a parts guy at my local Ducati dealership who said he thought they could check the injectors. So I might then try that as they can do a full check on them. I did wonder whether like a previous post it was cam timing wrong, but unlike his problem, when I look down the throttle body the inlet valves are both nice and shiny, so I don't think its blowing combustion chamber gas back through the inlet valves. Also the cam pulley timing marks align correctly, so unless someone has had the pulleys off the cams and put the wrong offset woodruffkeys in, the cam timing looks to be correct. It does seem odd though, that it is blowing a mist of fuel vapour back up the throttle bodies. The bike is stock, and as far as I can tell the eprom still has a ducati sticker on it. so I don't think its someone messed with the injector firing on the eprom, and although i'm not entirely sure, as theres only one crank sensor, wouldn't a reprogrammed eprom affect both cylinders? The other oddity is that when I open the throttle wide at low or medium revs in a high gear, there is a very loud engine roar that comes out from under the tank. Sounds like a blowing exhaust, but the exhaust pipes are fine, so my thoughts are its coming out through the airbox. All in all a real puzzle. Any pearls of wisdom anyone?
Agree - if valves were not giving a good seal for any reason then that may be a reason for the blowback
Guys, Thanks for the advice and assistance. A bit of an update, and a question..... Finally got time to investigate further. Cleaned the injectors. Thanks for the plug Chris, made the job a lot easier. Bought a compression tester. Manual quotes 9-11 bar. The "good" horizontal cylinder reads 6.5 bar, so may have an issue. The "bad" vertical cylinder reads 3 bar, so definitely an issue, and with the throttle closed i can definitely feel pressure coming back out the intake where the injector fits. I've checked my Sealey pressure gauge against a known, calibrated pressure source, and it is accurate to within 10% so both cylinders definitely down on pressure, but specially the vertical one. I'm guessin it is the valve shimming is long overdue and not been done, though reading threads, will check the rockers as well. My question is; Given the rear, (and possibly the front cylinder) valves have not been seating properly, would you just check and replace shims and hope, or would you strip the heads off and inspect/measure test thoroughly. The repair is now an over the winter project, so time is not a great issue. It would be useful to have the opinions of those that may have been here before.....
Geoff, taking the heads off is no big deal and a loss of compression could also be a dodgy ring, you really need to have proper look otherwise you will regret it in the longer term. How many miles and how long has this been like this? Do you have a decent support dealer near you?
The bike has done about 22,000 miles and it has probably had the problem since I bought it about 1000 miles ago, but has steadily been getting worse. That said, it still had enough grunt to put a smile on my face, get well over 3 figure speeds, and make my guzzi feel low powered by comparison. There is a dealer in Coventry, but its an old ST4 so getting them to fix it will probably land me with a bill close to the value of the bike. I do have a local mechanic who has ducati experience, but I am aslo quite mechanically adept, just new to Ducati's.
