I'm currently re-commissioning and MHR900 that hasn't been run for 7 or 8 years. The valve clearances have been checked, they're not spot on but not a mile out. New plugs. The float bowls removed and the jets checked to be clear. The idle mixture screws are at an initial position of 3 turns out. From cold I can get the thing to start and it will rev on the throttle no bother. I've been trying to keep it running for couple of minutes holding it on the throttle but then it spits and pops and cuts out, just like it ran out of fuel. There is a gallon of fresh fuel in the tank and the taps are turned to reserve. Normally I would keep it running for 2 or 3 minutes then screw up the throttle stops for a fast idle, adjust the idle mixture screws for maximum idle speed, back off the throttle stops to bring the idle speed down to around 1200 rpm, tweak the idle mixture screws again then finally set the idle speed but I can't keep this bike running long enough to do anything. I can usually sort most problems out but this one is proving rather difficult so I'm hoping that some of you bevel owners might have some ideas.
Sounds like you’re doing everything ok there Derek. Have you checked that the fuel lines are clear and the taps are flowing sufficiently? Also... more info! Is this yours, and what year? Bloody lovely bikes ❤️
Not sure of the year Ian (I can't remember the reg.no.) but it is a fairly early one. It has the one piece fairing but steel tank without the GRP cover. It's not my bike but one I've been working on for the local bike shop. (I do Ducati work for him). I'm also inclined to think it might be a problem with fuel flow, the rear carb definitely tickles faster than the front one. So maybe I should check the fuel tap filters aren't clogged.
Sounds as though it's running on what's in the float bowls but the fuel is not being replenished from the tank. Sticky floats? Clogged filters? The Bing carbs on my R80/7 used to stick sometimes and need a tap on the bowl to unstick them
On my MHR a couple of weeks ago I took off the fuel tank, emptied it, took out both petrol taps, and checked the filters and reserve pipes. Removed some debris and made sure the OFF/ON/RES positions work properly as per the markings (which is not necessarily the case on an old bike). I also tried to fit a pair of Malossi transparent float bowls so I could observe the fuel levels while the engine is running - except that the late DellOrto PHM 40 carbs have a different bottom nut from the early ones, so the Malossi float bowls did not fit. I have a spare pair of early PHM40s which I might substitute for the newer ones. Some need to be thoroughly tickled before they will start, others don't and flood the plugs. Which is it with the one you are fangling @Derek ?
That would certainly be part of the investigation to diagnose, yes. Was there plenty of cruft in the tank? Sounds like it's a 1980 ('79 has a GRP tank covering, '81 has 2 piece fairing - but usual Ducati "built with what was to hand" logic applies... ).
They're more like an SU. Derek intimated the carbs were good, I'd have a look at the tap filter next.
Agree with this, mine likes a good tickle on the rear vertical cylinder, as that's where I kick it from... however the bike seems to be starting from what Derek wrote, just presenting as fuel being starved at idle.
It needs a fair bit of tickling @Pete1950, for quite a long time before there is evidence of fuel at the carbs. I did manage to thoroughly flood it at one attempt though. I think the next move will be to check the taps which annoyingly will mean draining the tank. I could kick myself for not checking them while the tank was completely empty.
Well yes. If the fuel level in the float bowls (as controlled by the floats) is too low, and if he uses the ticklers before starting, the engine would start up and run until the fuel level drops, then starve. But if he is not using the ticklers before starting, that possibility would not apply. That's why I asked.
If fuel flow is good, carbs should only need tickling briefly. If the taps are clogged, or wrongly assembled, that might be your problem.
There is also a filter on the side of the carb body, where the fuel feed banjo is attached. That also might be clogged or wrongly assembled. Easy to check.
Problem solved. There just wasn't enough fuel in the tank! I set about draining the tank to check the taps and drained both sides until no more would come out and got maybe about a litre or two. I had thought there was about a gallon it (I didn't put it in myself). But when I unscrewed the taps from the tank, particularly the one for the rear cylinder about another litre or so came out. The taps were perfectly clear. So it seems that the tank needs a good head above the bottom of the tank to get a sufficient flow of petrol. I put it back together and this time made sure it had plenty of fuel, started it and it kept running fine. I now have the idle screws set at just over 2 turns out and the idle set for 1200 rpm. Next job is balance the carbs.
And ride it... they're blooming lovely to ride. Not the most comfy or accommodating of vehicles, but sublime.
That was my first thought, actually. But I hesitated to mention it because @Derek might be offended by the implication.
I don't recall my mates MHR (one of the first 200) having ticklers on the Dellortos. I know my LeMans didn't but it did have pumper carbs - big ones. I guess a big squirt from them was a good as a tickler.
The carbs are PHM40s. Ticklers and accelerator pumps too but no cold start circuit which was available on the PHF series.
