Full throttle problem

ansim · Post by **ansim** » Mon Sep 04, 2006 6:51 am

After change of needle and atomizer the engine dies at 3/4 -full throttle. The needle and atomizer were worn out.

I have checked almost everything, 4-5 times, involved in the fuel part.
Floathight set to 17.5mm.
New fuel filter, cleaned tank and "tanktap?" (outlet from tank).

The carbs are cleaned and blown with compressed air back and forth thru all jets.

The engine starts and idles fine. When the throttle goes up slow the rew increases until ~3/4, then dies, if not the throttle is twisted back. Lack of fuel.

Same throttle is ~1/4-1/3 and full throttle is set. The engine rews a bit and dies, if not the throttle is twisted back.

The bike have Dellorto PHM 40 and no fuelpump.

Now I'm very frustaded over the situation.

Any ideas?

ducapaso · Post by **ducapaso** » Mon Sep 04, 2006 9:17 pm

Which rev does it happens?
Is it about 6000 rpm?
Maybe yor spark plugs suffered because of some excess of fuel in some time of carb setting. You might try to change them (the burst plugs don't look "worn")
Otherwise the elder jets weren't original and they had been "customized" compare them with the new ones
have a nice work, Nicola

Post by **jcslocum** » Tue Sep 05, 2006 12:38 am

I would look at the fule line and make sure it's not pinched or collapsing inside. Mkae sure it routes as much in a downhill direction as possible.

Next would be the fuel filter. Make sure it's not clogged ro too small to flow all the fuel needed.

Check the vent or leave the cap open just to make sure it not getting starved by vacuum.

The float height seems ok according to my manual. You did check them with the float to the side not on top?

I have PHF36's on my paso. Is it possible that 40's are too big and it's not starving but flooding?

ansim · Post by **ansim** » Wed Sep 06, 2006 9:06 am

The 40s where on the bike when i bought it and I have not encountered this kind of problem before. I changed the needle, atomizer and the throttle grip to a Tommaselli 2 cable.

Fuel lines are in good shape and nice turns downhill. The filter is new.

I'll try with cap opened.

Floathight measusred with bottomcup of and then open the floats until gas starts flooding.

The flow of fuel thru the lines are ~500ml/min with not connected carbs.

The problem occurs when I goes to full throttle on all rews, idle/low or high (~6000).

I can get to ~6000 if i slowly increase the throttle up to 1/4-1/3, but after this the engine starts to starve. If I decrease the trhottle the engine goes ok again.

Currently I'm waiting for new coils, so new plugs and coils will be installed soon.

The action in the carbs when 1/2 to full trhottle is given, only the main jet, and the float parts(jet and float) involved.

//Anders

Post by **jcslocum** » Wed Sep 06, 2006 1:01 pm

ansim wrote:
Floathight measusred with bottomcup of and then open the floats until gas starts flooding.

I think you need to set the floats according to the Dellorto procedure to eliminate this as a possible problem. Do you have the Dellorto procedure? If not I can fax it to you or maybe I can find it online.

ansim · Post by **ansim** » Wed Sep 06, 2006 1:47 pm

I have the dellorto procedure available.
I'll compare to my way of measure, which I got from a very good Ducati shop in Sweden.

The way I measure is very correct, as you notice when the flow starts.

Keep the carb connected to the fuel line with the bottomcup removed so you have acces to the float.

Put the carb in level position, straight up, and close the float, move it upwards.

Slowly let the float downwards, when fuel is starting to flow, measure from the carb underside,where the bottomcup is attached, to the bottom of the float.

Quite tricky, but very accurate.

I will do some more testruns home. If not succeding it goes to a shop for service.

//Anders

Paul · Post by **Paul** » Wed Sep 13, 2006 5:25 pm

Anders,

I have twin Dell Orto PHM40s with the fuel pump still plumbed in. I tried bypassing the fuel pump and had very similar problems to you in that it wasn't happy to rev much beyond 5,000 revs and didn't want to respond to a snapped open throttle.

Putting the fuel pump back in sorted out the problem.

Paul

ansim · Post by **ansim** » Wed Sep 13, 2006 7:41 pm

Thanks for all hints, but I still have problem.

From the begining the bike had a fuelpump, which I removed succesfully.

No problem to run the bike without it, until now, when I changed needle and atomizer.

I did a flow test today.

Without carbs connected the flow was ~1 liter/min. Better than I wrote earlier.

With the carb connected and float bowl open, float not closing the flow was the same as not connected carbs.

I will try to switch back to the old needle and atomizer, just to check. But I doubt it will work.

//Anders

delagem · Post by **delagem** » Sat Sep 16, 2006 1:59 am

Well, you need to know if it's dying because it's too rich or too lean. You could try a couple of things:

Try to hold it running, but just at the point where it's starting to die, for about 15-20 sec's. Then pull the spark plugs and see if they're black or white.

Or, shut off the fuel, and as the fuel level in the carbs drops, keep trying to run the motor up to those revs. If it runs better as the level drops, before it runs totally out of fuel, it's getting too much fuel. I discovered a problem with the float height of a bike this way, totally by accident. Forgot to turn the fuel on! This bike had been giving me problems for hours and hours!

ansim · Post by **ansim** » Sat Sep 16, 2006 5:26 pm

jihaa,

Problem solved!!

It was the new needle and atomizer. When I installed the old ones the bike responded as supposed to, full throttle response well above 10'rpm without load.

The suggestion to switch back came from a service shop.

I'll contact the shop from where I got the parts and try to get some explanation

//Anders

ducapaso · Post by **ducapaso** » Tue Sep 19, 2006 5:16 pm

Maybe needle and atomizer have been machined by the elder owner, as I said before...

maybe the elder jets weren't original and they had been "customized" compare them with the new ones

ansim · Post by **ansim** » Tue Sep 19, 2006 6:15 pm

They're defenitly different.

I will run som test, changing one part at a time and see what happens.

Nice to have it sorted out.

//Anders

ansim · Post by **ansim** » Sat Sep 23, 2006 1:58 pm

Pinpointed the cause.

Wrong set of needles. I got V9 instead of K5.

Always double or tripple check that you receive the correct parts.
I missed that, assumed I got the correct ones.

I'll return the V9s and wait for K5.

//Anders